Radiological assessment was performed in cases with osteoarthritis (OA) of the ankle joints without definite origin, for example, trauma, infection etc. Among 25 OA cases unkown origin, 17 cases belonging to 8 males and 9 females ranging in age from 51 to 71 years (mean: 59.9yrs) were inversion types, 8 cases belonging to 2 males and 6 females ranging from 51 to 75 years (mean: 63.6yrs) were eversion types. Radiological mesurements were performed as follows, the basic line was drawn on the longitudinal axis of the distal third of the tibia, and the angle between this line and the mortise called ∠TAS on A-P view, called ∠TLS on lateral view, inclination of the articulus medio-malleoli on A-P view called ∠TMM. Measurements of normal material were parformed in 20 cases in the same manner. In normal material, ∠TAS was 89.2±3.0, ∠TLS was 81.2±4.1, ∠TMM was 23.8±5.9. In inverted OA, 86.6±3.5, 78.1±3.6, 78.1±3.6. In everted OA, 86.9±3.2, 76.1±3.8, 33.5±13.4. There were significant differences (p<0.05) in ∠TAS, ∠TLS, ∠TMM between normal and OA, but were not significant between inversion and eversion types. The positions of the Mikulicz line at the knee and ankle joints were measured in the two types. It was 30.4±7.9% from the medial edge of the knee in inversion type, 28.5% in eversion type, 22.2±28.5% from medial edge of ankle in inversion type, 63.0±23.4% in eversion type. There were no significant differences between the two types at knee, but there were significant differences (p<0.05) at the ankle joint. To clarify the reasons leading to the development of OA of unkown origin, it is suggested that the shape and range of motion of the subtalar joint, and instability of ankle be evaluated including dynamic assessment.
