Purpose

To determine the biomechanical effects of LMPR and Kaplan fiber tears in ACL-deficient knees and assess the impact of LMPR repair, modified Lemaire tenodesis, or both, after ACLR.
Study Design: Controlled laboratory study.

Methods

Ten paired cadaveric knees were randomized into four groups and mounted in a six degrees of freedom robotic system. The ACL, LMPR, and Kaplan fibers were sequentially sectioned in random order. After ACLR, LMPR repair and modified Lemaire extra-articular tenodesis (LET) were performed in random order. Tibial displacements and rotations were measured under internal rotation (IR) torque (5 Nm) and a simulated pivot shift (5 Nm IR torque, 5 Nm valgus torque, and 90 N anterior tibial translation) at 0°–90° knee flexion.

Results

Both the LMPR and Kaplan fibers act as secondary stabilizers to isolated IR and overall pivot shift loading in the ACL deficient knee, and Kaplan fiber tears have an additive biomechanical effect to the ACL deficient and LMPR tear knee state for isolated IR as well as for coupled IR and ATT during the pivot shift. ACLR alone did not fully restore stability, with significant residual increases in isolated IR (up to 5.3° ± 3.3° at 60°, p < 0.001), coupled IR (5.3° ± 3.7° at 60°, p < 0.001), coupled ATT (2.8 ± 4.5 mm at 15°, p < 0.001), and coupled valgus rotation (2.7° ± 2.5° at 90°, p < 0.001) during pivot shift. Adding an LET to ACLR, with or without LMPR repair, restored stability comparable to the intact knee for isolated IR, coupled IR, and coupled ATT during pivot shift. LMPR repair in ACLR with Kaplan fiber injury restored valgus rotation stability at most flexion angles.

Conclusion

Both the LMPR and Kaplan fibers act as secondary stabilizers to IR and pivot shift loading in the ACL deficient knee, with an additive biomechanical effect of the Kaplan fibers to the ACL with LMPR deficient knee for isolated IR and for coupled IR and ATT during the pivot shift. Furthermore, we found that the most important reconstruction state which best restored stability comparable to the ACL intact state was the addition of a LET to either the ACLR alone or ACLR with LMPR repair state, except for valgus rotation during pivot shift, where an LMPR repair contributes most.