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The Learning Curve for Anatomic and Reverse Total Shoulder Arthroplasty: A Systematic Review

Open AccessPublished:December 27, 2022DOI:https://doi.org/10.1016/j.xrrt.2022.12.001

      Abstract

      Background

      Despite the rising incidence of anatomic total shoulder arthroplasty (ATSA) and reverse total shoulder arthroplasty (RTSA) among surgeons, little is known about the learning curve associated with these procedures. The purpose of this systematic review was to (1) identify the learning curves associated with ATSA and RTSA, (2) evaluate the effect of the learning curves on clinical outcomes, and (3) determine the number of cases needed to achieve proficiency.

      Materials and Methods

      Four online databases [PubMed (NLM), MEDLINE (OVID), Cochrane Library (Wiley), and Scopus (Elsevier)] were systematically searched and screened according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses [PRISMA] guidelines. The search included results from the inception of each database to May 18, 2022. Data regarding study characteristics, patient demographics, learning curve analyses, patient reported outcome measures (PROMs), range of motion (ROM), complication rates, and reoperation rates were collected. A quality assessment for each article was performed according to the Methodological Index for Non-Randomized Studies (MINORS) criteria.

      Results

      A total of 13 studies of fair to good quality were included for analysis (one of level II evidence, five of level III, and seven of level IV) with the majority originating from the United States [n=8, 61.5%]. Overall, there were a total of 3,381 cases (1,861 RTSA and 1,520 ATSA), with a mean patient age of 72.6 years [range: 45-92 years]. From the studies analyzed in this systematic review, for RTSA, the approximate average number of cases surgeons need to perform to move to an acceptable position on the RTSA learning curve is 25 cases. For ATSA, a wider range of 16-86 cases was derived as only two studies reported on ATSA.

      Conclusion

      Progression along the learning curve for reverse and anatomic total shoulder arthroplasty results in decreased operative times, improved patient reported outcomes, and fewer complications. However, a true learning curve is difficult to quantify given the heterogeneity of reported outcome measures, individual surgeon experience at time of data collection, and statistical analyses used across studies.

      Keywords

      The incidence of anatomic total shoulder arthroplasty (ATSA) and reverse total shoulder arthroplasty (RTSA) in the United States have risen dramatically over the past decade.
      • Day J.S.L.E.
      • Ong K.L.
      • Williams G.R.
      • Ramsey M.L.
      • Kurtz S.M.
      Prevalence and projections of total shoulder and elbow arthroplasty in the United States to 2015.
      ,
      • Jain N.B.
      • Yamaguchi K.
      The contribution of reverse shoulder arthroplasty to utilization of primary shoulder arthroplasty.
      ,
      • Kim S.H.
      • Wise B.L.
      • Zhang Y.
      • Szabo R.M.
      Increasing incidence of shoulder arthroplasty in the United States.
      ,
      • Westermann R.W.
      • Pugely A.J.
      • Martin C.T.
      • Gao Y.
      • Wolf B.R.
      • Hettrich C.M.
      Reverse Shoulder Arthroplasty in the United States: A Comparison of National Volume, Patient Demographics, Complications, and Surgical Indications.
      Over 100,000 cases are performed each year with an expected increase in volume of 122% by 2040.
      • Rabinowitz J.K.
      • Kothandaraman V.
      • Lin J.
      • Li X.
      • Friedman R.J.
      • Eichinger J.K.
      Utilization of shoulder arthroplasty in the United States — An analysis of current trends and future predictions.
      Similarly, the incidence of shoulder arthroplasty among early-career surgeons within the first two years of independent practice has increased substantially over the past decade.
      • Carpenter D.P.
      • Feinstein S.D.
      • Van Buren E.D.
      • Feng-Chang L.
      • Amendola A.N.
      • Creighton R.A.
      • et al.
      Trends in open shoulder surgery among early career orthopedic surgeons: who is doing what?.
      However, ATSA and RTSA are not without risk and pose a considerable technical challenge
      • Matache B.A.
      • Lapner P.
      Anatomic Shoulder Arthroplasty: Technical Considerations.
      ,
      • Zumstein M.A.
      • Pinedo M.
      • Old J.
      • Boileau P.
      Problems, complications, reoperations, and revisions in reverse total shoulder arthroplasty: a systematic review.
      , particularly among surgeons with less experience.
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      The overall complication rates for RTSA and ATSA range from 0 to 75%6,22,41.43 and 4% to 15%, respectively.
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Kiet T.K.
      • Feeley B.T.
      • Naimark M.
      • Gajiu T.
      • Hall S.L.
      • Chung T.T.
      • et al.
      Outcomes after shoulder replacement: comparison between reverse and anatomic total shoulder arthroplasty.
      This variability suggests a lack of reproducibility among surgeons and presents an opportunity to characterize the learning curve for these procedures.
      The surgical learning curve was first coined by Luft et al in 1979.
      • Hopper A.N.J.M.
      • Lewis W.G.
      Learning curves in surgical practice.
      The curve consists of four stages
      • Hopper A.N.J.M.
      • Lewis W.G.
      Learning curves in surgical practice.
      : (1) a rapid ascent in a measured outcome at the onset of training; (2) a zone of diminishing returns, in which further experience only confers marginal improvements in the outcome; (3) a plateau, in which further experience has no additional benefit on the measured outcome; and (4) an age-related decline in the measured outcome. This can be depicted graphically by plotting an outcome (e.g., operative time, complication rate, re-operation rate, clinical outcome, etc.) against the number of procedures performed over time. The graph can then be analyzed to find a case number or time point in which performance plateaus, which represents the end of the learning period
      • Hopper A.N.J.M.
      • Lewis W.G.
      Learning curves in surgical practice.
      . Learning curves have important clinical implications as procedural experience has been correlated with cost-effectiveness, improved clinical outcomes, and patient safety.
      • Ekhtiari S.
      • Horner N.S.
      • Bedi A.
      • Ayeni O.R.
      • Khan M.
      The Learning Curve for the Latarjet Procedure: A Systematic Review.
      ,
      • Jain N.
      • Jowett A.J.
      • Clarke N.M.
      Learning curves in orthopaedic surgery: a case for super-specialisation?.
      Contrary to hip and knee arthroplasty procedures,
      • Nairn L.G.L.
      • Gyemi L.
      • Gouveia K.
      • Ekhtiari S.
      • Khanna V.
      The learning curve for the direct anterior total hip arthroplasty: a systematic review.
      ,
      • Sodhi N.
      • Khlopas A.
      • Piuzzi N.S.
      • Sultan A.A.
      • Marchand R.C.
      • Malkani A.L.
      • et al.
      The Learning Curve Associated with Robotic Total Knee Arthroplasty.
      it remains unclear whether a learning period for ATSA and RTSA has been adequately described
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      . The purpose of this systematic review was to (1) identify the reported learning curves associated with ATSA and RTSA (2) evaluate the effect of the stated learning curves on outcomes such as complication rates, operative time, reoperation rates, patient reported outcome measures (PROMs), and range of motion (ROM), and (3) determine a point on the learning curve after which a surgeon can be considered to have achieved proficiency. We hypothesize that with increased surgeon experience, there will be fewer complications and reoperations, improved patient outcomes, and reduced operative time.

      Materials and Methods

      Search Strategy

      Two reviewers conducted a systematic search strategy of the online databases PubMed (NLM), MEDLINE (OVID), Cochrane Library (Wiley), and Scopus (Elsevier) in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis [PRISMA] guidelines. The search focused on literature discussing the learning curve of ATSA and RTSA. The results of the search from the inception of each database to May 18, 2022 were considered. Inclusion criteria were: (1) all levels of evidence, (2) studies performed on human patients, (3) operative studies using primary or revision RTSA and/or ATSA with or without the use of navigation (4) a formal discussion or analysis of the learning curve based on the results of the study. Exclusion criteria were: (1) review articles, opinion pieces, editorials, or basic science studies and (2) multiple studies reporting on the same group of patients (only the most recent study was included).
      An initial limited search of PubMed and Scopus was conducted, followed by an analysis of keywords contained in the title and abstract and indexed terms using MESH. Once applicable keywords were identified, they were used to conduct thorough searches of each database. The search was comprised of terms to identify articles evaluating the learning curves and outcomes associated with anatomic and reverse shoulder arthroplasty (Appendix 1). A second search was conducted using keywords to measure the outcomes and complications related to the surgeon's experience. The references of included studies were checked to identify potentially eligible studies that were missed with the initial search.

      Screening of Studies

      Titles, abstracts, and full texts of all search results were screened in duplicate by two independent reviewers. Any disagreements at the title and abstract stages resulted in automatic inclusion for the next stage of screening. Disagreements at the full-text stage were resolved through a consensus decision between the reviewers and the senior author.

      Quality Assessment of Included Studies

      All included studies were assessed for quality using the Methodological Index for Non-Randomized Studies (MINORS) score. The MINORS score is a validated tool consisting of 12 items, each scored 0, 1, or 2. The maximum score is 16 for non-comparative studies and 24 for comparative studies.
      • Slim K.N.E.
      • Forestier D.
      • Kwiatkowski F.
      • Panis Y.
      • Chipponi J.
      Methodological index for non-randomized studies (minors): development and validation of a new instrument.
      ,
      • Waterman B.R.
      • Dunn J.C.
      • Bader J.
      • Urrea L.
      • Schoenfeld A.J.
      • Belmon Jr., P.J.
      Thirty-day morbidity and mortality after elective total shoulder arthroplasty: patient-based and surgical risk factors.

      Data Extraction

      The same two reviewers independently abstracted data from the full texts of included studies. Extracted data were entered into an electronic database [Excel; Microsoft]. Data regarding study characteristics, patient demographics, learning curve analyses, PROMs, ROM, complication rates, and reoperation rates were collected.

      Statistical Analysis

      In an attempt to optimize inter-reviewer agreement throughout the screening process, the Cohen kappa statistic (k) was calculated at each stage. Substantial agreement was defined as k>0.60, moderate agreement was defined as 0.21<k<0.60, and slight agreement was defined as k<0.21, according to recent literature.
      • McGinn T.W.P.
      • Wyer P.C.
      • Newman T.B.
      • Keitz S.
      • Leipzig R.
      • For G.G.
      Tips for learners of evidence-based medicine, 3: measures of observer variability (kappa statistic).
      Inter-rater agreement was evaluated by calculating an intraclass correlation coefficient (ICC) for MINORS scores. It was decided a priori to categorize the quality of the evidence using the MINORS score as previously described
      • Day J.S.L.E.
      • Ong K.L.
      • Williams G.R.
      • Ramsey M.L.
      • Kurtz S.M.
      Prevalence and projections of total shoulder and elbow arthroplasty in the United States to 2015.
      : very low: 0 < MINORS score < 6; low: 6 ≤ MINORS score < 10; fair: 10 ≤ MINORS score ≤ 14; and good: MINORS score > 14.

      Results

      Study Identification and Characteristics

      Of the 3,591 studies initially identified, 13 were included in the final analysis (Figure 1). There were seven case series of level IV evidence, five retrospective cohort studies of level III evidence, and one prospective cohort study or level II evidence. There was moderate to high agreement among reviewers at the title [k= 0.74, 95% CI, 0.7-0.9], abstract [k= 0.75, 95% CI, 0.7-0.97], and full-text screening stages [k=1.00, 95% CI, 1.00-1.00].
      Figure thumbnail gr1
      Figure 1PRISMA Literature Search and Inclusion Results

      Study Quality

      The mean MINORS score for non-comparative studies (n=7) was 12.4 +/- 1.4 [out of a possible 16], whereas that of the comparative studies (n=6) was 19.5 +/- 2.6, [out of a possible 24]. This indicates that the non-comparative studies were of fair quality while comparative studies were of good quality. Inter-rater agreement was high as evidence by an ICC of 0.95 (CI 0.5-0.99).

      Patient Demographics

      Overall, a total of 3,381 cases were performed (1,861 RTSA and 1,520 ATSA) across included studies (Table I). The mean age of included patients was 72.6 years [range: 45-92 years]. The included studies were conducted in the United States of America (eight studies), South Korea (two studies), the United Kingdom (one study), Australia (one study), and the Netherlands (one study).
      Table ICharacteristics of Included Studies
      StudyDateJournalLocationDesignProcedure AnalyzedNo. CasesMean Patient Age (years)Learning Curve Grouping of CasesLearning Curve MeasuresStatistical MethodMINORS Score
      Choi et al.
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      2019J Orthop Surg ResSouth KoreaRetrospective CohortRTSA3873.0First 18 v 19-38ORT, CR, PROMsDescriptive12
      Beazley et al.
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      2018Ann R Coll Surg EnglUnited KingdomRetrospective CohortRTSA/ATSA100 ATSA, 100 RTSA72.2First 100 ATSA; First 100 RTSACR, ROCUSUM20
      Groh et al.
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      2014JSESUnited States of AmericaCase SeriesRTSA11264.0First 20 v 93-112CR, ROComparative16
      Cho et al.
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      2017Clin Orthop SurgSouth KoreaCase SeriesRTSA4072.740 consecutivePROMs, CRComparative13
      Wang et al.
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      2020JSESAustraliaCase SeriesRTSA2473.924 consecutiveORTComparative17
      Riedel et al.
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      2010OrthopedicsUnited States of AmericaCase SeriesRTSA6272.0First 18 v 19-62ORTComparative11
      Blaas et al.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      2021JSES IntThe NetherlandsCase SeriesRTSA5077.150 consecutiveORT, CR, PROMsCUSUM15
      Kempton et al.
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      2011Clin Orthop Relat ResUnited States of AmericaCase SeriesRTSA20071.0First 40 v 41-200CR, ROComparative23
      Testa et al.
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      2020Shoulder ElbowUnited States of AmericaRetrospective CohortRTSA/ATSA1420 ATSA, 635 RTSANR2055 consecutiveORTComparative11
      Wierks et al.
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      2008Clin Orthop Relat ResUnited States of AmericaRetrospective CohortRTSA2073.0First 10 v 11-20CRComparative20
      Walch et al.
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      2012JSESUnited States of AmericaRetrospective CohortRTSA48072.0First 240 v 241-480PROMs, CR, ROComparative21
      Hasan et al.
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      2014Am J OrthopUnited States of AmericaCase SeriesRTSA6074.0First 15 v 16-60PROMs, CR, ROComparative13
      Levy et al.
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      2011Current Orthopaedic PracticeUnited States of AmericaProspective CohortRTSA4076.0131-151 v 152-171CRComparative12
      Key: ATSA=anatomic total shoulder arthroplasty; RTSA=reverse total shoulder arthroplasty; NR=not reported; ORT=operative time; CR=complication rate; RO=reoperation rate; PROMs=patient reported outcome measures; CUSUM=cumulative sum plots; J Orthop Surg Res=Journal of Orthopaedic Surgery and Research; Ann R Coll Surg Engl=Annals of the Royal College of Surgeons of England; JSES=Journal of Shoulder and Elbow Surgery; Clin Orthop Surg=Clinics in Orthopedic Surgery; JSES Int=Journal of Shoulder and Elbow Surgery International; Clin Orthop Relat Res=Clinical Orthopaedics and Related Research; Shoulder Elbow=Journal of Shoulder and Elbow Surgery; Am J Orthop=American Journal of Orthopedics

      Learning Curve Groups and Surgeon Experience

      Six studies
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Chalmers P.N.
      • Keener J.D.
      Expanding roles for reverse shoulder arthroplasty.
      ,
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      ,
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      ,
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      reported data on consecutive patients and presented a true “learning curve”, while the remaining seven studies divided patients into two groups (“early” group versus “late” group) of consecutive patients
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      ,
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      . For the studies that divided patients into two groups, one study
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      compared the first 18 cases to the last 18 cases, one study
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      compared the first 20 cases to the last 20 cases, one study
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      compared the first 18 cases to the last 44 cases, one study
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      compared the first 40 cases to the last 160 cases, one study
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      compared the first 10 cases to the last 10 cases, one study
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      compared the first 240 cases to the last 240 cases, and one study
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      compared the first 15 cases to the last 45 cases. All but two studies utilized a single surgeon.
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      ,
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      ,
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      ,
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      , however, few studies defined the years of experience of each surgeon. Testa et al
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      performed a retrospective cohort study that investigated eight surgeons, four of whom were considered “early-career” (i.e., <7 years post-fellowship) and four that were considered “late-career” (i.e., >10 years post-fellowship).
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      Walch et al
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      performed a retrospective cohort following two separate surgeons in the same institution; the authors did not comment on years of experience of each surgeon.

      Outcome Measures

      Ten studies
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      ,
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      used the complication rate to analyze the learning curve (Table II), five studies
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      used reoperation rates (Table V), five studies
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      used PROMs and ROM (Table III), and five studies
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      ,
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      ,
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      used operative times (Table IV).
      Table IINumber and type of complications associated with anatomic and reverse total shoulder arthroplasty learning curve
      StudyGroupings of OutcomesEarly GroupLate GroupOdds Ratio95% CIP valueOverall RateTypes of Complications
      Choi et al.
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      First 18 v 19-38NRNRNRNRNR15.7%Acromion fracture (n=1), glenoid fracture (n=1), periprosthetic humeral fracture (n=1), axillary nerve injury (n=1), infection (n=1), arterial injury (n=1)
      Beazley et al.
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      Complications < 3 months post-operatively (early) v. complications between 3-12 months post-operatively (late) for 100 patients in ATSA and RTSA groups4% (ATSA), 18% (RTSA)0% (both)NRNRNRNRATSA early group: stemless collapse (n=1), glenoid crack (n=3).

      RTSA early group: dislocation (n=5), glenoid fracture (n=4), ulnar nerve neuropathy (n=3), wound infection (n=2), dissociation of glenosphere (n=3), hematoma (n=1), acromial fracture (n=1), axillary nerve injury (n=1)
      Groh et al.
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      First 20 v 93-1120%5%NRNR0.967%Periprosthetic fracture (n=3), hematoma (n=1), acromion fracture (n=1), deep infection (n=1)
      Cho et al.
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      40 consecutiveNRNRNRNRNR20%Deep infection (n=1), glenoid fixation fracture (n=1), brachial plexus injury (n=3), acromial fracture (n=2), intra-operative humeral metaphyseal fracture (n=1)
      Blaas et al.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      50 consecutiveNRNRNRNRNR20%Nerve palsy (n=3), pain from cerclage wire fixation of tuberosities (n=3), subacromial impingement requiring revision (n=1), aseptic loosening of humeral stem requiring revision (n=1), shoulder dislocation (n=1)
      Kempton et al.
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      First 40 v 41-20023.1%6.5%4.31.6-11.5.005*9.9%Transient neuropathy (n=5), intraoperative anterior-inferior glenoid fractures (n-=2), intraoperative greater tuberosity fracture (n=1), intraoperative humeral shaft fracture (n=1), post-operative dislocation (n=3), incompletely seated glenosphere (n=1), intra-operative broken screw head (n=1), broken drill bit within the scapula (n=1), chronic subluxation (n=2), acromion fracture (n=1), painful cerclage cables (n=1)
      Wierks et al.
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      First 10 v 11-20n=15 (intraoperative complications)

      n=6 (postoperative complications)
      n=7 (intraoperative complications)

      n=5 (postoperative complications)
      NRNR0.025 (intraoperative complications)

      0.361 (postoperative complications)
      75%Glenoid fracture (n=2), calcar fracture (n=1), humeral shaft fracture (n=1), medial vault penetration (n=3), center glenoid hole too large (n=2), center glenoid hole re-drilled (n=2), poor screw fixation (n=8), no anterior screw (n=3), stitch abscess (n=4), wound infection (n=1), brachial plexus injury (n=2), dislocation (n=2), return to operating room, unspecified (n=2)
      Walch et al.
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      First 240 v 241-48019.0%10.8%NRNR0.019*12.9%First 240: dislocation (n=14), infection (n=8), glenoid loosening (n=7), nerve palsy (n=3), humeral loosening (n=2), prominent hardware (n=2), acromial fracture (n=2), vein thrombosis (n=0). Last 240: dislocation (n=7), infection (n=2), glenoid loosening (n=2), nerve palsy (n=8), humeral loosening (n=1), prominent hardware (n=0), acromial fracture (n=2), vein thrombosis (n=2)
      Hasan et al.
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      First 15 v 16-60NRNRNRNRNR24.6%Dislocation (n=4), dissociation of humeral socket (n=1), scapular spine fracture (n=3), acromion fracture (n=1), humeral stress fracture (n=1), post-operative hematoma (n=1), deltoid strain (n=1), cervical radiculopathy (n=1), altered mental status (n=2), bowel obstruction (n=1)
      Levy et al.
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      131-151 v 152-17125%25%NRNR125%Post-operative acromial fractures (n=5), intra-operative partial lesser tuberosity fracture (n=1), intra-operative greater tuberosity fracture (n=1), intra-operative humeral shaft fracture (n=1), intra-operative fracture of glenosphere set screw, (n=1), post-operative dislocation (n=1)
      Key: NR=not reported; ATSA = anatomic total shoulder arthroplasty; RTSA = reverse total shoulder arthroplasty
      Table VImpact of anatomic and reverse total shoulder arthroplasty learning curve on reoperation rates
      StudyGroupings of OutcomesEarly GroupLate GroupOverallP-value
      Beazley et al.
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ATSA group, RTSA group1% (ATSA)10% (RTSA)5.50%NR
      Groh et al.
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      First 20 v last 93-112 RTSANRNR5.30%0.02
      Hasan et al.
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      First 15 RTSA, last 45 RTSA33%6.7%13.3%<.05
      Kempton et al.
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      First 40 RTSA, last 160 RTSA7.7%2.6%3.6%0.150
      Walch et al.
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      First 240 RTSA, last 240 RTSA7.5%5%6.25%NR
      Key: NR=not reported; ATSA=anatomic total shoulder arthroplasty; RTSA=reverse total shoulder arthroplasty
      Table IIIImpact of reverse total shoulder arthroplasty learning curve on patient reported outcome measures and range of motion
      StudyGroupings of OutcomesPROMs/ROMEarly group (post-operative)Late group (post-operative)P value
      Choi et al.
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      First 18 v. 19-38UCLA shoulder score16.0 (range 3–35)27.9 (range 6–35)0.002*
      Constant Score41.4 (range 9–93)78.9 (range 17–96)< 0.001*
      Forward flexion ()99.9 (range 25–160)135.4 (range 30–170)0.001*
      Abduction ()69.2 (range 23–91)124.8 (range 112∼140)< 0.001*
      Internal rotationL5L30.015*
      External rotation ()32.4 (range 5–35)34.0 (range 10–45)0.764
      Cho et al.
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      40 consecutiveUCLA shoulder scoreNR27.0 ± 7.5NR
      ASES scoreNR73.3 ± 24.4NR
      Forward flexion ()NR131.0 ± 35.6NR
      Abduction ()NR112.3 ± 32.4NR
      Internal rotation ()NRL3NR
      External rotation ()NR38.8 ± 18.5NR
      Blaas et al.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      50 consecutiveConstant ScoreNR59 [40.0, 70.3]NR
      Forward flexion ()NR105.0 [81.8, 132.0]NR
      Abduction ()NR93.0 [77.3, 111.8]NR
      External rotation ()NR16.0 [4.0, 30.0]NR
      Walch et al.
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      First 240 v 241-480Constant Score59.766.9<0.001*
      Hasan et al.
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      First 15 v 16-60ASES score70±2173±22NR
      Forward Flexion ()106±38113±30NR
      Abduction ()99±3397±24NR
      Internal RotationL3L3NR
      External Rotation ()24±2530±21NR
      Key: NR=not reported; PROMs=patient reported outcome measures; UCLA=University of California-Los Angeles shoulder score; ASES=American Shoulder and Elbow Surgeons score.
      Table IVImpact of anatomic and reverse total shoulder arthroplasty learning curve on mean operative times
      StudyGroupings of OutcomesEarly Group (min)Late Group (min)Overall (min)P value
      Choi et al.
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      First 18 v. last 19-38108.6 (71-147)87.6 (61-121)NRNR
      Wang et al.
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      24 navigated RTSANRNR77.3NR
      Blaas et al.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      50 consecutiveNRNR125.5 (111.3-155.3)NR
      Riedel et al.
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      First 18 v. last 19-62110-26585-265NRNR
      Testa et al.
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      2055 consecutiveNRNR50-275NR
      Key: NR=not reported; RTSA=reverse total shoulder arthroplasty

      Learning Curve Analysis of Reverse Total Shoulder Arthroplasty

      Complication Rates

      Complications were defined as dislocations, component loosening, painful hardware, fractures of the humerus, acromion, or scapula, nerve or vascular injury, or infection. Ten studies
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      ,
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      used complication rates to analyze the learning curve associated with RTSA. Five studies
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      ,
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      divided patients into “early” and “late” groups, whereas five studies
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      reported on consecutive patients. In the five studies
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      that reported complications among consecutive patients, the overall complication rate ranged from 15.7-24.6%. One study
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      reported a learning curve of 12 RTSA procedures to reach the mean complication rate of the cohort (20%), one study
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      noted an acceptable complication rate (20%) after 40 cases of RTSA along the learning curve, and one study
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      noted no trend along the learning curve for RTSA to reduce the complication rate. Choi et al
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      noted a complication rate of 15.7% (6/38), where two out of the six complications occurred intra-operatively in the first 20 shoulders, and the other four occurred two months postoperatively, with learning curve plateau noted at 20 cases. Finally, Hasan et al
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      reported a 24.6% complication rate in the first 60 consecutive RTSA cases performed by one surgeon and suggested the learning curve spans the first 15-20 cases.
      Five studies
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      ,
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      directly compared complication rates among “early” and “late” groups. One study
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      found a statistically significant increase in intraoperative complication rate amongst the first cohort compared to the second cohort (p=0.025), proposing the learning curve is seven RTSA cases. In this study
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      , the authors noted that after adjusting for age group and gender, individuals in the “late” cohort were only 7% as likely to have an intraoperative complication as those in the “early” cohort (odds ratio = 0.07; 9% CI, 0.01-0.92; p=0.043), but found similar (p=0.361) complication rates between the first and second cohorts postoperatively. One study
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      reported a higher complication rate in the first 40 patients (23.1%) compared to the last 160 patients (6.5%, p=0.005), a result largely influenced by minor complications (p=0.017). Walch et al
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      also noted a higher complication rate in the “early” group of 38 cases (19.1%) compared to the “late” group of 24 patients (10.8%), however this finding was not statistically significant (p=0.19). Levy et al
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      found no significant difference in complication rates between the “early” and “late” groups (25% for both, p=1). Additionally, Groh et al
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      also failed to find statistically significant differences between the “early” group (first 20 cases) and the “late” group (last 20 cases), with complication rates of 0% and 5%, respectively (p=0.96). For the six studies that specifically identified a learning curve for RTSA based on complications, the average number of cases to achieve proficiency was 22.8.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.

      Reoperation Rates

      Reoperations were defined as a need to return to the operating room. Five studies
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      used the reoperation rate to analyze the learning curve associated with RTSA. Of the four studies
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      that directly compared reoperation rates between “early” and “late” groups, one
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      found a statistically significant decrease (p<0.05) in reoperation in the “late” group compared to the “early” group whereas three studies
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      did not identify a significant difference between groups or an RTSA learning curve. Hasan et al
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      reported 15-20 cases was required to achieve proficiency on the RTSA learning curve. Beazley et al
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      reported that RTSA had an 10% complication rate after 100 consecutive cases, but no point on the learning curve was identified.

      Patient Reported Outcome Measures and Range of Motion

      Patient reported outcome measures analyzed included the University of California-Los Angeles (UCLA) shoulder scores, Constant scores, American Shoulder and Elbow Surgeons (ASES) scores, and ROM (forward flexion, abduction, external rotation, and internal rotation). Five studies
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      used PROMs and/or ROM to analyze the learning curve associated with RTSA (Table III). Amongst these, two studies
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      reported UCLA shoulder scores (mean “early” group: 14.4 [3-35] vs mean “late” group: 27.45 [6-35]), two studies
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      reported Constant scores (mean “early” group: 50.55 [9-93]vs mean “late” group: 72.9 [17-96]), two studies
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      reported ASES scores (mean “early” group: 49.5 [29-70] vs mean “late” group: 73.2 [73-73.3]), and four studies
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      reported on ROM,. In the three studies
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      that compared “early” versus “late” groups, two
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      demonstrated statistically significant improvements in late group PROMs and ROM whereas one
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      did not identify statistically significant improvements. In the two studies
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      that evaluated consecutive RTSA cases, both achieved PROMs and ROM considered to be acceptable (UCLA shoulder score > 27, Constant score > 56, forward flexion/abduction > 80 degrees, internal rotation > 40 degrees, and external rotation > 30 degrees; of note ASES score has no defined “acceptable” score), except for external rotation in Blaas et al
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      noted to be 15 degrees. For the three studies
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      that specifically identified a learning curve for RTSA based on PROMs and ROM, the average number of cases to achieve proficiency was 25.8.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.

      Operative Time

      Five studies
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      ,
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      ,
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      used operative time to analyze the learning curve associated with RTSA. Choi et al
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      reported a decreased mean operative time from 108.6 minutes [range, 71-147] to 87.6 minutes [range, 61-121] when comparing the first 18 cases of RTSA to the last 18 cases with a significant decrease in operative time after the 15th case. Blaas et al reported an overall mean operative time of 125.5 minutes [range, 111.3-155.3] in their analysis of 50 consecutive cases with shorter operative times (compared to the overall mean) observed after the first 10-15 cases.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      Riedel et al
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      plotted surgical time against case number for 62 consecutive RTSA cases and a linear regression slope was calculated. The authors demonstrated a significantly negative case slope with the first 18 cases, which subsequently leveled thereafter (cases 19-62).
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      Testa et al
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      plotted consecutive case number versus operative time for each early versus each late career surgeons and used a two-step regression to determine the plateau point / end of the learning period. The authors reported a significant negative linear relationship (p=0.01; m=-1.1) with moderate correlation (R2=0.49) between annual case volume and operative time for early-career surgeons, but no significant linear relationship for late-career surgeons.
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      The breakpoint in RTSA for early career surgeons was determined to be between 12 and
      • Sudah S.Y.
      • Michel C.R.
      • Menendez M.E.
      • Plyler R.J.
      Wide variability of shoulder and elbow case volume in orthopedic surgery residency.
      cases.
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      Lastly, Wang et al
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      specifically evaluated the learning curve of a single experienced surgeon commencing intraoperative computer navigation of the glenoid implant placement in RTSA. Mean operative time was 77.3 min and regression analysis showed the “curve of best fit” was logarithmic with a downward trend (R2=0.190, p=0.038). The significant downward trend in operative time indicated navigated RTSA did not have a learning curve, however the curve began to flatten after the 8th case.
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      For the four studies
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      that specifically identified a learning curve for RTSA based on operative time, the average number of cases to achieve proficiency was 13.9.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      ,
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.

      Learning Curve Analysis of Anatomic Total Shoulder Arthroplasty

      Complication Rates

      Complications were defined as dislocations, component loosening, painful hardware, fractures of the humerus, acromion, or scapula, nerve or vascular injury, or infection. One study
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      used the complication rate to define the learning curve amongst 100 consecutive ATSA procedures. A main inflection point along the learning curve was identified at 16 cases, after which a trend of overall improved performance (i.e., significantly lower complication rate) was demonstrated at 40 cases. Based off of this study
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      , the average number of cases to achieve proficiency on the ATSA learning cure by complication rate was 40 cases.

      Reoperation Rates

      Reoperations were defined as a need to return to the operating room. One study
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      reported a reoperation rate of 1% in 100 consecutive ATSA cases and identified an inflection point after 16 cases. Based off of this study
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      , the average number of cases to achieve proficiency on the ATSA learning curve by reoperation rate was 16 cases.

      Operative Time

      Testa et al
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      also measured overall operative time for ATSA, noting a significant negative linear relationship (p=0.02; m=-0.8) with moderate correlation (R2=0.54) between mean annual case volume and operative time in early-career surgeons, with no such significant linear relationship noted for late-career surgeons. The authors indicated breakpoints (i.e., the number of cases at which operative time significantly decreased) along the learning curve between 16 and 86 cases.
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      Based off of this study
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      , the average number of cases to achieve proficiency on the ATSA learning cure by operative time was between 16-86 cases.

      Discussion

      This review attempted to define the learning curve for RTSA and ATSA. While no single ideal measure to assess progress along the learning curve has been identified, outcomes used to establish competence have been traditionally grouped into measures of patient outcomes or surgical efficiency.
      • Barrie J.
      • Jayne D.G.
      • Wright J.
      • Czoski-Murray C.J.
      • Collinson F.J.
      • Pavitt S.H.
      Attaining Surgical Competency and Its Implications in Surgical Clinical Trial Design: A Systematic Review of the Learning Curve in Laparoscopic and Robot-Assisted Laparoscopic Colorectal Cancer Surgery.
      ,
      • Jain N.B.
      • Yamaguchi K.
      The contribution of reverse shoulder arthroplasty to utilization of primary shoulder arthroplasty.
      The studies included in this review considered reduced operative time as a proxy for surgical efficiency and improvements in complication rate, reoperation rate, and PROMs to represent measures of patient clinical outcomes. We found that surgeons may achieve significantly decreased operative times, improved PROMs, and fewer complications/reoperations as his/her experience performing RTSA and ATSA procedures grows. Although we attempt to estimate the number of cases at which a surgeon achieves proficiency along the RTSA and ATSA learning curves, a true learning curve remains difficult to quantify given the heterogeneity of reported outcome measures and statistical analyses used across included studies.
      Previously, studies for total knee arthroplasty (TKA) have demonstrated significant differences in PROMs between surgeons with differing case volumes,
      • Katz J.N.
      • Mahomed N.N.
      • Baron J.A.
      • Barrett J.A.
      • Fossel A.H.
      • Creel A.H.
      • et al.
      Association of hospital and surgeon procedure volume with patient centered outcomes of total knee replacement in a population-based cohort of patients age 65 and older.
      ,
      • Nairn L.G.L.
      • Gyemi L.
      • Gouveia K.
      • Ekhtiari S.
      • Khanna V.
      The learning curve for the direct anterior total hip arthroplasty: a systematic review.
      but studies of total hip arthroplasty (THA) report no such difference for hip-specific PROMs.
      • Jolback P.
      • Rolfson O.
      • Mohaddes M.
      • Nemes S.
      • Karrholm J.
      Does surgeon experience affect patient-reported outcomes 1 year after primary total hip arthroplasty?.
      ,
      • Sinclair S.T.
      • Klika A.K.
      • Jin Y.
      • Piuzzi N.S.
      The Impact of Surgeon Variability on Patient-Reported Outcomes in Total Hip Arthroplasty.
      • Slim K.N.E.
      • Forestier D.
      • Kwiatkowski F.
      • Panis Y.
      • Chipponi J.
      Methodological index for non-randomized studies (minors): development and validation of a new instrument.
      • Sodhi N.
      • Khlopas A.
      • Piuzzi N.S.
      • Sultan A.A.
      • Marchand R.C.
      • Malkani A.L.
      • et al.
      The Learning Curve Associated with Robotic Total Knee Arthroplasty.
      It has been suggested that this difference may be due to the technical challenge of TKA in comparison to THA,
      • Katz J.N.
      • Mahomed N.N.
      • Baron J.A.
      • Barrett J.A.
      • Fossel A.H.
      • Creel A.H.
      • et al.
      Association of hospital and surgeon procedure volume with patient centered outcomes of total knee replacement in a population-based cohort of patients age 65 and older.
      ,
      • Nairn L.G.L.
      • Gyemi L.
      • Gouveia K.
      • Ekhtiari S.
      • Khanna V.
      The learning curve for the direct anterior total hip arthroplasty: a systematic review.
      which may help to explain the similar findings we found with ATSA and RTSA as surgeons gain more experience with these complex procedures. This is especially consequential as indications for both ATSA and RTSA continue to expand to more complex conditions which may have lower preoperative scores.
      • Chalmers P.N.
      • Keener J.D.
      Expanding roles for reverse shoulder arthroplasty.
      ,
      • McGinn T.W.P.
      • Wyer P.C.
      • Newman T.B.
      • Keitz S.
      • Leipzig R.
      • For G.G.
      Tips for learners of evidence-based medicine, 3: measures of observer variability (kappa statistic).
      Given the technical challenges that come along with these procedures, we predicted increasing proficiency with increasing case volume, despite a slightly less steep learning curve.
      Complication rates were among the most commonly reported outcomes used in the evaluation of surgical skill in this review. The overall complication rate for RTSA ranged from 0-25% (mean 17.02%) for early cases and from 5-25% (mean 9.45%) for late cases
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      ; Wierks et al
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      did not specify the exact number of patients with complications in their “early” versus “late” cohort, however the group had an overall complication rate of 75%. For the studies reporting overall complication rates, these ranged from 7-75% (mean 23.3%)
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      ,
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      . Thus, the learning curve for RTSA based on complication rate from six studies which reported a specific case number ranged from 7-40 cases.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      . The remaining four studies which analyzed complication rate did not identify a learning.
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      The reason these studies did not identify a learning curve possibly include the surgeon already having passed the “inflection point” on the learning curve when the study was conducted as most surgeons were considered high volume
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Groh G.I.
      • Groh G.M.
      Complications rates, reoperation rates, and the learning curve in reverse shoulder arthroplasty.
      ,
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      or there was too short follow-up time to accurately reflect all complications and observe a difference
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      . For ATSA, the early group complication rate was 4%.
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      Based on this one study, the learning curve for ATSA was demonstrated at 40 cases, after which a trend of overall improved performance (i.e., significantly lower complication rate) was observed.
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      In the reported literature, the overall complication rates for RTSA and ATSA range from 0 to 75%
      • Boileau P.W.D.
      • Watkinson D.J.
      • Hatzidakis A.M.
      • Balg F.
      Grammont reverse prosthesis: design, rationale, and biomechanics.
      ,
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Matache B.A.
      • Lapner P.
      Anatomic Shoulder Arthroplasty: Technical Considerations.
      ,
      • Parada S.A.
      • Flurin P.H.
      • Wright T.W.
      • Zuckerman J.D.
      • Elwell J.A.
      • Roche C.P.
      • et al.
      Comparison of complication types and rates associated with anatomic and reverse total shoulder arthroplasty.
      ,
      • Werner C.M.
      • Steinmann P.A.
      • Gilbart M.
      • Gerber C.
      Treatment of painful pseudoparesis due to irreparable rotator cuff dysfunction with the Delta III reverse-ball-and-socket total shoulder prosthesis.
      .
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      and 4% to 15%, respectively, which was observed in this review.
      • Beazley J.
      • Evans J.P.
      • Furness N.D.
      • Smith D.C.
      Comparative learning curves for early complications in anatomical and reverse shoulder arthroplasty.
      ,
      • Kiet T.K.
      • Feeley B.T.
      • Naimark M.
      • Gajiu T.
      • Hall S.L.
      • Chung T.T.
      • et al.
      Outcomes after shoulder replacement: comparison between reverse and anatomic total shoulder arthroplasty.
      In addition, it is important to consider the lack of consistency in the classification (i.e., type and timing) of complications reported by included studies as this may affect the validity of the results. Three studies noted that the reduction of intraoperative or minor complications may disproportionately contribute to the decrease in complication rates observed for late cases.
      • Kempton L.B.
      • Ankerson E.
      • Wiater J.M.
      A complication-based learning curve from 200 reverse shoulder arthroplasties.
      ,
      • Levy J.C.
      • Blum S.M.
      Reverse shoulder replacement: Initial complication rate after fellowship experience.
      ,
      • Wierks C.
      • Skolasky R.L.
      • Ji J.H.
      • McFarland E.G.
      Reverse total shoulder replacement: intraoperative and early postoperative complications.
      Use of the complication rate to assess proficiency also neglects to account for varying surgical indications or case complexity of individual cases that may represent varied degrees of difficulty. In a review of complications after RTSA, Barco et al linked the expanding indications of RTSA to more complex conditions and the implementation of changing implant designs to a higher risk of complication.
      • Barco R.
      • Savvidou O.D.
      • Sperling J.W.
      • Sanchez-Sotelo J.
      • Cofield R.H.
      Complications in reverse shoulder arthroplasty.
      ,
      • Ekhtiari S.
      • Horner N.S.
      • Bedi A.
      • Ayeni O.R.
      • Khan M.
      The Learning Curve for the Latarjet Procedure: A Systematic Review.
      Implant designs in this study were diverse, with studies reporting use of either the Grammont-style or glenoid-based lateralized implants, which each have unique complications at differing rates.
      • Barco R.
      • Savvidou O.D.
      • Sperling J.W.
      • Sanchez-Sotelo J.
      • Cofield R.H.
      Complications in reverse shoulder arthroplasty.
      ,
      • Ekhtiari S.
      • Horner N.S.
      • Bedi A.
      • Ayeni O.R.
      • Khan M.
      The Learning Curve for the Latarjet Procedure: A Systematic Review.
      Lastly, there has been evolution of ATSA and RTSA knowledge base over time, allowing for fine tuning of the procedure in order to decrease complication rates of more recently performed surgeries as opposed to remote surgeries; all studies in this review were performed in varying years.
      Furthermore, longer operative times for ATSA and RTSA have been associated with worse postoperative outcomes, including increased risk of infection and peripheral nerve injury.
      • Kim S.H.
      • Wise B.L.
      • Zhang Y.
      • Szabo R.M.
      Increasing incidence of shoulder arthroplasty in the United States.
      ,
      • Waterman B.R.
      • Dunn J.C.
      • Bader J.
      • Urrea L.
      • Schoenfeld A.J.
      • Belmon Jr., P.J.
      Thirty-day morbidity and mortality after elective total shoulder arthroplasty: patient-based and surgical risk factors.
      ,
      • Westermann R.W.
      • Pugely A.J.
      • Martin C.T.
      • Gao Y.
      • Wolf B.R.
      • Hettrich C.M.
      Reverse Shoulder Arthroplasty in the United States: A Comparison of National Volume, Patient Demographics, Complications, and Surgical Indications.
      ,
      • Wilson J.M.
      • Holzgrefe R.E.
      • Staley C.A.
      • Spero Karas
      • Gottschalk M.B.
      • Wagner E.R.
      The effect of operative time on early postoperative complications in total shoulder arthroplasty: An analysis of the ACS-NSQIP database.
      Accordingly, operative time has been used as a measure of proficiency as an indicator of individual surgical skill.
      • Kim S.H.
      • Wise B.L.
      • Zhang Y.
      • Szabo R.M.
      Increasing incidence of shoulder arthroplasty in the United States.
      ,
      • Wilson J.M.
      • Holzgrefe R.E.
      • Staley C.A.
      • Spero Karas
      • Gottschalk M.B.
      • Wagner E.R.
      The effect of operative time on early postoperative complications in total shoulder arthroplasty: An analysis of the ACS-NSQIP database.
      Four studies reported a decrease in operative time with progression along the learning curve for RTSA and reported the learning curve between 10-36 RTSA cases, with an average of 13.9 cases.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      ,
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      . In addition, Testa et al
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      also evaluated operative time for ATSA in addition to RTSA, reporting the number of cases at which operative time significantly decreased along the learning curve between 16 and 86 cases.
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      However, it should be noted that utilizing reduced operative time as an indicator for surgeon proficiency may be confound by external factors. In particular, as surgeons become comfortable with performing a procedure, they may require less assistance from more experienced surgeons or undertake more complex cases, ultimately affecting overall operative time.
      • Day J.S.L.E.
      • Ong K.L.
      • Williams G.R.
      • Ramsey M.L.
      • Kurtz S.M.
      Prevalence and projections of total shoulder and elbow arthroplasty in the United States to 2015.
      ,
      • Hoppe D.J.
      • De Sa D.
      • Simunovic N.
      • Bhandari M.
      • Safran M.R.
      • Larson C.M.
      • et al.
      The learning curve for hip arthroscopy: a systematic review.
      The reported studies also did not identify how many individuals assisted the operating surgeon.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      ,
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      ,
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      In addition, further confounding may be the inclusion of time for anesthesia induction or patient positioning resulting in artificial inflation of operative time.
      • Day J.S.L.E.
      • Ong K.L.
      • Williams G.R.
      • Ramsey M.L.
      • Kurtz S.M.
      Prevalence and projections of total shoulder and elbow arthroplasty in the United States to 2015.
      ,
      • Hoppe D.J.
      • De Sa D.
      • Simunovic N.
      • Bhandari M.
      • Safran M.R.
      • Larson C.M.
      • et al.
      The learning curve for hip arthroscopy: a systematic review.
      In this review, only two studies defined the operative time as the time from skin incision to closure.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      Moreover, Wang et al
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      specifically evaluated the learning curve of a single experienced surgeon commencing intraoperative computer navigation of the glenoid implant placement in RTSA using operative time. Regression analysis demonstrated a significant downward trend in operative time of the “curve of best fit”, indicating navigated RTSA did not have a learning curve.
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      This study
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      demonstrates technical change in operative technique of experienced surgeons later in careers may not require a learning period or significantly affect surgical proficiency. As not all papers explicitly defined after how many years a surgeon was considered “experienced,” operating surgeons may have had varying degrees of training prior to conducting their analysis of the learning curve. This heterogeneity may have confounded the derived learning curves, or lack thereof, as more “experienced” surgeons may have already plateaued on the learning curve at the time the study was conducted.
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Riedel B.B.
      • Mildren M.E.
      • Jobe C.M.
      • Wongworawat M.D.
      • Phipatanakul W.P.
      Evaluation of the learning curve for reverse shoulder arthroplasty.
      ,
      • Testa E.J.
      • Lowe J.T.
      • Namdari S.
      • Gillespie R.J.
      • Sears B.W.
      • Johnston P.S.
      • et al.
      Operative duration-based learning period analysis for reverse and total shoulder arthroplasty: A multicenter study.
      ,
      • Wang A.W.
      • Hayes A.
      • Gibbons R.
      • Mackie K.E.
      Computer navigation of the glenoid component in reverse total shoulder arthroplasty: a clinical trial to evaluate the learning curve.
      Various PROMs, including the UCLA shoulder score,
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      Constant score,
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.
      ,
      • Choi S.
      • Bae J.H.
      • Kwon Y.S.
      • Kang H.
      Clinical outcomes and complications of cementless reverse total shoulder arthroplasty during the early learning curve period.
      ,
      • Walch G.
      • Bacle G.
      • Lädermann A.
      • Nove-Josserand L.
      • Smithers C.J.
      Do the indications, results, and complications of reverse shoulder arthroplasty change with surgeon's experience?.
      , ASES score
      • Cho C.H.
      • Song K.S.
      • Koo T.W.
      Clinical Outcomes and Complications during the Learning Curve for Reverse Total Shoulder Arthroplasty: An Analysis of the First 40 Cases.
      ,
      • Hasan S.S.
      • Gordon M.P.
      • Ramsey J.A.
      • Levy M.S.
      Reverse shoulder arthroplasty using an implant with a lateral center of rotation: outcomes, complications, and the influence of experience.
      , in addition to ROM
      • Blaas L.S.
      • Yuan J.Z.
      • Lameijer C.M.
      • van de Ven P.M.
      • Bloemers F.W.
      • Derksen R.J.
      Surgical learning curve in reverse shoulder arthroplasty for proximal humerus fractures.