INTERNAL FORCES AND MOMENTS IN THE FEMUR DURING WALKING

The forces exerted by the soft and hard tissues of the thigh together represent a system in equilibrium. This balance of loads must be consi dered when the system components are examined independently. However, in many biomechanical analyses of the thigh, the femur is studied with out considering soft tissue loading. To improve the understanding of f emoral loading a three-dimensional model was developed. Taking into ac count all thigh muscles, body weight and contact forces at the hip, pa tello-femoral and knee joints, the internal loads of the bone were cal culated. Internal loads of the femur decreased as a result of muscle a ctivity from proximal to distal at the hip and from distal to proximal at the knee. The load reduction could be up to 50% of the internal fo rces at the hip, depending on gait phase. Maximal forces were found be tween 40 and 60% of the stance phase, whereas maximal torsional moment s occurred shortly after heel strike. This model demonstrated that mus cles play a substantial role in balancing the loads within the femur. In general, the bone is loaded axially, rather than in bending, with m aximum shear forces at the proximal and distal ends. Bending moments a re relatively small compared to models which do not consider muscle ac tivity. From one gait phase to another, the femur experiences alternat ing, rather than one-sided bending load. (C) 1997 Elsevier Science Ltd .