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 video-based three-dimensional kinematic data acquisition system, with kinetic force plate data, using rigid body mechanics, to compare RA and normal (NL) feet during gait. Eight RA feet (4 RA subjects) and 14 NL feet (7 NL subjects) were studied for eight variables while walking at a comfortable pace. Forces were measured in Newtons and normalized to body weight and, where appropriate, to foot length. Findings showed reduced RA vertical loading of the foot at heel strike and toe-off (mean RA=100=.2% body weight (BW), NL=115.2% BW); reduced longitudinal loading of the foot at toe-off (RA=6A% BW, NL=20.5% BW); reduced and delayed RA max ankle dorsiflexion moments (RA=1.04 at 94.8% stance phase, NL=1.43 at 90.5% stance phase); decreased RA ankle motion at heel strike and toe-off (RA=23.9 degrees, NL=38.9 degrees); and decreased RA heel rise at lift off (RA=42.2 degrees, NL=78.7 degrees). Progression of the center of pressure along the RA foot was delayed in reaching 50 percent of distance from ankle joint to front of the foot (RA=50.8% stance phase, NL=72.4% stance phase). The 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. One new patient was evaluated this year.
