Effect of Meniscal Ramp Repair on Knee Kinematics, ACL In Situ Force and Bony Contact Forces - A Biomechanical Study

OBJECTIVES: While recent studies showed that all inside meniscal ramp repair is able to restore knee kinematics, the effects of ramp repairs on ACL in-situ forces (ISF) and bony contact forces is still unclear. Therefore, the purpose of this study is to determine the effect of ramp lesion repair on knee kinematics, the ACL-ISF and bony contact forces using a 6-degree-of-freedom (DOF) robotic testing system. It was hypothesized that ramp repair will restore kinematics, ACL-ISF and bony contact forces comparably to the forces of the intact knee. METHODS: 5 fresh-frozen human cadaveric knee specimens were tested using a 6-DOF robotic testing system (FRS2010) to continuously flex the knee from 0° to 90° and apply continuous loading conditions: 134 N anterior load + 200 N compressive load (CL), 4 Nm internal torque + 200 N CL, 4 Nm external torque + 200 N CL. Loading conditions were applied to the: 1) Intact knee 2) Arthroscopically induced 25 mm ramp lesion via posteromedial portal 3) All inside ramp repair 4) ACL deficient knee + ramp repair 5) soft tissue removal 6) Transection of the lateral condyle. To mimic an ideal ACL reconstruction the native ACL was kept intact. By replaying kinematics, ACL-ISF and bony contact forces were determined. Repeated measure ANOVAs were performed to compare knee states at each flexion angle (p<0.05). RESULTS: Ramp repair significantly reduced anterior translation compared to the ramp deficient knee in high flexion under anterior load and CL (mean diff. -0.8 mm, range 0.6-0.9 mm) and at all flexions angles while applying internal torque and CL (mean diff. -2.3 mm, range 1.8-3.3 mm). Increased medial translation and valgus position were observed in all loading conditions at all flexion angles. Both ACL-ISF and medial bony contact forces were not significantly altered by the ramp lesion and repair under any applied loading and flexion angle. In contrast, ramp repair significantly increased lateral bony contact forces by under external torque and CL at 60° and 70° flexion compared to the ramp deficient knee, 32 N and 37 N respectively. No significant differences between intact and ramp deficient knee were detected with respect to kinematics, ACL-ISF and bony contact forces. CONCLUSION: In this study ramp repair decreased anterior translation, increased valgus rotation, and increased bony contact forces in the lateral compartment, disproving the hypothesis under study. The data from this study puts into question potential overconstraint when repairing ramp lesions utilizing all inside devices in 10 degrees of knee flexion. Contrasting previous literature that showed the restoration of the intact state, the results might be attributable to added CL forces and missing influence of the ACL reconstructions. The findings of this study also imply that untreated ramp lesion might not affect ACL-ISF. Future research is needed to better understand the influence of different techniques for repair of ramp lesions and the effect of chronicity on ramp lesions in patients.