Peroneus Tertius Tendon Rupture
This horse presented with acute lameness in the right hind limb. No heat or swelling was palpable, and the digital pulses were normal. The horse was also negative to hoof testers. The lameness was noted slightly at a walk, but the horse was weight bearing. Upon examination, when the limb was picked up, the hock abnormally extended. The common calcanean tendon (also known as the achilles tendon in people) was very lax.
Diagnosis: Peroneus Tertius Tendon Rupture
Clinical Signs: The hock can be extended without having to also extend the stifle. The common calcanean tendon will dimple or be very lax while in this position as well. Typically these horses are not painful as long as there are no other structures damaged.