Increased muscle stiffness after anterior cruciate ligament reconstruction--memory on injury?

Residual impairment of knee function was tested in 25 patients 6 to 12 months after successful unilateral reconstruction of the anterior cruciate ligament. The control group comprised 25 healthy individuals. Jumping onto one foot from a height of 20 cm was taken as a prototype of similar everyday activities. We measured maximum flexion of the knee during the landing phase of the jump, and the degree of knee flexion at the time of maximum deceleration of the knee against gravity during jumping using the three-dimensional optical motion analysis system-ELITE. In the group of patients, measured parametres were significantly smaller on the operated side than on the unaffected side. These two measured values were significantly smaller on both legs in group of patients as compared to the values in the control group. The results of our study indicate that functional disturbance persisted for 6 to 12 months after anterior cruciate reconstruction. This may be due to the changed muscle activation pattern of the knee causing increased stiffness of knee muscles. It seems that re-programming of the central nervous system occurred in order to protect the injured lower extremities from another injury.