By Top Dog Health

What is Semitendinosus and Gracilis Myopathy?

The semitendinosus and gracilis muscles are found on the back and inner aspects of the thigh, and are responsible for flexing the stifle, or knee joint. The tendons of these muscles also form part of the Achilles tendon. Semitendinosus and gracilis myopathy, also known as fibrotic myopathy, occurs when the normally elastic muscle tissue is replaced with dense connective tissue, similar to scar tissue. Because the connective tissue is not able to stretch like muscle does, the affected muscle become shortened, or contracted. It can occur in other muscles as well, such as the quadriceps, infraspinatus, and supraspinatus muscles. 

Who gets Semitendinosus and Gracilis Myopathy?

Semitendinosus and gracilis myopathy is a relatively uncommon condition, but occurs most frequently in German Shepherds. Belgian Shepherds, Greyhounds, Doberman Pinschers, Rottweilers, St. Bernards, Boxers, and Old English sheepdogs may also be affected. Dogs with fibrotic myopathy tend to be young adult dogs, and may develop the condition as early as 8 to 9 months of age.

What are the Signs of Semitendinosus and Gracilis Myopathy?

Dogs with semitendinosus and gracilis myopathy usually have a history of gradual onset of hind limb lameness, weakness, and pain. The formation of scar tissue in replace of muscle leads to decreased range of motion. It also produces a very characteristic gait, in which the dog’s stride is shorter with a rapid elastic inward rotation of the paw, and an internal rotation of the stifle (knee). At first, the lameness gets progressively worse, but signs plateau weeks to months after onset. 

How is Semitendinosus and Gracilis Myopathy Diagnosed?

Your veterinarian can diagnose this condition based on a history of lameness, and the altered gait described above. Upon physical exam, the affected muscles will feel firmer than normal due to the formation of the connective tissue. Diagnosis can be confirmed usually ultrasound of the muscle, and can help assess the extent and severity of the condition.

Why did my dog get Semitendinosus and Gracilis Myopathy?

The definitive cause of semitendinosus and gracilis myopathy is unknown, but is hypothesized to be caused by trauma, immune-mediated disease, or may be secondary to a disease process involving the nerves (neuropathy).

How is Semitendinosus and Gracilis Myopathy Treated?

Unfortunately, there is no known treatment that is entirely effective in correcting this condition. Surgery can be performed to remove the affected muscle, but recurrences of clinical signs are usually seen anywhere from 6 weeks to 5 months post-op, due to the formation of new scar tissue. In some cases, aggressive physical therapy may be beneficial, but usually is most effective in combination with surgery.