Finite element analysis of four different implants inserted in different positions to stabilize an idealized trochanteric femoral fracture.

Biomechanical analysis of the ideal placement of new intramedullary implants for stabilization of trochanteric fractures is not currently available. The aim of the presented study is to determine to what extent four intermedullary nails (Gliding-Nail, Gamma-Nail, PFN-A and Targon-PF), inserted in different positions, differ mechanically. A proximal femur was reconstructed on the basis of clinical CT data as a surface model. Load application equivalent to the one-leg stance phase during gait was assumed, taking into account a limited number of active muscle forces. The four implants were inserted cranially and caudally into the bone structure and a model of a trochanteric fracture was created. Criteria with point ratings were introduced to quantify a favourable fracture healing situation. Finite element simulation showed clear differences between the different implants with regard to the distributions of stress and strain at the two fracture surfaces in the model and the von Mises stress in the implant itself. It was apparent for three implants under investigation that the caudal position generated better fracture healing conditions than the cranial position. Only the Targon PF demonstrated better fracture healing conditions in the cranial position. Evaluation based on the point rating system revealed that the caudal position was the ideal position for the PFN-A, Gamma-Nail and Gliding-Nail. The Targon-PF demonstrated some advantages over the other implants in the caudal position.