Peroneus Tertius Rupture

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The peroneus tertius is an almonst entirely tendinous muscle that plays an important part in the reciprocal apparatus in the hindlimb of the horse. It originates from the extensor fossa of the distal femur, runs over the cranial aspect of the tibia and inserts, after dividing into two, on the fibular, third and fourth tarsal bones and proximal third metatarsus. It coordinates flexion of the hock and stifle joints.

Rupture is associated with overextension of the hock which can occur in foals as a result of dystocia, or in adults struggling to free a trapped limb or in traumatic injury to the region.

Clinical Signs

The clinical presentation is pathognomonic.

Disruption of the tendon allows extension of the hock while the stifle is flexed, which means that as the limb moves forward, the hock joint does not flex. The horse will usually bear weight and pain is not a feature.


The stifle can be flexed, the hock extended, and a characteristic dimpling of the gastrocnemius tendon can be revealed to diagnose the condition.

Ultrasonography can be used to assess the extent of the disruption.


Rest is the treatment option of choice, with complete box rest for 6-8 weeks followed by a gradual increase in exercise over a further 3 months. This usually results in complete recovery in adult horses, although reinjury might occur if repair is inadequate.

The outcome may not be as satisfactory in some foals and their athletic ability might be compromised.

Peroneus Tertius Rupture Learning Resources
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Equine Orthopaedics and Rheumatology Q&A 08


Stashak, T. (1996) Practical Guide to Lameness in Horses Wiley-Blackwell

McAuliffe, S. (2008) Color Atlas of Diseases and Disorders of the Foal Saunders

Stashak, T. (2002) Adams' Lameness in Horses Wiley-Blackwell

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