Is premorbid scapulohumeral rhythm restored with anatomic or reverse shoulder arthroplasty for cuff-intact osteoarthritis? An in-vivo dynamic radiography study.

Background: Anatomic total shoulder arthroplasty (aTSA) and reverse total shoulder arthroplasty (rTSA) are both treatment options for advanced glenohumeral osteoarthritis with an intact rotator cuff; however, decision making is controversial, especially among younger active patients. Restoring native shoulder kinematics may be an important consideration for implant longevity and ultimate shoulder function, but Methods: A retrospective analysis was performed on 71 shoulders that underwent arthroplasty for cuff-intact osteoarthritis, aTSA (n = 28) and rTSA (n = 43), who had dynamic digital radiography performed more than 6 months postoperatively and compared these to 32 normal controls. SHR was calculated by dividing the change in glenohumeral abduction (ΔH) by the change in scapular upward elevation (ΔS) using the formula SHR = ΔH/ΔS, across the total range of abduction below 120° and between the 0°-30°, 30°-60°, 60°-90°, and 90°-120° abduction intervals. A paired subgroup analysis was performed on 14 aTSA and 14 rTSA shoulders with both pre- and postoperative dynamic digital radiography. Descriptive statistics were used to summarize data and differences between groups were analyzed using unpaired Student's Results: The aTSA cohort had a similar median rest-120° SHR of 2.00 compared to 1.95 for the rTSA cohort ( Conclusion: Patients who underwent aTSA and rTSA for rotator cuff-intact glenohumeral osteoarthritis are associated with lower SHRs than normal asymptomatic patients; however, SHRs significantly improved from preoperative levels. There was no difference between postoperative SHRs for rTSA and aTSA. aTSA and rTSA both partially restore coordination between the glenohumeral and scapulothoracic joints, although not to the extent of normal healthy shoulders.