An urgent telephone call one evening from a distraught client reporting that her favourite riding horse had a possible broken hind leg resulted in an emergency visit.
The mare had for some reason had become startled in her paddock by a low flying helicopter,had tried to jump the fencing ,and got one hind leg caught on the top rail which had not given way. The mare was found to be lame on the left hind, which the owner thought was at a peculiar angle.
The mare had been brought into a stable and on examination was found to be standing quite normally and showed no distress. When made to move the left hind leg showed an abnormal extension as if having difficulty in bringing it under itself. When the limb was picked up the hock was able to be completely extended with the stifle still flexed. There was a characteristic dimpling of the structures at the back and just above the hock. Severe lameness was noted at the trot.
These findings immediately showed there to be a rupture of the Peroneus Tertius . The hind leg was subsequently examined ultrasonographically to confirm the rupture.
Treatment consisted of total stable confinement for 4 months, followed by a slow exercise program. The mare 7 months later is now being ridden regularly by its owner.
The Peroneus tertius is a fibrous band of tissue which originates at the distal aspect of the femur and inserts at the proximal cannon bone. This structure is an important part of what is known as the reciprocal apparatus enabling the hock to flex when the stifle is flexed. Rupture can occur anywhere along its length and is caused by overextension of the hock. This usually occurs when a hind leg is trapped and the animal struggles to free itself or can occur with overexertion such as jumping.