Muscle fiber atrophy in the quadriceps in knee-joint disorders. Histochemical studies on 112 cases.

In order to determine whether there is a different susceptibility of muscle fiber types in the m. vastus lateralis (VL) in knee-joint disorders, histochemical studies were performed on 112 cases. Anterior cruciate ligament (ACL) injuries affected 51 patients; ACL injuries associated with meniscus (ACL + M) injuries affected 29. Twenty-five patients had sustained meniscus injuries and seven had injuries of the collateral ligaments (CL). Fifty-two were athletic and 60 were not. On each biopsy, fiber-type distribution was obtained and the degree of atrophy of each fiber type was estimated from two parameters, the mean diameter and the percentage of atrophied fibers. The distribution of type-1 fibers averaged 38.0% +/- 12.0%. There were no significant differences among disorders in the distribution of type-1 fibers. Both parameters of fiber atrophy revealed a difference in susceptibility between type-1 and type-2 fibers. Atrophy of type-1 fibers was found only in ACL and ACL + M injuries. Type-2 fibers were atrophied in all four disorders. Atrophy of type-2 fibers could be a nonspecific change due to the inactivity of the VL, but type-1 fiber atrophy may relate specifically to the condition of ACL insufficiency.