Stresses in the growth plate of the developing proximal femur

Finite element models of the proximal femur at birth, 2 years of age, and a t 8 years of age were constructed to investigate stress patterns under diff erent loading conditions. These loading conditions represent typical activi ties of a normal developing child and abnormal activity associated with mus cle spasticity. The hypothesis is that the shear stresses in the growth pla te correlate with the neck-shaft angle as associated with valgus and normal development. Loads for the finite element models were derived from a separ ate muscle model used to calculate the forces across the hip joint for an a rbitrary subject and activity. Results show there is an inverse relationshi p between the relative magnitude of the shear stress in the growth plate an d the developing neck-shaft angle. The relatively high shear stresses gener ated by normal activity in the 2-year-old's growth plate correlate with the decrease in neck-shaft angle that accompanies normal development. Alternat ively, lower shear stresses are generated in the growth plate by loading co nditions representing spasticity. These lower magnitude shear stresses corr elate with a valgus deformity, which is often observed clinically.