A Mechanical Study to Investigate the Free Play of 3 Different Nail Designs Used for Fixation of Subtrochanteric Femoral Fractures

Patients with subtrochanteric fractures treated by intramedullary fixation frequently report marked post-treatment pain associated with movement. The free distance, clearly visible in the lateral view X-rays, between the inner cortex of the medullary cavity and outer implant surface shows that anterior-posterior movement is possible when using a single bolt for stabilisation of the nail position. The movement behaviour of three standard nail types (Proximal Femur Nail / Synthes, Gamma Nail / Howmedica, Trochanteric Nail / Howmedica) was investigated by mechanical testing and a mathematical model. The results of mechanical testing closely matched the mathematical model. The nail tip length from the locking bolt axis to its distal end was crucial in determining nail movement. The Proximal femur nail (60 mm) shows the least movement (best performance), the Trochanteric nail (20 mm) shows the largest movements, the movement associated with the Gamma nail (40 mm) was between those of the two other nails. We believe that the Trochanteric nail results in too large a movement and is the least suitable implant for stabilisation of subtrochanteric femoral fractures.