Type I fiber atrophy in the vastus lateralis muscle in dogs with femoral fractures treated by hyperextension.

A syndrome characterized by limb hyperextension, generalized muscle atrophy, abducted gait, and a limited range of joint motion is reported in five dogs, four of which were immature. Distal femoral fractures, of traumatic origin, were found in all dogs; four dogs were subjected to limb immobilization in extension for three to seven weeks. Lesions in muscle biopsies included fiber size variability, increased prominence of subsarcolemmal nuclei, increased perimysial fibrosis and focal necrosis. Histochemical and morphometric studies demonstrated a significant (p less than 0.05), Type I fiber atrophy in the vastus lateralis muscles in the limbs with femoral fractures treated by hyperextension. The shortest time period between onset of fracture and the presence of type I fiber atrophy was seven weeks.