The characteristic restricted hind limb excursion of a horse with fibrotic myopathy often makes it difficult for that horse to perform to its potential. The affected horse’s cranial phase of the stride shortens, and the hoof slaps the ground during the caudal phase of the stride. This aberrant limb motion is not usually due to pain but rather is caused by mechanical restriction from scar tissue.
Diagnosis is confirmed by palpation of a hard, fibrous band along the semitendinosus muscle of the thigh and with ultrasound examination of the caudal thigh. A retrospective study from the University of California, Davis, veterinary hospital of 22 horses, 14 of which were Quarter Horses, reviewed long-term prognosis for comfort and return to athletic success following standing fibrotic myotomy [Noll, C.V.; Kilcoyne, I.; Baughan, B.; Galuppo, L.D. Standing myotomy to treat fibrotic myopathy: 22 cases (2004–2016). Veterinary Surgery March 18, 2019; DOI: 10.1111/ vsu.13209].
It is not always just the semitendinosus muscle that is affected. Fibrosis can occur within the semimembranosus, gracilis or biceps femoris muscles. Cause of injury in many cases is due to trauma such as a slip, fall or kick, but it can also be due to incisional postoperative complications, intramuscular injection of irritating substances or vaccine abscess.
While tenotomy has been a more standard treatment for this malady, standing myotomy offers a low-cost, simple option. The standing procedure enables palpation of the affected area and transection of the fibrotic tissue while the horse is fully weight-bearing. The horse also can be moved in and out of the stocks during the procedure to assess response to surgical efforts.
In the study with 22 horses, only two experienced intraoperative complications, including hemorrhage due to transection of a major blood vessel. Complications in 18% included drainage issues or infection that resulted in suture dehiscence. Those wounds were allowed to heal via secondary intention.
After surgery, horses were stall confined for two weeks and hand walked for 10 minutes three times a day. Following suture removal at two weeks, trotting began for five minutes per day; this was increased by five minutes per week, including a trot on gentle inclines. By four weeks post-op, two minutes of canter were added each day, increased by two minutes each week.
Other potentially beneficial rehab possibilities exist, such as underwater treadmill therapy, therapeutic laser and cavalletti exercises. Throughout the two-month rehabilitation period, it was recommended to owners that they perform passive range-of-motion exercises twice daily for five minutes each session. By two months, the horses were put into regular work and/or turned out to pasture.
Follow-up involved phone conversations and a questionnaire with 16 of the 22 owners between six months and 11 years following myotomy surgery. Ten of 16 owners expressed satisfaction with the long-term outcome. Half of the 16 horses did experience recurrence, with four horses developing recurrence when returned to pasture. Eight of 12 athletic horses were able to return to their former level of use. The other four were not and were retired to pasture. The other four horses that were athletes had to have revision surgery.
Rehabilitation following surgery was extremely important to the overall success of the procedure, and not all owners were willing or able to pursue the recommended two-month rehabilitation protocol.
The study concluded: “Standing myotomy as a treatment for fibrotic myopathy leads to a fair outcome with minimal surgical complications. Half of the horses returned to their intended use.”