This narrative review explains the biomechanical rationale behind reverse shoulder arthroplasty design. It covers why the cuff-deficient shoulder fails mechanically and how implant choices govern stability, range of motion, scapular notching, and baseplate survival. The central question: what must surgeons understand about shoulder mechanics to use RSA intelligently?
The Grammont Delta III was a landmark implant, but its medialized geometry created predictable mechanical problems: the deltoid acts as a distracting force when bone loss is present, driving dislocation rates up to 30%, and the fixed-fulcrum articulation creates a notching pattern in 44–96% of cases.
When planning RSA, use a central lag screw with locked 5.0-mm peripheral screws. This single hardware decision reduced glenoid failure from roughly 10% to 0.4% in clinical practice.
When you see superior glenoid wear preoperatively, do not implant at native glenoid inclination. Superior tilt was the shared radiographic finding in early fixation failures. Preferentially ream the inferior glenoid to achieve 15° inferior tilt and normalize interface forces.
Favor lateral offset designs when external rotation matters. Lateral offset retensions residual cuff fibers, restores a compressive deltoid vector, and improves abduction ROM linearly with increasing offset. Patients without external rotation improvement after RSA report lower satisfaction scores.
How Reverse Shoulder Arthroplasty Works
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This narrative review explains the biomechanical rationale behind reverse shoulder arthroplasty design. It covers why the cuff-deficient shoulder fails mechanically and how implant choices govern stability, range of motion, scapular notching, and baseplate survival. The central question: what must surgeons understand about shoulder mechanics to use RSA intelligently?
The Grammont Delta III was a landmark implant, but its medialized geometry created predictable mechanical problems: the deltoid acts as a distracting force when bone loss is present, driving dislocation rates up to 30%, and the fixed-fulcrum articulation creates a notching pattern in 44–96% of cases.
When planning RSA, use a central lag screw with locked 5.0-mm peripheral screws. This single hardware decision reduced glenoid failure from roughly 10% to 0.4% in clinical practice.
When you see superior glenoid wear preoperatively, do not implant at native glenoid inclination. Superior tilt was the shared radiographic finding in early fixation failures. Preferentially ream the inferior glenoid to achieve 15° inferior tilt and normalize interface forces.
Favor lateral offset designs when external rotation matters. Lateral offset retensions residual cuff fibers, restores a compressive deltoid vector, and improves abduction ROM linearly with increasing offset. Patients without external rotation improvement after RSA report lower satisfaction scores.