The most common muscle tear injury of the canine rear limb involves the iliopsoas muscle. This painful injury is often seen in young, athletic dogs such as those competing in agility competitions. Along with the pectineus muscle, these account for virtually all muscle injuries seen in the rear legs.
The iliopsoas is actually the fusion of two muscles, the iliacus and the psoas. The iliacus muscle originates at the inner aspect of the hip bone, while the psoas arises from the underside of the lumbar spinal vertebrae. These muscles join together to form a common tendon, which attaches to the lesser trochanter of the upper thigh bone. The ilipsoas acts to flex the hip and to turn the thigh bone outward, but animals can actually function without it.
Iliopsoas muscle tears and tendon strains are relatively common, but are difficult to diagnose unless the veterinarian keeps this condition in mind when examining a case of rear leg lameness. The injury is often acute in nature, but if the dog gets through the initial painful period, it assumes a chronic nature that waxes and wanes according to the dog's exertion and ability to heal.
Radiographs, ultrasound, CAT scans and MRI usually fail to show abnormalities in the region unless the chronically-affected tissue begins to calcify. Diagnosis is most frequently based on obtaining a thorough history of the lameness, ruling out other potential causes, and performing specific tests that demonstrates discomfort in this muscle.
Pain can sometimes be elicited by direct palpation of the muscle and/or tendon. The more definitive test is to extend the limb and twist the paw inward — this can result in discomfort that demonstrates the location of the injury.
Medical therapy, rest, and rehabilitation are usually the initial treatments of choice. Muscle relaxants are prescribed to decrease muscle spasm and help control pain. Non-steroidal anti-inflammatories are useful in the acutely injured dog to control inflammation and further help with pain. These medications are not used in the chronically-affected animal because inflammation is required as part of the healing process.
Elimination of strenuous exercise is essential. Icing the area is helpful. Rehabilitation consists of passive range of motion exercise to maintain joint freedom, muscle/tendon flexibility, and to prevent muscle contracture. Laser therapy is an important modality utilized to ameliorate discomfort, control inflammation and swelling, improve circulation, and hasten the healing of tissue. E-stimulation minimizes muscle atrophy, while slow and progressive weight bearing is beneficial.
Other rehab techniques in acute cases (Cavaletti poles, wobble board, and para standing) are done to gradually increase strength, flexibility, and normal function.
The chronically affected patient is treated with stretching, heat therapy, deep muscle massage, laser therapy, and ultrasound treatments. The goal is to stretch out the tissue, control pain, and regain strength and endurance. This therapy can last for months.
Surgical intervention is recommended in dogs failing to respond to medical therapy and rehabilitation. Surgery involves severing the iliopsoas tendon as it attaches to the lesser trochanter of the upper femur. Surgery is very successful in alleviating pain, and limbs usually return to normal function. Care must be taken not to over-exert the patient afterward however, because the possibility of injuring the other iliopsoas or other structure structures in the hip area do exist.