[Changes in the femoral nerve and medial articular nerve after medial arthrotomy and replacement of the anterior cruciate ligament].

The effect of combined medial arthrotomy (Payr's approach) and replacement of the anterior cruciate ligament upon the femoral nerve and the medial articular nerve has been studied. Resection and prosthetic replacement of the anterior cruciate ligament was performed on the right hindlimb of twelve Merino sheep. Three unoperated animals served as controls. Eight to 48 weeks after the operation, myelinated axons of the femoral nerve and the medial articular nerve were examined using morphological and morphometric methods. Compared with the un-operated control side, only discrete morphological alterations were detectable, such as an increase in non-circular axons. In contrast, considerable morphometric changes were observed: A decrease in large axons and an increase in small axons were found in the femoral nerve of the operated side resulting in a significant reduction in axon diameter (p < or = 0.05). This decrease in axon diameter was associated with a significant increase in the number of axons. Both changes persisted throughout the period examined (48 weeks). Similar changes, i.e. increase in small axons, decrease in large axons and reduction in mean axon diameter were also observed in the medial articular nerve. The results show that medial arthrotomy with prosthetic replacement of the anterior cruciate ligament results in irreversible changes of the femoral nerve and the medial articular nerve. These findings indicate that the medial articular nerve is injured during medial arthrotomy. Mechanisms are discussed which may explain the alterations observed in the femoral nerve a long distance (30 to 35 cm) away from the operation site.