THE NUMBER OF DISTAL LOCKING CROSS SCREWS REQUIRED FOR SUFFICIENT STABILISATION OF FEMORAL FRACTURES USING INTRAMEDULLARY NAILING SYSTEM

Abstract

Distal locking screw fixation, in intramedullary nail (IMN) fixation, remains the most technically demanding and problematic portion of the procedure being responsible for as much as one-half of the exposure of the surgeon‘s hands to radiation.

This biomechanical study was undertaken to compare the effectiveness of using one distal locking cross screw instead of two cross screws in femoral fractures fixed with IMN system.

A composite model made from a stainless steel IMN (12mm×1mm), was axially loaded to 2kN (3 times body weight) to reproduce the forces experienced during weight bearing, or until a maximum displacement of 1 mm was reached. The distal locking end of the intramedullary nail was attached to the centre of the cylinder, representing different parts of the distal femur, with a dedicated single or two rods (5mm diameter), made from stainless steel and titanium, to represent the distal locking cross screw.

In the 50mm×5mm cylinder (diaphyseal femur), the mean stability of fracture model using either single or two screws were similar. But in the 75mm×5mm and 100mm×3mm cylinders (metaphyseal and distal femur), the mean stability of the fracture model significantly decreased (50%) with single distal locking cross screw fixation when compared to two distal locking cross screws fixation. Similarly, stainless steel alloy provided more stability compared to titanium alloy cross screws in 75mm×5mm and 100mm×3mm cylinders. However there was no difference between the cross screws performance for 50mm×5mm when comparing both the alloys.

As shown in this experiment, femoral shaft (diaphyseal) fractures fixed with shorter IMN had the same stability for one or two distal locking cross screws. However fractures fixed with longer IMNs, to fix diaphyseo-metaphyseal junction fractures and extreme distal femoral fractures, single distal locking cross screw fixation provide poorer fracture stability compared to two distal locking cross screws fixation.