• Franz K. Fuss
Keywords: tibialis posterior muscle, sports trauma, kinematics, axiometry


Introduction: The tibialis posterior muscle functions mainly in supination control and also guarantees the stability of the foot arch. The aim of this study was to analyze the pronation-supination equilibrium in normal test persons and in patients with suspected tibialis posterior insufficiency. Methods: Ten normal test-persons and five patients with suspected tibialis posterior insufficiency were examined. The muscle insufficiency resulted from ski traumas with hyper-dorsiflexion of the foot. All patients reported pain in the foot arch when standing on the affected foot. A computer-axiometry system (Fuss 1993, 1994) was used to analyze the kinematics (position and direction of the finite helical axes, helical translation and rotation and helical axes surfaces) of the plantarextension, beginning in the normal zero position (lower leg perpendicular to the floor) and progressing to a tiptoeing position. The subjects tiptoed on both feet simultaneously, while holding on to the examination table. The complete movement was captured by the software, namely in steps of 3°. Nine different data sets were taken for each leg. After having printed the finite helical axes in the xy- and xz-planes, the angle (‘axis angle’) between the finite helical axes (of the different stages of movement) and the reference coordinate system was measured. A deviation from the horizontal base line indicates compulsory motion. The results were evaluated for the first 10° of the movement, in order to uncover discrepancies in the axes’ positions. Results: The first 10° of motion are not solely a plantarextension, as compulsory motion simultaneously arises. In the initial phase of motion a combined adduction/ supination occurs, which decreases in the course of further motion. However, following insufficiency of the tibialis posterior muscle, an abduction/pronation combination arises. Conclusions: The clinical significance of ankle joint axiometry lies in the possibility of objectively documenting the kinematic implications of muscle function disorders (muscle injuries, paralysis following nerve lesion) and joint injuries. Application possibilities are: additional method for the diagnosis of muscular disorders, handicap detection for expert opinions in liability suits, decision aid in therapy strategies (this study showed that the tibialis posterior is indispensable and that insufficiency or even rupture thereof must be treated immediately or a muscle replacement executed), success assessment after surgery and during rehabilitation. References: Fuss, F.K. (1993). Helical axis surface of the knee joint. 14th Congress of the International Society of Biomechanics, Paris. Fuss, F.K. (1994). A new method of clinical assessment of shoulder kinematics by means of the parameters of helical axes. In European Journal of Physical Medical Rehabilitation. 4,152-130.