Magnetic resonance imaging in osteoarthritis: which method best reflects synovial membrane inflammation?

Summary

Objectives

: To study synovial membrane (SM) inflammation near the patella with different magnetic resonance imaging (MRI) approaches performed using a T1-injected sequence in knee osteoarthritis (OA), and to compare MRI results with macroscopic, microscopic and clinical findings.

Methods

Fifteen patients fulfilling American College of Rheumatology (ACR) criteria for knee OA and requiring joint lavage completed a functional index (Lequesne's functional index) and a pain visual analog scale (VAS). SM inflammation near the patella was assessed on axial fat saturation post-injected T1 MRI images using three different methods: (1) semi-quantitative score = MRI synovitis score; (2) synovial membrane volume (SMV) analysis; (3) SMV with low (SMVL) (<0.3%/s⁻¹), intermediate (SMVI) (0.3%/s⁻¹ to 1%/s⁻¹) and high (SMVH) (≥1%/s⁻¹) speed of enhancement. Chondral lesions and SM inflammation were macroscopically graded and SM biopsies performed for microscopic scoring.

Results

All MRI approaches exhibited excellent intra- and inter-observer reproducibility. MRI synovitis score correlated well with macroscopic (r = 0.61, P = 0.003) and total microscopic scores (r = 0.55, P = 0.03). Correlations between SMV and macroscopic (r = 0.60, P = 0.02) and microscopic congestion (r = 0.63, P = 0.01) were good. SMVH was correlated only with microscopic congestion (r = 0.79, P = 0.01). Low SMV was associated with neither macroscopic nor microscopic scores. However, it did correlate well with pain-VAS score (r = 0.61, P = 0.03) and moderately with a functional index (r = 0.46, P = 0.10).

Conclusion

The three MRI approaches used here provided highly reproducible information on SM inflammation near the patella in knee OA. Compared to SMV, MRI synovitis score seems sufficient to assess synovial inflammation but high SMV is an appropriate indicator of vascular congestion, and low SMV reflects pain in knee OA.