Evaluating rotational kinematics of the knee in ACL-ruptured and healthy patients using 3.0 Tesla magnetic resonance imaging

Abstract

Rotational knee laxity is an important measure in restoring knee stability following anterior cruciate ligament (ACL) injury, but is difficult to quantify with current clinical tools. The hypothesis of the study is that there is greater tibial rotation (TR) in women than men, and also in ACL-deficient than healthy knees. Sixteen healthy (8 men, 26.8±6.4years; 8 women, 26.9±3.8years) and ten ACL-deficient (5 men, 33.6±10.5years; 5 women, 36.3±10.7years) subjects received bilateral knee MRI in 15° of flexion using a custom device to apply a constant axial compressive load (44N). A rotational torque (3.35Nm) was sequentially applied to obtain images at internal and external rotation positions. T (2)-weighted images were acquired in internal and external rotation. Images were segmented and TR was calculated. To assess reproducibility, six knees were scanned twice on separate days. Group comparisons were made with unpaired t tests, while intrasubject comparisons were made using paired t tests. Healthy women demonstrated greater TR than men (13.6°±4.7° vs. 8.3°±3.6°; P=0.001). Male ACL-deficient knees showed greater TR than the contralateral knee (15.7°±6.9° vs. 7.7°±5.6°; P=0.003), and compared to male controls (P=0.002). ACL-deficient women showed greater TR compared to their contralateral leg (15.1°±2.3° vs. 10.0°±4.3°; P=0.01). The intraclass correlation coefficient of the TR measurement was 0.913, and the SEM=1.1°. Kinematic MRI is a reproducible method to quantify total knee rotation. Women have more rotational laxity than men, particularly in the external rotation position. ACL rupture leads to increased rotational laxity of the knee. Retrospective case-control series, Level III.