Failed blood supply can lead to loose chips in joints

Osteochondrosis affects both people and a range of domestic animals including horses, cows, pigs and dogs. The disease is especially common among Norwegian horses, in particular warmblood, and can lead to the development of loose flakes within the joint. These loose pieces can cause irritation, causing the joint to swell and the horse to become lame.

The disease is usually treated by surgical removal of the loose pieces, a procedure that is associated with risk to the horse and expense for the owner. Osteochondrosis is heritable, and affected horses can be denied certification for breeding programs if the disease is discovered on x-ray.

It was established in the 1970’s that osteochondrosis arises in the so-called growth cartilage. This is specialised tissue that is only found in the long bones of the skeleton before an animal attains its mature size.

For many years it was thought that cartilage is a non-vascular tissue, that is, without its own blood supply. Olstad and a research team from the equine clinic have now, however, discovered and described a rich blood supply running in so-called cartilage canals. This blood flow is, however, time-limited, and in the case of the hock joint, it disappears at around the age of two months. This explains to a large degree why the blood supply to the cartilage has been so poorly described previously.

Using a microscope, Olstad and the research group showed an association between the earliest stages of osteochondrosis and a failure of the blood flow to the growth cartilage.

The cartilage canals are repeatedly forced to cross the boundary between bone and cartilage. Studies have shown the blood vessels in these vascular channels failed at precisely the point where they crossed from solid bone over into the softer growth cartilage.

Olstad and the research team discovered that when the blood flow failed, the cartilage cells around the cartilage canals died, since they no longer received the oxygen and nourishment they depended on. Small areas of dead growth cartilage became isolated as weakened points under the joint surfaces. Upon loading, these areas could develop cracks and loosen, causing loose flakes within the joint.

Kristin Olstad B. V. Sc. , Cert. V.R,., M.R.C.V.S. defended her Philosophiae Doctor thesis with the title “Cartilage Canals in the Pathogenesis of Osteochondrosis in Horses”, at the Norwegian School of Veterinary Science, on February 29, 2008.