Identification of optimal screws positions for internal fixation of femoral neck fracture: A simulation study based on femoral neck safe zone.

Abstract

Purpose: It is often difficult for surgeons to accurately implant the cannulated screws for fixing femoral neck fractures under C-arm fluoroscopy. Our simulation study attempts to help surgeons identify the optimal positions of screws on anteroposterior and lateral radiographs.

Methods: Softwares were used for 3-dimensional reconstruction and cross-sections construction of 60 femoral necks. The contours of all cross-sections along the axis of the femoral neck were stacked to identify a safe zone for screws placement. A simulation experiment was carried out with 3 circles of diameter 6.5 mm in the safe zone. The absolute and relative positions of every screw in the anteroposterior radiographs and lateral radiographs were measured.

Results: The morphologies of the safe zones for screws placement were anteriorly flat ellipses. The best dispersion was obtained with the inverted triangle shape in this zone: the inferior was positioned near the lower 1/10 on the anteroposterior view and near the anterior 3/5 on the lateral view. The anterosuperior and posteriosuperior screws were positioned near the upper 1/5 and 1/4, respectively, on the anteroposterior view, and near the anterior 1/10 and posterior 1/5, respectively, on the lateral view.

Conclusion: Simulated screws implantation demonstrates the distribution characteristics of screws in anteroposterior and lateral radiographs. This can help decrease the risk of perforation and iatrogenic injury.