Impact of ulnar collateral ligament tear on posteromedial elbow biomechanics

Ulnar collateral ligament insufficiency has been shown to result in changes in con-tact pressure and contact area in the posteromedial elbow. This study used new digital technology to assess the effect of a complete ulnar collateral ligament tear on ulnohumeral contact area, contact pressure, and valgus laxity throughout the throwing motion. Nine elbow cadaveric specimens were tested at 90° and 30° of el-bow flexion to simulate the late cocking/early acceleration and deceleration phases of throwing, respectively. A digital sensor was placed in the posteromedial elbow. Each specimen was tested with valgus torque of 2.5 Nm with the anterior band of the ulnar collateral ligament intact and transected. A camera-based motion analy-sis system was used to measure valgus inclination of the forearm with the applied torque. At 90° of elbow flexion, mean contact area decreased significantly (107.9 mm² intact vs 84.9 mm² transected, P=.05) and average maximum contact pressure increased significantly (457.6 kPa intact vs 548.6 kPa transected, P<.001). At 30° of elbow flexion, mean contact area decreased significantly (83.9 mm² intact vs 65.8 mm2 transected, P=.01) and average maximum contact pressure increased nonsig-nificantly (365.9 kPa intact vs 450.7 kPa transected, P=.08). Valgus laxity increased significantly at elbow flexion of 90° (1.1° intact vs 3.3° transected, P=.01) and 30° (1.0° intact vs 1.7° transected, P=.05). Ulnar collateral ligament insufficiency was associated with significant changes in contact area, contact pressure, and valgus lax-ity during both relative flexion (late cocking/early acceleration phase) and relative extension (deceleration phase) moments during the throwing motion arc.