ROTATION DEFORMITY OF THE TIBIA DUE TO MECHANICAL PROPERTIES OF THE SUBTALAR JOINT AXIS IN CLUB FOOT
The foot in the standing position usually makes combined motions of the three joint axes, i. e. the subtalar joint, the talocrural joint and the calcaneo-contact joint (between lateral margin of the foot and the floor). Correlation between the abnormalities of the directions of these axes and the elements of the deformity of the congenital club foot were studied. From the fact that the abnormal inclination of the subtalar joint axis is likely to cause the abnormal rotating movement of the tibita, the relation formula concerned was obtained by the projection drawing: The inversion is: ∠θ＝tan-1 (( tanβ／cosα') × sin (α°- n°)) The eversion is: ∠θ＝tan-1 (tanβ × sin n°+ tanα × cos n°) The lateral rotation deformity of the tibia is influenced, not only by the residual adduction deformity, but also by the inversion deformity. The lateral rotatory position of the tibia is related to the flat-top talus, but it is difficult for the flat-top talus to appear in the pes equinus or decreased inclination angle of the subtalar joint axis on the sagittal plane.