Interaction between the ACL graft and MCL in a combined ACL plus MCL knee injury using a goat model

The optimal treatment for the MCL in the combined ACL and MCL-injured knee is still controversial, Therefore, we designed this study to examine the me chanical interaction between the ACL graft and the MCL in a goat model usin g a robotic/universal force-moment sensor testing system. The kinematics of intact, ACL-deficient, ACL-reconstructed, and ACL-reconstructed/MCL-defici ent knees, as well as the in situ forces in the ACL, ACL graft, and MCL wer e determined in response to two external loading conditions: 1) anterior ti bial load of 67 N and 2) valgus moment of 5 N-m. With an anterior tibial load, anterior tibial translation in the ACL-defici ent knee significantly increased from 2.0 and 2.2 mm to 15.7 and 18.1 mm at 30 degrees and 60 degrees of knee flexion, respectively, The in situ force s in the MCL also increased from 8 to 27 N at 60 degrees of knee flexion. A CL reconstruction reduced the anterior tibial translation to within 2 mm of the intact knee and significantly reduced the in situ force in the MCL to 17 N, However, in response to a valgus moment, the in situ forces in the AC L graft increased significantly by 34 N after transecting the MCL. These fi ndings show that ACL deficiency can increase the in situ forces in the MCL while ACL reconstruction can reduce the in situ forces in the MCL in respon se to an anterior tibial load. On the other hand, the ACL graft is subjecte d to significantly higher in situ forces with MCL deficiency during an appl ied valgus moment. Therefore, the ACL-reconstructed knee with a combined AC L and MCL injury should be protected from high valgus moments during early healing to avoid excessive loading on the graft.