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Review
, 12 (4), 542-553

Reverse Total Shoulder Arthroplasty: Biomechanics and Indications

Affiliations
Review

Reverse Total Shoulder Arthroplasty: Biomechanics and Indications

Caitlin M Rugg et al. Curr Rev Musculoskelet Med.

Abstract

Purpose of review: Over the past decade, our understanding of the biomechanics of the reverse total shoulder arthroplasty (RTSA) has advanced, resulting in design adjustments, improved outcomes, and expanding indications. The purpose of this review is to summarize recent literature regarding the biomechanics of RTSA and the evolving indications for its use.

Recent findings: While Grammont's principles of RTSA biomechanics remain pillars of contemporary designs, a number of modifications have been proposed and trialed in later generations to address complications such as impingement and glenoid failure. Clinical and biomechanical literature suggest that less medialized, more inferior glenospheres result in less impingement and notching. On the humerus, a more vertical neck cut is associated with less impingement. Indications for RTSA continue to expand beyond the classic indication of cuff tear arthropathy (CTA). Patients without a functional cuff but no arthritis now have a reliable option in the RTSA. RTSA has also replaced hemiarthroplasty as the implant of choice for displaced three- and four-part proximal humerus fractures in the elderly. Finally, updated design options and modular components now allow for treatment of glenoid bone loss, failed arthroplasty, and proximal humerus tumors with RTSA implants. Reverse total shoulder arthroplasty design has been modernized on both the glenoid and humerus to address biomechanical challenges of early implants. As outcomes improve with these modifications, RTSA indications are growing to address complex bony pathologies such as tumor and bone loss. Longitudinal follow-up of patients with updated designs and novel indications is essential to judicious application of RTSA technology.

Keywords: Biomechanics; Proximal humerus fracture; Reverse total shoulder arthroplasty; Rotator cuff; Scapular notching.

Conflict of interest statement

Caitlin M. Rugg, Monica J. Coughlan and Drew. A. Lansdown declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
(ad) Biomechanical improvements of the reverse total shoulder implants. a The natural center of rotation (COR) and deltoid lever arm (DL) in a native shoulder. (b) Starting with the Grammont implant, more modern reverse total shoulder arthroplasty implants medialize and distalize the center of rotation, which minimizes shear forces (FS), and increases compressive forces (FC), to create an overall favorable force vector (FV) at the bone-glenoid interface, as well as re-tensions the deltoid to provide a mechanical advantage. (c) In a native shoulder, the middle deltoid (red) and part of the anterior deltoid (light red) provide an abduction force. The posterior deltoid in dark red provides extension force. (d) With medialization of the center of rotation in a reverse total shoulder arthroplasty, a larger part of the anterior deltoid and posterior deltoid are recruited and contribute to the active abduction force. (Adapted from Berliner et al, JSES 2015 and Boileau et al, JSES 2005)
Fig. 2
Fig. 2
(a, b) Massive rotator cuff tear with anterosuperior escape treated with reverse total shoulder arthroplasty. (a) A weighted abducted AP view demonstrates anterosuperior escape of the humeral head, indicating a lack of functional rotator cuff. (b) Post-operative radiograph demonstrating cemented reverse total shoulder arthroplasty
Fig. 3
Fig. 3
(ac) Reverse total shoulder arthroplasty for a proximal humerus fracture. (a, b) Anterior-posterior (a) and lateral (b) radiograph of the right shoulder demonstrates a displaced four-part proximal humerus fracture. (c) Following reverse total shoulder arthroplasty with a cemented stem with suture fixation of the greater and lesser tuberosities around the humeral component
Fig. 4
Fig. 4
(ae) Reverse total shoulder arthroplasty with an augmented glenoid component. Grashey (a) and axillary lateral (b) radiographs demonstrate glenohumeral arthritis with superior migration of the humeral head. (c) CT scan axial cuts demonstrate a dysplastic Walch C type glenoid. AP (d) and axillary lateral (e) radiographs following reverse total shoulder arthroplasty. The glenoid baseplate consists of a porous metal backed lateralizing augment, marked with a yellow arrow. Note the restoration of glenoid version with the posteriorly augmented component
Fig. 5
Fig. 5
(ad) Reverse total shoulder reconstruction with endoprosthesis for tumor. (a) AP radiograph of the right shoulder demonstrates a lytic lesion in the right humeral head and metaphysis with pathologic fracture from metastatic hepatocellular carcinoma. (b) T2-weighted axial MRI image demonstrates a T2-bright heterogenous lesion replacing the bone of the humeral head. (c and d) Post-operative AP (c) and axillary lateral (d) radiographs of the right shoulder and humerus following proximal humerus resection and reconstruction with long-stemmed, cemented reversed polarity implant, which was performed with a shoulder arthroplasty-trained surgeon and an orthopaedic oncology surgeon

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