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 features with corresponding histological findings.

METHODS

We studied 18 fully encapsulated right knee joints from a population of rhesus monkeys with a high incidence of degenerative arthritis resembling human OA. Relaxation times (T1 and T2) spin density, and cartilage thickness were determined along 8 contiguous anteroposterior segments of articular cartilage. Histological slides, prepared in the same plane as the MR image, were assessed for OA severity. Using a modification of Mankin's OA classification, each quadrant was grouped into normal (0), mild (1), moderate (2), or severe OA (3). Histopathological scores served as the standard and corresponding MR quadrants were classified accordingly.

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 measurements were not observed. MR signal intensity abnormalities in selected regions 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 regions of collagen condensation showed low signal intensity on MR images (TR = 3000 ms; TE = 10 ms) and corresponded with decreased T1 and T2 relaxation times.

CONCLUSION

Topological quantitative MRI relaxation time assessment demonstrates increasing cartilage matrix quality variation with OA progression.