Osteochondrosis is a pathological condition in rapidly growing large breed dogs that leads to a painful disturbance in joint cartilage development. In osteochondrosis, the cartilage cells dont differentiate in a normal manner. The joint cartilage becomes thickened, and large, decayed areas develop. At this point, an intermittently tender, but manageable, osteochondrosis has occurred and represents one of the true "growing pains" of adolescence.
If the puppy is active and traumatizes this soft, decayed area, cracks, or fissures, form and extend into the normal cartilage until a large cartilage flap forms. At this stage, pain is present in the joint every time the patient tries to walk. When the cartilage flap falls into perfect position discomfort is minimal. As it shifts position, pain becomes acute, with joint swelling that is increasingly sensitive. Osteochondritis refers to presence of the inflammatory reaction in the bone marrow and joint, while dissecans refers to the flap of cartilage that is dissected away from its base.
The sites most commonly affected include the shoulder, the elbow, the knee, and the ankle (hock) in young dogs. The syndrome can be bilateral and, on occasion, involves several joints.
Osteochondrosis of the shoulder affects the caudal aspect of the humeral head. It is most often seen in male large breed dogs. Clinical signs include lameness, which is worse after exercise, and pain on palpation of the shoulder joint. It is seen most frequently in animals between four and seven months of age. Radiographs (x-rays) are used to diagnose the lesion. Early radiographic changes include an abnormal contour or flattening of the humeral head. Later in the disease there is a radiolucent defect in the shoulder joint surface. Treatment for this syndrome is surgery to remove the flap as soon as it is formed (Fig. 1).
Osteochondrosis occurs in the elbow on the medial condyle of the humerus. It is most common in large or giant breed dogs from four to seven months of age. The clinical signs include an acute or chronic intermittent weightbearing lameness of one or both forelimbs. The treatment of choice is surgery, with the prognosis depending on the severity of the arthritis (degenerative joint disease) already present.
Osteochondrosis in the stifle (knee) can be difficult to clinically diagnose, as the lameness is frequently obscure and is often confused with the "slinky" gait of hip dysplasia. The lesion is seen as a flattening or radiolucent defect in the lateral or medial femoral condyle. The prognosis is only fair even if surgery is performed early in the course of the disease and should not be considered as favorable as with surgery in the elbow or shoulder.
Osteochondrosis lesions in the hock occur on the caudal aspect of the medial ridge of the talus bone. Affected animals are usually four to five months of age and present with slight lameness of the hind limbs. The ankle joints appear straight and swollen, and are painful upon flexion and extension. Radiographs demonstrate displaced cartilage and bone fragments and bone spurs due to secondary degenerative joint disease. The prognosis is good if surgery is performed before the onset of secondary arthritis. Again, once arthritis is advanced, surgery is helpful in relieving any intense pain but does not afford the results expected with surgery in the elbow or shoulder.
Ununited anconeal process is a failure of the growth center of the anconeal process, in the elbow joint, to unite properly with the ulna. This fusion should be completed by 16 to 24 weeks of age. Instead of a normal bony union, the ununited anconeal process represents a large piece of bone connected to the ulna by a strand of fibrous tissue. The diagnosis is confirmed by radiography. Surgical removal of this unstable bony fragment minimizes progressive arthritis and is indicated as soon as possible to prevent further joint degeneration (Fig. 2).
The coronoid process is a prominent medial projection of the ulna just distal to the elbow. Fragmented coronoid process is difficult to document radiographically for several reasons. Visualization of the fragment can be difficult because of the superimposed radial head in most radiographic projections. Therefore, the radiographs usually appear normal until the onset of secondary degenerative joint disease. Arthritis appears as early as a few months of age and is first expressed by small bone spurs on the anconeal process and on the condyles of the humerus. On occasion, special diagnostic tests, such as a bone scan or even a MRI, may be required to diagnose those "hidden" fragments of bone before they create debilitating cartilage damage (Fig. 3).
Older dogs with this syndrome usually have severe arthritis of the entire elbow joint. Again, surgical removal of the unstable bony fragments minimizes progressive arthritis and is indicated as soon as possible to prevent further arthritic changes. While the intense pain and crippling arthritis seen in chronic cases is greatly improved by surgical removal of the coronoid fragments, residual arthritis will require some intermittent antiinflammatory medication.
Panosteitis is the most common and painful of the "growing pains" with the age of onset usually between 5 and 12 months. It has been reported in a dog as young as 2 months of age, and as old as 5 years. Usually affecting large or giant breeds of dogs, it can affect the Basset Hound for an uncommonly long time interval.
Clinically, there is pain in the long bones (humerus, ulna, radius, femur, and tibia) which is manifested by a slight to severe lameness which can last from a few days to several weeks (Fig. 4). Some animals may be reluctant to move at all. Often the lameness shifts from one limb to another every 2 to 3 weeks, with apparent lapses in clinical manifestations of up to 3 months between episodes. Multiple bone involvement is seen in about one-half of the cases. The classic finding on physical examination is pain on deep palpation of the long bones. Some animals may have reduced appetite and activity during the painful periods. The complete course of the disease is usually 2 to 3 months, but it can range from a week to 6 or 8 months.
RADIOGRAPHIC (X-RAY) SIGNS
Ultimately, the diagnosis of panosteitis is made radiographically, by confirming the presence of the lesion that is suspected by physical examination. In difficult cases, a radioisotope bone scan will diagnose those which have no lesions on radiographs.
Inasmuch as the cause of panosteitis is not known, only symptomatic treatment is recommended for those animals who need pain relief. Antiinflammatory drugs such as aspirin and corticosteroids are probably the most commonly used agents. The disease will eventually run its course and resolve at maturity.
1998, Southern California Veterinary Surgical Group