Morphological characteristics of subchondral bone cysts in medial femoral condyles of adult horses as determined by computed tomography

Walker WT, Silverberg JL, Kawcak CE, Nelson BB, Fortier LA. Am J Vet Res. 2016 Mar; 77(3): 265-74.

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.

Large animal: