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Open Access Research

Forefoot pathology in rheumatoid arthritis identified with ultrasound may not localise to areas of highest pressure: cohort observations at baseline and twelve months

Catherine J Bowen12*, David Culliford23, Ruth Allen1, James Beacroft1, Anita Gay1, Lindsey Hooper12*, Jane Burridge1, Christopher J Edwards45 and Nigel K Arden246

Author Affiliations

1 Faculty of Health Sciences, University of Southampton, Southampton, UK

2 Musculoskeletal Biomedical Research Unit, University of Oxford, Oxford, UK

3 Faculty of Medicine, University of Southampton, Southampton, UK

4 Department of Rheumatology, Southampton University Hospitals NHS Trust, Southampton, UK

5 Wellcome Trust Clinical Research Facility, Southampton University Hospitals Trust, Southampton, UK

6 MRC Epidemiology Resource Centre, University of Southampton, Southampton, UK

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Journal of Foot and Ankle Research 2011, 4:25  doi:10.1186/1757-1146-4-25

Published: 23 November 2011

Abstract

Background

Plantar pressures are commonly used as clinical measures, especially to determine optimum foot orthotic design. In rheumatoid arthritis (RA) high plantar foot pressures have been linked to metatarsophalangeal (MTP) joint radiological erosion scores. However, the sensitivity of foot pressure measurement to soft tissue pathology within the foot is unknown. The aim of this study was to observe plantar foot pressures and forefoot soft tissue pathology in patients who have RA.

Methods

A total of 114 patients with established RA (1987 ACR criteria) and 50 healthy volunteers were assessed at baseline. All RA participants returned for reassessment at twelve months. Interface foot-shoe plantar pressures were recorded using an F-Scan® system. The presence of forefoot soft tissue pathology was assessed using a DIASUS musculoskeletal ultrasound (US) system. Chi-square analyses and independent t-tests were used to determine statistical differences between baseline and twelve months. Pearson's correlation coefficient was used to determine interrelationships between soft tissue pathology and foot pressures.

Results

At baseline, RA patients had a significantly higher peak foot pressures compared to healthy participants and peak pressures were located in the medial aspect of the forefoot in both groups. In contrast, RA participants had US detectable soft tissue pathology in the lateral aspect of the forefoot. Analysis of person specific data suggests that there are considerable variations over time with more than half the RA cohort having unstable presence of US detectable forefoot soft tissue pathology. Findings also indicated that, over time, changes in US detectable soft tissue pathology are out of phase with changes in foot-shoe interface pressures both temporally and spatially.

Conclusions

We found that US detectable forefoot soft tissue pathology may be unrelated to peak forefoot pressures and suggest that patients with RA may biomechanically adapt to soft tissue forefoot pathology. In addition, we have observed that, in patients with RA, interface foot-shoe pressures and the presence of US detectable forefoot pathology may vary substantially over time. This has implications for clinical strategies that aim to offload peak plantar pressures.