Quantification of B2 glenoid morphology in total shoulder arthroplasty.

BACKGROUND B2 glenoid morphology is challenging to address with shoulder reconstruction. Deformity often renders current techniques inadequate, necessitating compromises that limit long-term implant durability. The purpose of this study was to perform in vivo measurements of glenoid deformity to better appreciate the orientation of the B2 biconcavity demarcation and erosion that surgeons face intraoperatively. MATERIALS AND METHODS A consecutive 106 total shoulder arthroplasty cases for primary glenohumeral osteoarthritis were studied. We classified glenoids by direct visualization and noted lines of biconcavity demarcation and erosion in B2s. We then calculated the "angle of erosion" as that between the back side of the unsupported, smooth-backed glenoid sizer disk and the neoglenoid. We obtained depth measurements throughout the reaming process and monitored subchondral bone. RESULTS We classified 43 of 106 glenoids (41%) as B2. A biconcavity demarcation line between the paleoglenoid and the neoglenoid was present, on average, from the 1-o'clock to the 7-o'clock position for a left shoulder. Mean depth of erosion was 4.4 mm, occurring at 114° on a Cartesian coordinate system for a left shoulder. The mean angle of erosion was 18° (range, 8°-43°). Despite reaming, 20 of 43 B2 glenoids (47%) had incompletely supported components at final seating. CONCLUSIONS Arthritic B2 glenoids are common, and their maximal erosion is usually posteroinferior. Use of standard glenoid components to reconstruct them may require significant subchondral bone removal to achieve complete bone support. Alternatively, as a compromise, maintenance of subchondral bone in these cases requires implanting components with incomplete bony support.