Assessing forefoot bursitis in rheumatoid arthritis: a comprehensive approach with ultrasound, MRI, and baropodometry

In rheumatoid arthritis (RA), forefoot bursitis is prevalent, with limited studies comparing ultrasonography (US) and Magnetic Resonance Imaging (MRI). This study aims to evaluate these bursae, providing a comparative analysis of US and MRI, and explore associations with demographic, disease-related factors, pain, clinical examination, and baropodometryin RA patients.

Participants with RA were recruited from the day-hospital clinic. The forefeet were assessed clinically, and the selected foot was examined by US and MRI to evaluate intermetatarsal (IMB) and submetatarsal bursitis (SMB). Baropodometry assessed plantar pressures and contact surfaces.

Thirty-five RA patients were enrolled, 85.7% females, mean age 59.2 (11.3) years, mean body mass index (BMI) 26.5 (5.7) kg/m2, median disease duration of 36.0 (16.5-114.0) months, and 34.3% with painful forefoot. A total of 140 intermetatarsal and 175 submetatarsal spaces were evaluated. Agreement between US and MRI was high (PA=97.14%, k=0.801, p<0.001), and interobserver reliability for both modalities was excellent (US: PA=98.73%, k=0.888, p<0.001; MRI: PA=98.41%, k=0.900, p<0.001). IMB was negatively associated with disease duration (the only independent predictor) and linked to clinical signs like the opening toes sign and hammer toe deformity. SMB showed an association with BMI and erosions. Baropodometric analysis indicated no significant differences in plantar pressures for IMB, and larger contact surfaces in SMB regions.

US and MRI are valuable tools for forefoot bursitis evaluation. IMB is associated with disease duration (negative association), the opening toes sign, and hammer toe deformity, while SMB correlates with BMI, erosions, and foot architectural deformity. Baropodometry revealed larger contact surfaces in regions with SMB.