Abstract
Transection of the anterior cruciate ligament in the dog leads to osteoarthritis. This study defines the kinematic changes in the unstable knee after transection of the cruciate ligament (six dogs) and after a sham operation (four dogs). In the dogs that were anterior cruciate ligamentβdeficient (ACLβD), the duration of stance 1 week postoperatively decreased 38% from the preoperative value, but only a 4% decrease was seen at 6 weeks. The duration of double hindlimb support increased from 6 to 19% of the entire cycle 1 week after surgery but returned to the baseline value by 18 weeks. As the unstable limb contacted the treadmill belt, the initial flexion (yield) and subsequent extension (propulsive) phases were not evident or were markedly attenuated in every ACLβD dog throughout the 26βweek period of observation. The angular velocity patterns were characterized by a slight extension velocity at touchdown (compared with a zero value preoperatively) and a decrease in the peak velocities (both flexion and extension) during the remainder of the stance phase. None of these changes was observed in the animals that had a sham operation. These data indicate that, in the dog, the nervous system compensates for instability of the knee by altering angular, but not temporal, parameters. The extension velocity at touchdown and the reduction in peak flexion velocity during the yield component of the stance phase may reduce the ability of the limb to absorb impact forces and lead to the development of osteoarthritis of the knee. Alternatively, the reductions in flexion and extension of the knee during the stance phase and in the values for peak velocity presumably reflect protective muscular reflexes that may slow the rate of progression of joint breakdown.