Abstract
BACKGROUND: The asynchronous changes in articular cartilage (AC) and the osteochondral junction (OCJ) in early knee osteoarthritis (KOA) remain controversial, and the utilization of quantitative magnetic resonance imaging (MRI) to investigate the pathogenesis of KOA in vivo has yet to be firmly established. This study investigates the sequential order of pathophysiological changes in the AC and OCJ in early KOA, based on MRI-derived T2 values of the AC and ultrashort echo time (UTE)-T2* values of the OCJ. METHODS: 3D WATS (three-dimensional water-selective), T2 mapping and UTE-T2* mapping were performed on 34 healthy knees and 42 early osteoarthritis knees. Each knee was divided into medial femoral condyle (MFC), lateral femoral condyle (LFC), medial tibial plateau (MTP), lateral tibial plateau (LTP), patellar region and trochlear region. The cartilage T2 and OCJ T2* values were measured in each area. The cartilage from the surface of the cartilage to the tidemark was segmented on 3D WATS images. T2 values were then measured on T2 maps. OCJ was segmented on the UTE subtraction images, and T2* values were obtained from UTE-T2* maps. RESULTS: The cartilage T2 values were significantly higher in the early KOA group for MFC (P<0.001), MTP (P=0.04), patellar region (P<0.001), and trochlear region (P=0.01) relative to those in the healthy control groups. The OCJ T2* value of KOA group in MFC (P<0.001) showed a significant increase, followed by MTP (P<0.001), LTP (P=0.01), patellar (P=0.03) and trochlear (P=0.01). In the patellar region, the area under the curve (AUC) for diagnosing early KOA using AC T2 values (AUC =0.78, P<0.001) was higher than that using OCJ UTE-T2* values (AUC =0.64, P=0.04). There was a positive correlation between cartilageT2 values and OCJ T2* values (r=0.30, P<0.001). CONCLUSIONS: The T2 and UTE-T2* values, respectively, provide quantitative and non-invasive measures of the degeneration in the AC and the OCJ during the early stages of KOA. Quantitative MRI biomarkers reveal biochemical alterations in both the AC and the OCJ during early KOA, indicating the potential existence of interactions between these two regions.