In vivo bone strain in the equine tibia before and after transection of the peroneus tertius muscle.

The present study was undertaken to determine the influence of the peroneus tertius muscle on the loading regime of the tibia in the horse. Strain gauge rosettes were bonded to the cranial and caudal cortices of the left and right tibiae in six Shetland ponies. In vivo bone strain recordings were made before and after unilateral transection of the peroneus tertius muscle. Relatively large individual variations in response to transection were observed in both the experimental and the contralateral control limbs. The principal strain values on the cranial and caudal cortices increased during the second peak in the support phase by approximately 10 per cent; the angle between the larger principal strains and the long axis of the bone, measured proximal to the gauges, rotated approximately 4 degrees medially in experimental limbs, but did not change in the control limbs. It seems unlikely that the peroneus tertius muscle has a substantial influence on the loading regime of the tibia during normal walking.