Load Sharing of the Deep and Superficial Medial Collateral Ligaments, the Effect of a Partial Superficial Medial Collateral Injury, and Implications on ACL Load.

Background: Injuries to the deep medial collateral ligament (dMCL) and partial superficial MCL (psMCL) can cause anteromedial rotatory instability; however, the contribution of each these injuries in restraining anteromedial rotatory instability and the effect on the anterior cruciate ligament (ACL) load remain unknown.
Purpose: To investigate the contributions of the different MCL structures in restraining tibiofemoral motion and to evaluate the load through the ACL after MCL injury, especially after combined dMCL/psMCL injury.
Study Design: Controlled laboratory study.
Methods: Sixteen fresh-frozen human cadaveric knees were tested using a 6 degrees of freedom robotic simulator. Tibiofemoral kinematic parameters were recorded at 0°, 30°, 60°, and 90° of knee flexion for the following measurements: 8-N·m valgus rotation, 4-N·m external tibial rotation (ER), 4-N·m internal tibial rotation, and a combined 89-N anterior tibial translation and 4-N·m ER for both anteromedial rotation (AMR) and anteromedial translation (AMT). The kinematic parameters of the 3 different MCL injuries (dMCL; dMCL/psMCL; dMCL/superficial MCL (sMCL)) were recorded and reapplied either in an ACL-deficient joint (load sharing) or before and after cutting the ACL (ACL load). The loads were calculated by applying the principle of superposition.
Results: The dMCL had the largest effect on reducing the force/torque during ER, AMR, and AMT in extension and the psMCL injury at 30° to 90° of knee flexion ( P < .05). In a comparison of the load through the ACL when the MCL was intact, the ACL load increased by 46% and 127% after dMCL injury and combined dMCL/psMCL injury, respectively, at 30° of knee flexion during ER. In valgus rotation, a significant increase in ACL load was seen only at 90° of knee flexion.
Conclusion: The psMCL injury made the largest contribution to the reduction of net force/torque during AMR/AMT at 30° to 90° of flexion. Concomitant dMCL/psMCL injury increased the ACL load, mainly during ER.
Clinical Relevance: If a surgical procedure is being considered to treat anteromedial rotatory instability, then the procedure should focus on restoring sMCL function, as injury to this structure causes a major loss of the knee joint's capacity to restrain AMR/AMT.
Competing Interests: One or more of the authors has declared the following potential conflict of interest or source of funding: This study was supported by Smith & Nephew, in the form of a research grant that funded the presented research; Ossur, in the form of an educational grant for our research fellowship position; the Natural Sciences and Engineering Research Council Discovery: RGPIN-2018-05693; the Ontario Early Researcher Award ER18-14-197; and the Canadian Foundation for Innovation JELF and Ontario Research Fund–Research Infrastructure, 38141. A.G. has received consulting fees from Smith & Nephew; is on the advisory board and holds stock in Spring Loaded Technology; and holds stock in Precision OS, LinkX Robotics, and Ostesys Robotics. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.