Measurement of knee cartilage thickness using MRI: a reproducibility study in a meniscectomized guinea pig model of osteoarthritis.

The in vivo precision (reproducibility) of quantitative MRI is of particular importance in osteoarthritis (OA) progression of small magnitude and response to therapy. In this study, three-dimensional high-resolution MRI performed at 7 T was used to assess the short-term reproducibility of measurements of mean tibial cartilage thickness in a meniscectomized guinea pig model of OA. MR image acquisition was repeated five times in nine controls (SHAM) and 10 osteoarthritic animals 3 months after meniscectomy (MNX), in vivo. The animals were then killed for histomorphometric assessment and correlation with the MRI-based measurements. Medial tibial cartilage thickness was measured on MR images using semi-automatic dedicated 3D software developed in-house. The reproducibility of measurements of cartilage thickness was assessed by five repeated MRI examinations with a short recovery delay between examinations (48 h). The computed coefficients of variation were 8.9% for the SHAM group and 8.2% for the MNX group. The coefficients of variation were compatible with expected thickness variations between normal and pathological animals. A positive agreement and significant partial correlation (Spearman r' = 0.74; P < 0.01) between the MRI and histomorphometric data was established. Three-dimensional high-resolution MRI is a promising non-invasive research tool for in vivo follow-up. This modality could be used for staging and monitoring therapy response in small-animal models of OA.