Immature bone has two areas of cartilage cells (chondrocytes) at each end which can multiply to increase the size of the bone. These are the articular cartilage at the joint surface and the growth plate (epiphysis) located at the end of the bone shaft. As the cartilage expands blood vessels invade the old cartilage and minerals are deposited eventually forming bone (ossification).

It is thought osteochondritis is a disturbance to this ossification where it fails to keep pace with the cartilage growth leading to an area of thickened articular cartilage. The chondrocytes furthest away from the joint surface in these thickened areas then die forming a cartilage plug which fails to become mineralized. The articular cartilage may subsequently crack leading to the formation of a loose cartilage flap.

The most commonly effected joints are the shoulder (humeral head), knee (stifle -lateral and medial femoral condyles), and elbow ( medial humeral condyle). Clinical signs generally become apparent between six and twelve months of age. These signs include lameness, loss of range of movement of the joint, and pain on full extension or flexion of the joint.

Radiographs (Xrays) are used to identify OCD however the flap may be difficult to clearly identify.

In most cases the cartilage flap will eventually break down and be absorbed however surgery to remove the loose cartilage is usually recommended to reduce the long term damage to the joint. Dogs with OCD which don't undergo surgery should be maintained on a moderate exercise program to help with the removal of any loose cartilage.