Fibrotic myopathy most commonly affects German Shepherds
This condition has a very characteristic gait
The prognosis is poor in spite of all therapies tried
The semitendinosus and the gracilis muscles are located on the back and inner aspects of the thigh. These muscles are responsible for flexion of the knee joint. They also have tendons that pass down to the tip of the heel bone and form a part of the Achilles tendon.
What is fibrotic myopathy?
This uncommon disorder occurs as a result of injury to the muscle with subsequent scar tissue formation within the muscle. This shortens the functional length of the muscle due to contracture of the scar tissue within the muscle. Thus, affected dogs are unable to fully extend the ankle, knee, and hip joints to their maximal extent.
This condition most commonly affects male German Shepherds between 8 to 9 months of age; however, this condition also has been reported in the Doberman Pinscher, Rottweiler, St. Bernard, Boxer, and Old English Sheedog. Clinical signs include lameness, weakness of the affected limb, pain in the acute phases, decreased range of motion of the joints and firm scar tissue within the affected muscle. A characteristic gait alteration is associated with this condition in which the stride is shortened in extension and a rapid and has an elastic inward rotation of the paw is seen just prior to the limb landing on the ground (mid to late swing phase of the stride). The video right is a milder case of this condition. To see a more severe case, go to this link and click video 4.
The diagnosis is generally based on physical examination findings of a fibrotic (firm) muscle and the characteristic gait. Gracilis and semitendinosus myopathy will have a similar gait. Ultrasound of the muscles of the hind limb will define which muscle is affected if physical exam findings are not conclusive.
Unfortunately, there is no treatment that works well. Surgical removal of the affected muscle provides temporary relief of the problem, but recurrences of clinical signs are seen within about 2.5 months (range= 6 weeks to 5 months) due to formation of new scar tissue. Aggressive rehabilitation therapy may be beneficial.
Because of recurrences of this problem following treatment, the prognosis is generally poor.
Lewis DD, Shelton GD, Pias A, et al. Gracilis or semitendinosus myopathy in 18 dogs. J Am Anim Hosp Assoc 1997; 33:177-188.