There are some diseases of bones and joints that occur in the young growing animal. These include osteochondrosis, panosteitis and hypertrophic osteodystrophy.
Osteochondrosis / Osteochondritis Dissecans (OCD)
A portion of the growth of long bones comes from a process called endochondral ossification where the cartilage on the end of the bones changes from cartilage into bone. Under normal conditions the layer of cartilage remains uniformly thin as bone is developed below the cartilage. Osteochondrosis is a failure of part of the cartilage to develop into bone. The cause for this developmental defect is unknown but is thought to have a hereditary component as well as some relation to rapid growth and overnutrition. As cartilage is nourished from the joint fluid rather than blood vessels, the thickened cartilage becomes malnourished and necrotic. A cleft forms between the calcified and non calcified layers. Through normal activity fissures will form and a flap of thickened cartilage will loosen from the underlying bone. This process causes pain and inflammation within the joint. Sometimes the flap will break free from the bone and move about the joint. The formation of this flap constitutes osteochondritis dissecans (OCD). (See figure 1) The end result is degenerative joint disease. The disease can affect the shoulder, knee, elbow and hock (ankle) joints and is often bilateral.
OCD occurs most commonly in the shoulder of large and giant breed dogs including Labradors, golden retrievers, and spaniels. The age of onset is generally between 5-8 months. Clinical signs include mild to severe forelimb lameness that worsens with exercise. Diagnosis is based on signalment, pain on shoulder flexion and a characteristic flattening of the humeral head on radiographs. Treatment is removal of the flap and abnormal cartilage through arthroscopy. With two small incisions we are able to visualize the defect and remove the flap. After removal the underlying abnormal bone is removed until healthy tissue is exposed. The defect will fill in with fibrocartilage. The prognosis for shoulder OCD is generally good and the patient is comfortable within a few days of surgery.
OCD of the elbow occurs on the distal end of the humerus (medial condyle). Affected dogs are 5-8 month large breed dogs. Forelimb lameness and pain on elbow manipulation are commonly seen. A defect in the humerus on radiographs or visualization of the lesion with arthroscopy is diagnostic. The treatment is removal of the flap with treatment of the underlying bone as above. Prognosis depends on the amount of arthritis in the elbow at the time of surgery but in general is not as favorable as shoulder OCD.
OCD of the stifle or hock affects a similar population of dogs with rear limb lameness and pain on joint manipulation. The medial surface of the lateral femoral condyle is the most common location in the stifle and the medial trochlear ridge of the talus in the hock are the sites of predilection. As with previous locations a characteristic defect in the bone is seen on radiographs and treatment is removal of the abnormal tissue. Sometimes an open approach to the stifle and hock joints is needed rather than arthroscopy for proper treatment of the disease. Prognosis depends on the presence of degenerative joint disease but generally is less successful than shoulder OCD treatment.
Panosteitis
Another developmental bone disorder is panosteitis. This disease is characterized by shifting leg lameness and pain in the long bones. Dogs are generally less than 2 years old with most between 5 and 12 months. Large breed males are most commonly affected with Basset Hounds showing a prolonged form of the disease. Any of the long bones can be affected and often the lameness will shift from one leg to another. The cause of the disease is unknown. Pathologic changes in the bone include new bone formation along the lining of the marrow cavity and some reaction along the outer bone surface. The diagnosis is based on signalment, pain when pressure is applied to long bones and characteristic changes on radiographs of increased bone density in the marrow cavity. The treatment of panosteitis is directed at controlling clinical signs of pain. Non-steroidal anti-inflammatory drugs (NSAIDS) are most commonly used. No surgery is indicated. The disease is generally self-limiting and carries a good prognosis although relapses can occur up until maturity.
Hypertrophic Osteodystrophy (HO)
A disease of young (2-4 months) large breed dogs characterized by acute lameness in all four limbs often accompanied by fever, inappetence and lethargy. The cause for HO is unknown at this time. Proposed theories include vitamin C deficiency, oversupplementation with calcium and infectious causes including a link to canine distemper virus. The pathologic changes are seen in the metaphyseal region of long bones and are characterized by delayed ossification of the physis (growth plate). The distal ends of the long bones are swollen, warm and painful with the forelimbs usually most affected. Affected puppies are depressed, anorexic and may have a fever up to 106 degrees. Radiographs of the affected limbs show a characteristic change in the physis of the long bones called a double physeal line. Treatment is supportive with NSAIDS commonly used first and steroids if no response is noted. Severely affected animals may require hospitalization with fluid therapy and supportive care. The disease usually runs its course in 7-10 days but relapses are common. Deformity of the long bones due to physeal damage is sometimes noted following resolution of clinical signs.
