Forces acting on the juvenile hip joint in the one-legged stance.

A two-dimensional biomechanical model of the juvenile hip joint was developed to describe the forces acting on the capital epiphysis and the greater trochanter apophysis in the one-legged stance. Based on anatomic femur specimens of 16 children, ranging from toddlers to teenagers, and radiographic studies of 1,350 hip joints of healthy children, we showed that the apophysis of the greater trochanter is a pressure apophysis. If the muscular forces acting on the apophysis of the greater trochanter are added, the unit sum may be considered a resultant force acting from a craniolateral direction. The trochanteric resultant force near the end of the growth period is equivalent to approximately 1.7 times body weight. The trochanteric resultant force stimulates craniolateral growth of the greater trochanteric apophysis. This mechanism is responsible for the direction of the forces exerted by the hip abductors and thus the direction and magnitude of Pauwels' hip-joint resultant, and finally influences the neck-shaft angle.