Characterization of OA Severity in Knee Articular Cartilage in-Vivo Using MR Imaging and Loading Techniques

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Abstract and keywords

Early osteoarthritis (OA) is primarily associated with proteoglycan (PG) loss and changes in collagen structure. MR T2 imaging of knee under in-vivo loading may help to further reveal the differences between healthy and OA cartilage.

This study investigated the in-vivo loading effect on MR T2 values of human knee patellar cartilage. The results demonstrated T2 value distributions in patellar cartilage were inhomogeneous. In-vivo loading had a site-specific influence on participants’ T2 values. The in-vivo loading produced a significant difference on T2 values in the middle region of interest (ROI) of patellar cartilage (p=0.004<0.025), but not at the superior or inferior ROIs. The T2 value variation for the OA group during loading was lower than that of the healthy group (p=0.016<0.025).

The T2 recovery ratio was presented in this study as a new variable. The findings indicated the T2 recovery ratio of the OA group was significantly lower than the healthy group (p=0.042<0.05) in the patellar cartilage middle ROI. It suggests that the OA cartilage had weaker ability to restore its original status after off-loading than healthy cartilage.

This study examined the glycosaminoglycan (GAG) mass% concentration (relating PG) in human cadaveric patellar cartilages using biochemical assay. Results showed that the GAG mass% concentrations in OA lesion positions were lower than that in comparative healthy positions (p<0.001). MR T2 imaging of healthy and OA cadaver knee joints were performed. Correlations between T2 values and the GAG mass(%) of cadaver patellar cartilage specimens were established. As PG concentration of in-vivo human articular cartilage cannot be directly measured non-invasively, the correlation of cadaveric patellar cartilage may serve as an important bridge between the T2 value and GAG mass% for living human assessment. The findings provide an indirect approach to estimate PG concentration of in-vivo patellar cartilage based on an individual’s cartilage T2 values to evaluate the extent of degradation within cartilage.

This subject specific method is especially suitable for longitudinal evaluation of OA. By position-matched comparison of previous and current T2 images, the GAG mass% variation may be estimated to assess OA progression non-invasively

Keywords: Osteoarthritis; patellar cartilage; MR T2 imaging; in-vivo loading; proteoglycan

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