Reverse shoulder arthroplasty (RSA) was introduced in 1985 by Grammont for patients with gleno-humeral osteoarthritis and severe rotator cuff damage. Internal rotation (IR) is limited in some patients after RSA. The objective of this study was to identify pre- and intra-operative factors associated with good IR outcomes 6 months after RSA.

The condition of the residual cuff (usually the sub-scapularis and teres minor) and inferior glenosphere overhang are the main factors associated with IR outcomes after RSA.

A total of 36 patients who underwent RSA between 2 November 2015 and 10 January 2017 were enrolled prospectively. The inclusion criterion was massive rotator cuff tear with or without osteoarthritis and gleno-humeral osteoarthritis with asymmetrical glenoid wear. The pre-operative work-up included determination of the Constant score, Subjective Shoulder Value (SSV), and passive and active motion ranges; standard radiographs; and computed tomography. The same clinical and radiological parameters were recorded in all patients during a visit 6 months after surgery.

After surgery, all motion ranges were improved except IR with the elbow by the side (IR1, ability to place the hand on the back). IR1 to or above L3 was significantly associated with a lower body mass index (p=0.04), good passive IR before surgery (p=0.056), a smaller pre-operative glenoid inclination angle, and greater glenosphere overhang (p=0.03). Neither the condition of the sub-scapularis nor sub-scapularis repair were significantly associated with post-operative IR1. IR1 was significantly more limited in patients whose teres minor was normal.

Satisfactory active IR1 correlated with good passive IR1. IR1 was better in thin individuals who had non-concentric gleno-humeral osteoarthritis. Inferior glenosphere overhang of 6mm or more was associated with a greater range of IR.

IV, prospective observational cohort study.