Biomechanical considerations in intramedullary nailing of femoral shaft fractures

Abstract

Recent laboratory investigations have led to clinically useful information about intramedullary nailing. These studies have identified several mechanical variables that are important during nail insertion. In particular, a high degree of bending stiffness of the nail combined with an anterior position of the starting hole can cause the femur to burst. Other studies of nail-bone constructs have demonstrated that a femur with a subtrochanteric fracture fixed with a slotted interlocking nail is about 2% as stiff as an intact femur in torsion and about 80% as stiff in bending. Using a closed-section, unslotted nail increases the torsional stiffness to 50% of the stiffness of an intact femur in torsion. Locking rods have been found to support 300% to 400% of a typical person's body weight in axial loading and to fail under load by bending, cracking along the axis of the proximal screw hole, or protruding with the screw through the greater trochanter.