Equine Orthopaedics and Rheumatology Q&A 08

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The figure illustrates a 13-year-old show jumping pony with a moderate, sudden onset lameness of the right hindlimb which developed after a fall in a competition.

Question	Answer		Article
What structure has been damaged?	The peroneus tertius has ruptured. The classical signs shown here are extension of the hock with the stifle flexed, and ‘puckering’ of the Achilles tendon (gastrocnemius and superficial digital flexor tendons).		Link to Article
What is its function?	The peroneus tertius is an almost completely tendinous structure that 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 is an important part of the reciprocal apparatus, which mechanically flexes the hock when the stifle joint is flexed.		Link to Article
How does the injury occur?	The injury occurs as a result of extension of the hock as the stifle flexes. This can happen when an animal: struggles to free a trapped limb; slips with the limb extended backwards; falls in a full hindlimb cast; exerts itself coming out of a starting stall at the beginning of a race.		Link to Article
How would you treat this pony, and what is its long-term prognosis?	There is no suitable surgical treatment. Complete box rest for 6–8 weeks, followed by a graduated exercise programme over the next 8–12 weeks, is the treatment of choice. The prognosis is fair to good. Healing is by scar tissue formation between the ruptured tendon ends. Return to a functional unit may not occur, or the peroneus tertius may be injured when the animal returns to work. The location of the injury affects the prognosis. Avulsion of the origin of the peroneus tertius may result in an intra-articular fracture with a hopeless prognosis.		Link to Article