Purpose: The purpose of our work was to report causes and results of treatment of anterior shoulder instability after implantation of a shoulder prosthesis.

Material and methods: This retrospective multicentric study included 51 patients with prosthetic anterior instability: 42 patients after first-intention shoulder prosthesis and nine after prosthesis revision. There were 39 women (79%) and 12 men, mean age 67 years, who underwent total shoulder arthroplasty (n=29, 57%) or hemiarthro-plasty (n=22, 43%). Thirty-eight patients (75%) had prosthetic dislocation and 13 (25%) subluxation associated with pain an loss of anterior elevation. The initial prosthesis was implanted for degenerative disease (n=29), rheumatoid arthritis (n=7), or fracture (n=15). Anterior prosthetic instability occurred early in 23 shoulders (first six weeks) and lat in 28 shoulders (7 after trauma, 21 without trauma). Conservative treatment by reduction-immobilisation was performed in 16 cases and prosthetic revision in 35. The patients were reviewed radiographically at mean 41 months follow-up (range 24–62).

Results: Subscapular tear or incompetence was the main cause of prosthetic anterior instability, observed in 87% of the cases. Technical errors concerning the prosthesis were also observed: oversized head, malrotation of the prosthesis. Associated complications were frequent: glenoid loosening (24%), polyethylene dissociation from the metal glenoid implant (10%), infection (10%), humeral fracture (4%). The final Constant score was 54 points and 55% of the patients were disappointed or dissatisfied. None of the shoulders were stable after consevative treatment. The prosthetic revision provided disappointing results with 51% recurrent anterior instability.

Discussion: Anterior instability of shoulder prostheses is a serious complication which responds poorly to treatment. Loosening of the subscapular suture is the main cause.