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Large image of Figure 1.

Figure 1

5-mm round burr to create the entry hole at the superior apex of the humeral head.

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Figure 2

Humeral resection utilizing an intramedullary humeral cutting guide.

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Figure 3

Sequential broaching of the humeral canal.

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Figure 4

Heart shaped metaphyseal surface after osteophyte removal.

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Figure 5

Patient specific guide with depth control

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Figure 6

Schematic demonstrating the preservation of bone with use of the augmented glenoid reaming system.

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Figure 7

High side glenoid reaming with the patient specific guide.

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Figure 8

Low side glenoid reaming with the augmented reamer guide.

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Figure 9

Insertion of the augmented baseplate

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Figure 10

Glenosphere is dialed to the appropriate offset prior to implantation to titrate the soft tissue tension.

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Figure 11

Humeral tray offset options.

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Figure 12

Humeral tray with +6 offset on humerus selected to optimize central position on the resected surface.

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Figure 13

Postoperative radiographs of different offset tray configurations to demonstrating the ability to tension each shoulder as desired.

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Figure 14

Humeral stem inserted into the prepared canal in neutral alignment.

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Figure 15

Humeral stem positioned centrally in the prepared canal.

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Figure 16

Final construct with offset humeral tray minimizing medial overhang.

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Figure 17

Subscapularis closure after placement of final components.

Large image of Figure 18.

Figure 18

Preoperative and postoperative anterior-posterior radiograph of an arthritic shoulder treated with a RSA with an offset humeral tray and augmented baseplate.

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Abstract

Reverse total shoulder arthroplasty (RSA) has become the most utilized form of arthroplasty of the shoulder. Acromial (ASF) and scapular spine (SSF) stress fractures are rare, yet well-recognized complications of RSA with ongoing studies identifying whether patient factors or prosthetic designs serve as risk factors. Specifically, it remains unclear if or how the position of the humeral tray (inlay or onlay) in RSA affects rates of periscapular fractures. The purpose of this article is to describe our technique for RSA using an onlay prosthesis, variable-offset humeral tray, and augmented glenoid baseplate, as well as to review the published results of acromial and scapular spine fractures after RSA based on humeral implant design.

Reverse total shoulder arthroplasty (RSA) is a well-established and increasingly utilized procedure for improving pain relief and function in patients with rotator cuff insufficiency and glenohumeral osteoarthritis.40x40Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. J Clin Med. 2021; 10https://doi.org/10.3390/jcm10215151

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In recent years, periprosthetic scapular spine fractures (SSF) and acromial fractures (AF) have been recognized as a unique complication of RSA.11x11Crosby, L.A., Hamilton, A., and Twiss, T. Scapula fractures after reverse total shoulder arthroplasty: classification and treatment. Clin Orthop Relat Res. 2011; 469: 2544–2549https://doi.org/10.1007/s11999-011-1881-3

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,28x28Levy, J.C., Anderson, C., and Samson, A. Classification of postoperative acromial fractures following reverse shoulder arthroplasty. J Bone Joint Surg Am. 2013; 95: e104https://doi.org/10.2106/jbjs.K.01516

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Biomechanical investigations have suggested etiologies for these fractures to include alterations in deltoid strain21x21Kerrigan, A.M., Reeves, J.M., Langohr, G.D.G., Johnson, J.A., and Athwal, G.S. The influence of reverse arthroplasty humeral component design features on scapular spine strain. Journal of Shoulder and Elbow Surgery. 2021; 30: 572–579https://doi.org/10.1016/j.jse.2020.06.011

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,41x41Shah, S.S., Gentile, J., Chen, X., Kontaxis, A., Dines, D.M., Warren, R.F. et al. Influence of implant design and parasagittal acromial morphology on acromial and scapular spine strain after reverse total shoulder arthroplasty: a cadaveric and computer-based biomechanical analysis. J Shoulder Elbow Surg. 2020; 29: 2395–2405https://doi.org/10.1016/j.jse.2020.04.004

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,50x50Wong, M.T., Langohr, G.D.G., Athwal, G.S., and Johnson, J.A. Implant positioning in reverse shoulder arthroplasty has an impact on acromial stresses. Journal of Shoulder and Elbow Surgery. 2016; 25: 1889–1895https://doi.org/10.1016/j.jse.2016.04.011

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, glenoid baseplate screws as potential stress risers20x20Kennon, J.C., Lu, C., McGee-Lawrence, M.E., and Crosby, L.A. Scapula fracture incidence in reverse total shoulder arthroplasty using screws above or below metaglene central cage: clinical and biomechanical outcomes. J Shoulder Elbow Surg. 2017; 26: 1023–1030https://doi.org/10.1016/j.jse.2016.10.018

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, and variations in implant and arm positioning.21x21Kerrigan, A.M., Reeves, J.M., Langohr, G.D.G., Johnson, J.A., and Athwal, G.S. The influence of reverse arthroplasty humeral component design features on scapular spine strain. Journal of Shoulder and Elbow Surgery. 2021; 30: 572–579https://doi.org/10.1016/j.jse.2020.06.011

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,41x41Shah, S.S., Gentile, J., Chen, X., Kontaxis, A., Dines, D.M., Warren, R.F. et al. Influence of implant design and parasagittal acromial morphology on acromial and scapular spine strain after reverse total shoulder arthroplasty: a cadaveric and computer-based biomechanical analysis. J Shoulder Elbow Surg. 2020; 29: 2395–2405https://doi.org/10.1016/j.jse.2020.04.004

Abstract | Full Text | Full Text PDF | PubMed | Scopus (13)
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,50x50Wong, M.T., Langohr, G.D.G., Athwal, G.S., and Johnson, J.A. Implant positioning in reverse shoulder arthroplasty has an impact on acromial stresses. Journal of Shoulder and Elbow Surgery. 2016; 25: 1889–1895https://doi.org/10.1016/j.jse.2016.04.011

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Reported rates of acromial and scapular stress fractures have been estimated around 0.6%-5%.8x8Cho, C.H., Jung, J.W., Na, S.S., Bae, K.C., Lee, K.J., and Kim, D.H. Is Acromial Fracture after Reverse Total Shoulder Arthroplasty a Negligible Complication?: A Systematic Review. Clin Orthop Surg. 2019; 11: 427–435https://doi.org/10.4055/cios.2019.11.4.427

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,27x27Lau, S.C. and Large, R. Acromial fracture after reverse total shoulder arthroplasty: a systematic review. Shoulder Elbow. 2020; 12: 375–389https://doi.org/10.1177/1758573219876486

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,31x31Marigi, E., Bartels, D., Tangtiphaiboontana, J., Ivanov, D., Nguyen, N.-T., and Sanchez-Sotelo, J. Acromial and spine fractures after reverse arthroplasty: Prevalence and risk factors. Seminars in Arthroplasty: JSES. 2020; 30: 237–241https://doi.org/10.1053/j.sart.2020.07.006

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,34x34Patterson, D.C., Chi, D., Parsons, B.O., and Cagle, P.J. Jr. Acromial spine fracture after reverse total shoulder arthroplasty: a systematic review. J Shoulder Elbow Surg. 2019; 28: 792–801https://doi.org/10.1016/j.jse.2018.08.033

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,41x41Shah, S.S., Gentile, J., Chen, X., Kontaxis, A., Dines, D.M., Warren, R.F. et al. Influence of implant design and parasagittal acromial morphology on acromial and scapular spine strain after reverse total shoulder arthroplasty: a cadaveric and computer-based biomechanical analysis. J Shoulder Elbow Surg. 2020; 29: 2395–2405https://doi.org/10.1016/j.jse.2020.04.004

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, with a recent systematic review reporting an overall incidence of 2.6% among modern RSA designs.41x41Shah, S.S., Gentile, J., Chen, X., Kontaxis, A., Dines, D.M., Warren, R.F. et al. Influence of implant design and parasagittal acromial morphology on acromial and scapular spine strain after reverse total shoulder arthroplasty: a cadaveric and computer-based biomechanical analysis. J Shoulder Elbow Surg. 2020; 29: 2395–2405https://doi.org/10.1016/j.jse.2020.04.004

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To date, several clinical investigations have identified possible risk factors for acromial and scapular spine fractures (SSF) following RSA. These risk factors include female sex30x30Mahendraraj, K.A., Abboud, J., Armstrong, A., Austin, L., Brolin, T., Entezari, V. et al. Predictors of acromial and scapular stress fracture after reverse shoulder arthroplasty: a study by the ASES Complications of RSA Multicenter Research Group. J Shoulder Elbow Surg. 2021; 30: 2296–2305https://doi.org/10.1016/j.jse.2021.02.008

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, poor bone stock23x23Kirzner, N., Paul, E., and Moaveni, A. Reverse shoulder arthroplasty vs BIO-RSA: clinical and radiographic outcomes at short term follow-up. J Orthop Surg Res. 2018; 13: 256https://doi.org/10.1186/s13018-018-0955-2

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,30x30Mahendraraj, K.A., Abboud, J., Armstrong, A., Austin, L., Brolin, T., Entezari, V. et al. Predictors of acromial and scapular stress fracture after reverse shoulder arthroplasty: a study by the ASES Complications of RSA Multicenter Research Group. J Shoulder Elbow Surg. 2021; 30: 2296–2305https://doi.org/10.1016/j.jse.2021.02.008

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,33x33Otto, R.J., Virani, N.A., Levy, J.C., Nigro, P.T., Cuff, D.J., and Frankle, M.A. Scapular fractures after reverse shoulder arthroplasty: evaluation of risk factors and the reliability of a proposed classification. J Shoulder Elbow Surg. 2013; 22: 1514–1521https://doi.org/10.1016/j.jse.2013.02.007

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,48x48Werthel, J.-D., Schoch, B.S., van Veen, S.C., Elhassan, B.T., An, K.-N., Cofield, R.H. et al. Acromial Fractures in Reverse Shoulder Arthroplasty: A Clinical and Radiographic Analysis. Journal of Shoulder and Elbow Arthroplasty. 2018; 2: 2471549218777628https://doi.org/10.1177/2471549218777628

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, prior acromioplasty31x31Marigi, E., Bartels, D., Tangtiphaiboontana, J., Ivanov, D., Nguyen, N.-T., and Sanchez-Sotelo, J. Acromial and spine fractures after reverse arthroplasty: Prevalence and risk factors. Seminars in Arthroplasty: JSES. 2020; 30: 237–241https://doi.org/10.1053/j.sart.2020.07.006

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, rheumatoid arthritis30x30Mahendraraj, K.A., Abboud, J., Armstrong, A., Austin, L., Brolin, T., Entezari, V. et al. Predictors of acromial and scapular stress fracture after reverse shoulder arthroplasty: a study by the ASES Complications of RSA Multicenter Research Group. J Shoulder Elbow Surg. 2021; 30: 2296–2305https://doi.org/10.1016/j.jse.2021.02.008

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,38x38Routman, H.D., Simovitch, R.W., Wright, T.W., Flurin, P.H., Zuckerman, J.D., and Roche, C.P. Acromial and Scapular Fractures After Reverse Total Shoulder Arthroplasty with a Medialized Glenoid and Lateralized Humeral Implant: An Analysis of Outcomes and Risk Factors. J Bone Joint Surg Am. 2020; 102: 1724–1733https://doi.org/10.2106/jbjs.19.00724

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, and rotator cuff tear arthropathy.30x30Mahendraraj, K.A., Abboud, J., Armstrong, A., Austin, L., Brolin, T., Entezari, V. et al. Predictors of acromial and scapular stress fracture after reverse shoulder arthroplasty: a study by the ASES Complications of RSA Multicenter Research Group. J Shoulder Elbow Surg. 2021; 30: 2296–2305https://doi.org/10.1016/j.jse.2021.02.008

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,38x38Routman, H.D., Simovitch, R.W., Wright, T.W., Flurin, P.H., Zuckerman, J.D., and Roche, C.P. Acromial and Scapular Fractures After Reverse Total Shoulder Arthroplasty with a Medialized Glenoid and Lateralized Humeral Implant: An Analysis of Outcomes and Risk Factors. J Bone Joint Surg Am. 2020; 102: 1724–1733https://doi.org/10.2106/jbjs.19.00724

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Furthermore, recent efforts have been made to identify modifiable procedural and implant related risk factors for scapular fractures, with variable and conflicting results. Proposed risk factors have included superior glenoid baseplate screw placement4x4Ascione, F., Kilian, C.M., Laughlin, M.S., Bugelli, G., Domos, P., Neyton, L. et al. Increased scapular spine fractures after reverse shoulder arthroplasty with a humeral onlay short stem: an analysis of 485 consecutive cases. J Shoulder Elbow Surg. 2018; 27: 2183–2190https://doi.org/10.1016/j.jse.2018.06.007

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, increased deltoid length9x9Cho, C.H., Rhee, Y.G., Yoo, J.C., Ji, J.H., Kim, D.S., Kim, Y.S. et al. Incidence and risk factors of acromial fracture following reverse total shoulder arthroplasty. J Shoulder Elbow Surg. 2021; 30: 57–64https://doi.org/10.1016/j.jse.2020.04.031

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,48x48Werthel, J.-D., Schoch, B.S., van Veen, S.C., Elhassan, B.T., An, K.-N., Cofield, R.H. et al. Acromial Fractures in Reverse Shoulder Arthroplasty: A Clinical and Radiographic Analysis. Journal of Shoulder and Elbow Arthroplasty. 2018; 2: 2471549218777628https://doi.org/10.1177/2471549218777628

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, glenoid over-lateralization50x50Wong, M.T., Langohr, G.D.G., Athwal, G.S., and Johnson, J.A. Implant positioning in reverse shoulder arthroplasty has an impact on acromial stresses. Journal of Shoulder and Elbow Surgery. 2016; 25: 1889–1895https://doi.org/10.1016/j.jse.2016.04.011

Abstract | Full Text | Full Text PDF | PubMed | Scopus (59)
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, and the use of an onlay humeral component design.3x3Ascione, F., Bugelli, G., Domos, P., Neyton, L., Godeneche, A., Bercik, M.J. et al. Reverse Shoulder Arthroplasty with a New Convertible Short Stem: Preliminary 2- to 4-year Follow-up Results. Journal of Shoulder and Elbow Arthroplasty. 2017; 1: 2471549217746272https://doi.org/10.1177/2471549217746272

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,4x4Ascione, F., Kilian, C.M., Laughlin, M.S., Bugelli, G., Domos, P., Neyton, L. et al. Increased scapular spine fractures after reverse shoulder arthroplasty with a humeral onlay short stem: an analysis of 485 consecutive cases. J Shoulder Elbow Surg. 2018; 27: 2183–2190https://doi.org/10.1016/j.jse.2018.06.007

Abstract | Full Text | Full Text PDF | PubMed | Scopus (53)
| Google ScholarSee all References
,15x15Haidamous, G., Lädermann, A., Frankle, M.A., Gorman, R.A. 2nd, and Denard, P.J. The risk of postoperative scapular spine fracture following reverse shoulder arthroplasty is increased with an onlay humeral stem. J Shoulder Elbow Surg. 2020; 29: 2556–2563https://doi.org/10.1016/j.jse.2020.03.036

Abstract | Full Text | Full Text PDF | PubMed | Scopus (21)
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Modifications to humeral component design have evolved over the years, with efforts focused on reducing rates of scapular notching and addressing range-of-motion (ROM) deficits that were common with traditional Grammont style inlay prostheses.40x40Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. J Clin Med. 2021; 10https://doi.org/10.3390/jcm10215151

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Early biomechanical studies by Virani et al46x46Virani, N.A., Cabezas, A., Gutiérrez, S., Santoni, B.G., Otto, R., and Frankle, M. Reverse shoulder arthroplasty components and surgical techniques that restore glenohumeral motion. Journal of Shoulder and Elbow Surgery. 2013; 22: 179–187https://doi.org/10.1016/j.jse.2012.02.004

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suggested that ROM deficits and impingement seen with the Grammont style prosthesis were primarily related to implant positioning, with humeral implant design (inset vs. onset) having little impact.46x46Virani, N.A., Cabezas, A., Gutiérrez, S., Santoni, B.G., Otto, R., and Frankle, M. Reverse shoulder arthroplasty components and surgical techniques that restore glenohumeral motion. Journal of Shoulder and Elbow Surgery. 2013; 22: 179–187https://doi.org/10.1016/j.jse.2012.02.004

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These findings led Dr. Frankle and their group to modify the principles of reverse shoulder arthroplasty in order optimize soft tissue tension and range of motion. This was achieved, in part, by utilizing a thicker glenosphere and a more vertical 135 degree opening angle humeral component.40x40Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. J Clin Med. 2021; 10https://doi.org/10.3390/jcm10215151

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These concepts have carried over into the contemporary prostheses in use today.40x40Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. J Clin Med. 2021; 10https://doi.org/10.3390/jcm10215151

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Contemporary humeral component designs can be broadly categorized as either inlay or onlay, with onlay prostheses offering the benefit of bone preservation40x40Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. J Clin Med. 2021; 10https://doi.org/10.3390/jcm10215151

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, improved ROM 3x3Ascione, F., Bugelli, G., Domos, P., Neyton, L., Godeneche, A., Bercik, M.J. et al. Reverse Shoulder Arthroplasty with a New Convertible Short Stem: Preliminary 2- to 4-year Follow-up Results. Journal of Shoulder and Elbow Arthroplasty. 2017; 1: 2471549217746272https://doi.org/10.1177/2471549217746272

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, lower rates of scapular notching12x12Franceschetti, E., Palumbo, A., Baldari, A., De Angelis D'Ossat, G.M., Paciotti, M., Papapietro, N. et al. Clinical results of humeral stem lateralization in reverse shoulder arthroplasty: Comparative study of 145° onlay curved stem vs 155° inlay straight stem. Seminars in Arthroplasty: JSES. 2020; 30: 181–187https://doi.org/10.1053/j.sart.2020.08.005

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, and easier conversion from anatomic total shoulder arthroplasty (aTSA).40x40Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. J Clin Med. 2021; 10https://doi.org/10.3390/jcm10215151

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Alternatively, inlay prostheses have also demonstrated improvement in shoulder pain, ROM, and function, with the added theoretical benefit of increased bone-implant interface when compared to onlay prostheses.39x39Rugg, C.M., Coughlan, M.J., and Lansdown, D.A. Reverse Total Shoulder Arthroplasty: Biomechanics and Indications. Curr Rev Musculoskelet Med. 2019; 12: 542–553https://doi.org/10.1007/s12178-019-09586-y

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However, specific analyses of humeral component design and it’s relationship to acromial and scapular spine fractures have yielded conflicting results.3x3Ascione, F., Bugelli, G., Domos, P., Neyton, L., Godeneche, A., Bercik, M.J. et al. Reverse Shoulder Arthroplasty with a New Convertible Short Stem: Preliminary 2- to 4-year Follow-up Results. Journal of Shoulder and Elbow Arthroplasty. 2017; 1: 2471549217746272https://doi.org/10.1177/2471549217746272

Crossref
| Google ScholarSee all References
,4x4Ascione, F., Kilian, C.M., Laughlin, M.S., Bugelli, G., Domos, P., Neyton, L. et al. Increased scapular spine fractures after reverse shoulder arthroplasty with a humeral onlay short stem: an analysis of 485 consecutive cases. J Shoulder Elbow Surg. 2018; 27: 2183–2190https://doi.org/10.1016/j.jse.2018.06.007

Abstract | Full Text | Full Text PDF | PubMed | Scopus (53)
| Google ScholarSee all References
,12x12Franceschetti, E., Palumbo, A., Baldari, A., De Angelis D'Ossat, G.M., Paciotti, M., Papapietro, N. et al. Clinical results of humeral stem lateralization in reverse shoulder arthroplasty: Comparative study of 145° onlay curved stem vs 155° inlay straight stem. Seminars in Arthroplasty: JSES. 2020; 30: 181–187https://doi.org/10.1053/j.sart.2020.08.005

Abstract | Full Text | Full Text PDF | Scopus (3)
| Google ScholarSee all References
,15x15Haidamous, G., Lädermann, A., Frankle, M.A., Gorman, R.A. 2nd, and Denard, P.J. The risk of postoperative scapular spine fracture following reverse shoulder arthroplasty is increased with an onlay humeral stem. J Shoulder Elbow Surg. 2020; 29: 2556–2563https://doi.org/10.1016/j.jse.2020.03.036

Abstract | Full Text | Full Text PDF | PubMed | Scopus (21)
| Google ScholarSee all References
,32x32Merolla, G., Walch, G., Ascione, F., Paladini, P., Fabbri, E., Padolino, A. et al. Grammont humeral design versus onlay curved-stem reverse shoulder arthroplasty: comparison of clinical and radiographic outcomes with minimum 2-year follow-up. J Shoulder Elbow Surg. 2018; 27: 701–710https://doi.org/10.1016/j.jse.2017.10.016

Abstract | Full Text | Full Text PDF | PubMed | Scopus (64)
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,35x35Polisetty, T., Baessler, A., Levy, J., and Badman, B. Onlay versus Inlay Reverse Total Shoulder Arthroplasty: A Retrospective Comparison of Radiographic and Clinical Outcomes. Seminars in Arthroplasty. 2020; : 31https://doi.org/10.1053/j.sart.2020.11.013

Abstract | Full Text | Full Text PDF | Scopus (6)
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,51x51Zmistowski, B., Gutman, M., Horvath, Y., Abboud, J.A., Williams, G.R. Jr., and Namdari, S. Acromial stress fracture following reverse total shoulder arthroplasty: incidence and predictors. J Shoulder Elbow Surg. 2020; 29: 799–806https://doi.org/10.1016/j.jse.2019.08.004

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Recently, offset humeral trays have been introduced, however there is little information available on the technique of implantation and impact on soft tissue tensioning with reverse arthroplasty. Notably, offset humeral trays are unique to onlay prosthesis designs, conferring one additional potential benefit. This article presents key technical aspects of RSA implantation and tensioning, using an onlay humeral prosthesis with offset humeral tray and augmented glenoid baseplate of one specific commercially available implant system.

Clinical Evaluation and Surgical Technique

Patients presenting with shoulder pain undergo a standard comprehensive workup including complete history and physical exam, with special attention to the course of their shoulder pathology and clinic status of the deltoid and rotator cuff. Standard imaging includes antero-posterior and axillary radiographs to characterize glenohumeral joint pathology, joint space narrowing, and variations in glenohumeral morphology. Computed tomography is frequently obtained to further characterize the glenoid version and bone loss, in addition to obtaining radiographic data for patient specific instrumentation.

The most common indication for RSA is glenohumeral arthritis in the setting of rotator cuff deficiency and an intact deltoid with persistent symptoms despite a comprehensive course of nonoperative management. Additional common indications are listed below. Patients presenting with failure of previous shoulder surgery undergo further assessment, including evaluation of the prior implant type and expected bone loss in addition to examination of the rotator cuff and deltoid function.

Indications:

  • Rotator cuff arthropathy

  • Glenohumeral arthritis with deficient rotator cuff

  • Unreconstructable proximal humerus fractures particularly in the elderly

  • Massive irreparable rotator cuff tears in the elderly

  • Rotator cuff deficiency, bone loss, deformity, or instability not conducive to aTSA

  • Patients who have failed prior shoulder arthroplasty with rotator cuff failure and / or instability

Contraindications

  • Axillary nerve damage or a non-functioning deltoid muscle

  • Excessive glenoid vault deficiency not amenable to baseplate fixation

  • Active infection.

Surgical Technique

Successful RSA implantation requires surgeon expertise in shoulder anatomy, kinematics, implant design, and operative technique, among others. Here we describe one surgeon’s preferred technique using an onlay, variable-offset humeral component with augmented glenosphere baseplate, highlighting the key technical aspects as they relate to soft tissue tensioning and mitigating scapular and acromial strains.

Patient positioning

The patient is induced under general anesthesia with or without the use of an interscalene block. Afterward, the patient is positioned in the standard supine beach-chair position, with the medial border of the scapula positioned at the edge of the bed. A rolled-up towel is selectively placed posteriorly between the scapulae to support and stabilize the ipsilateral scapula during glenoid implantation.

Approach and initial exposure

One of the most challenging parts of RSA implantation is glenoid exposure. Glenoid exposure is facilitated through four key steps including an appropriate humeral head cut, humeral osteophyte removal, capsule release and deltoid mobilization. All of these steps occur on the humeral side. Therefore, the key to glenoid exposure is on the humeral rather than the glenoid side.

A deltopectoral approach is carried out in standard fashion, ensuring excellent exposure of the glenoid and proximal humerus. A 10 cm skin is incision is created just lateral to the coracoid, beginning proximally at the level of the anterior clavicle. Distally, the incision lies just medial to the midpoint of the arm. The deltopectoral interval is identified just inferior to the level of the coracoid and is developed further distally. According to surgeon preference, the cephalic vein is preserved and retracted medially. Access to the subdeltoid space is achieved just proximal to the deltoid insertion, and a plane is developed between the deltoid and lateral humerus. The subacromial space is then developed bluntly, at which point a Darrach elevator may be used to gently free subacromial adhesions as needed. The arm is adducted and externally rotated, at which point a plane is developed between the conjoint tendon and the subscapularis. Next, the anterior humeral circumflex artery and veins are identified and ligated.

Deep exposure and Subscapularis release

The long head of the biceps is tenodesed to the tendinous insertion of the pectoralis major tendon using two #2 non-absorbable sutures. In revision cases, or in cases with difficult exposure, the proximal 1 cm of pectoralis major tendon may be released to improve visualization. While subscapularis tenotomy, peel, and lesser tuberosity osteotomy are all validated options for subscapularis management, our preferences is to perform a subscapularis tenotomy or peel.24x24Lachance, A.D., Peebles, A.M., McBride, T., Eble, S.K., and Provencher, M.T. Subscapularis repair techniques for reverse total shoulder arthroplasty: A systematic review. Journal of ISAKOS. 2022; https://doi.org/10.1016/j.jisako.2022.05.001

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Subsequently, a retention stitch placed in the superolateral corner and lateral midportion of the subscapularis tendon. Subsequently, the joint capsule is released from the humerus, first ensuring complete release of lateral humeral attachments and then along the inferomedial humeral neck to the mid-sagittal line of the humerus.

Humeral preparation

The humerus is dislocated using gentle adduction, extension, and external rotation. The bursal and articular aspects of the rotator cuff are carefully evaluated to verify the expected rotator cuff pathology. The medullary canal of the humerus is opened using a 5-mm round burr, starting at the superior apex of the humeral head (Figure 1). An ice pick is used to define the path of the intramedullary canal. Circular reamers are then sequentially introduced until firm resistance is encountered. At this point, the intramedullary humeral cutting guide is attached, and the humeral resection is completed in 30° of retroversion approximately 1 mm superior to the rotator cuff insertion (Figure 2). If there are any proximal humeral defects or deficiencies, cancellous autograft from the resected humeral head is acquired, using a rongeur, to later bone graft the area in question. Sequential broaching of the humeral canal is then performed, ensuring appropriate depth and rotational stability of the final trial size (Figure 3). Throughout humeral canal instrumentation both reaming and broaching are performed to promote a neutral stem position and avoid varus or valgus alignment. Humeral preparation is then completed using a rongeur to remove any residual humeral osteophytes (Figure 4). Any remaining posterior capsule is then released off the posterior calcar up to the teres minor insertion.

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Figure 1

5-mm round burr to create the entry hole at the superior apex of the humeral head.

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Figure 2

Humeral resection utilizing an intramedullary humeral cutting guide.

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Figure 3

Sequential broaching of the humeral canal.

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Figure 4

Heart shaped metaphyseal surface after osteophyte removal.

Glenoid Preparation

Attention is then directed toward the glenoid, at which point the patient may be placed in additional reverse Trendelenburg so that the longitudinal axis of the glenoid is positioned vertically. To improve glenoid exposure, the arm is placed in 70-90° of abduction and slight forward flexion. A Fukuda or glenoid access retractor is then placed on the postero-inferior glenoid rim to retract the humerus posteriorly and a double-pronged glenoid retractor is placed between the subscapularis and the anterior capsule on the anterior glenoid. It is helpful to have a posterior retractor that has an opening or window that facilitates access to a circular reamer. Electrocautery is used to circumferentially remove the glenoid labrum in a subperiosteal plane. The anterior capsule is then divided, starting superiorly, and carried along the anterior rim and postero-inferiorly to approximately the 8 o’clock position (right shoulder). The anterior double-pronged glenoid retractor is then repositioned directly onto the glenoid bone anteriorly. Careful attention is paid to ensure the true inferior glenoid rim is exposed.

Once adequate exposure is obtained, glenoid wear, version, and inclination are evaluated and correlated with preoperative imaging. In select cases, patient specific guides are printed to provide a detailed understanding of the glenoid pathology (Figure 5). In our practice, we aim to position the glenosphere with 10 degrees of inferior tilt, which has been demonstrated to improve stability and reduce the risk of atraumatic dislocation.36x36Randelli, P., Randelli, F., Arrigoni, P., Ragone, V., D'Ambrosi, R., Masuzzo, P. et al. Optimal glenoid component inclination in reverse shoulder arthroplasty. How to improve implant stability. Musculoskelet Surg. 2014; 98: 15–18https://doi.org/10.1007/s12306-014-0324-1

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have shown that there is on average 21° of superior tilt on the inferior aspect of the glenoid where the glenoid baseplate is placed. Therefore, on average 31° of tilt must be corrected in all cases (21° of superior tilt and the desired 10° of inferior tilt). There are three ways for the surgeon to correct the superior tilt: bone grafting, eccentric reaming, and use of an augmented baseplate. Recent literature from Rothmann Institute and Mayo Clinic have reported high rates of bone graft resorption and failure in the primary and revision setting.18x18Ho, J.C., Thakar, O., Chan, W.W., Nicholson, T., Williams, G.R., and Namdari, S. Early radiographic failure of reverse total shoulder arthroplasty with structural bone graft for glenoid bone loss. J Shoulder Elbow Surg. 2020; 29: 550–560https://doi.org/10.1016/j.jse.2019.07.035

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Eccentric reaming removes a large amount of bone and the best quality cortical bone. There has been recent supportive literature of bone preservation with use of augmented baseplates, as such our practice has migrated to using augmented baseplates in nearly all reverse cases (Figure 6).1x1Abdic, S., Knowles, N.K., Walch, G., Johnson, J.A., and Athwal, G.S. Type E2 glenoid bone loss orientation and management with augmented implants. J Shoulder Elbow Surg. 2020; 29: 1460–1469https://doi.org/10.1016/j.jse.2019.11.009

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Figure 5

Patient specific guide with depth control

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Figure 6

Schematic demonstrating the preservation of bone with use of the augmented glenoid reaming system.

First, a placement guide and Steinmann pins are placed into the glenoid vault at the desired version and inclination. This is typically centered over the inferior glenoid with 5 - 10° of inferior tilt. The high side (less deficient) of the glenoid is reamed so that 50% of the articular surface is prepared (Figure 7). Within this system, patient specific instrumentation (PSI) in the form of reaming guides can be generated to provide more precise glenoid preparation. This is typically acquired in cases of advanced glenoid wear or glenoid dysplasia. Next, augmented sizing guides are used to determine the appropriate augmented glenoid baseplate size and orientation. An augmented reamer guide is placed, and an augment reamer is used to ream the low side (more deficient) of the glenoid (Figure 8). Having the ability to precisely prepare and then place the augmented baseplate in the identical rotation is critical. It has been shown that five degrees of malrotation of the baseplate can result in a loss of greater than 50% contact with the underlying native bone.40x40Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. J Clin Med. 2021; 10https://doi.org/10.3390/jcm10215151

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The augmented baseplate is impacted into position and is secured to the glenoid (Figure 9). Typically, all 4 screws are utilized paying close attention to insert a screw into the superior glenoid at the base of the coracoid, and the inferior glenoid aiming into the scapular pillar. The anterior and posterior screws are generally shorter screws providing additional support with lengths ranging from 14-16 mm. As needed a trial glenosphere is placed and dialed to the appropriate offset so that the inferior aspect of the glenosphere extends 1 – 2 mm below the inferior rim of the glenoid. Inferior offset of the glenosphere below the glenoid rim is effective in preventing scapular notching.13x13Friedman, R.J., Barcel, D.A., and Eichinger, J.K. Scapular Notching in Reverse Total Shoulder Arthroplasty. J Am Acad Orthop Surg. 2019; 27: 200–209https://doi.org/10.5435/jaaos-d-17-00026

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However, it has been suggested that that one does not need to maximize the amount of the glenosphere offset below the bottom part of the glenoid to prevent notching, as maximizing overhang can result in excessive deltoid tension and compromised glenoid fixation.13x13Friedman, R.J., Barcel, D.A., and Eichinger, J.K. Scapular Notching in Reverse Total Shoulder Arthroplasty. J Am Acad Orthop Surg. 2019; 27: 200–209https://doi.org/10.5435/jaaos-d-17-00026

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Additionally, the less the glenosphere is dialed inferiorly, the less humeral bone that needs to be resected to obtain the optimal soft tissue tensioning.13x13Friedman, R.J., Barcel, D.A., and Eichinger, J.K. Scapular Notching in Reverse Total Shoulder Arthroplasty. J Am Acad Orthop Surg. 2019; 27: 200–209https://doi.org/10.5435/jaaos-d-17-00026

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The final glenosphere is then dialed to match the desired offset and impacted into position. (Figure 10)

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Figure 7

High side glenoid reaming with the patient specific guide.

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Figure 8

Low side glenoid reaming with the augmented reamer guide.

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Figure 9

Insertion of the augmented baseplate

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Figure 10

Glenosphere is dialed to the appropriate offset prior to implantation to titrate the soft tissue tension.

Humeral Component Placement

Attention is returned to the humerus for component trialing and implantation. Standard and offset humeral trays are attached to the trial broach, selecting the tray that is positioned most centrally over the resected surface, minimizing any overhang of the components, as well as optimizing soft tissue tension (Figure 11). The desired trial humeral bearing is then attached, and the shoulder is reduced to assess soft tissue tensioning, range of motion, and implant stability (Figure 12). Special attention is placed on the combined lateralization generated from the implant configuration to create the desired amount of tension on the deltoid and rotator cuff. Specifically, the baseplate, glenosphere, humeral tray, and humeral bearing thickness as well as humeral tray offset can be varied to achieve optimal tensioning and positioning. In most cases, we utilize a lateralized baseplate with a standard thickness glenosphere and adjust the modular humeral components to ensure that we are promoting impingement free ROM while balancing the soft tissue tension.

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Figure 11

Humeral tray offset options.

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Figure 12

Humeral tray with +6 offset on humerus selected to optimize central position on the resected surface.

One key technologic development is the use of offset humeral trays. The use of a lateral offset humeral tray results in medialization and distalization of the implant. This is helpful in the setting of lateralized RSA designs that may lead to a lateralized center of rotation. The offset trays can decrease acromial-humeral impingement as well as making the construct less tight. This allows the surgeon to adjust the tension on the humeral side (Figure 13).

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Figure 13

Postoperative radiographs of different offset tray configurations to demonstrating the ability to tension each shoulder as desired.

Once satisfied with humeral component trialing, the trial broach is removed. At this point, if the surgeon determines that there are proximal humeral deficiencies preventing adequate stem fit, crushed humeral cancellous autograft may be manually impacted with finger pressure along the deficient areas prior to final implant placement. Finally, the final humeral stem is impacted into position with the desired height and retroversion (Figure 14 and 15). There is evidence noting that there is nine times less wear with vitamin E impregnated polyethylene, therefore, while not all manufactures offer Vit-E polyethylene components, our preference is to use this on all reverse arthroplasty cases.2x2Alexander, J.J., Bell, S.N., Coghlan, J., Lerf, R., and Dallmann, F. The effect of vitamin E-enhanced cross-linked polyethylene on wear in shoulder arthroplasty-a wear simulator study. J Shoulder Elbow Surg. 2019; 28: 1771–1778https://doi.org/10.1016/j.jse.2019.01.014

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The final humeral tray and bearing are then implanted, the shoulder is reduced, and the shoulder is irrigated with pulse lavage (Figure 16).

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Figure 14

Humeral stem inserted into the prepared canal in neutral alignment.

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Figure 15

Humeral stem positioned centrally in the prepared canal.

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Figure 16

Final construct with offset humeral tray minimizing medial overhang.

Closure and rehabilitation

The subscapularis is repaired to its tendinous insertion on the lesser tuberosity using multiple interrupted braided non-absorbable sutures. Of note, use of an offset tray with slight medialization also facilitates closure of the subscapularis tendon (Figure 17). The deltopectoral interval is then approximated with braided absorbable suture and the remaining subcutaneous tissue and skin are closed in layers (Figure 18). Postoperatively, the shoulder is placed in a shoulder immobilizer for 6 weeks. Passive ROM exercises are initiated on postoperative day 1 and active assisted ROM exercise is introduced at 6 weeks postoperatively. Active ROM exercises are initiated once full active-assisted ROM is achieved. By week 8, strengthening is initiated, first with isometric strengthening exercises, followed by elastic band exercises at week 12. After week 12, patients are encouraged to return to all previous activities.

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Figure 17

Subscapularis closure after placement of final components.

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Figure 18

Preoperative and postoperative anterior-posterior radiograph of an arthritic shoulder treated with a RSA with an offset humeral tray and augmented baseplate.

DISCUSSION

Acromial and scapular spine fractures following RSA and are associated with adverse clinical outcomes.10x10Colliton, E.M., Jawa, A., and Kirsch, J.M. Acromion and Scapular Spine Fractures Following Reverse Total Shoulder Arthroplasty. Orthop Clin North Am. 2021; 52: 257–268https://doi.org/10.1016/j.ocl.2021.03.006

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,17x17Hattrup, S.J. The influence of postoperative acromial and scapular spine fractures on the results of reverse shoulder arthroplasty. Orthopedics. 2010; 33https://doi.org/10.3928/01477447-20100329-04

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,29x29Lópiz, Y., Rodríguez-González, A., García-Fernández, C., and Marco, F. Scapula insufficiency fractures after reverse total shoulder arthroplasty in rotator cuff arthropathy: What is their functional impact?. Rev Esp Cir Ortop Traumatol. 2015; 59: 318–325https://doi.org/10.1016/j.recot.2015.01.003

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,45x45Teusink, M.J., Otto, R.J., Cottrell, B.J., and Frankle, M.A. What is the effect of postoperative scapular fracture on outcomes of reverse shoulder arthroplasty?. J Shoulder Elbow Surg. 2014; 23: 782–790https://doi.org/10.1016/j.jse.2013.09.010

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Specifically, patients have demonstrated worse pain17x17Hattrup, S.J. The influence of postoperative acromial and scapular spine fractures on the results of reverse shoulder arthroplasty. Orthopedics. 2010; 33https://doi.org/10.3928/01477447-20100329-04

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, ROM17x17Hattrup, S.J. The influence of postoperative acromial and scapular spine fractures on the results of reverse shoulder arthroplasty. Orthopedics. 2010; 33https://doi.org/10.3928/01477447-20100329-04

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,29x29Lópiz, Y., Rodríguez-González, A., García-Fernández, C., and Marco, F. Scapula insufficiency fractures after reverse total shoulder arthroplasty in rotator cuff arthropathy: What is their functional impact?. Rev Esp Cir Ortop Traumatol. 2015; 59: 318–325https://doi.org/10.1016/j.recot.2015.01.003

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| Google ScholarSee all References
,45x45Teusink, M.J., Otto, R.J., Cottrell, B.J., and Frankle, M.A. What is the effect of postoperative scapular fracture on outcomes of reverse shoulder arthroplasty?. J Shoulder Elbow Surg. 2014; 23: 782–790https://doi.org/10.1016/j.jse.2013.09.010

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, and functional outcome scores.17x17Hattrup, S.J. The influence of postoperative acromial and scapular spine fractures on the results of reverse shoulder arthroplasty. Orthopedics. 2010; 33https://doi.org/10.3928/01477447-20100329-04

Crossref | Scopus (74)
| Google ScholarSee all References
,29x29Lópiz, Y., Rodríguez-González, A., García-Fernández, C., and Marco, F. Scapula insufficiency fractures after reverse total shoulder arthroplasty in rotator cuff arthropathy: What is their functional impact?. Rev Esp Cir Ortop Traumatol. 2015; 59: 318–325https://doi.org/10.1016/j.recot.2015.01.003

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| Google ScholarSee all References
,45x45Teusink, M.J., Otto, R.J., Cottrell, B.J., and Frankle, M.A. What is the effect of postoperative scapular fracture on outcomes of reverse shoulder arthroplasty?. J Shoulder Elbow Surg. 2014; 23: 782–790https://doi.org/10.1016/j.jse.2013.09.010

Abstract | Full Text | Full Text PDF | PubMed | Scopus (69)
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. Various studies have identified possible risk factors for acromial and scapular spine fractures following RSA, with conflicting results when specifically evaluating for onlay and inlay humeral stem designs.40x40Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. J Clin Med. 2021; 10https://doi.org/10.3390/jcm10215151

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In a non-randomized retrospective review of 100 patients undergoing RSA with onlay humeral prosthesis, Ascione et al3x3Ascione, F., Bugelli, G., Domos, P., Neyton, L., Godeneche, A., Bercik, M.J. et al. Reverse Shoulder Arthroplasty with a New Convertible Short Stem: Preliminary 2- to 4-year Follow-up Results. Journal of Shoulder and Elbow Arthroplasty. 2017; 1: 2471549217746272https://doi.org/10.1177/2471549217746272

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reported a 5% rate of scapular fractures. In a subsequent publication, Ascione et al4x4Ascione, F., Kilian, C.M., Laughlin, M.S., Bugelli, G., Domos, P., Neyton, L. et al. Increased scapular spine fractures after reverse shoulder arthroplasty with a humeral onlay short stem: an analysis of 485 consecutive cases. J Shoulder Elbow Surg. 2018; 27: 2183–2190https://doi.org/10.1016/j.jse.2018.06.007

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reported an updated series of 485 RSA with onlay humeral stems with a 4.3% scapular fracture rate. In this series, they found that most fractures occurred in the scapular spine, with 57% of fractures occurring at the tip of the superior glenoid baseplate screw. In 2020, Haidamous et al15x15Haidamous, G., Lädermann, A., Frankle, M.A., Gorman, R.A. 2nd, and Denard, P.J. The risk of postoperative scapular spine fracture following reverse shoulder arthroplasty is increased with an onlay humeral stem. J Shoulder Elbow Surg. 2020; 29: 2556–2563https://doi.org/10.1016/j.jse.2020.03.036

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published a multicenter retrospective review of scapular spine fractures following RSA. In this investigation, they reported an 11.9% incidence of scapular fracture among 84 RSA onlay prostheses, and a 4.7% incidence of acromial stress fractures in 342 RSA inlay prostheses (P = .043). While the difference in fracture rate was statistically significant in this study, their conclusions were limited by short follow-up of just one year, a small number of onlay prostheses implanted, and 37% of patients being lost to follow-up.

Contrary to these findings, several publications have failed to identify a significant difference in scapular fracture rates between onlay and inlay prosthesis designs.5x5Ascione, F., Schiavone Panni, A., Braile, A., Corona, K., Toro, G., Capuano, N. et al. Problems, complications, and reinterventions in 4893 onlay humeral lateralized reverse shoulder arthroplasties: a systematic review (part I-complications). J Orthop Traumatol. 2021; 22: 27https://doi.org/10.1186/s10195-021-00592-w

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,32x32Merolla, G., Walch, G., Ascione, F., Paladini, P., Fabbri, E., Padolino, A. et al. Grammont humeral design versus onlay curved-stem reverse shoulder arthroplasty: comparison of clinical and radiographic outcomes with minimum 2-year follow-up. J Shoulder Elbow Surg. 2018; 27: 701–710https://doi.org/10.1016/j.jse.2017.10.016

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,41x41Shah, S.S., Gentile, J., Chen, X., Kontaxis, A., Dines, D.M., Warren, R.F. et al. Influence of implant design and parasagittal acromial morphology on acromial and scapular spine strain after reverse total shoulder arthroplasty: a cadaveric and computer-based biomechanical analysis. J Shoulder Elbow Surg. 2020; 29: 2395–2405https://doi.org/10.1016/j.jse.2020.04.004

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,51x51Zmistowski, B., Gutman, M., Horvath, Y., Abboud, J.A., Williams, G.R. Jr., and Namdari, S. Acromial stress fracture following reverse total shoulder arthroplasty: incidence and predictors. J Shoulder Elbow Surg. 2020; 29: 799–806https://doi.org/10.1016/j.jse.2019.08.004

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Merolla et al32x32Merolla, G., Walch, G., Ascione, F., Paladini, P., Fabbri, E., Padolino, A. et al. Grammont humeral design versus onlay curved-stem reverse shoulder arthroplasty: comparison of clinical and radiographic outcomes with minimum 2-year follow-up. J Shoulder Elbow Surg. 2018; 27: 701–710https://doi.org/10.1016/j.jse.2017.10.016

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conducted a review comparing outcomes following 36 inlay and 38 onlay RSA prostheses. Though limited by a small sample size, they reported no difference in scapular fracture rates between groups and significantly higher rates of scapular notching among the inlay group. Similarly, Zmistowski et al51x51Zmistowski, B., Gutman, M., Horvath, Y., Abboud, J.A., Williams, G.R. Jr., and Namdari, S. Acromial stress fracture following reverse total shoulder arthroplasty: incidence and predictors. J Shoulder Elbow Surg. 2020; 29: 799–806https://doi.org/10.1016/j.jse.2019.08.004

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published a review of 958 RSA with no differences in the rates of acromial or scapular spine fractures between onlay and inlay prostheses. With respect to systematic analyses, Jackson et al19x19Jackson GR, Meade J, Young BL, Trofa DP, Schiffern SC, Hamid N, et al. Onlay versus inlay humeral components in reverse shoulder arthroplasty: A systematic review and meta-analysis. Shoulder & Elbow.0(0):17585732211067171 doi:10.1177/17585732211067171.

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demonstrated no differences between AF or SSF among onlay and inlay humeral designs after a systematic review of 306 shoulders. Additionally, while not a comparative study, Routman et al38x38Routman, H.D., Simovitch, R.W., Wright, T.W., Flurin, P.H., Zuckerman, J.D., and Roche, C.P. Acromial and Scapular Fractures After Reverse Total Shoulder Arthroplasty with a Medialized Glenoid and Lateralized Humeral Implant: An Analysis of Outcomes and Risk Factors. J Bone Joint Surg Am. 2020; 102: 1724–1733https://doi.org/10.2106/jbjs.19.00724

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published an acromial and scapular fracture rate of 1.77% among 4125 reverse arthroplasties utilizing an onlay design, much lower than the rates reported in aforementioned studies.

Of note, it has been suggested that categorizing humeral prosthesis into onlay and inlay groups may be an oversimplification when attempting to understand the relationship between prosthesis design and scapular fractures.40x40Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. J Clin Med. 2021; 10https://doi.org/10.3390/jcm10215151

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This may explain the variability in reported fracture rates among primary investigations, as simply comparing onlay versus inlay humeral prosthesis fails to account for variations in implant positioning and surgical techniques, which alter deltoid and scapular strains. Ultimately, stresses experienced by the acromion and scapular spine following RSA are dependent on the complex interaction of variables including glenoid and humeral implant design, size, and positioning, patient anatomy, and patient activity.40x40Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. J Clin Med. 2021; 10https://doi.org/10.3390/jcm10215151

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There is significant variation in glenoid and humeral component positioning achieved with the various implants in use today, with overlap existing between onlay and inlay designs.49x49Werthel, J.D., Walch, G., Vegehan, E., Deransart, P., Sanchez-Sotelo, J., and Valenti, P. Lateralization in reverse shoulder arthroplasty: a descriptive analysis of different implants in current practice. Int Orthop. 2019; 43: 2349–2360https://doi.org/10.1007/s00264-019-04365-3

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For example, a large “inlay” prosthesis may not always be fully accommodated by the humeral metaphysis, resulting in final position that is more comparable to onlay prostheses.40Alternatively, with a larger humeral head resection, an “onlay” humeral component may be positioned so that the bearing surface rests below the original anatomic neck, as would be expected with inlay prostheses.40x40Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. J Clin Med. 2021; 10https://doi.org/10.3390/jcm10215151

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Considering these limitations, investigations focusing on measures of glenoid and humeral positioning may offer better insight into the effects of component implantation on scapular fractures. Recent studies have used the RSA component classification described by Routman et al37x37Routman, H.D., Flurin, P.H., Wright, T.W., Zuckerman, J.D., Hamilton, M.A., and Roche, C.P. Reverse Shoulder Arthroplasty Prosthesis Design Classification System. (2015)Bull Hosp Jt Dis. 2013; 73: S5–14 (No doi)

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which classifies components as having a medialized glenoid (MG), lateralized glenoid (LG), medialized humerus (MH), or lateralized humerus (LH). Some studies have proposed that MH configurations may be a risk factor for scapular fractures.8x8Cho, C.H., Jung, J.W., Na, S.S., Bae, K.C., Lee, K.J., and Kim, D.H. Is Acromial Fracture after Reverse Total Shoulder Arthroplasty a Negligible Complication?: A Systematic Review. Clin Orthop Surg. 2019; 11: 427–435https://doi.org/10.4055/cios.2019.11.4.427

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,16x16Hamilton, M.A., Diep, P., Roche, C., Flurin, P.H., Wright, T.W., Zuckerman, J.D. et al. Effect of reverse shoulder design philosophy on muscle moment arms. J Orthop Res. 2015; 33: 605–613https://doi.org/10.1002/jor.22803

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,21x21Kerrigan, A.M., Reeves, J.M., Langohr, G.D.G., Johnson, J.A., and Athwal, G.S. The influence of reverse arthroplasty humeral component design features on scapular spine strain. Journal of Shoulder and Elbow Surgery. 2021; 30: 572–579https://doi.org/10.1016/j.jse.2020.06.011

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Kerrigan et al21x21Kerrigan, A.M., Reeves, J.M., Langohr, G.D.G., Johnson, J.A., and Athwal, G.S. The influence of reverse arthroplasty humeral component design features on scapular spine strain. Journal of Shoulder and Elbow Surgery. 2021; 30: 572–579https://doi.org/10.1016/j.jse.2020.06.011

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reported decreased acromial strain with LH designs in a cadaveric model. Alternatively, Hamilton et al16x16Hamilton, M.A., Diep, P., Roche, C., Flurin, P.H., Wright, T.W., Zuckerman, J.D. et al. Effect of reverse shoulder design philosophy on muscle moment arms. J Orthop Res. 2015; 33: 605–613https://doi.org/10.1002/jor.22803

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used digital bone models to demonstrate improved deltoid efficiency with LH designs. These findings are supported by a systematic review by Cho et al8x8Cho, C.H., Jung, J.W., Na, S.S., Bae, K.C., Lee, K.J., and Kim, D.H. Is Acromial Fracture after Reverse Total Shoulder Arthroplasty a Negligible Complication?: A Systematic Review. Clin Orthop Surg. 2019; 11: 427–435https://doi.org/10.4055/cios.2019.11.4.427

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found an 8.4% fracture rate among MG/MH designs, compared to 4.0% for LG/MH designs and 2.8% for MGLH designs. However, the systematic review by Shah et al42x42Shah, S.S., Roche, A.M., Sullivan, S.W., Gaal, B.T., Dalton, S., Sharma, A. et al. The modern reverse shoulder arthroplasty and an updated systematic review for each complication: part II. JSES International. 2021; 5: 121–137https://doi.org/10.1016/j.jseint.2020.07.018

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evaluating postoperative complications of over 14,000 shoulders reported no differences in AF or SSF between various implant designs, with rates of 2.8%, 2.5%, and 2.2% in LG/MH, MG/MH, and MG/LH designs, respectively.

This article presents a technique for RSA utilizing an onlay humeral component design with variable-offset humeral tray and augmented glenoid baseplate, highlighting technical pearls that optimize soft tissue tension and help to mitigate scapular and acromial strains. Technical pearls to consider include an appropriate correlation of preoperative advanced imaging, clinical glenoid wear pattern, restoring the appropriate soft tissue tension to avoid impingement, and avoiding undue stress on the acromion and scapular spine. This is accomplished with utilization of offset humeral trays to titrate the soft tissue tension on the deltoid and scapular musculature. Additionally, this ability to modify the humeral components allows for appropriate positioning of the humeral tray over the anatomic humeral neck cut, which can help limit the extent of strain across the scapula.

CONCLUSION

Acromial stress and scapular spine fractures remain a relevant complication in modern RSA. Conflicting results exist regarding an onlay vs. inlay humeral stem design as it relates to fractures, with recent investigations suggesting no differences. As such there remains no clear consensus regarding implant design and positioning, and cases should likely be evaluated based on individual patient characteristics. This article presents our preferred technique for RSA implantation with the use of a modern onlay humeral stem design with variable-offset humeral tray and augmented glenoid baseplate, highlighting technical pearls that optimize soft tissue tension and help to mitigate scapular and acromial strains.

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