The femoral neck safe zone: a radiographic simulation study to prevent cortical perforation with multiple screw insertion.

OBJECTIVES

To calculate the probability of iatrogenic perforation when screws seem to be safe on radiographs. A risk zone (RZ) gradient is mapped to help surgeons determine the suitable screw positions.

METHODS

Using computed tomography data and image-processing software, 24 proximal femurs were reconstructed. The anteroposterior, lateral, and axial views were then simulated, and the safe zone and RZ were identified and calculated on the axial graphs. Each original axial graph was zoomed and compiled to match a calculated average image, and a gradient figure of the RZs was visualized.

RESULTS

All 24 femoral necks had cortical perforation RZs. The average risk percentage was 23.7%. The individual risk per quadrant was as follows: anterosuperior 2.5%, posteroinferior 3.8%, posterosuperior 6.7%, and anteroinferior 10.7%. Four safe and cortex-touching zones and a safe region were identified in femoral neck for 6.5-mm screws.

CONCLUSIONS

Surgeons should be wary of screws that appear close to the cortex on both radiographs, especially in the posterosuperior and anteroinferior quadrants, because such screws probably perforate the cortex. To minimize iatrogenic perforation, screw position should be assessed using a gradient figure of the RZs.