Accuracy of guide wire placement for femoral neck stabilization using 3D printed drill guides

Abstract

Background: The goal of stabilization of the femoral neck is to limit morbidity and mortality from fracture. Of three potential methods of fixation, (three percutaneous screws, the Synthes Femoral Neck System, and a dynamic hip screw), each requires guide wire positioning of the implant(s) in the femoral neck and head. Consistent and accurate positioning of these systems is paramount to reduce surgical times, stabilize fractures effectively, and reduce complications. To help expedite surgery and achieve ideal implant positioning in the geriatric population, we have developed and validated a surgical planning methodology using 3D modelling and printing technology.

Methods: Using image processing software, 3D surgical models were generated placing guide wires in a virtual model of an osteoporotic proximal femur sawbone. Three unique drill guides were created to achieve the optimal position for implant placement for each of the three different implant systems, and the guides were 3D printed. Subsequently, a trauma fellowship trained orthopedic surgeon used the 3D printed guides to position 2.8 mm diameter drill bit tipped guide wires into five osteoporotic sawbones for each of the three systems (fifteen sawbones total). Computed Tomography (CT) scans were then taken of each of the sawbones with the implants in place. 3D model renderings of the CT scans were created using image processing techniques and the displacement and angular deviations at guide wire entry to the optimal sawbone model were measured.

Results: Across all three percutaneous screw guide wires, the average displacement was 3.19 ± 0.12 mm and the average angular deviation was 4.10 ± 0.17^o. The Femoral Neck System guide wires had an average displacement of 1.59 ± 0.18 mm and average angular deviation of 2.81 ± 0.64^o. The Dynamic Hip Screw had an average displacement of 1.03 ± 0.19 mm and average angular deviation of 2.59 ± 0.39^o.

Conclusion: The use of custom 3D printed drill guides to assist with the positioning of guide wires proved to be accurate for each of the three types of surgical strategies. Guides which are used to place more than 1 guide wire may have lower positional accuracy, as the guide may shift during multiple wire insertions. We believe that personalized point of care drill guides provide an accurate intraoperative method for positioning implants into the femoral neck.

Keywords: 3D printing; Drill guide; Dynamic hip screw; Femoral neck system; In silico; Percutaneous screws; Prophylaxis.

Fig. 1

Three possible methods of femoral neck stabilization: percutaneous screws (left) [12] Synthes Femoral Neck System (FNS) (middle) [13], and dynamic hip screw (DHS) (right) [14]

Fig. 2

a Comparison of threaded tip guide wire (right) vs drill-bit tip guide wire (left). b Bending of thread-tip wire in the femur model during the second iteration of the drill guide with the ideal (gold) and experimental (red) paths traversed by the threaded tip guide wire shown

Fig. 3

3D overlay of expected model over CT-scan generated mask simulations. Green structures are the femur, gold are the ideal guide wires generated by the 3D modelling software, and the red structures are actual wires from 3D generated models based on overlayed CT scans (left to right: Percutaneous Screw Guide, FNS Guide, DHS Guide). Drill-bit tip guide wires were used in all scenarios

Fig. 4

Displacement of 3D model guide wire from physically drilled guide wire. Through ANOVA and t-test statistical analysis, we determined that PERC-S1, PERC-S2, and PERC-S3 were significantly higher in displacement compared with FNS and DHS

Fig. 5

Angle between 3D model guide wire and drilled guide wire at entry to sawbone. Through ANOVA and t-test statistical analysis, we determined that the guide for the DHS was significantly lower in angular deviation compared to the guide for the percutaneous screws