The epidemiology and clinical importance of forefoot bursae in patients with rheumatoid arthritis

Abstract

The epidemiology of foot complications in patients with rheumatoid arthritis (RA) is poorly understood. A number of patients report ongoing foot-related pain, impairment, footwear restriction and activity limitation, despite developments in pharmacological disease management. Forefoot bursae (fluid filled sacks, FFB) have been previously shown to be highly prevalent and related to foot complications in patients with RA. However, the longitudinal epidemiology and clinical importance of FFB in this patient population remains unclear.

It is anticipated that an improved understanding of the mechanisms by which FFB are responsive to, or contribute to, fluctuations in RA disease activity will inform future evaluation of foot health and novel therapeutic targets.

Through a series of four experimental studies this work has shown that ultrasound (US) detectable FFB are highly prevalent in patients with RA compared to healthy volunteers (HV) and are clinically relevant. The natural history of FFB remains consistent longitudinally in a cohort of patients with established RA disease at baseline. US-detectable FFB were determined to be significant prognostic indicators of foot-related disability after three years. Furthermore, the distribution of US-detected FFB across forefoot sites was identified as significantly different between HV and patients with predominantly inflammatory or degenerative arthritis; uniquely patients with RA have a number of FFB within the central forefoot region, in addition to those located laterally, which were frequently present in all comparative groups. Thus, in patients with RA ~50% of US-detected FFB may be of greatest clinical relevance, due to their positioning within the central forefoot region.

Detection of FFB using MRI defined a series of FFB characteristics of clinical relevance in patients with RA. The presence of plantar forefoot fluid lesions or intermetatarsal soft tissue lesions was significantly related to RA disease activity. The presence of plantar soft tissue lesions was significantly related to increased biomechanical impairment. However, a high proportion of plantar predominantly soft tissue FFB was also noted to be actively inflamed whilst other MRI-based markers of disease activity within the forefoot were minimal.

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Identifiers

ORCID for Lindsey Hooper: orcid.org/0000-0002-3165-1004

ORCID for Catherine J. Bowen: orcid.org/0000-0002-7252-9515

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