Fibrotic myopathy is a condition that is most commonly associated with sliding stops (see video below) by reining Quarter Horses and Polo horses. It is typically due to repeated tearing and stretching of muscle fibres of the semitendinosus muscles, and less commonly the semimembranosus and biceps femoris muscles. These represent the muscles of the hamstring or the caudal thigh muscles. Adhesions form between the muscles and limits the action of the semitendinosis muscle creating a mechanical lameness. The lameness is not painful and does not improve with non-steroidal anti-inflammatory drugs. Additionally, there is no affect of flexion tests on the gait. It has also been described secondary to intramuscular injections as well as a congenital form.
The characteristic gait is most obvious at the walk. There is a shortened anterior phase of the stride, and then a slapping of the foot to the ground. The abnormal gait is most obvious at the walk and often can’t be seen at the trot. Firm fibrous muscles may be detected on palpation of the caudal aspect of the limb at the level of the stifle.
For acute muscle tears rest, cold hosing, and anti-inflamatories may help. Physical therapy may also be very helpful in the early stages of the condition. Surgical treatments have been described for chronic cases, and include resection of the fibrotic band and a semitendinosus myotenectomy, but recurrence is common. Transection of the semitendinosus tendon insertion on the tibia has a higher success rate with less postoperative trauma.