Trauma to the muscles and the tendons in dogs result in various types of myopathies.
Abnormal Contracture of the Shoulder Muscle
The shoulder muscle called infraspinatus may become stiffened and contracted due to injuries. This abnormality is usually observed in hunting dogs and breeds used for specific works. Pain and inflammation of the shoulder and a temporary lameness may be the initial symptoms displayed by the injured dogs. But they may develop a peculiar gait in about 2-4 weeks following the original trauma because of the thickening of the muscle and the resultant tightening. The elbow may be pulled inwards while the foreleg is extended outwards, resulting in an abnormal gait. When the dog walks, the forelimbs move in a circular motion with the wrist and the paw rotating.
Surgery is the main treatment for correcting the contracture. Part of the muscle is removed, and the tendon is cut, to relieve the muscle contracture. Immediate improvement in the limb function is usually obtained with the above surgical correction and the dog may recover completely.
Biceps Brachii Tendon Inflammation
The Biceps Brachii tendon as well as its sheath may get inflamed when the forelimbs are injured. This condition generally occurs in mature dogs of larger breeds. Both direct and indirect injuries, often resulting from overuse of the limbs, may lead to Biceps Brachii tendon inflammation. Small pieces of cartilage that get separated from the head on the bones and float freely in the joint cavity may also cause this condition. It may develop on one limb, or both forelimbs may be affected at the same time.
The typical symptom of Biceps Brachii tendon inflammation is progressive lameness that becomes worse after exertion and becomes better after a period of rest. The veterinarian may note marked reduction in the range of motion of the shoulder joint and wasting away of the muscles there on physical examination. The dog may react in extreme pain if the biceps tendon is pressed while the shoulder is being moved. The diagnosis based on the symptoms and the physical examination can be confirmed by x-rays as well as ultrasonography. A minimally invasive endoscopic examination may be conducted to assess the damage.
The vet may advice rest and prescribe non-steroidal anti-inflammatory drugs (NSAIDs) for oral administration in milder cases. The NSAIDs may be given as injections if the inflammation is acute. Corticosteroid injections are given if the disease is chronic, but if it is not effective surgery is the next option. If joint mice are found to be the cause of the inflammation, they may be surgically removed too. Dogs usually recover with appropriate treatment, but if severe joint degeneration has already occurred, the dog may remain lame even after the treatment.
Quadriceps Contracture (Stiff Stifle Disease)
This condition is a post surgical complication occurring in young dogs that have undergone surgical repair of fractured thigh bone or femur. The quadriceps muscles get thickened and become stiff, as the fractured bone and its covering made up of connective tissue, and the muscle fibers get fused together with scar tissue. This affects the movement of the muscles and the dog may keep the limb extended and stiff, hence the common name ‘stiff stifle disease’ for this condition. Disuse of the affected limb results in the degeneration of its muscular and skeletal tissues leading to various deformities. Osteoarthritis and osteoporosis may develop.
The only option is surgical correction of the contracture. The fibrous scar tissue that binds the muscles with the bone has to be removed. If deformities have developed due to the contracture, they may have to be corrected too. The operated joint is kept in bandages, and the mobility of the dog is restricted to allow the tissues to heal. This has to be followed by physiotherapy to restore mobility. The final outcome depends on many factors, including the performance of the dog after recovery.
Quadriceps contracture can be prevented by taking extra care during surgeries on young dogs with femoral fractures.
Achilles Tendon Disruption
The Achilles tendon is extremely vulnerable to injury in active breeds of dogs. In Achilles tendon disruption, the tendon gets separated from the bone as a result of a severe injury or trauma. The disruption may be partial or total.
The dog becomes severely lame as it cannot apply any weight on the injured leg. The tarsus (wrist) may be overextended with the heel of the foot touching the ground, hence the common name ‘dropped hock’ given to this condition. Pain and inflammation of the affected area is common. The torn ends of the tendon may be apparent. X-ray images may give a better picture of the injury as they may show all the pieces that got separated from the bone too.
The torn tendon can be repaired and reattached to its normal position on the bone. The effectiveness of the surgery depends on the duration and extent of injury. The injured joint has to be stabilized with splints for many weeks following the surgery. While early surgical intervention may give a better outcome, the performance of the dog after it recovers cannot be predicted.
The skeletal muscles may develop tumors, but many of them may be benign. Malignant (cancerous) tumors may grow fast and spread to other tissues nearby. The tumor cells can travel to distant parts and cause secondary tumor growths elsewhere in the body too.
Inflammation of the muscles is usually the first symptom. The dog may become lame if the tumor interferes with muscular movements. Surgical removal of the tumor may restore normal functioning of the limbs. But if malignancy is suspected, the veterinarian may take a biopsy of the tumor tissue for testing. If it is cancerous, not only the tumor, but the surrounding tissues, and sometimes the entire limb, may have to be removed too. The surgery may have to be followed by radiation and chemotherapy to destroy the remaining cancer cells and secondary growths.