Resurfacing humeral prosthesis: do we really reconstruct the anatomy?

Background The goal of a resurfacing shoulder arthroplasty is to reproduce the individual’s anatomy while preserving the bone stock of the humeral head. This study investigated the hypothesis that resurfacing the humeral prosthesis restores normal glenohumeral relationships and correlates with the final clinical results. Materials and methods A resurfacing shoulder implant was performed in 61 patients (64 shoulders). Indications were primary osteoarthritis in 26, secondary osteoarthritis in 21, avascular necrosis in 4, rheumatoid arthritis in 4, dysplasia in 4, and for others indications in 5. Results At an average of 36 months (range, 24-65) of follow-up , the Constant score reached 68 points and the Quick-Disabilities of Arm, Shoulder and Hand score reached 28 points. Preoperative and postoperative radiographic analysis showed a decrease of the humeral head diameter (51 ± 5 vs 48 ± 5 mm) and of the height of the humeral head (21 ± 4 vs 19 ± 2 mm), without modification of the radius of curvature or the height of the center of rotation. The medial humeral offset increased from 3.3 ± 3.5 to 6.4 ± 3 mm and the lateral offset from 6.8 ± 9 to 10.4 ± 9 mm. The implant was mainly in varus postoperatively compared with preoperative values (122° ± 11° vs 134° ± 7°). Postoperative radiographic analysis and at the last follow-up did not show any significant difference, except for the increase of the depth of the glenoid from 4.2 ± 1.4 to 4.9 ± 1.8 mm. Conclusions The resurfacing shoulder arthroplasty reproduces the normal anatomy and compensates glenohumeral wear. However, there was a tendency to position the prosthesis in varus because of technical imperfections. With follow-up, medialization of the humerus with glenoid wear was observed and was correlated in some patients with reappearance of pain.