Incidence of pedicle breach following open and minimally invasive spinal instrumentation: A postoperative CT analysis of 513 pedicle screws applied under fluoroscopic guidance

Abstract

Background: Even though pedicle screw application is a common procedure, and in-spite of spine surgeons being proficient with the technique, mal-positioning of pedicle screws can still occur. We intend to determine by postoperative CT analysis, the incidence of pedicle screw breach in the thoracolumbar spine despite satisfactory intraoperative placement confirmed by fluoroscopy.

Materials and methods: Consecutive patients diagnosed with thoracolumbar fractures who underwent open or minimally invasive posterior stabilization under fluoroscopic guidance were retrospectively reviewed. Postoperative CT scans of patients were analysed to determine the incidence of pedicle breach despite satisfactory intraoperative placement, and also to determine the factors that can predict a breach during intraoperative assessment.

Results: A total of 61 patients with 513 thoracolumbar pedicle screws were available for analysis. Based on our postoperative CT assessment, 28 screws (5.5%; 18 thoracic screws; 10 lumbar screws) had breached the pedicle. There were 14 minor (<3 mm) and 14 major (≥3 mm) breaches. The minimally invasive technique had a significantly lower breach rate compared to open surgery (1.9% vs. 7.9%). By retrospectively analysing the intra-operative fluoroscopic images, we determined certain parameters that could predict a breach during surgery.

Conclusion: Pedicle breaches can still be present despite satisfactory placement of screws visualized intra-operatively. A medial breach is most likely when the length of the pedicle screw spans only up to 50% of the vertebral body as seen on the lateral view but the pedicle screw tip has already transgressed the midline as seen on an AP view. A lateral breach is likely when the tip of the pedicle screw is overlapped by the screw head or is only minimally visualized on an AP view.

Keywords: Fluoroscopy; Pedicle Screws; Spinal Fractures; Spine; Vertebral column.

Fig. 1

Post-operative axial CT image depicting a) Minor breach (<3 mm) and b) Major breach (≥3 mm).

Fig. 2

Postoperative CT image showing various directions of pedicle screw breach. a) Medial; b) Lateral; c) Superior.

Fig. 3

a) Intra-operative fluoroscopy image showing the left lumbar level 2 pedicle screw tip touching the midline on a PA view; b) Screw length spanning up to 50% of the vertebral body in the lateral view; c) Post-operative axial CT image showing a major medial breach of the pedicle.

Fig. 4

a) Intra-operative fluoroscopy image showing the tip of the left thoracic level 10 pedicle screw being overlapped by the screw head; b) Postoperative axial CT image showing a major lateral beach of the pedicle.