The Biomechanics of the Foot

These words of the old master of ortho­ paedics, Georg Hohmann, from his book "Fuss und Bein" are still applicable today. Thirty years later, the biomechanics of the foot have still not been completely explained, and there are many questions yet unanswered. The many, more or less articulated connec­ tions of the foot allow a variety of changes which make it difficult to understand the move­ ment as a homogeneous process. Too many factors can only be qualified, but not quanti­ fied. Nor may we forget the reciprocal influence of the position of the foot, knee, and hip joints. Each change in the position of one of these joints automatically involves a change in the position of the other two joints. For example, in the upright position, the neck of the femur forms a posteriorly open angle of approximately 20 degrees. This is de­ termined by the anatomical factors in relation to the frontal plane of the body. The direction of the axis of the hip joint corresponds fairly accurately to the connection inner-malleolus/ outer-malleolus, which have an exterior rota­ tion of approximately 20 to 30 degrees in rela­ tion to the frontal plane. Consequently, there is a conformity between the ankle axis and the hip axis. In the upright position, the knee is practi­ cally locked due to the automatic rotation and so the position of this axis is of minor impor­ tance. When walking, the pelvis rotates ap­ proximately 20 degrees forward. As the lower leg also rotates inwardly in relation to the upper leg during flexion, the ankle axis rotates in­ wardly and the foot takes up a straight position in the swing phase. CHARACTERISTICS OF THE FOOT