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Incomplete rupture of the gastrocnemius and superficial digital flexor muscles in a Quarter Horse stallion.

CASE DESCRIPTION
A 16-year-old 500-kg (1,100-lb) Quarter Horse stallion was examined because of acute severe lameness involving the left hind limb.


CLINICAL FINDINGS
Examination revealed signs of failure (concurrent flexion of the tarsus and extension of the stifle [femorotibial] joint) of the caudal component of the reciprocal apparatus. Results of radiographic evaluation ruled out fracture or joint injury as causes of the lameness. During the next 48 hours, the reciprocal apparatus on the left hind limb progressively deteriorated until the horse became non-weight bearing on the limb.


TREATMENT AND OUTCOME
The horse wore a full-limb splint over a Robert-Jones bandage on the plantar aspect of the limb for 30 days. Thirty-four days after the initial injury, the horse had weak function of the reciprocal apparatus and limited ability to bear weight. Six days after removal of the splint, laminitis developed in the contralateral hind limb. The horse was managed with a sling for 5 weeks, during which time deep digital flexor tendon contracture developed. Eleven weeks after the initial injury, the stallion was discharged from the hospital and walking comfortably with a 1-cm-high block under the heel of the left hind foot.


CLINICAL RELEVANCE
Incomplete failure of the caudal component of the reciprocal apparatus is an unusual injury that likely occurs during a fall with a hind limb extended under the body, resulting in forced extension of the muscle while it is engaged in contraction. Conservative management of this injury in a heavily muscled adult horse is possible.