Dynamic impression insole in rheumatoid foot with metatarsal pain

Background: Custom molded insoles with metatarsal supports are used to redistribute excessive loading under the metatarsal heads in patients with metatarsalgia. However, these pressure reductions are usually insufficient for the rheumatoid foot with painful deformed metatarsal heads. We developed an effective insole made by sequential foam padding under successive walking impression. Methods: Seventeen consecutive rheumatoid arthritic outpatients with metatarsal pain participated in this repeated measures study of 7-mm flat Ethylene Vinyl Acetate, custom molded and dynamic impression insoles. Peak plantar pressure, pressure-time integral, contact area and mean force were measured by a Pedar-X mobile system. Pain levels were assessed using a Visual Analog Scale (0-10). Findings: Compared to the Ethylene Vinyl Acetate control, the metatarsal head peak pressure and pressure-time integral were significantly reduced in dynamic impression insoles by 46.3% (P <0.001) and 48.9% (P <0.001), respectively. Compared to the custom molded insole, the dynamic impression insole significantly reduced 18.3% of peak pressure (P <0.001) and 20.1% of pressure-time integral (P <0.001) by increasing 8.1% of contact area (P = 0.005) at the metatarsal heads, but there were no significant differences in all variables at the heel. After using the dynamic impression insole, the mean pain score was significantly reduced from 7.6 to 1.1 (P <0.001), and six participants experienced total pain-relief in walking. Interpretation: Dynamic impression insoles effectively relieve metatarsal pain because of a larger weight-bearing area. Forefoot shape during walking should be taken into consideration in orthotic designs for maximum pressure reduction. Consequently, we recommend using materials with memory properties to dynamically accommodate painful metatarsal heads.