Treating Bone Cysts in Young Horses: Choose Your Weapon

Juvenile horses with subchondral bone cysts can lead successful athletic careers if managed appropriately. Because all three of the main treatment protocols result in similar outcomes, owners and veterinarians have the freedom to choose the best option for each patient.

Bone cysts are fluid-filled defects in subchondral bone found at the ends of long bones. Normally, subchondral bone is covered with a layer of smooth articular cartilage that permits frictionless motion during movement. When a bone cyst forms, the cartilage and bone are both damaged, resulting in joint inflammation, discomfort, and lameness. This is particularly true when the cysts develop on a direct weight-bearing surface, such as the medial, or inner, aspect of the femur within the stifle joint.

“Various theories have been proposed to explain how bone cysts form. In juvenile horses, experts suggest that the bone and cartilage fail to develop properly, resulting in a cystic lesion in the bone and disrupted articular cartilage,” explained Kathleen Crandell, Ph.D., a nutritionist for Kentucky Equine Research.

Leaving horses untreated will result in poor performance, as well as possible lameness and development of osteoarthritis.

Multiple treatment options are currently available, including:

• Surgical debridement (removal of the cystic material);
• Intralesional injection of corticosteroids; and
• Intralesional injection of stem cells.

Success rates for these techniques ranged from 56% to 82%. The measures of success in those studies were, however, highly variable. Because of this, veterinarians wanted to re-evaluate “treatment success” using two clear outcome measures: (1) to train productively and (2) to compete in a parimutuel race.

In the study, medical records from 107 Thoroughbreds were reviewed.^* All of the horses were less than 24 months of age and had been treated for subchondral bone cysts of the medial femoral condyle (inner weight-bearing aspect of the stifle joint). Approximately half of the horses (53%) were treated with arthroscopic debridement, while 18% and 29% were treated with intralesional stem cells and corticosteroids, respectively.

More horses (84%) treated with intralesional stem cells raced after treatment compared with either arthroscopy (72%) or intralesional injection of corticosteroids (68%). Those differences were not, however, significantly different from a statistical perspective, meaning that all three surgeries were considered equally successful.

“There is no clearly preferred method of treatment among these three approaches. The prognosis for the ability to train and race for the three methods of treatment assessed serves as an objective benchmark for comparison with other treatment methods,” concluded the research team.

Even if treatment is deemed successful, the long-term joint health of those horses must be considered.

“Once joint lesions develop, an inflammatory reaction begins that can lead to the development of osteoarthritis, even in young, athletic horses. I recommend early support of joint tissues with quality sources of hyaluronic acid, glucosamine, and chondroitin sulfate to delay joint deterioration and development of osteoarthritis,” advised Crandell.

^*Klein, C.E., L.R. Bramlage, D. Stefanovski, A.J. Ruggles, R.M. Embertson, and S.A. Hopper. Comparative results of 3 treatments for medial femoral condyle subchondral cystic lesions in Thoroughbred racehorses. Veterinary Surgery 51(3):455-463.