November: Peroneus Tear

November Case of the Month: Peroneus Tear

Fancy came in from her paddock with a hind limb lameness. Her owner noticed a little bit of heat above her hock but no obvious swelling. The most unique finding was that when her owner picked up her hind leg to examine it, she had a lot of difficulty and Ellie extended the leg backwards instead. When Dr Danica came to examine Fancy, it took less than 5 minutes to diagnose her rare injury. Fancy tore her peroneus tertius, likely slipping on the ice. The peroneus tertius is part of the reciprocal apparatus in the hindlimb that functions in the concurrent flexion and extension of the hock and stifle. This apparatus aids horses to ‘lock’ their hind limbs in extension to allow them to sleep standing up. Injury to this structure has a tell-tale sign: you can extend the hock while the stifle is flexed. The horse can weight-bare but there is delayed protraction of the limb due to the hock remaining in extension. Good news is that with conservative treatment of 3-4 months rest followed by slow return to exercise typically results in full return to athletic performance.