[Manipulation of the step borer as cause of too shallow boring depth in the femoral neck with the gamma nail system].

The gamma nail step drill has been sold over 500,000 times worldwide. Depending on the construction used and the way it is handled, it can lead to a drill depth in the femoral head that is too shallow if the anatomic dimension of the femoral neck is rather long. Whenever the relationship between rotational speed and drive force is unfavorable, as it is by hand reaming, the triple-bladed drill only produces a triangular hole in the lateral cortical bone. Subsequently, it draws itself through this hole like a screw, without forming the hole into a complete circle. The drill shaft expands conically along its length preventing it from passing through the hole in the cortical bone at a depth of 90 mm. Until now, this phenomenon has been traced back to blunt drills or perhaps curved guide wires. Since the lag screws that have been used could not be screwed into undrilled cancellus bone, screws have sometimes been implanted at a sub-optimal length. The problem was noticed, however, and documented in experiments, and potential solutions were proposed.