Joint space narrowing is the first roentgenologic sign of osteoarthrosis of the ankle. In this report the dependence of ankle joint width on plantar flexion was investigated. In 30 adult volunteers without ankle symptoms, standardized anteroposterior views of the left ankle joint in neutral position and in 25° plantar flexion were obtained. The average width of the joint space in neutral position was 2.7 mm in women, and 3.0 mm in men. A 25 per cent increment of the joint width following 25° plantar flexion was observed. Accurate standardized positioning of the ankle appears to be decisive for the estimation of ankle joint width.
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