Reverse Shoulder Prosthesis with Concentric vs Eccentric Glenosphere. A Multicentric Study

Purpose: Reverse shoulder prosthesis may lead to scapular notching, caused by attrition of the upper humeral component with scapular neck. We compared the clinical and radiographic results obtained with a SMR prosthesis, which allows a concentric or an eccentric glenosphere to be applied. Patients and methods: 67 patients,mean age 73 years, were treated with reverse prosthesis using concentric and eccentric glenosphere. In patients with concentric glenosphere, the glenosphere extended about 4 mm below the glenoid. The eccentric glenosphere protected the upper glenoid neck by its inferior pro|ongment.Patients were followed for a mean of 33 months. At fina! F-L1 the Constant Score ( C.5.) and the score with the Simple Shoulder test (5.5.11 ) were calculated. Racliographs were obtained to evaluate the presence of scapular notching, psna (prosthesis-scapular neck angle), pgrd (peg- glenoid rim distance) and DBSNG (distance between scapular neck and glenosfere). Included in this study were patients, as much homogeneous as possible by age and pathology, 25 with concentric (Group 1) and 20 with eccentric (Group II) glenosphere, who had a minimum F-U of 24 months. Statistical analysis was performed with a paired t- test. Results: In Group 1 mean elevation improved from 7B° to 122° and mean abduction from 71° to 98"; in Group II from 69° to 129° and 64° to 102°. External and internal rotations were similar in both groups. 14 (56%) patients of Group I, and none of Group II had scapular notching (p<0,001). C5 increased from 38% to 69% in Group I and from 30% to 70% in Group II. Conclusions: Low implantation of glenosphere did not eliminate scapular notching. Instead, no notching was detected with eccentric glenosphere, which also increased the ROM. The PSNA, DBSNG, PGRD are rellable measures to predict scapular notching.