464 Loading of the medial knee ligaments and anterior cruciate ligament during clinical tests of anteromedial rotatory instability

Objectives/Goals: Injury to the medial knee ligaments (sMCL, dMCL, POL) and anterior cruciate ligament (ACL) can cause anteromedial rotatory instability (AMRI). AMRI can cause knee instability and ACL graft failure, but it is unclear how the sMCL, dMCL, POL, and ACL resist AMRI. We aimed to characterize the in-situ forces of the sMCL, dMCL, POL, and ACL under loading conditions involved with AMRI. Methods/Study Population: We characterized the in situ forces of the sMCL, dMCL, POL, and ACL under 1) isolated external tibial rotation torque (ER), 2) isolated anterior tibial force (Ant), and 3) combined ER+Ant loading. Twenty-eight human cadaveric knees (18 male; mean age, 48±13; 21–65 years) were tested on a robotic manipulator with force sensing. Tibiofemoral kinematics were recorded under isolated ER (4Nm, 0–90°), isolated Ant (134N at 0–90°), and combined ER+Ant (4Nm+100N at 15, 30, 90°). The sMCL, dMCL, POL, and ACL were dissected in random order. The in situ force (N) in the sMCL, dMCL, POL, and ACL at the peak applied load for each loading condition was calculated using superposition and compared with Kruskal–Wallis tests with post hoc pairwise testing using a Bonferroni–Holm correction for multiple comparisons (α = 0.05). Results/Anticipated Results: Under isolated ER, the force in the sMCL (32–52N) from 0°-90° exceeded that of the ACL, dMCL, and POL at each flexion angle (p0.05). Force in the ACL was the second highest (26–6N from 0°-90°). Force in the dMCL and POL was low (≤12N). Under isolated Ant, the ACL carried the highest force at all flexion angles (≥113N) (p0.05), but at 90° the sMCL carried the highest force of all ligaments (p0.05). At 90°, force in the dMCL diminished ( Discussion/Significance of Impact: We show that the sMCL is the major stabilizer to external rotation torques and combined anterior and external loading conditions related to anteromedial rotatory instability across the arc of knee flexion, while the dMCL, POL, and ACL play a less prominent role, with the exception of the ACL and dMCL near full extension.