Investigation on the distal screw of a trochanteric intramedullary implant (Fi-nail) using a simplified finite element model

Numerous studies have been published concerning the characteristics and the behaviour of the intramedullary devices in the treatment of the intertrochanteric hip fractures. However, there is still room for further exploration and exploitation concerning the implant behaviour with respect to the parts of the implant assembly (nail, lag screw and distal screw). Towards this direction, the present paper aimed at revealing the effect of the position of the distal screw on the mechanical behaviour of the fixation device. For this purpose, a simplified model was developed and analysed with the finite element method. In total, five different locations for the distal screw were examined. In all cases, the bone was fixed at its distal end while the external load was applied at the tip of the lag screw towards the hip and in the form of orthonormal force components applied individually. The results of the FE analyses were illustrated in appropriately formed plots revealing the sensitivity of the behaviour of the implant with respect to the location of the distal screw. The main conclusion derived from the present investigation was that moving the distal screw apically decreases the stresses on the distal screw but increases the stresses on the lag screw. In turn, this indicates the existence of a location for the distal screw that compromises these two effects in an optimum way.