Assessment of a novel computed tomography ratio to characterize B2 glenoid morphology with total shoulder arthroplasty

Abstract

BackgroundThe B2 glenoid poses significant challenges for reconstruction with shoulder arthroplasty. A variety of techniques has been used to quantify the B2 glenoid and is often used for surgical decision-making. The critical B2 glenoid ratio is a novel measure and is defined as the ratio between the paleoglenoid length (original glenoid surface) and the total glenoid length. This study aims to define inter and intrarater reliability of the critical B2 ratio and to compare it to conventional methods of measurement. MethodsA convenience sample of patients with Walch B2 glenoid morphology was generated from a prospectively collected multicenter shoulder arthroplasty registry. The axes of preoperative computed tomography (CT) images were reoriented in the scapular plane. Three sports medicine surgeons experienced in arthroplasty measured the critical B2 glenoid ratio in addition to posterior humeral subluxation, version, and glenoid bone loss at 2 timepoints greater than 1 week apart. Inter-rater and intra-rater reliability were calculated for all readers and CT measures with the intraclass correlation coefficient (ICC). The critical B2 glenoid ratio was compared to conventional measurements using Spearman’s rank correlation coefficients and receiver operating characteristic (ROC) curves. ResultsThe critical B2 glenoid ratio demonstrated good inter-rater reliability among the 3 measurers with ICCs of 0.89 and 0.799 for the 1st and 2nd measurement sessions, respectively. The critical B2 glenoid ratio showed excellent intrarater reliability for 2 of the measurers (ICC 0.933 and 0.98) and good intrarater reliability for 1 of the measurers (ICC 0.820). A significant correlation was observed between glenoid bone loss along Friedman’s line and the critical B2 ratio (P < .001). ROC curves found a B2 ratio = 0.4 was found to be an inflection point for 15° of neoglenoid (posterior erosion surface) retroversion. ROC curves to assess if humeral head subluxation >70% correlated to a threshold B2 ratio value revealed no significant threshold. ConclusionsThe critical B2 glenoid ratio is a novel and reproducible CT-based measure that is defined as the ratio between the paleoglenoid length and the total glenoid length. It has high reproducibility based on inter and intra-rater reliability among a group of shoulder surgeons. A critical B2 ratio of less than or equal to 0.4 correlates with significant neoglenoid retroversion and may be a threshold beyond which to avoid corrective eccentric reaming for anatomic shoulder arthroplasty.