Femoral neck fracture after removal of the standard gamma interlocking nail: a cadaveric study to determine factors influencing the biomechanical properties of the proximal femur.

We retrospectively analyzed 1334 patients who were implanted standard gamma interlocking nails (SGN) to stabilize trochanteric femoral fractures over the years 1992-1998. Reoperation to remove the nails was performed in 37 patients, in 9 of them purely because of pain. Three out of these 9 patients with removed SGN suffered femoral neck fractures in the early postoperative course after having been mobilized to full weight-bearing capacity. This complication was not observed with other implant systems and, considering the notoriously high complication rate of femoral neck fractures, severely reduces the value of the SGN concept per se. These findings in combination with other known shortcomings of SGNs prompted us to conduct an experimental study on the fracture force of excavated femurs addressing the hypothesis that the specific design of the SGN is responsible for the occurrence of fatigue fractures of the femoral neck. Eighteen matched pairs of fresh human cadaveric proximal femurs, which were treated by insertion and removal of (i) SGNs or (ii) dynamic hip screws (DHS) or (iii) by excavation in the absence of an implant, were subjected to incremental loading cycles and compared to the untreated contralateral femurs. Overall, the fracture force was found to be significantly lower among the treated than among the untreated bones. However, the fracture force required after removal of the DHS system was still significantly higher than for SGN or excavation alone. In this way, our findings demonstrate that removing relatively big implants such as SGN can cause serious complications such as femoral neck fractures. We therefore recommend to leave this type of device in place even after fracture healing except in cases of deep and chronic infection.