The influence of metatarsophalangeal lesions on the position of the center of plantar pressure in rheumatoid patients was analyzed by a photoelastic method. Fifteen patients were divided radiographically into three groups (A to C) based on the degree of destruction of the metatarsophalangeal joints. Fifteen age-matched non-rheumatoid subjects were studied as a control group. As parameters expressing the position of the centre of plantar pressure, longitudinal ratio (λ) and transverse ratio (η) were defined and analyzed respectively. The λ of group B was significantly lower than those of group A and C (A: 44.6 ± 6.4, B: 39.0 ± 0.5, P = 0.0327
B: 39.0 ± 0.5, C: 44.7 ± 4.9, P = 0.0075). The η of group B was significantly lower than those of group A and C (A: 46.2 ± 3.4, B: 43.4 ± 7.4, P = 0.0161
B: 43.4 ± 7.4, C: 46.4 ± 1.9, P = 0.0075). By comparing the above data with the control data and combinations of patterns in both parameters, the positions of the centre of plantar pressure were divided into four types. The most common type in group A and C was 'anterolateral (steady)', and that in group B was 'posteromedial (unsteady)'. Based on the result, we conclude that the treatment of the lesions in group B is the most necessary to maintain the stability of standing.