Osteochondrosis is a disease that is known for causing loose fragments in joints. In spite of the disease being extremely common in Norwegian horses, the causes and mechanisms behind it are not well known. Recently, veterinary surgeon Kristin Olstad of the Equine Clinic at the Norwegian School of Veterinary Science completed a PhD which concluded that failure of the blood supply to growth cartilage was a cause of osteochondrosis in horses.
Osteochondrosis is a disease that affects the developing joints of human patients and several animal species including horses, cattle, pigs and dogs. The disease is especially common among Norwegian Standardbreds, and can cause loose fragments consisting of cartilage and bone within joints. The fragments may lead to inflammation and swelling of the affected joint, in which case the horse may experience pain, lameness and reduced athletic performance.
The disease is generally treated by surgical removal of the fragments, a procedure that contains an element of risk for the horse and financial outlays for the owner. The disease has been demonstrated to have a heritable component, and certain breed associations exclude horses from breeding based on the presence of osteochondrosis on mandatory radiographic examination.
Osteochondrosis arises in growth cartilage
During the 1970ies, it was discovered that osteochondrosis arises due to primary disease of the so-called growth cartilage. This specialised tissue is only present in the body until such a time that the individual has finished growing and reached adult size. Historically, cartilage has been considered an avascular tissue, that is: a tissue without a blood supply of its own.
While it remains true that articular cartilage is an avascular tissue, Olstad and the Equine Clinic research team demonstrated that equine growth cartilage had a rich blood supply during the early stages of development. The blood supply ran in so-called cartilage canals. It was time limited, and in the case of the hock joint, it had largely disappeared by the age of 2 months old. This limited presence probably explains why the blood supply often has been overlooked in previous descriptions of growth cartilage and osteochondrosis.
Failure of the blood supply leads to lesions of osteochondrosis
Olstad and the Equine Clinic research team found that when the blood supply to growth cartilage failed, a small area of the growth cartilage around the failing cartilage canal would die as it no longer received the oxygen and nutrition it depended upon. Small areas of dead or necrotic growth cartilage persisted as weak spots under the articular surface of the developing joint. The joint would then be subjected to biomechanical force as the foal continued to walk around, in which case the cartilage over the weak spot could crack open and break off, resulting in the formation of a loose fragment within the joint.
BVSc CertVR MRCVS Kristin Olstad defended her Thesis for the Degree of Philosophiae Doctor entitled "Cartilage Canals in the Pathogenesis of Osteochondrosis in Horses" on February 29th, 2008.
Kristin Olstad was born in Tromsø, Norway in 1973. She was admitted to the University of Bristol, England via the Norwegian School of Veterinary Science, where she in 1999 completed her Bachelor of Veterinary Science. Olstad worked at three different specialist equine hospitals in England for five years and obtained a post-graduate qualification in veterinary radiology, before returning to Norway in 2004 in order to complete her PhD at the Norwegian School of Veterinary Science. She is currently employed as a researcher at the Equine Clinic of the Norwegian School of Veterinary Science.
Photo: Kim Egenes, NVH