Selective atrophy of red muscle fibres in the quadriceps in long-standing knee-joint dysfunction

A histochemical study has been made of muscle biopsy material from 11 patients with injuries of the anterior cruciate ligament of the knee-joint. The material consists of 1 case of acute injury and 10 with long-standing injury. All biopsies were made from the vastus medialis. The muscle fibres were divided into two groups on the basis of staining reactions for myofibrillar ATPase and the groups were measured separately when assessing muscle fibre areas in cross section. Eight of the cases, with clinical evidence of muscular atrophy, showed marked differences in size between the red and white muscle fibres. These differences were expressed as a quotient between the mean value for cross-sectional area of the white and red fibres in each particular case. In these cases the quotients were 1.48-1.97. The red fibres exhibited a comparatively low mean value, which was interpreted as being due to selective atrophy of this group of fibres. The patient with an acute injury and two with more long-standing injury, all of whom lacked clinical signs of atrophy of the quadriceps, showed roughly equally-sized red and white fibres with quotients of 0.90-1.12. These size relationships conformed to those obtained in the normal quadriceps muscle. The results are discussed in relation to earlier and similar studies of muscle biopsy material obtained from patients with upper motor neurone lesions and Parkinsonism.