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Reverse Shoulder Arthroplasty, Does it Work?: Kinematic Analyses, Clinical Evaluation and New Developments

BACKGROUND: Reverse Shoulder Arthroplasty (RSA) and Total Shoulder Arthroplasty (TSA) effectively decrease pain and improve clinical outcome. However, indications and biomechanical properties vary greatly. Aim: analyze both active and passive shoulder motion (ToracoHumeral, GlenoHumeral and ScapuloThoracic) and determine the kinematical differences between RSAs and TSAs. METHODS: During three ROM tasks (forward flexion, abduction, axial rotation) the motion patterns of 16 RSA patients (19 shoulders), average age 69±8 years (range 58-84 years) and 17 TSA patients (20 shoulders), average age 72±10 years (53-87), were measured. Average follow-up: RSAs 22±10 months (6-41), TSAs 33±18 months (12-87). Kinematic measurements were performed with a 3D electromagnetic tracking device. RESULTS: All patients demonstrated better passive than active ROM. This difference is significantly larger for RSAs than TSAs (sagittal plane TH: 20 vs. 8°, GH: 16 vs. 7°, p=0.001, p=0.003; scapular plane TH: 15 vs. 2°, GH: 12 vs. 0° and ST: 3 vs. −2°, p<0.001, p<0.001, p=0.032). This also demonstrates that in the scapular plane TSAs hardly have any difference between active and passive ROM. Furthermore, TSAs have a 16 to 17° larger active TH motion, 15° GH motion and 8° ST motion compared to RSAs. The GH/ST ratio’s demonstrated similar figures for both types of prosthesis. CONCLUSION: TSA patients have a larger active TH motion because in the scapular plane, they completely utilize the possible GH motion provided by the prosthetic design. This larger active ROM in TSA patients only applies for elevation and abduction, not for axial rotations or the passive ROMs. The active and passive kinematic difference between primary reverse and total shoulder prostheses 43