Finite element analysis of the stress distributions in the proximal end of the femur after stabilization of a pertrochanteric model fracture: a comparison of two implants.

The study investigated the influence of two different implants--the dynamic hip screw (AOR) 135 degrees with 2-hole-plate and the 135 degrees gamma-nail (HowmedicaR)--on the resulting stress and strain distributions in the proximal femur after stabilization of an idealized trochanteric fracture under typical physiological loading conditions. Data recorded for the uninjured femur were used for comparison. Two-dimensional plane stress finite element models of the femur and the implants were used for the calculations. The three-dimensional nature of this problem was approximated by an appropriate distribution of element thickness according to the real geometry in combination with an overlay technique, superimposing special finite element layers for each constituent of the bone-implant system (i.e. steel, cortical and cancellous bone). Three variations of the idealized fracture were introduced, i.e. free, with callous and bony bridging, the screw being modelled in a movable ('dynamic') as well as in a locked state. As far as the resulting stress distributions are concerned, neither of the two implants proved to be significantly superior to the other for stabilization of the idealized fracture selected.