LONGITUDINAL MEASUREMENT OF TIBIAL MOTION RELATIVE TO THE FEMUR DURING PASSIVE DISPLACEMENTS IN THE CAT BEFORE AND AFTER ANTERIOR CRUCIATE LIGAMENT TRANSECTION

Passive anterior-posterior displacement and medial-lateral rotation of the tibia on the femur in the feline knee were assessed before transe ction of the anterior cruciate ligament, immediately after transection , and 2 and 4 months after transection. Four anaesthetized experimenta l and three sham-operated control animals were positioned in a stereot axic frame. Motions of the tibia relative to the femur were measured w ith use of 60-Hz video motion analysis, while a strain-gauged system a llowed measurement of forces and moments applied to the tibia. Displac ement at 15 N of anterior force and 30 degrees of knee flexion increas ed by an average of 6 mm following transection, and stiffness decrease d by an average of 6 N/mm. At 2 and 4 months following transection, th ere were statistically significant reductions in this abnormal displac ement. Stiffness during anterior displacement of the tibia at 30 degre es increased significantly from immediately after transection to 4 mon ths. At 90 degrees, mean anterior displacement decreased from 5.1 mm i mmediately after transection to 2.9 mm at 4 months. Medial rotation at 30 degrees of knee flexion was significantly decreased from a mean of 16.5 degrees after transection to a mean of 10.7 degrees at 4 months. Changes in medial rotation at 90 degrees, lateral rotation at 90 degr ees, and lateral rotation at 30 degrees were not statistically signifi cant. These results indicate a significant change in secondary constra ints to tibial motion in response to knee instability.