Is cavus foot affected by midfoot flattening in rheumatoid arthritis?

Abstract

Objective: The painful feet are likely to flatten in rheumatoid arthritis (RA), and there is an optimal time to prescribe plantar orthoses in rheumatoid arthritis to correct deformity of the subtalar joint complex. We aimed to determine which type of foot is likely to become flattened to improve localized treatment of the rheumatoid foot. Methods: Three hundred and two rheumatoid feet (RF) in 151 patients with RA were compared with 200 feet in 100 consecutive patients with neck pain (control group, CF). The two groups were homogeneous for sex, age, and laterality of the foot. Lateral weight-bearing radiographs were obtained for each foot. Feet were classified as cavus, normal, and flat according to their angular variations. Results: On radiographs in weight-bearing, the frequency of cavus foot was similar in both groups regardless of age, before and after age 50 years. The frequency of normal foot was slightly lower in rheumatoid than in control feet (P = 0.036), while flat foot was much more frequent in rheumatoid feet (P = 0.0005). The frequency of flat foot increased significantly with age in both groups, and this increase occurred earlier in the RF group (P = 0.05). Intragroup comparison showed that the frequency of flat foot was higher after age 50 in both the RF (P = 0.026) and the CF (P = 0.002) group, and in the CF group, the increase of flat foot was more marked after 50 years than in the RF group. Conclusion: On the whole, the cavus foot did not flatten in RA or flattens less. Preventive plantar orthoses and appropriate footwear are therefore particularly indicated in the painful "normal" RF to avoid flat foot and in painful flat RF to avoid worsening of the flat foot.