Semitendinosus and Gracilis Myopathy

What Is It?

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

Who Gets It?

This is a relatively uncommon condition but occurs most frequently in:

  • German Shepherds
  • Belgian Shepherds
  • Greyhounds
  • Doberman Pinschers
  • Rottweilers
  • St. Bernards
  • Boxers
  • Old English sheepdogs

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?

Dogs with this condition 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 a decreased range of motion. It also produces a very characteristic gait. 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 It 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 connective tissue formation. Diagnosis can be confirmed, usually ultrasound of the muscle, and can help assess the condition’s extent and severity.

Why Did This Happen To My Dog?

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

How Is It Treated?

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

Can It Be Prevented?

Because so little is known about the cause of fibrotic myopathy, it cannot be said whether or not the condition is preventable. However, if muscle injury occurs and is identified early, intermittent rest and ice may minimize permanent muscle damage. Following an acute injury, strengthening and range of motion exercises should be performed, taking precautions to minimize additional muscle trauma.

What Is The Prognosis For My Dog?

Prognosis is generally poor or guarded because even with surgery, clinical signs will return. Long-term physical rehabilitation following surgery may improve the prognosis.

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