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Objective

Foot and ankle deformities greatly affect the quality of life of rheumatoid arthritis (RA) patients. The aim of this study was to elucidate the pattern of destruction of the RA foot and its impact on patients.

Methods

We cross-sectionally investigated RA patients (274 patients and 542 feet) using radiographs. The grade of joint destruction was assigned using Larsen's grading system for 12 joints in the foot and ankle. Cluster analysis was performed using the K-means method to classify the pattern of joint destruction. Of the 274 patients evaluated radiographically, 212 were assessed for functional disability using questionnaires.

Results

Cluster analysis revealed that 542 feet were divided into 5 clusters, named according to the characteristic distribution of joint destruction: cluster I (normal type), cluster II (forefoot type), cluster III (midfoot type), cluster IV (mid-hindfoot type), and cluster V (combined type). Radiographic measurements revealed the characteristic deformities of each cluster: splay foot for cluster II, flat foot for cluster III, hindfoot malalignment for cluster IV, and mixtures of these characteristics for cluster V. A distribution map of each cluster based on disease duration revealed that cluster III peaked in cases of 5–10-year disease duration and subsequently decreased, followed by a gradual increase of cluster IV and cluster V. Cluster IV and cluster V showed significant changes in functional disability compared to cluster III.

Conclusion

This report is the first to reveal the pattern of RA foot deformities and their impact on patients using statistical measures in a large series.