[Biomechanical analysis of locomotion patterns in the lower limb. II. Forces in joints]

After the introduction of a tri-sectional schematic model of the human body it was possible to investigate the simple dynamic locomotion pattern (braking process after a free fall); from this, the effective weight force and the ground recoil forces could be calculated. Once the external forces and the locomotion pattern are known the forces in the knee and hip joint can be determined with simplified joint structures, both for static bending of the knee as well as for the braking process during locomotion. This general calculation of internal forces is performed according to the so-called cross-section principle, since even this permits a basic comparison to be made between the forces acting at rest and during movement. The calculations show that during movement there is a relatively slight increase in the forces in the hip joint; on the other hand, following a free fall from 1.5 m and up to a kneebending angle of 100 degrees, the bearing force in the knee joint during braking increases to 21 times body weight. Thus, there is a massive increase in the internal forces during movement owing to the need for transmission of torque. Conclusions can be drawn from this concerning the development o much greater than f gonarthrosis in cases where there has been relatively little previous damage (for example), recurrent effusions, slight defects of the leg axes, slight instabilities of capsular ligaments).