Osteochondrosis (OC) / Osteochondritis dissecans (OCD) process
Both processes happen simultaneously at both ends of every long bone in the body, and stops at different ages for each bone to keep the limbs in the correct proportions.
This allows the bone to grow in length and width, AND to allow joints to form in the correct shape.
This process can be disturbed by several factors including:
- Genetic factors
- Overall growth rate
- Calorie intake
- Nutritional balance (e.g. calcium levels)
Disturbance at the growth plate will obviously result in a bone of the wrong overall length (usually shorter) or occasionally a curved bone if only one part of the growth plate is disturbed. The effect of this depends on which bone is affected, how severe the degree of deformity is, and the secondary effects on nearby joints.
In contrast, disturbance at the joint surface will simply leave a thickened patch of cartilage that has failed to convert to bone. This is called Osteochondrosis. In some dogs this may not cause any problem at all. However, because the cartilage is thicker than it should be, the cartilage cells in the centre cannot get adequate nutrition from the joint fluid, and the soft cartilage cap is weaker than it should be.
As a result of this weakening of the cartilage, it can crack forming a flap of cartilage, which may break away completely, leaving a crater in the joint surface. This is known as Osteochondritis Dissecans (OCD) because the cartilage flap “dissects” away.
Because the joint fluid comes into contact with bone instead of cartilage, this causes inflammation, pain and eventually arthritis.
Commonly affected joints include the shoulder, elbow, stifle (knee) and hock (ankle). Most affected dogs will become lame at under one year old.