Muscle Rupture in Dogs

 

A normal muscle can be stretched, pinched, or injured directly, resulting in fiber disruption, weakening, and immediate or delayed separation of the uninjured portions. Normal activity may cause muscle disruption. Alternatively, the muscle structure may be compromised by systemic or iatrogenic (physician-caused) conditions. The rupture may be complete or incomplete, and may be in the middle of the muscle or at the muscle-tendon junction. The acute (sudden and severe) stage is characterized by a typical inflammatory reaction that becomes chronic over time, with cross-linking, and adhesion development over time. Frequently, the acute phase is overlooked, as the signs may be temporary and respond well to rest. The chronic effects are often progressive and unresponsive to support therapies.

 

The muscles of the limbs, and the chewing muscles are the primary structures affected. Traumatic injury is indiscriminate, though certain activities may predispose because of exposure. The ruptures that are apparently unrelated to trauma seem to affect middle-aged to older working dogs, with no reported gender predilection.

 

Symptoms and Types

 

Acute injury

• Immediate lameness that is characterized by the specific muscle affected
• Localized swelling, heat, and pain
• Generally present for a few days to a week
• Chronic phase (if it develops)

Progressive

• Painless
• Usually associated with scar tissue that impedes normal function of an extremity

 

Causes

 

• Trauma
• Overextension
• Myositis (inflammation)
• Degenerative (unknown etiology)
• Myopathy (a neuromuscular disease), secondary to medical conditions
• Apparent risk factor for dogs is involvement in hunting, tracking, or similar activities in the outdoors that put stress on the muscles

 

 

Diagnosis

 

Your veterinarian will conduct a thorough physical examination, looking for evidence of neurologic dysfunction and tendon rupture. Diagnostic imaging will include X-rays to look for evidence of bone fragment defects and translocations, and ultrasound to look for swelling and disorientation of the normal muscle fiber at the site of injury in acute cases. Scar tissue and contracted areas of fibrous tissue can be seen in the muscle in chronic cases. Magnetic resonance imaging (MRI) can be used to look for edema and hemorrhage, and to achieve localization of the problem that will help to identify the type of problem.

 

Your doctor will also test your dog’s joints for evidence of joint instability or malalignment. Measurable differences between normal and abnormal sides may be useful in documenting the affected muscle site. Another thing your doctor can do is conduct a biopsy of the affected muscle to detect the presence of fibrous tissue and loss of muscle cells. Differentiating atrophy due to disuse from neurologic atrophy, and from injury-induced scarring, may be impossible without corroborating evidence.

 

Treatment

 

There is no documented evidence to support a single best way to treat acute muscle injuries, or to prevent fibrous contracture (shortening of muscular or connective tissue) and adhesions. It is generally believed that immediate post injury care should involve rest and local cold application followed within hours by heat and passive physical therapy. An essential part of muscle repair is effective tension relief for the injured muscle so that healing can occur without disruption as function returns. Analgesics and anti-inflammatory drugs should be used for several days to weeks to control inflammation and pain. Light or non-weight bearing activity is appropriate for an extended period of time (4-6 weeks).

 

Internal or external orthopedic devices may be necessary to provide effective tension relief. Scar-related problems can affect your dog’s gait in the long-term. It is inappropriate to hospitalize or cage a recently injured animal for muscle problems unless surgical repair is planned. Surgery may be performed within a few days of the injury to repair obvious, acute muscle rupture that results in a separation of the uninjured muscle segments.

 

Once the muscle injury becomes chronic and is associated with contracture or adhesions, treatment is aimed at function salvage of the muscle. Instantaneous symptomatic relief often accompanies surgical release of the adhesions or fibrous tissue bands. The prevention of re-adhesion and progressive contracture is much less rewarding.

 

Specific muscle injuries have widely disparate prognoses. Rotator cuff contracture responds well to surgical excision of the tendon of insertion. Gracilis (hamstring) contracture has a 100 percent recurrence rate after surgical resection. Quadriceps contracture has a similarly dismal failure rate after surgery.

 

Muscle injuries that have healed in an elongated state have a better prognosis for surgical improvement of function than contracted muscles. The most common elongation injury affects the muscles of the Achilles group. Hock hyperflexion can be surgically reconstructed to return affected dogs to relatively normal function. Shortening the Achilles tendon rather than surgically repairing the injured muscle usually accomplishes this.

 

Living and Management

 

Your veterinarian will want to monitor repetitive range of motion, along with taking steps to control inflammation. Non-weight bearing passive physical therapy may be beneficial for recovery.