We analyzed the radiographs and computed tomography (CT) scans of 143 knees operated on for symptomatic patellar instability and 67 contralateral asymptomatic knees, together with 190 control knee radiographs and 27 control knee scans, to determine the factors affecting patellar instability. Four factors were relevant in knees with symptomatic patellar instability: (1) Trochlear dysplasia (85%), as defined by the crossing sign (96%) and quantitatively expressed by the trochlear bump, pathological above 3 mm or more (66%), and the trochlear depth, pathologic at 4 mm or less. (2) Quadriceps dysplasia (83%), defined a present when the patellar tilt in extension is more than 20% on the CT scans. (3) Patella alta (Caton-Deschamps) index greater than or equal to 1.2 (24%). (4) Tibial tuberosity-trochlear groove, pathological when greater than or equal to 20 mm (56%). The factors appeared in only 3%-6.5% of the control knees. The etiology of patellar instability is multifactorial. Determination of the factors permits an effective elective therapeutic plan which aims at correcting the anomalies present.

We reviewed 80 shoulders (77 patients) at a mean follow-up of 44 months after insertion of a Grammont inverted shoulder prosthesis. Three implants had failed and had been revised. The mean Constant score had increased from 22.6 points pre-operatively to 65.6 points at review. In 96% of these shoulders there was no or only minimal pain. The mean active forward elevation increased from 73 degrees to 138 degrees. The integrity of teres minor is essential for the recovery of external rotation and significantly influenced the Constant score. Five cases of aseptic loosening of the glenoid and seven of dissociation of the glenoid component were noted. This study confirms the promising early results obtained with the inverted prosthesis in the treatment of a cuff-tear arthropathy. It should be considered in the treatment of osteoarthritis with a massive tear of the cuff but should be reserved for elderly patients.

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The reverse total shoulder arthroplasty prosthesis can produce good results when used for the treatment of a number of other complex shoulder problems in addition to cuff tear arthropathy. Patients with posttraumatic arthritis and those undergoing revision arthroplasty may have less improvement and higher complication rates in comparison with patients with other etiologies. The advanced age of the patients in the present series and the relatively short duration of follow-up suggest that the prosthesis should continue to be used judiciously.

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