Comparative Distribution of Ultrasound‐Detectable Forefoot Bursae in Patients With Osteoarthritis and Rheumatoid Arthritis

Objective To investigate the prevalence and distribution of forefoot bursae (FFB) in individuals with osteoarthritis (OA), individuals with rheumatoid arthritis (RA), and healthy controls (HCs), and to identify mechanical or inflammatory factors predicting FFB count. Methods A cross‐sectional observational study was completed in 3 cohorts: OA (n = 50), RA (n = 56), and HC (n = 50). FFB were recorded as present if detectable in 2 ultrasound (US) scanning planes. The comparative probabilities of FFB presence between groups were expressed as odds ratios. Mechanical factors, including joint deformity, range of motion, and foot posture, were determined for both patient groups. Inflammatory factors, including serology, Disease Activity Score in 28 joints, and US‐detected metatarsophalangeal joint hypertrophy and metatarsal head erosion, were determined for RA patients. Multiple linear regression analyses were used to determine factors related to FFB count in the patient groups. Results FFB were highly prevalent in both the OA and RA groups (94 per 100 patients and 88 per 100 patients, respectively) compared with the HC group (56 per 100 participants). FFB distribution significantly differed between the patient groups (RA‐OA: χ2 = 15.64, P ≤ 0.001). In OA patients, FFB were commonly located in the medial/lateral forefoot region, but were located across all regions for RA patients. In OA patients, reduced ankle joint range of motion predicted FFB count (R2 = 0.09, P = 0.037). In RA patients, erosion presence was related to FFB count (R2 = 0.18, P ≤ 0.001). Conclusion FFB were highly prevalent in patients with OA and RA. FFB distribution significantly differed between the patient groups. FFB in patients with OA may be related to mechanical factors.