Radiographic characterization of the B2 glenoid: the effect of computed tomographic axis orientation

Background: Glenoid retroversion may accelerate glenoid loosening after total shoulder arthroplasty. Accurate measurement of preoperative glenoid deformity is critical for decision-making and prognostication. The purpose of this study was to determine whether glenoid version, inclination, and depth and humeral subluxation measurements on computed tomography (CT) scan slices oriented in the plane of the body differ from those oriented in the scapular plane and those obtained by automated 3-dimensional reconstruction software in the setting of a biconcave B2-type glenoid. Methods: Thirty-one preoperative CT scans in patients undergoing total shoulder arthroplasty withWalch B2-type glenoids underwent a standardized measurement protocol by 3 observers. Glenoid version, inclination, and depth and humeral subluxation were measured on 2-dimensional CT images in the plane of the body, on 2-dimensional images in the plane of the scapula, and by a validated, automated 3-dimensional software program. Results: Correction of CT slice axis into the plane of the scapula decreased measured retroversion by 2.4 degrees to 4.7 degrees (P <.004) and inclination by 21 degrees (P < .001). Whereas uncorrected version measurements do not differ from automated software measurements, corrected measurements do (P < .001). Whereas corrected inclination measurements do not differ from automated measurements, uncorrected measurements do (P < .001). Automated measurements differed from both corrected and uncorrected subluxation (P < .001 in both cases). Conclusion: If CT images are not reoriented into the plane of the scapula, version and inclination will be significantly overestimated. In the setting of a retroverted, deformed glenoid, automated software may produce similar inclination measurements to corrected 2-dimensional CT, but it produces significantly altered measurements of version and subluxation. (C) 2017 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.