Flattening of the rheumatoid foot in tarsal arthritis on X-ray.

222 consecutive and unselected patients suffering form classical or definite rheumatoid arthritis wee studied. 397 of their feet were examined. Talonavicular arthritis was the commonest finding (31.5% of all patients), followed by sub-talar (23.3%), cuneo-navicular (20.4%) cuneo-metatarsal (14.9%) and tibio-tarsal arthritis (12.6%). Rheumatoid disease of the tarsus becomes commoner as the disease progresses. The incidences of involvement of the talo-navicular and sub-talar joints show a similar pattern, with a leap of 25% between 5 years of duration of the disease and 10 years. The same is seen with involvement of the cuneo-navicular and cuneo-metatarsal joints, between a duration of 10 years of the disease and 15 years. The percentage of flat foot is greater in feet with tarsal arthritis (p less than 0.001). The authors observed a relationship between tarsal arthritis, the length of history of rheumatoid arthritis, and flat foot. The method of investigation is discussed, and theories about evolution of the rheumatoid foot are considered.