Dynamic load in the human knee joint during voluntary active impact to the lower leg.

: The aim of the study was to get an insight into the nature of the dynamic load in a joint caused by impacts of physiological magnitude to the distal part of an extremity of normal, live human subjects. A method was developed for the calculation of two components of the impulse reaction (parallel and perpendicular to the lower leg) as a measure of the dynamic load in the knee. A theoretical model regarding the lower limb as a double pendulum was chosen and equations developed. Five subjects were studied during kicking situations and the components of the impulse reaction were calculated. With a normal kicking motion pattern the direction of the components of the impulse reaction in the knee joint caused by the impact to the lower leg are usually distal and anterior. The impulse reaction thus tends to cause a traction of the lower leg from the thigh and an anterior displacement of the proximal part of the lower leg in relation to the distal part of the thigh. Anatomical structures which can prevent this displacement are discussed.