Analysis of the transverse force couple in the Walch B2 and Walch A2 omarthrosis

Abstract

BackgroundWalch type B2 glenoids are frequent (about 40% of primary osteoarthritis) and complex to manage. Nonetheless, the origin of this deformity remains elusive to this day. The rotator cuff muscle volume, more particularly the transverse force couple (TFC = Infraspinatus (IS) + Teres minor (Tm) + Subscapularis (SS)) could, play a role in the origin of Walch type B2 deformity. The objective of this study was to analyze the TFC in patients with Walch B2 compared with Walch A2 shoulder osteoarthritis. We hypothesize there is a TFC imbalance in favor of the external rotators in Walch B2 shoulder osteoarthritis. Method120 computed tomography scans were analyzed, 65 scans with Walch B2 and 55 scans with Walch A2 shoulder osteoarthritis. On each study, the volume analysis of the SS, IS, and Tm was assessed by two surgeons. The ratio of SS volume/(IS volume + Tm volume) was compared in patients with Walch B2 and A2 shoulder osteoarthritis. ResultsThe ratio of SS volume/(IS volume + Tm volume) was significantly lower (P < .0001) in Walch B2 glenoid (0.99) than in Walch A2 glenoid (1.24). The volume of the posterior group (IS and Tm) was significantly greater in the B2 glenoid 103.1 (76.7-134.5) cm3 than in the A2 glenoid 86.2 (68.00-105.25) cm3 (P = .026). Regarding SS volume, there was no significant difference between B2 glenoid 103.7 cm3 (73.3-146.2) and A2 glenoid 101.3 cm3 (83.0-135.9) P = .885. ConclusionThere is no imbalance of TFC in Walch B2 glenoid. However, the TFC ratio is lower in Walch B2 glenoid compared to Walch A2 glenoid. This is related to a significantly greater volume of the external rotators in the Walch B2 patients.