AGE RELEVANT DISTRIBUTION OF FORCES AT TH E PROXIMAL END OF THE FEMUROF THE NORMALLY DEVELOPING-CHILD

In a group of normally developed children and adolescents the age depe ndent distribution of forces at the proximal end of the femur was to b e described. The results should explain why the shape of the proximal end of the femur changes significantly during the time of growth and w hy the neck shaft angle decreases. The method applied was the biomecha nical computation analyzing in the coronal plane according to Pauwels' biomechanical hip model. The necessary age relevant data was derived from 675 anteroposterior pelvis radiographs of healthy children of bot h sexes and of varying age. The following can be put down as a result: 1. The proximal end of the femur is stressed by two resultant forces: the hip resultant force R controls the growth of the capital growth p late, the trochanteric resultant force R(T) regulates the growth of th e greater trochanter growth plate. 2. During the growing period the hi p resultant force R adjusts itself less vertically: during the second year of Life it inclines at an average of 11,6 degrees towards the ver tical, towards the end of the growing period it is incident with an in clination angle of 20 degrees. With the older child the magnitude of t he hip resultant force R decreases in relation to the exerting body we ight. 3. During the time of growth the trochanteric resultant force R( T) maintains its direction stability with inclination angles of 50-52 degrees towards the vertical. Its magnitude increases significantly (i n relation to the exerting body weight). 4. From age 2 to 10 the proje cted neck shaft angle decreases from an average of 148.2 degrees to 13 3.7 degrees and usually remains stable. It can be concluded that the s hape of the proximal end of the femur is determined by the muscle forc es stimulating the greater trochanter apophysis and by gravity. With i ncreasing age the growth of the greater trochanter apophysis shifts th e insertions of abductor muscles laterally. As a result the directions of the hip abductors and the hip resultant force R incline. The neck shaft angle decreases consecutively.