Rupture of the peroneus tertius
💥Have you ever seen this before?💥
This is pathognomonic of the injury: a rupture of the peroneus (fibularis) tertius, while the stifle is in flexion, the hock can be extended. The rupture is usually due to overextension of the hock (i.e. horse falling/slipping with the leg straight behind).
In a sound horse, the reciprocal apparatus is mechanically flexing the hock when the stifle joint is flexed, those 2 joints are always moving simultaneously.
The reciprocal apparatus is made up of tendinous muscles on either side of the tibia: on the cranial aspect, there is the peroneus tertius, and on the caudal aspect, there is the superficial digital flexor tendon (see the figure).
🔸DIAGNOSTIC:
Diagnostic is therefore based on clinical signs but can be confirmed by ultrasonography to localise the rupture on the tendon.
🔸CLINICAL SIGNS:
Watch the video to see the pathognomonic signs visible during examination.
When the foot is on the ground the horse has no problem bearing weight and doesn’t show too much pain. At walk the gastrocnemius and superficial digital flexor muscles appear rather flaccid and the limb below the hock tends to hang limp. As the horse trot an obvious lameness is usually evident, with delayed protraction of the limb due to overextension of the hock.
🔸TREATMENT and PROGNOSIS:
Complete rest in box stall is the best treatment, surgical intervention is not recommended. Most cases heal well and most horses can return to previous level of work after few months.
Figure: Adams & Stashak’s lameness in horses.
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