Medial femoral condyle morphometrics and subchondral bone density patterns in Thoroughbred racehorses

Abstract

To characterize medial femoral condyle (MFC) morphometrics and subchondral bone density patterns in Thoroughbred racehorses and to determine whether these variables differ between left and right limbs. Stifle joints harvested from 6 Thoroughbred racehorses euthanized for reasons other than hind limb lameness. The distal portion of the left and right femurs of each cadaver was scanned via CT. Hounsfield units were converted to dipotassium phosphate equivalent densities through use of a phantom on each specimen. Medial femoral condyle width, length, height, and curvature; subchondral bone plate densities; and subchondral trabecular bone densities were analyzed in multiple sections in 5 frontal planes and 3 sagittal planes and were compared between left and right MFCs. MFC width, length, and height did not differ between left and right limbs. Regions of interest in the right caudoaxial subchondral bone plate and subchondral trabecular bone were significantly denser than their corresponding left regions of interest in the frontal and sagittal planes. A concavity in the otherwise convex articular surface of the cranial aspect of the MFC was identified in 11 of 12 specimens. A disparity was identified between left and right subchondral bone density patterns at the caudoaxial aspect of the MFC, which could be attributable to the repetitive asymmetric cyclic loading that North American Thoroughbred racehorses undergo as they race in a counterclockwise direction. The uneven region at the cranial aspect of the MFC could be associated with the development of subchondral bone cysts in horses.