3D-Printed Screw-Rod Auxiliary System for Unstable Atlas Fractures: A Retrospective Analysis

Abstract

Objective: To develop and validate the efficacy of a 3D-printed screw-rod auxiliary system for unstable atlas fractures.

Methods: This research is a retrospective analysis, and a total of 14 patients, including 11 males and three females, were enrolled in our hospital from January 2017 to March 2019 who underwent occipitocervical fusion assisted by the 3D-printed screw-rod auxiliary system were reviewed, and with an average age of 53.21 ± 14.81 years, an average body mass index (BMI) of 23.61 ± 1.93 kg/m² . The operation time, blood loss and radiation times during the operation were recorded. The maximum fracture displacement values of pre- and post-operation were measured based on CT imaging. All screw grades were evaluated after surgery. The occipital-cervical 2 (O-C₂ ) angle and occipitocervical inclination (OCI) angle of pre-operation, post-operation and the last following-up were measured. The dysphagia scale 3 months after surgery and at the last follow-up, the Neck Disability Index (NDI) 3 months after surgery and at the last follow-up were assessed.

Results: All patients were completed the surgery successfully. There was no patient with severe dysphagia or aggravation of nerve injury. The follow-up was from 12 to 14 months, and with an average of 12.5 months. The average surgery time, average blood loss and average radiation times for the 14 patients were 112.14 min, 171.43 mL and 5.07 times, respectively. There was a significant difference in maximum fracture displacement between pre- and post-operation values (P < 0.05). A total of 56 screws were inserted in 14 patients, among them, three screws were classified as grade 1, and the other screws were classified as grade 0. There was a significant difference in the O-C₂ between pre-operation and 3 days after operation (P = 0.002); There was a significant difference in OCI angles between pre-operation and 3 days after operation (P < 0.05); there was no significant difference in the O-C₂ or OCI angle between 3 days after the operation and the last follow-up (P = 0.079; P = 0.201). The dysphagia scales of two patients were assessed as mild at 3 months after surgery, and the others were assessed as normal at 3 months after surgery. All patients' dysphagia scores returned to normal at the last follow-up. The average NDI and average neck Visual Analogue Scale (VAS) scores at the last follow-up were 2.53 and 8.41, respectively.

Conclusion: It can objectively restore the OCI to normal with few post-operative complications under the assistance of a screw-rod auxiliary system to perform occipitocervical fusion for unstable atlas fractures and atlantooccipital joint instability.

Keywords: 3D printing; Atlas fractures; Navigation templates; Occipitocervical fusion; Occipitocervical inclination angle.

Fig. 1

Model establishment and design of the screw‐rod auxiliary system. (A) Constructed model of the cervical occiput, lateral view and dorsal view; (B, D) the virtual occipital screws and axial pedicle screws were placed, lateral view and dorsal view; (C, E) the screw‐rod auxiliary system was designed based on the virtual model and screws, lateral view and dorsal view; (F) the screw‐rod auxiliary system was fixed; (G) structural drawing of the separated screw‐rod auxiliary system, including the reference model of the occipitocervical angle and the navigation templates of occipital screws and axial pedicle screws.

Fig. 2

Simulated surgery based on the 3D‐printed model. (A) Simulated screw placement assisted by the 3D‐printed navigation template; (B) the reference model of the occipitocervical angle was placed to verify its effectiveness.

Fig. 3

Surgical procedure. (A) Occipital screws were inserted, assisted by the navigation template; (B) axial pedicle screws were inserted, assisted by the navigation template; (C) the occipitocervical angle was adjusted according to the reference model of the occipitocervical angle; (D) according to the occipitocervical angle reference model, the connecting rod with an appropriate length was applied and then bent; (E) completed occipitocervical fusion.

Fig. 4

(A) Measurement of the OCI angle. Point 1 is the most caudal point on the midline occipital curve, point 2 is located in the posterosuperior aspect of the hard palate; Point 3 and point 4 are located in the vertebral body edge of C₄. The OCI angle is defined as the angle between McGregor's line and the vertebral body edge of C₄. (B) Measurement of the O‐C₂ angle. Points 5 and 6 are located in the inferior endplate of the axis. The O‐C₂ angle is defined as the angle between McGregor's line and the inferior endplate line of C₂.

Fig. 5

The imaging of patient NO. 10, male, diagnosed with a fracture of the lateral mass of C₁, type 4. (A) Axial CT of C₂; (B) 3D imaging of C₂; (C) Pre‐operation O‐C₂ angle of 6.71°; (D) postoperative atlas reduction; (E) C₂ pedicle screw with grade 0; (F) occipital screw with grade 0; (G) OCI angle of 79.56° and O‐C₂ angle of 14.12° immediately post‐operation; (H) OCI angle of 77.45° and O‐C₂ angle of 14.79° at the last follow‐up; (I) registration of post‐ and pre‐operation CT, screw placement and occipitocervical angle consistent with the preoperative design.