Quantitative Assessment of Synovitis in Legg-Calve-Perthes Disease Using Gadolinium Enhanced MRI

PURPOSE: Hip synovitis in LCPD is associated with pain, decreased motion, and poor outcome. However, a reliable quantitative method to assess hip synovitis, its progression, and response to therapy is not currently available. Gadolinium MRI (Gd-MRI) has been used to assess synovitis in other inflammatory conditions, but no study has been performed to quantify hip synovitis in LCPD. Purposes of the study are to develop a reliable quantitative method to measure hip synovitis using Gd-MRI in LCPD and to determine the temporal progression of synovitis. METHODS: 22 patients (22 hips) were enrolled based on the following criteria: first Gd-MRI obtained during active stage of LCPD (Waldenström Stage I to II) and serial MRI obtained using the same protocol (average number of MRIs 3±1, range 2-6). The areas of synovial enhancement in all slices of Gd-MRIs were measured using digital image analysis software. Individual areas were converted to volumes and the measurements were compared over time and Waldenström stage of disease. Intra-/ inter-observer reliabilities of measurements were assessed by 2 independent observers. Intraclass correlation coefficient (ICC) was analyzed. Total volume of synovitis was compared between the affected and unaffected sides using a t-test with statistical significance at p<0.05.
RESULTS: Age at diagnosis ranged from 5 to 11 years (mean 7.4 ± 1.6). The first Gd-MRI was obtained at a mean duration of 1.0 ± 1.2 months after diagnosis (range 0 - 3 months). Synovial enhancement on initial Gd-MRI was significantly higher on the affected side (7031 ± 3109 mm3) vs. the unaffected side (367 ± 308 mm3, p<0.001). On final MRI, mean synovial enhancement was 4184 ± 3030 mm3 on the affected vs. 484 ± 415 mm3 (p<0.001) on the unaffected side (Figure 1). Mean synovial enhancement (synovitis) decreased with progression of Waldenström Staging from Stage I (avg. 7535 ± 3524 mm3) to Stage III (avg. 3800 ± 2413 mm3). The intraclass correlation coefficient was 0.98. The interobserver agreement was 0.94 CONCLUSION: Synovitis is highly prevalent in LCPD and most severe during the early stages of the disease. Overall, synovitis decreased within the first 20 months after diagnosis. This decrease correlated with the progression of the Waldenström stage.
SIGNIFICANCE: A reliable quantitative method to assess synovitis in LCPD using Gd-MRI was developed. LCPD is associated with chronic synovitis which decreased with Waldenström stage.