The Effect of Medial Meniscal Injury on Rotational Instability following ACL Reconstruction

Abstract

Clinical outcomes and patient satisfaction scores following ACL reconstruction have been thought to be associated primarily with the condition of the repaired ACL. This is one component in the outcome, but associated injuries such as medial meniscal damage may play as great of a role as the condition of the ACL. Previous studies have reported conflicting views on whether the condition of the medial meniscus affects knee stability after ACL reconstruction. The medial meniscus has been previously described as a secondary constraint to AP translation. The effect of the meniscal condition on tibial rotation has not been elucidated with conflicting results from previous studies. The purpose of this study was to determine the effect of the condition of the meniscus on AP translation and tibial rotation during in-vivo testing with a robotic knee tester. Forty-two patients who underwent ACL reconstruction and 5 ACL deficient patients volunteered to participate in this IRB-approved study. Within the ACL reconstruction group, 23 patients had no meniscal injuries, 9 patients had a medial meniscus injury that had been repaired, and 10 patients had a medial meniscal injury that resulted in a medial meniscectomy. All patients were positioned supine within the RKT with knees at 25°-30° of flexion. The subject's feet were attached to footplates on the RKT and both thighs were placed within clamps to limit femur motion. A clamp was also placed over each patella with a downward force of 20 N. Electromagnetic sensors were positioned on the proximal tibia and on the frame over each femur. Three single-plane tests were performed in sequence in which the RKT system bilaterally cycled the knees first into anterior/posterior translation (ATT, PTT), then external/internal rotation (ER,IR), and lastly valgus/varus rotations (VL,VR). Following 3 preconditioning cycles of each motion, 3 test cycles were performed with tibial kinematics relative to the femur being recorded for both knees. The effect that the condition of the medial meniscus had on AP translation and internal/external rotation of the tibial was determined using one-way ANOVA's. Loss of the medial meniscus due to menisectomy resulted in a side-to-side increase in internal rotation of the knee while repair of the medial meniscus resulted in a decrease in side-to-side internal rotation compared between three groups: Group 1: ACL Reconstruction alone; Group 2: ACL Reconstruction and medial menisectomy; and Group 3: ACL Reconstruction and medial meniscal repair (ANOVA p<0.05). Loss of medial meniscus results in a greater than 5 times wider variance in translation laxity (variance=24.8) compared to patients having a meniscal repair (variance=4.49) (F-Test p=0.014). KOOS and VAS scores demonstrated significant differences between all three groups (ANOVA p<0.001). The most important finding in this study is that the loss of the medial meniscus during anterior cruciate ligament surgery has a significant impact on both the biomechanical function of the knee and validated subjective questionnaire scores. Most importantly the loss of the medial meniscus has a surprising impact on anterior/posterior laxity as well as rotational laxity in the post-operative anterior cruciate ligament reconstructed knee.