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

Abstract

Background ContextCervical 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). PurposeThis study aimed to understand the perforation tendencies of CPS insertion angles in relation to anatomical PTA. Study DesignThis is a retrospective chart review. Patient SampleThe study enrolled 151 consecutive patients (95 men and 56 women, with a mean age of 64.6 years). Outcome MeasuresAnatomical PTA and CPS insertion angles were evaluated by axial CT images. MethodsThe 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. ResultsThe 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. ConclusionFor 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.