The peroneus tertius muscle can be forcibly avulsed from its insertion by accidents associated with mounting or, more frequently, by the inexperienced use of ropes to restrain a hindlimb.
The hock is abnormally extended, while the stifle remains flexed. The animal cannot advance the limb normally, the calcanean tendon is flaccid, and the hooves may be dragged. The site of avulsion may be painful to the touch. A specific diagnostic feature is that the limb can be pulled backward without any resistance from the animal.
The condition may improve slowly if the animal is confined in a stall (loose) for several months.
Last full review/revision September 2015 by Paul R. Greenough, FRCVS