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          O.C.D. - OSTEOCHONDROSIS OF THE SHOULDER

 You MUST consult your Veterinary Surgeon if your dog shows any signs of being lame.

OSTEOCHONDROSIS OF THE SHOULDER

Overview
Osteochondrosis (OCD) occurs commonly in the shoulders of immature, large and giant-breed dogs. The lesion appears on the caudal surface of the humeral head (Figure 1). Although your dog may be lame in only one leg, this condition is often present in the opposite leg. This condition results in a cartilage flap found on the humeral head. In some cases, the resulting defect occupies half of the area of the humeral head. The cartilage flap may completely detach from the underlying bone and become lodged in the back of the joint pouch.

Hlth Cond: OCD Fig1

Figure 1.   Location of OCD of the shoulder.

Osteochondrosis begins with a failure of endochondral ossification (bone formation from the cartilage precursor) of the humeral head. Failure of endochondral ossification leads to abnormal cartilage thickening (Figure 2). Increased cartilage thickness may result in malnourished, necrotic chondrocytes (cells within the cartilage). Loss of chondrocytes deep in the cartilage layer leads to formation of a cleft at the junction of calcified and noncalcified tissues. Subsequently, normal activity may cause fissures in the cartilage that eventually communicate with the joint, forming a cartilage flap (Figure 3). This communication allows cartilage fragments and inflammatory mediators to reach the synovial fluid and induce joint inflammation and degenerative joint disease. OCD does not apparently cause clinical signs until a loose cartilage flap forms. Free cartilage flaps can lodge in joints and may increase in size with calcification becoming joint “mice” which can be seen on radiographs.

Hlth Cond: OCD Fig2

  Figure 2.   Thickening of the cartilage

Hlth Cond: OCD Fig3

Figure 3.   Formation of the flap

Causes
The causes of OCD considered to be multifactorial with input from management, genetic and nutritional interactions in young growing dogs.

Incidence and Prevalence
Large and giant-breed dogs are commonly affected. Males are more commonly affected than females.

Signs and Symptoms
Clinical signs often develop when the dog is between 4 and 8 months of age. Dogs usually show a lameness of one forelimb. In many cases, there is a gradual onset of lameness that improves after rest and worsens after exercise.

Risk Factors
Risk factors for OCD include age, gender, breed (genetic), rapid growth, and nutrient excesses, primarily calcium excesses. The hereditary nature is suggested because of high frequency of occurrence within certain breeds of dogs and within certain bloodlines. Males are more commonly affected than females.

When to Seek Veterinary Advice
If your young large breed dog is persistently lame in a forelimb, especially after exercise, you should have a physical exam performed. If the dog is painful on palpation of the shoulder, usually during shoulder extension and flexion, then radiographs of the shoulder should be made to evaluate for OCD.

Exam, Screening Tests, and Imaging
For physical examination, the shoulder should be palpated and moved through a complete range of motion. Affected animals usually exhibit pain when the shoulder is moved into extreme extension Extreme flexion of the shoulder may also cause pain. Diagnosis of OCD is based on seeing a defect present on the humeral head on lateral views of the shoulders. Both shoulders should be radiographed because this condition is often present in both shoulders, despite apparent lameness in only one limb. The earliest radiographic sign of OCD is flattening of the subchondral bone of the caudal humeral head. As the disease progresses, a larger saucer-shaped defect may be seen. In older dogs who have had the problem for a while, large calcified joint mice are often seen in the caudoventral joint pouch.

Hlth Cond: OCD Fig4
Figure 4: Radiographic images of the shoulder, the first image shows an OCD lesion of the humeral head. The second image is a normal humeral head. 

Differential Diagnosis
Front leg lameness in young large dogs can be caused by many diseases affecting the elbow (osteochondritis dissecans, ununited anconeal process, or fragmented coronoid process of the elbow) the long bones (panosteitis, premature closure of the growth plates, and hypertropic osteodystrophy. Physical examination should identify the shoulder as the problem.

Complications Caused by the Disease
OCD incites the development of osteoarthritis or degenerative joint disease of the shoulder. Osteoarthritis generally develops despite treatment, but may or may not cause clinical signs or problems.

Treatment Options
Limiting the activity of the dog and treating with non-steroidal anti-inflammatory drugs (NSAIDS) may help some dogs with OCD of the shoulder. A trial period of exercise restriction (brief leash walks only) for a minimum of 6 weeks can be attempted. If lameness resolves, surgery may not be indicated; however, if lameness persists more than 6 weeks, surgical removal of the flap is indicated.

Surgical treatment involves exploratory arthrotomy and removal of the cartilage flap. This may be done with arthroscopy as a minimally invasive procedure. Surgical treatment is indicated in dogs with persistent lameness that are unresponsive to rest and NSAIDS. The goals of surgery are to remove the cartilage flap from the humeral head and curette the edges of the bony defect to ensure removal of all affected cartilage.

Potential Complications Following Treatment
Potential complications related to surgery include infection and postoperative seroma (fluid accumulation within the incision site) formation. Progressive osteoarthritis generally occurs after treatment but many or may not cause clinical signs.

Aftercare
Your dog will generally come home within 1 or 2 days after surgery. The dog’s activity should be limited for approximately 1 month to allow the incision to heal. The dog can then be returned gradually to full activity. The incision site should be observed for seroma formation, which will usually resolve without therapy.

—Ann Johnson, DVM, MS
Diplomate ACVS