Prognostic indicators of foot-related disability in patients with rheumatoid arthritis: results of a prospective three-year study

Objective: To determine the prevalence and natural history of foot-related disability in patients with rheumatoid arthritis (RA). A secondary aim was to identify explanatory variables, including forefoot bursae, that are either associated with or predictive of disabling foot complications in patients with RA.

Methods: A longitudinal prospective cohort study recruited patients with RA from a rheumatology outpatient clinic. Data were collected at baseline (n = 149) and 1-year (n = 120) and 3-year followup (n = 60). Patient-reported disabling foot complications were evaluated using the subscales of the Foot Impairment Score (FIS): foot impairment/footwear restriction (FIS(IF)) and activity limitation/participation restriction (FIS(AP)). Explanatory variables investigated included ultrasound-detectable forefoot pathology and markers of disease activity.

Results: Disabling foot complications were highly prevalent on all occasions. Changes in foot impairment and activity limitation were significantly associated with fluctuations in disease activity (Disease Activity Score in 28 joints using the erythrocyte sedimentation rate [DAS28-ESR]: r = 0.455, P < 0.0001; ESR: r = -0.356, P = 0.008 and DAS28-ESR: r = 0.433, P = 0.001; ESR: r = -0.439, P = 0.001 for the FIS(IF) and FIS(AP), respectively), and approaching a significant association with changes in forefoot bursae (FIS(IF): r = 0.255, P = 0.063 and FIS(AP): r = 0.255, P = 0.063). The presence of disease duration and forefoot bursae was a significant prognostic indicator of foot impairment (P = 0.009 and P = 0.012, respectively), explaining 16% of score variability in the final regression model. Disease duration, forefoot bursae, and erosion presence were identified as significant prognostic indicators of activity limitation (P = 0.002, P = 0.006, and P = 0.019, respectively), explaining 35% of score variability in the final regression model.

Conclusion: Despite advances in disease management, patients report disability associated with foot problems. Forefoot bursae should be considered for targeted therapy.