T2 Relaxation Time Mapping of Proximal Tibiofibular Cartilage by 3-Tesla Magnetic Resonance Imaging

Background: The proximal tibiofibular joint (PTFJ) can be considered the fourth compartment of the knee joint. However, there have been no studies of the T2 values (T2 relaxation time) of PTFJ cartilage. Purpose: To assess the T2 values of PTFJ cartilage at 3T magnetic resonance imaging (MRI), and to show the clinical utility of T2 values of PTFJ cartilage for the diagnosis of osteoarthritis (OA). Material and Methods: 118 patients who had knee MR imaging and knee radiography were enrolled. MRI was performed using a 3T MRI scanner, and T2 maps were calculated from a sagittal multi-echo acquisition. Two regions of interest (ROIs) were positioned within PTFJ cartilage and medial femoral condyle (MFC) cartilage. The average T2 value and standard deviation (SD) of each ROI were recorded. Using PTFJ cartilage as a standard reference, the T2 index ((MFC/PTFJ) x 100) and T2(SD) index ((MFCSD/PTFJ(SD)) x 100) were calculated. A paired t test was performed to compare the mean and SD of ROIs within PTFJ and MFC cartilage. Correlation analyses were performed among the parameters age, Kellgren-Lawrence (KL) score, means and SDs of ROIs within PTFJ and MFC cartilage, T2 index, and T2(SD) index. Results: PTFJ cartilage had a significantly shorter T2 value than did MFC cartilage (P < 0.0001). ROIs within PTFJ cartilage showed significantly smaller SDs than did those within MFC cartilage (P < 0.0001). The average T2 value and SD of MFC and the T2(SD) index showed a positive correlation to the KL score (P <0.05). The correlation coefficients for the average T2 value, SD, and T2(SD) index of MFC were R=0.203, 0.254, and 0.268, respectively. However, there was no significant correlation between T2 values of PTFJ cartilage and KL score (P = 0.643). Conclusion: PTFJ cartilage showed shorter and more homogeneous T2 values with a small SD than did MFC cartilage, regardless of the degree of OA at femorotibial compartments. PTFJ cartilage may be a useful internal standard reference to diagnose OA and would be a good candidate as a standard reference for cartilage imaging.