Anatomical relationship between the medial head of the gastrocnemius and the occurrence of a dystrophic bony lacuna.

A bony lesion with identical radiological features was seen in the medial part of the distal femoral metaphysis in five patients who practised cross-country motorcycling. These findings suggested that the cause of the lesions was of muscular origin. The nature and physiopathogenesis of the lesions were studied by roentgenography, computerized tomography and analysis of anatomical specimens. The results of these procedures were compared to observations made peroperatively. The lesion was identified as a specific, dystrophic bony lacuna resulting from the action of the medial head of the gastrocnemius (caput mediale m. gastrocnemii). In certain conditions this powerful biarticular muscle induces multiple microtrauma via traction on the structures of its tendinous insertion, especially the underlying bone, thus leading to bony avulsion. It is shown in this study that the bone-tendon-muscle complex forms a veritable biomechanical unit.