12/04/2024
Case of the Month!
A three-year-old Thoroughbred filly race horse presented with severe atrophy of the left gluteal muscles and a significant knuckling over left hind fetlock gait abnormality.
The causative agent of the muscle atrophy was found to be EPM. The subsequent focal de-innervation of the rump created a disparity in muscle tone between the seemingly normally innervated inner muscles of the thigh (semimembranosus and semitendinosus) and those greatly affected and atrophied laterally. It is thought that those stronger muscles created more tension than the affected muscles could counteract and left the fetlock in an abnormal position.
The severity of the fetlock positioning would alter the filly’s ability to walk normally and would likely result in significant hoof deformation over time left untreated.
Conservative treatment was initially sought to improve the fetlock articulation via a wedged Nanric ultimate cuff, which proved unsuccessful. Secondly, a custom thermoplastic leg brace was fitted in an effort to gently stretch the soft tissue muscle attachments and position the fetlock in an extended manner. Unfortunately, the reciprocal apparatus of the horse’s hindlimb created an issue of lifting the heel within the leg brace during movement and eventually created pressure sores over the heel bulbs.
The decision was made to cut (tenotomy) the superficial digital flexor tendon mid-cannon to release the tension preventing the fetlock from achieving its normal anatomical configuration. A half limb cast was applied while the horse was suspended in a sling in an effort to prevent potentially catastrophic loading of the deep digital flexor tendon and suspensory while the superficial was healing. There was no way to know prior to surgery, but there was also a certain amount of deep digital flexor tendon contracture that became apparent after the superficial tenotomy seen in the video close up of the hoof and fetlock. With the fetlock now capable of normal anatomic position, it was decided to not pursue a deep digital flexor tendon tenotomy at that time.
After approximately four weeks in a half limb cast, the mare was once again placed in a wedged shoe to accommodate the tension within the deep digital flexor tendon while the surgery site continued to heal.
A neurologist with the aid of an EMG study, applied Botox to the neuromuscular junctions of the medial gluteal muscles in an effort to relax the musculature and lengthen the musculo-tendinous unit with some apparent success. The heels do remain slightly elevated from the ground barefoot at rest and the mare remains in a modified reduced wedge ultimate cuff. She is quite comfortable turned out in a field daily and is currently pregnant.