The use of an eccentric glenosphere compared with a concentric glenosphere in reverse total shoulder arthroplasty: two-year minimum follow-up results.

PURPOSE: The current models of reverse shoulder arthroplasty (RSA) expose the procedure to the risk of scapular notching, possibly leading to loosening of the glenoid. We compared the clinical and radiographic results obtained with a concentric or eccentric glenosphere to assess whether the eccentric design might give better clinical results and avoid or decrease the risk of scapular notching
METHODS: Of our patients, 31 underwent RSA using a concentric glenosphere (group A), while 29 had an eccentric glenosphere (group B). Postoperatively, patients were followed-up at one to 12 months and annually thereafter, with the mean being 33 months in group A and 27.5 in group B. In both groups the minimum follow up (F-U) was 24 months. Preoperatively and at each F-U starting from six months, patients were assessed using the Constant score. On radiographs, prosthesis scapular neck angle (PSNA), distance between scapular neck and glenosphere (DBSNG) and peg-glenoid rim distance (PGRD) were calculated. The severity of notching was classified in four grades.
RESULTS: In group A the mean Constant score increased by 30 points compared to the preoperative score and the active ROM increased considerably. At latest F-U, the mean PSNA, DBSNG and PGRD were, respectively, 87°, 3.4 mm and 19.8 mm. Glenoid notching was present in 42% of cases. In group A, the mean Constant score increased by 34 points and the mean ROM was better than in group A. The average PSNA, PGRD and DBSNG were, respectively, 92°, 21.2 mm and 4.3 mm. Radiographs showed no inferior scapular notching.
CONCLUSIONS: The eccentric glenosphere yielded better clinical results than the concentric glenosphere and was associated with no scapular notching.