Digital Assessment of the Implantation Angle of Proximal Femoral Nail Antirotation Helical Blade Using CT Three-dimensional Reconstruction.

Objectives: To facilitate simple and safe manipulation during proximal femoral nail antirotation (PFNA) operation, we studied the range of safe implantation angle of the helical blade of the PFNA system by using a digital-based three-dimensional reconstruction model of CT images.

Methods: Thirty-five healthy volunteers were recruited. Original multilayer helical CT scan data of the left femur were collected and imported into Mimics software. Anatomic features of the femur, including the safe implantation angle, anterior and posterior angle, were measured. Differences in each angle between male and female subjects were compared using Student's t test, and the determinants of each angle were analyzed by linear regression.

Results: The mean safe implantation angle was 30.09° ± 4.73°, the mean anterior angle was 15.82° ± 2.07°, and the mean posterior angle was 14.27° ± 3.19°. All the three angles were greater in males than females (P < 0.05). Neck shaft angle and the diameter of the femoral neck and head were linearly correlated with the safe implantation angle, the anterior and posterior angle, respectively. Femoral neck diameter was a significant determinant of the safe implantation angle and posterior angle, respectively. Moreover, femoral neck diameter and femoral head diameter were significant determinants of the anterior angle.

Conclusions: The study has introduced and delineated a novel parameter, the safe implantation angle, for FPNA surgery, which may help orthopedic surgeons in deciding a safe range of PFNA operation and improve the accuracy of PFNA helical blade implantation.