Longitudinal measurement of tibial motion relative to the femur during passive displacements in the cat before and after anterior cruciate ligament transection

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Abstract
Passive anterior‐posterior displacement and medial‐lateral rotation of the tibia on the femur in the feline knee were assessed before transection of the anterior cruciate ligament, immediately after transection, and 2 and 4 months after transection. Four anaesthetized experimental and three sham‐operated control animals were positioned in a stereotaxic frame. Motions of the tibia relative to the femur were measured with use of 60‐Hz video motion analysis, while a strain‐gauged system allowed measurement of forces and moments applied to the tibia. Displacement at 15 N of anterior force and 30° of knee flexion increased by an average of 6 mm following transection, and stiffness decreased by an average of 6 N/mm. At 2 and 4 months following transection, there were statistically significant reductions in this abnormal displacement. Stiffness during anterior displacement of the tibia at 30° increased significantly from immediately after transection to 4 months. At 90°, mean anterior displacement decreased from 5.1 mm immediately after transection to 2.9 mm at 4 months. Media rotation at 30° of knee flexion was significantly decreased from a mean of 16.5° after transection to a mean of 10.7° at 4 months. Changes in medial rotation at 90°, lateral rotation at 90°, and lateral rotation at 30° were not statistically significant. These results indicate a significant change in secondary constraints to tibial motion in response to knee instability.