Accuracy of freehand pedicle screws versus lateral mass screws in the subaxial cervical spine.

STUDY

DESIGN

Radiographic comparative study with prospectively collected data.

OBJECTIVES

To assess the accuracy of subaxial cervical pedicle screw (CPS) placement with freehand technique compared to lateral mass screws (LMS). The freehand cervical pedicle screw insertion technique guided by intraoperative lateral C-arm imaging has been shown to be both safe and effective. However, no study has performed a 100% audit of this technique using pre- and postoperative computed tomography (CT) to determine its true accuracy, as well as its reduction capability of CPS and LMS instrumentation.

METHODS

36 consecutive patients treated surgically by a single surgeon with the exclusive practice of LMS and subsequently CPS over 2 years were included. CT and EOS slot scanner were performed pre- and post-operatively to determine the extent of pedicle screw breach and to assess sagittal alignment reduction between CPS and LMS groups. Predictors of pedicle screw breaches were also identified using multivariate analysis.

RESULTS

CPS fixation was more effective in restoring global cervical angle and had superior reduction capability of cervical lordosis at the levels of C3/4 (5.00 ± 3.92, p = 0.008), C4/5 (6.63 ± 5.5, p = 0.010) and C5/6 (7.22 ± 6.19, p = 0.004) compared to LMS fixation. Pedicle screw breaches occurred most commonly at C4 (p = 0.003), and most commonly involved the lateral pedicle wall (p < 0.001). Placement of freehand pedicles screws on the concavity of rotated vertebrae was predictive of pedicle screw breach (OR 2.567, 95% CI 1.058-6.228, p = 0.037). There was no significant difference in the complication rate.

CONCLUSIONS

Although freehand cervical pedicle screw fixation is technically more demanding, it is generally safe and effective. However, the increased risk of screw breaches in the context of a rotated spine should be taken into consideration. Lateral mass screw fixation is advised if spinal realignment is not necessary.