Concomitant Lateral Meniscus Injury Aggravates Rotational Laxity of the Anterior Cruciate Ligament Injured Knees

OBJECTIVES: Residual rotational laxity in the anterior cruciate ligament (ACL) reconstructed knees is a remaining problem after the ACL reconstruction. Improper detection and treatment of the secondary restraint for the knee rotational laxity after the ACL were considered as the major reason for the problem. Although anterolateral ligamentous structure of the knee has increasingly been focused on, meniscus injury is frequently accompanied with the ACL injury and assumed to have significant impact on the rotational laxity based on previous studies. The purpose of this study was to determine the effect of the meniscus tear on the rotational laxity in the ACL-deficient knees. METHODS: Fifty-seven unilateral ACL-injured patients (26 males and 31 females, 24 ± 10 y.o.) were tested. The protocol of this study was approved by the IRB in Kobe University, and the informed consent was obtained from all the patients. The pivot-shift test was performed under general anesthesia during their ACL reconstruction. (Fig.1) Clinical grading according to the IKDC (none, glide, clunk, and gross) was determined, whereas the quantitative assessment of the pivot-shift was conducted using electromagnetic measurement system to provide the tibial acceleration (m/sec(2)). Meniscus injuries were finally confirmed under arthroscopy during the ACL reconstruction. The difference of clinical grading and tibial acceleration between the ACL-injured knees with and without additional meniscus tear was assessed, followed by subgroup analysis for each medial and lateral meniscus tear separately. Statistical significance was set at p-value of 0.05. RESULTS: Concomitant meniscus tear was confirmed in 32 knees. Clinical grading was different between the ACL-injured knees with and without meniscus tear (p<0.05), while the quantitative evaluation did not find a statistical significance (meniscus-injured knees 1.6 ± 1.1 m/sec(2) vs meniscus-intact knees 1.3 ± 0.8 m/sec(2), p=0.09). Subgroup analysis demonstrated increased tibial acceleration in the ACL-deficient knees with lateral meniscus tear (1.8 ± 1.1 m/sec(2), n=19) compared to the meniscus-intact knees (p<0.05), whereas the rotational laxity did not rise in the medial meniscus torn knees (1.4 ± 1.0 m/sec(2), n=20, p=0.33). CONCLUSION: Although the meniscus injury is the most common in addition to the ACL injury, the impact of the meniscus injury on the knee rotational laxity has not been fully examined. This study demonstrated the significant impact of the meniscus injury, especially lateral meniscus injury, on the rotational laxity in the ACL-deficient knees, which was successfully detected by using the quantitative measurement device. A careful inspection of the lateral meniscus tear should be required in the ACL-deficient knees with a substantial pivot-shift and, if there is any, it should be repaired as much as possible to avoid additional rotational laxity.