Biomechanical changes after reverse total shoulder arthroplasty: a systematic review of advanced measurement technologies

Reverse total shoulder arthroplasty (rTSA) consistently improves pain and function; however, the biomechanical mechanisms underpinning post-operative function and joint-level adaptations remain incompletely defined. Advanced measurement tools, including motion capture, electromyography (EMG), inertial measurement units, and accelerometry, enable objective assessment of joint motion, muscle activation, and real-world arm use. This systematic review synthesizes evidence from studies using advanced biomechanical methods to evaluate post-operative kinematics, upper-limb activity, and muscle activation after rTSA. Seven databases (1985-2025) were searched for observational studies reporting quantitative biomechanical outcomes after rTSA, compared with pre-operative baselines, contralateral shoulders, or healthy controls. Outcomes were categorized as kinematics, real-world upper-limb activity, or neuromuscular activation. Methodological quality was assessed using Joanna Briggs Institute criteria, and levels of evidence were classified according to Journal of Shoulder and Elbow Surgery guidelines. Twenty-four studies (10 cohort and 14 case-control; all Level III) met inclusion criteria. Twenty-one had moderate risk of bias and 3 high risk. Implant designs, surgical indications, and follow-up durations were heterogeneous. High-rigor optical and electromagnetic motion capture studies showed consistent gains in forward elevation, while glenohumeral contribution, axial rotation, and scapulohumeral rhythm remained reduced relative to contralateral or healthy shoulders. Elevation occurred predominantly through increased scapulothoracic upward rotation, retraction, and posterior tilt. Laboratory-based inertial measurement unit studies showed similar patterns of greater scapular contribution despite nonstandardized coordinate systems. Wearable sensors reported increased post-operative arm use and improved interlimb symmetry, although time spent above shoulder height remained limited. EMG studies demonstrated increased deltoid and upper-trapezius activation with limited posterior cuff recruitment. rTSA restores forward elevation primarily via compensatory scapulothoracic motion and deltoid-driven neuromuscular strategies rather than normalization of glenohumeral mechanics. Standardized, longitudinal studies integrating high-fidelity kinematics, EMG, and real-world activity monitoring, with explicit reporting of implant construct parameters, are needed to clarify how surgical technique and implant design influence post-operative biomechanics and functional recovery.