Effects of a contoured foot orthosis versus a flat sham insert on plantar loading in midfoot osteoarthritis

Midfoot osteoarthritis is common and results in pain and disability. We compared the effects of an arch contouring foot orthosis and a flat sham insert on plantar loading in people with midfoot osteoarthritis.

Plantar loading was collected while walking with: (i) shoe-only, and either (ii) a flat sham insert or (iii) an arch contouring orthosis. Differences within groups were tested using paired samples t-tests, and differences between groups were tested using analyses of covariance. Effect sizes for within-group comparisons were calculated using Cohen's d.

Forty-two adults were analysed (38 women and 4 men, mean ± SD age 66.3 ± 6.7 years). The arch contouring orthosis significantly increased contact area (adjusted mean difference [MD] 3.0 cm², 95% confidence interval [95% CI] 0.0 to 5.9; p = 0.047) and maximum force (MD 30.3 N, 95% CI 16.0 to 44.7; p < 0.001) at the medial midfoot, decreased maximum force at the lateral forefoot (MD -28.2 N, 95% CI -42.9 to -13.5; p < 0.001), decreased peak pressure at the heel (MD -36.2 kPa, 95% CI -65.1 to -7.4; p = 0.015) and increased peak pressure at the medial midfoot (MD 19.8 kPa, 95% CI 7.0 to 32.5; p = 0.003). Within the arch contouring orthosis group, increases in maximum force and peak pressure at the medial midfoot were large and very large (d = 0.90 and 1.21, respectively).

The arch contouring orthosis increased plantar loading at the medial midfoot and decreased loading at the heel. Further studies are required to investigate if these effects are related to symptomatic improvements.