Optimal cervical screw insertion angle determined by means of computed tomography scans pre- and postoperatively

Background context: Cervical pedicle screw (CPS) insertion is technically demanding and carries a risk of serious neurovascular complications when screws perforate. To avoid such serious risks, we currently perform CPS insertion using a computed tomography (CT)-guided navigation system. However, there remains a low probability of screw perforation during CPS insertion that is affected by factors such as CPS insertion angle and anatomical pedicle transverse angle (PTA).

Purpose: This study aimed to understand the perforation tendencies of CPS insertion angles in relation to anatomical PTA.

Study design: This is a retrospective chart review.

Patient sample: The study enrolled 151 consecutive patients (95 men and 56 women, with a mean age of 64.6 years).

Outcome measures: Anatomical PTA and CPS insertion angles were evaluated by axial CT images.

Methods: The medical records of 151 consecutive patients who underwent CPS insertion using a CT-based navigation system were reviewed. We examined the relationships between PTA and CPS insertion angle on axial CT images according to vertebral level.

Results: The average preoperative PTA at each vertebral level was 32.1° for C2, 41.5° for C3, 41.0° for C4, 39.4° for C5, 34.4° for C6, and 27.3° for C7. Corresponding CT-determined pedicle screw insertion angles were 24.9°, 31.3°, 28.7°, 27.8°, 28.0°, and 26.0°, respectively. The CPS insertion angles at C2-C6 were significantly smaller than those for PTA (p<.01). In evaluations of angle thresholds from C3 to C5 that predicted a higher risk of perforation, the receiver operating characteristic curve analysis determined CPS insertion angles of <24.5° and >36.5° for the identification of lateral and medial perforations, respectively.

Conclusion: For CPS insertion into the C3-C5 pedicles using CT, there is an increased likelihood of lateral or medial perforation for insertion angles of <24.5° or >36.5°, respectively.