Three-dimensional kinematics at the ankle joint complex in rheumatoid arthritis patients with painful valgus deformity of the rearfoot

Objective. To evaluate the three-dimensional (3D) kinematics of the ankle joint complex (AJC) in rheumatoid arthritis (RA) patients with painful valgus deformity of the rearfoot. Methods. Fifty patients with RA underwent gait analysis using electromagnetic tracking techniques to measure 3D kinematics at the AJC under barefoot and shod walking conditions. Three axial rotations (dorsiflexion/plantarflexion, inversion/eversion and internal/external rotation) were measured during the gait cycle, and the angular positions at key gait events, range of motion and the motion: time integral were measured. Descriptive and analytical comparisons were made with normative data derived from a sex- and age-matched population (n=45). Results. AJC dysfunction in RA was characterized by excessive eversion motion (within an eversion range) and no inversion motion through the neutral joint position for the subtalar component of the joint complex, in both barefoot and shod walking conditions. Motion was coupled such that internal rotation of the leg relative to the rearfoot was greater than normal. AJC motion was different for all rotations between barefoot and shod conditions, but in both situations there were statistically significant between-group differences in the motion:time integral for inversion/eversion (barefoot, P<0.0001; shod, P<0.0001) and external/internal rotation (barefoot, P<0.0001; shod, P<0.0001). There were no statistically significant differences between RA and normative data for dorsiflexion/plantarflexion motion under barefoot (P=0.16) and shod (P=0.50) walking conditions. Conclusion. Painful valgus deformity of the rearfoot is associated with changes in the 3D kinematics affecting eversion at the AJC and internal rotation of the leg, both when walking barefoot and in shoes.