Correlation between magnetic resonance imaging and clinical outcomes after cartilage repair surgery in the knee: A systematic review and meta-analysis

Background: Magnetic resonance imaging (MRI) is often used to assess cartilage after surgical repair. The correlation between MRI and clinical outcomes is not well understood. Hypothesis: Postoperative MRI findings correlate with clinical outcome measures in patients after articular cartilage surgery of the knee. Study Design: Meta-analysis. Methods: A systematic review of the literature was performed to identify studies in which MRI and clinical outcomes were correlated after autologous chondrocyte implantation (ACI), osteochondral autograft transfer system (OATS), or microfracture. Studies that reported correlation coefficients (r) for different MRI parameters were then included in a meta-analysis. Results: A total of 26 studies were identified for inclusion in this systematic review, 15 of which were included in the metaanalysis. Most of the studies (n = 19) involved ACI, although studies were available for OATS (n = 5) and microfracture (n = 4). The strongest MRI correlates with clinical outcomes after ACI were graft hypertrophy (r = 0.72) and repair tissue signal (r = 0.71). After microfracture, the strongest MRI correlates were the Henderson score (r = 0.97), subchondral edema (r = 0.77), and repair tissue signal (r = 0.76). Correlations after OATS were not as strong, with defect fill (r = 0.53) and repair tissue structure (r = 0.51) being the strongest. Conclusion: The MRI findings do correlate with clinical outcomes after cartilage repair surgery in the knee, although the specific parameters that correlate best vary by the type of procedure performed. No current MRI classification system has been shown to correlate with clinical outcomes after all types of cartilage repair surgery.