Stresses Associated with Subchondral Bone Cysts - A Finite Element Analysis on an Extended Stifle Joint

Abstract

Subchondral cystic lesions (SCL), sometimes referred to as subchondral bone cysts (SBC) or subchondral lucencies, occur in the medial femoral condyle (MFC) of horses and can cause lameness. They are more common in horses ≤ 2 years of age, but can occur in older horses. The causes of SCL are not well understood, however, trauma and osteochondrosis are most commonly implicated. Radiographs of young horses that develop SCLs indicate a progression from sclerosis to MFC flattening, and then a defect (SCL) that enlarges. Treatments are directed at reducing local inflammation and promoting bone and cartilage healing, with approximately 50-75% of horses becoming sound enough for work. However, bone healing after surgery is inconsistent, occurring in <20% of patients. Recently, a treatment of MFC SCL using a lag screw was reported to improve the rate of lameness resolution and is the first study to report significant and consistent bone healing. This suggests a biomechanical approach can improve the treatment of equine SCL, but very little is known about the stresses within the equine stifle and how the surgical procedure may be optimized. The equine stifle is a complex biological system and direct collection of biomechanical data would be difficult, if not impossible. The objective of this current study is to investigate the stresses in the subchondral femoral bone at different stages of cyst progression using finite element analysis. This information can help us better understand the mechanics associated with SCLs that will allow clinicians to develop and implement rational treatment strategies.