Degree of synovitis on MRI by comprehensive whole knee semi-quantitative scoring method correlates with histologic and macroscopic features of synovial tissue inflammation in knee osteoarthritis

Objective: To evaluate the association between synovitis on contrast enhanced (CE) MRI with microscopic and macroscopic features of synovial tissue inflammation. Method: Forty-one patients (mean age 60 years, 61% women) with symptomatic radiographic knee OA were studied: twenty underwent arthroscopy (macroscopic features were scored (0-4), synovial biopsies obtained), twenty-one underwent arthroplasty (synovial tissues were collected). After haematoxylin and eosin staining, the lining cell layer, synovial stroma and inflammatory infiltrate of synovial tissues were scored (0-3). T1-weighted CE-MRI's (3T) were used to semi-quantitatively score synovitis at 11 sites (0-22) according to Guermazi etal. Spearman's rank correlations were calculated. Results: The mean (SD) MRI synovitis score was 8.0 (3.7) and the total histology grade was 2.5 (1.6). Median (range) scores of macroscopic features were 2 (1-3) for neovascularization, 1 (0-3) for hyperplasia, 2 (0-4) for villi and 2 (0-3) for fibrin deposits.The MRI synovitis score was significantly correlated with total histology grade [. r=0.6], as well as with lining cell layer [. r=0.4], stroma [. r=0.3] and inflammatory infiltrate [. r=0.5] grades. Moreover, MRI synovitis score was also significantly correlated with macroscopic neovascularization [. r=0.6], hyperplasia [. r=0.6] and villi [. r=0.6], but not with fibrin [. r=0.3]. Conclusion: Synovitis severity on CE-MRI assessed by a new whole knee scoring system by Guermazi etal. is a valid, non-invasive method to determine synovitis as it is significantly correlated with both macroscopic and microscopic features of synovitis in knee OA patients.

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