Geometrical analysis results of 42 resurfacing shoulder prostheses: A CT scan study.

BACKGROUND: Shoulder resurfacing arthroplasty was introduced in Scandinavia in the early 1980s then developed by SA Copeland. HYPOTHESIS: Resurfacing prostheses restore the normal anatomy of the proximal humerus. Here, our objective was to evaluate humeral resurfacing prosthesis position on radiographs and computed tomography (CT) images.
MATERIALS AND METHODS: We retrospectively reviewed 42 consecutive cases seen at a single centre between 2004 and 2009. Mean patient age was 65 years. CT was performed routinely before prosthesis implantation and at re-evaluation. The Copeland Mark III(®) (Biomet France SARL, 26903 Valence, France) implant was used in 32 cases and the Aequalis Resurfacing Head(®) (Tornier France, 38334 Saint-Ismier, France) in 10 cases. The post-implantation CT images were used to measure the angle of inclination, medial humeral offset, lateral glenohumeral offset, and version of the implant.
RESULTS: Mean follow-up was 18 months. Compared to baseline, no significant changes were found at re-evaluation for the angle of inclination or lateral glenohumeral offset. In contrast, medial humeral offset increased by 3.47mm, and excessive anteversion of 4.23° compared to the bicondylar line was noted. DISCUSSION: Humeral head resurfacing prostheses restore the overall anatomy of the proximal humeral head. Our CT scan evaluation protocol seems reproducible and enables an evaluation of implant geometry. In our experience, resurfacing arthroplasty restored the native humeral offset. Inadequate retroversion was noted and was probably related to insufficient exposure during surgery. LEVEL OF EVIDENCE: Level IV, retrospective study.