OSTEOARTHRITIS IN RHESUS MACAQUE KNEE-JOINT - QUANTITATIVE MAGNETIC-RESONANCE-IMAGING TISSUE CHARACTERIZATION OF ARTICULAR-CARTILAGE

Objective. To assess cartilage matrix quality variation by anatomical location and extent of osteoarthritis (OA) using quantitative magnetic resonance imaging (MRI) and to compare the anatomic MR morphologic fe atures with corresponding histological findings. Methods. We studied 1 8 fully encapsulated right knee joints from a population of rhesus mon keys with a high incidence of degenerative arthritis resembling human OA. Relaxation times (T1 and T2), spin density, and cartilage thicknes s were determined along 8 contiguous anteroposterior segments of artic ular cartilage. Histological slides, prepared in the same plane as the MR image, were assessed for OA severity. Using a modification of Mank in's OA classification, each quadrant was grouped into normal (0), mil d (1), moderate (2), or severe OA (3). Histopathological scores served as the standard and corresponding MR quadrants were classified accord ingly. Results. Cumulative results revealed a significant decrease in T1 relaxation time (p = 0.04) and an increase in T2 relaxation time (p = 0.03) in the mild and severe OA groups, respectively. Statistically significant changes in spin density and cartilage thickness measureme nts were not observed. MR signal intensity abnormalities in selected r egions of interest were demarcated and studied histologically. Regions with histological proliferating chondrocytes or fibrillated cartilage showed bright signal intensity on MR images (TR = 3000 ms; TE = 10 ms ) and corresponded with elevated T1 and T2 values. Histological region s of collagen condensation showed low signal intensity on MR images (T R = 3000 ms; TE = 10 ms) and corresponded with decreased T1 and T2 rel axation times. Conclusion. Topological quantitative MRI relaxation tim e assessment demonstrates increasing cartilage matrix quality variatio n with OA progression.