Osteochondrosis occurs commonly in the shoulders of immature, large, and giant-breed dogs. The lesion appears on the caudal (back) surface of the humeral head. Osteochondrosis begins with a failure of cartilage to form bone in the humeral head. This failure leads to abnormal cartilage thickening. Increased cartilage thickness may result in malnourished cartilage cells that die. Loss of these cartilage cells deep in the cartilage layers leads to formation of a defect at the junction between cartilage and bone. Subsequently, normal activity may cause fissures in the cartilage that eventually communicate with the joint, forming a cartilage flap. It is upon this flap formation that osteochondrosis becomes osteochondritis dissecans (OCD). OCD is the form of osteochondrosis that is associated with pain and dysfunction. In some cases, the resulting flap occupies as much as half the humeral head. The cartilage flap may completely detach from the underlying bone and become lodged in the back of the joint pouch. Free cartilage flaps can lodge in joints and may increase in size with calcification becoming joint “mice” which can be seen on radiographs.
The causes of OCD are multifactorial with genetic and nutritional interactions implicated. Risk factors for OCD include:
Nutrient excesses (primarily calcium excesses)
Due to the high frequency of occurrence within certain breeds of dogs and within certain bloodlines, hereditary may be a factor. Males are more commonly affected than females.
Signs and Symptoms:
Clinical signs often develop when the dog is between four and eight months of age. Dogs usually begin limping on one of their forelimbs. In many cases, a gradual onset of lameness improves after rest and worsens after exercise. Although your pet may be lame on only one leg, this condition may be present in the opposite leg too.
Diagnosis of OCD is based on seeing a defect (flattening) present in the humeral head on X-rays of the shoulder. Radiograph both shoulders because this condition may be present in both shoulders, despite apparent lameness in only one limb. Often, older dogs that have had the problem for a while have large calcified joint mice.
Seek veterinary advice if your young large breed dog is persistently lame in a forelimb, especially after exercise. Surgical treatment involves removal of the cartilage flap from the joint and scraping the edges of the bony defect to ensure removal of all affected cartilage. Dogs with persistent lameness that is unresponsive to medical treatment may require surgical treatment.
Aftercare and Outcome:
Your pet’s activity should be limited as directed by your primary care veterinarian in order to allow the incision(s) to heal. Gradually return your pet to full activity. Potential complications related to surgery include infection and postoperative seroma (fluid accumulation within the incision site) formation. Progressive osteoarthritis can occur with this condition, but is uncommonly associated with symptoms.