The constraint-mechanism of the human tarsus. A roentgenological experimental study

The main purpose of this investigation was to extend the work of Huson, Ambagtsheer and Van Langelaan to living subjects. It may thus be regarded as the logical continuation of Van Langelaan's study. The investigation consists of three main parts: In part 1 (Chapter 2), stepwise supination of the tarsus of fixed osteoligamentous preparations (the mode of supination studied by Van Langelaan) was compared with continuous supination. We found that stepwise supination of lower leg foot-preparations differs little from the continuous supination. The speed at which the continuous movement is carried out, and the amount of vertical loading, have only very slight effects. We could discern clearly that the visco-elastic properties of the tissues caused a difference in the paths of the supinating and pronating movements, the hysteresis effect. During this investigation we discovered by coincidence that the input moment to be applied to the tibia to supinate the tarsus by rotation varied greatly from one individual to another. The same was true for the vertical tibial translation during supination. This finding that differently shaped feet also differ in biomechanical behaviour prompted an extra line of investigation with which we attempted to quantify this biomechanical behaviour by measuring moments and recording vertical tibial translations, combining the two and relating them to a new roentgenological classification of the tarsus. The traditional specification criteria were found to be unsuitable. A strong correlation was found to exist between moment (M) and vertical tibial translation (S). Another strong correlation was observed between M and S and the tarsal index it, calculated with the equation (Formula: see text) The index is determined entirely by the relative positions of the talus and calcaneus. Part 2 (Chapter 3) comprises a study of fresh amputation material, as a step in the direction of live material. Two amputated lower legs were analyzed kinematically, according to Van Langelaan and Spoor's photogrammetric method; dynamically, by measuring moments (M) and recording vertical tibial translations (S); and finally by comparing the stepwise and continuous supination and pronation of one specimen (female 29). Each method was applied both to the completely intact specimen and to the dissected osteo-ligamentous preparations. As kinematic parameters we used the helical axes. We calculated both the relative axes (of the movements of one tarsal bone in relation to another) and the absolute discrete axes (of the tarsal bones in relation to the fixed reference system in the test setup) of supination from 0 degree -30 degrees and return.(ABSTRACT TRUNCATED AT 400 WORDS)