The effect of screw insertion site and unused drill holes on stability and mode of failure after fixation of basicervical femoral neck fracture.

The intent of this biomechanical study is to characterize the effect of unused drill holes and cannulated screw insertion site on the fixation stability and mode of failure after fixation of basicervical femoral neck fractures. Fourteen matched pairs of embalmed human cadaver femora were sorted into four groups according to the level of screw insertion along the lateral cortex. Screws inserted at higher positions along the lateral cortex afforded higher rigidity, thus decreasing the amount of motion at the fracture site. In addition, higher insertion positions reduced the rate of permanent displacement, thus better maintaining reduction. Although all specimens failed at the neck, post-failure inspection revealed upward translation of the inferior screw head when inserted 20 mm below the lesser trochanter. Unused drill holes and guidepin holes had no observed affect on stability or failure mode.