Validation of magnetic resonance imaging for measurement of equine articular cartilage and subchondral bone thickness.

OBJECTIVE To validate use of magnetic resonance images (MRIs) for measurement of equine articular cartilage and subchondral bone thickness by comparison with measurements in histologic specimens. SAMPLE POPULATION 32 cadaveric carpal joints from 16 horses. PROCEDURE Magnetic resonance imaging was performed by use of 3-dimensional fast spoiled gradient echo (SPGR) and T2* 3-dimensional fast gradient echo (GRE) pulse sequences with and without fat saturation. Standard sites on the medial and lateral facets of the intermediate, radial, and third carpal bones were used for subchondral bone and articular cartilage thickness measurements. Digital image analysis software was used for MRI measurements 10 mm from the dorsal extent and perpendicular to the articular surface. Histomorphometric measurements of hyaline, calcified cartilage, and subchondral bone thickness were obtained at selected sites. Comparisons between histomorphometric and MRI measurements and between magnetic resonance pulse sequences were evaluated. RESULTS There were significant correlations between GRE and SPGR and SPGR and histologic measurements of articular cartilage, with no significant difference between measurements and good agreement. When calcified cartilage was excluded from the histologic measurement, MRI measurements were significantly greater than histologic measurements. For subchondral bone thickness, there was significant correlation between GRE and SPGR but GRE was significantly greater than SPGR measurements. Histomorphometric and MRI measurements were strongly correlated and not significantly different. CONCLUSIONS AND CLINICAL RELEVANCE Magnetic resonance imaging provides a good representation of cartilage and subchondral bone thickness, supporting its use in the study and clinical diagnosis of osteochondral structure and alteration.