Subchondral bone cysts, are a serious cause of lameness in the horse that can warrant a guarded prognosis for athletic potential.1,2 They most commonly cause lameness in the first two years of life, and are associated with bone growth. They have beenidentified primarily in the medial femoral condyle of the femur and in the bones of the digit (metacarpus/tarsus and phalanges) but can occur in any location. The two major hypotheses of etiology are 1) that the cyst is a developmental failure of ossification, or 2) cysts are caused by subchondral bone trauma. Both theories accept that inflammation (as manifest by high cytokine concentrations in the cyst tissues) within the cyst is responsible for cyst enlargement. Clinically significant bone cysts occur most commonly at areas of increased weight bearing, supporting the trauma hypothesis. This hypothesis has been intentionally reproduced experimentally by creation of a cartilage defect with subchondral bone damage, which was followed by secondary invasion of synovial fluid. This hypothesis is regarded as the hydraulic theory because weight bearing leads to increased mechanical pressure on the subchondral bone due to synovial fluid being pumped into the defect.
展开▼
