This narrative review examines how the scapulothoracic complex behaves after reverse total shoulder arthroplasty (rTSA). It asks how altered ball-and-socket mechanics change scapular kinematics and scapulohumeral rhythm. It frames how posture and scapulothoracic orientation should influence component selection, planning, and rehabilitation.
When your rTSA patient elevates well on the planning software but stiff in clinic, suspect scapulothoracic factors the plan ignored. RTSA converts the deltoid into the primary elevator using the glenosphere as a fixed fulcrum, and this shifts more of the elevation burden onto the scapula. Reduced scapulohumeral rhythm (as low as 1.3:1 versus the native 2:1) is the biomechanical signature of that shift.
The practical lever is posture. The Moroder A/B/C classification links kyphotic, protracted scapulae (type C) to worse component matching, and supine CT with retracted scapulae underestimates that protraction. Match component retrotorsion (20° to 40°) and glenosphere choice to scapulothoracic orientation, and keep baseplate tilt neutral to inferior to avoid impingement and notching.
This is an emerging topic: the evidence is largely biomechanical and modeling-based, and the exact degree of rhythm change remains debated.
This narrative review examines how the scapulothoracic complex behaves after reverse total shoulder arthroplasty (rTSA). It asks how altered ball-and-socket mechanics change scapular kinematics and scapulohumeral rhythm. It frames how posture and scapulothoracic orientation should influence component selection, planning, and rehabilitation.
When your rTSA patient elevates well on the planning software but stiff in clinic, suspect scapulothoracic factors the plan ignored. RTSA converts the deltoid into the primary elevator using the glenosphere as a fixed fulcrum, and this shifts more of the elevation burden onto the scapula. Reduced scapulohumeral rhythm (as low as 1.3:1 versus the native 2:1) is the biomechanical signature of that shift.
The practical lever is posture. The Moroder A/B/C classification links kyphotic, protracted scapulae (type C) to worse component matching, and supine CT with retracted scapulae underestimates that protraction. Match component retrotorsion (20° to 40°) and glenosphere choice to scapulothoracic orientation, and keep baseplate tilt neutral to inferior to avoid impingement and notching.
This is an emerging topic: the evidence is largely biomechanical and modeling-based, and the exact degree of rhythm change remains debated.