Subchondral Bone Cysts

careers and an absolute requirement for even travel (dressage), the standard of success is much higher. In horses with MFC SBC, conservative therapy results in 57-67% of horses becoming sound15, and similar outcomes are achieved for most surgical treatments. Cyst size and patient age also seem to have an impact on success rates. The similarity of success rates for surgical debridement and conservative therapy questions the unqualified endorsement of SBC debridement for the treatment of MFC cysts in all horses.

There is little case information available on the treatment SBC in locations other than the MFC. Reports of SBC in locations other than the MFC report a high rate for success for surgically treated horses and a much lower rate for conservatively treated horses, but conclusions about treatment should be drawn carefully as these case reports include multiple locations for SBC, occasionally evidenced a case selection bias (horses with pre-existing osteoarthritis were treated conservatively) and often had the goal of describing a surgical treatment. In the last 50 years, orthopedic patients of all kinds have benefited from a greater understanding of the biomechanical forces on normal and abnormal bone, and how properly addressing biomechanics can improve fracture healing. There is very little information known about the biomechanics of equine joints and how it changes in the presence of a defect in the medial femoral condyle. It is unlikely that load is normally transmitted through the cyst, and the presence of sclerosis around the cyst and in the proximal tibia under the SBC suggests bone is adapting to altered loading. To address this possibility, we have begun using external fixation to alter the biomechanics of the bone in the region of a SBC to promote bone healing. This technique has been attempted in digital SBC16, and independently, we developed a technique for the medial femoral condyle. Biologic therapies have been used adjunctively13, and may also provide some benefit. It is our goal and our hope that the optimal treatment for bone cysts can be found to reduce the impact of this lesion on the performance careers of horses.

 References

1. Baxter GM. Subchondral cystic lesions in horses. In: C.W. McIlwraith and G. W. Trotter, eds. Joint disease in the horse. Philadelphia: WB Saunders, 1996;384-397.
2. Bramlage LR. Osteochondrosis-related bone cysts. Proc Am Ass equine Practnrs 1993;39:83-85
3. von Rechenberg B, Guenther H, McIlwraith CW, et al. Fibrous tissue of subchondral cystic lesions in horses produces local mediators and neutral metalloproteinases and cause bone resorption in vitro. Vet Surg 2000;29:420-9.
4. Ray CS, Baxter GS, McIlwraith CW, et al. Development of subchondral cystic lesions after articular cartilage and subchondral bone damage in young horses. Equine Vet J 1996;28:225-232.
5. Kold SE, Hickman J, and Melsen F. An experimental study of the healing process of equine chondral and osteochondral defects. Equine Vet J 1986;18:18-24.