Improved understanding of the biomechanics of rheumatoid arthritis (RA) of the foot and ankle during gait are needed for advances in orthotic and surgical management of the foot to occur. This study used a videobased three dimensional kinematic data acquisition system, with kinetic force plate data, utilizing rigid body mechanics, to compare RA and normal feet during gait. Eight RA feet (4 RA subjects) and 14 normal (NL) feet (7 NL subjects) were studied walking at a comfortable pace. Eight variables were studied. Forces were measured in Newtons and normalized to body weight and, where appropriate, to foot length. Findings were reduced vertical loading of the foot at heel strike and toe-off, mean RA=100.2% Boyd Weight (BW), NL=115.2% BW: reduced longitudinal loading of the foot at toe off RA=6.4% BW, NL=20.5% BW; reduced and delayed max ankle dorsiflexion moment RA=1.04 at 94.8% Stance Phase, NL=1.43 at 90.5% Stance Phase: decreased ankle motion at heel strike and toe-off RA=23.9 degs, NL=38.9 degs. decreased heel rise at lift off RA=42.2 degs, NL=78.7 degs. Progression of the center of pressure along the foot was delayed in reaching 50% of distance from ankle joint to front of foot RA=50.8% Stance Phase, NL=72.4% Stance Phase. Mediolateral path of center of pressure in both NL and RA feet was highly variable. A distinctive pattern was found with RA feet showing reduced vertical and longitudinal loading of the foot at toe off, decreased ankle motion and heel rise especially late in stance, delay in transfer of forces to the forefoot until late in stance, and reduced ankle moments.
