Effect of unstable meniscal injury on three-dimensional knee kinematics during gait in anterior cruciate ligament-deficient patients

Background: Our purpose was to clarify the differences of three-dimensional knee kinematics in anterior cruciate ligament (ACL)-deficient patients between with and without meniscal injury using gait analysis. Methods: A total of 72 knees in 36 young athletes with primary and unilateral ACL injury, with a mean age of 22 years, participated. Gait analysis was done before surgery. According to the arthroscopic findings, patients were divided into two groups. The patients with an unstable meniscal tear were allocated to the meniscal injury group (ACL + M group), and the patients without a meniscal tear were allocated to the no meniscal injury group (ACL group). In the gait analysis, three-dimensional knee kinematics was evaluated and compared. Results: The patients in both groups exhibited lower sagittal plane knee excursions and peak knee extension angles on the affected limb than on the unaffected limb during the mid-stance. In terms of the axial plane, a rotation angle was significantly smaller in the affected knees than in the unaffected knees in the ACL group. On the other hand, an opposite phenomenon was observed in the ACL + M group. Moreover, a significantly larger rotation angle in the affected knees during the stance phase and the whole gait cycle was observed in the ACL + M group than in the ACL group. Conclusion: Increased rotational motion during the gait was observed in the ACL-deficient knees combined with unstable meniscal injuries. Meniscal condition may be a key factor for compensatory gait mechanics to prevent rotatory instability in ACL-deficient patients patients.Level of evidence III.