In-shoe pressure redistribution to provide relief of forefoot pain in rheumatoid arthritis (RA) is based on assumed links between pressure and pain. However, little is known about the size of the pressure change required to reduce pain or the capacity of other plantar regions to bear increased pressure. Our primary aim was to quantify the plantar pressure pain threshold (PPT) in RA and compare it to age- and gender-matched control participants.
This controlled trial involved 10 RA participants and 10 age- and gender-matched control subjects. PPT, measured using a force gauge, and touch sensitivity, measured via Semmes-Weinstein monofilaments, were tested in 19 plantar regions.
RA plantar PPTs were significantly reduced in eight foot regions (p < 0.05) and were more uniform across the plantar surface. Touch sensitivity was not different between groups. Plantar PPT was significantly related to age (p < 0.05) and to touch sensitivity (p < 0.05) in multiple foot regions of the control group but not in RA. PPT was significantly correlated with disease duration (p < 0.05).
Plantar PPTs in RA were 60% to 80% of the control group and may be helpful in predicting the amount of pressure reduction needed to relieve pain. This study provides further evidence that RA disturbs normal pain sensory mechanisms.