• Julie R. Steele
Keywords: ACL deficiency, ground reaction forces, tibiofemoral forces


INTRODUCTION: Physiological loading imposed on the knee is composed of joint forces that the knee must transmit to support, accelerate and decelerate body mass, and muscle forces acting to control knee motion and provide stability. Although not representing quantification of muscle forces, ground reaction forces (GRF) are often used to estimate knee loading, particularly in studies examining injury mechanisms such as anterior cruciate ligament (ACL) rupture. The purpose of this study was to examine the relationship between GRF and tibiofemoral forces generated by control and ACL deficient (ACLD) patients during a task known to stress the knee, namely abrupt deceleration. METHODS: Eleven functional chronic unilateral ACLD patients and 11 uninjured matched controls landed in single-limb stance on a Kistler force platform after catching a chest level pass and then decelerating abruptly. Sagittal plane kinematics of each subject’s landing action were digitized (200 Hz) and GRF data were sampled (1000 Hz) for 3 trials per lower extremity. Joint reaction forces and sagittal planar net moments of force for the knee were calculated using Newtonian equations of motion and inverse dynamics. Tibiofemoral joint shear (FS) and compressive forces (FC) were derived using the method of Kuster et al. (1994). Pearson product moment correlations were calculated between temporal (ms) and magnitude (BW) aspects of the GRF and tibiofemoral force data to determine the relationship between these parameters for the two subject groups, analysed both individually and when the results were combined. RESULTS: Although the relationship between the magnitude of the anteriorposterior (Fx) and vertical (Fy) GRF components and the magnitude of FS and FC was high for controls, it was low for ACLDs (Table 1). However, the time from initial foot-ground contact (IC) to peak Fx was highly related to the time from IC to peak FS in both subject groups. CONCLUSIONS: It was concluded that the magnitude of GRF data should not be used to estimate loading imposed on the tibiofemoral joint in ACLD patients. However, timing of Fx may provide insight into timing of shear forces at the knee during dynamic tasks. Kuster, M., Wood, G. A., Sakurai, S., Blatter, G. (1994). Downhill Walking: A Stressful Task for the Anterior Cruciate Ligament? A Biomechanical Study with Clinical Implications. Knee Surgery, Sports Traumatology, Arthroscopy, 2, 2-7.