Objective—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.
Sample—Stifle joints harvested from 6 Thoroughbred racehorses euthanized for reasons other than hind limb lameness.
Procedures—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.
Results—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.
Conclusions and Clinical Relevance—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.
OBJECTIVE To determine morphological characteristics of subchondral bone cysts (SBCs) in medial femoral condyles (MFCs) of adult horses with orthopedic disease.
SAMPLE CT scans of 7 MFCs with SBCs from 6 adult horses.
PROCEDURES CT was used to determine the volume, surface area, and centers of the articular cyst opening and SBC in each MFC. Cysts were ordered from smallest to largest on the basis of volume. Osseous pathological characteristics of the MFC were assessed in the frontal plane. Three-dimensional distance of displacement between the center of the articular cyst opening and center of the cyst was determined for each SBC. Cyst surface area-to-volume ratio was evaluated and compared with that of a true sphere.
RESULTS All SBCs had a defect in the subchondral bone plate at the cranial 15% to 20% of the MFC. Cyst center was located in a caudal, proximal, and abaxial direction with respect to the center of the articular cyst opening for each horse. Small- and intermediate-volume SBCs were irregular and multilobulated, whereas large-volume SBCs were smooth and discrete with a surface area-to-volume ratio approaching that of a sphere.
CONCLUSIONS AND CLINICAL RELEVANCE Consistency in morphological characteristics suggested a common etiopathogenesis for SBCs in MFCs of adult horses. Cyst enlargement may have been attributable to a biomechanical predisposition to decrease the surface area-to-volume ratio, resulting in a spherical cyst.