Accuracy of Percutaneous Lumbosacral Pedicle Screw Placement Using the Oblique Fluoroscopic View Based on Computed Tomography Evaluations

Abstract

Study design: Retrospective.

Purpose: This study aims to investigate the accuracy of the oblique fluoroscopic view, based on preoperative computed tomography (CT) images for accurate placement of lumbosacral percutaneous pedicle screws (PPS).

Overview of literature: Although PPS misplacement has been reported as one of the main complications in minimally invasive spine surgery, there is no comparative data on the misplacement rate among different fluoroscopic techniques, or comparing such techniques with open procedures.

Methods: We retrospectively selected 230 consecutive patients who underwent posterior spinal fusion with a pedicle screw construct for degenerative lumbar disease, and divided them into 3 groups, those who had undergone: minimally invasive percutaneous procedure using biplane (lateral and anterior-posterior views using a single C-arm) fluoroscope views (group M-1), minimally invasive percutaneous procedure using the oblique fluoroscopic view based on preoperative CT (group M-2), and conventional open procedure using a lateral fluoroscopic view (group O: controls). The relative position of the screw to the pedicle was graded for the pedicle breach as no breach, <2 mm, 2-4 mm, or >4 mm. Inaccuracy was calculated and assessed according to the spinal level, direction and neurological deficit. Inter-group radiation exposure was estimated using fluoroscopy time.

Results: Inaccuracy involved an incline toward L5, causing medial or lateral perforation of pedicles in group M-1, but it was distributed relatively equally throughout multiple levels in groups M-2 and controls. The mean fluoroscopy time/case ranged from 1.6 to 3.9 minutes.

Conclusions: Minimally invasive lumbosacral PPS placement using the conventional fluoroscopic technique carries an increased risk of inaccurate screw placement and resultant neurological deficits, compared with that of the open procedure. Inaccuracy tended to be distributed between medial and lateral perforations of the L5 pedicle, as a result of pedicle morphology and the PPS pathway. Oblique fluoroscopic views, based on CT measurement, may allow accurate PPS insertion with a shorter fluoroscopy time.

Keywords: Accuracy; Minimally invasive; Oblique view; Pedicle screw fixation; Percutaneous.

Fig. 1. Obliquity of fluoroscopy was chosen on the basis of preoperative computed tomography (CT) (group M-2). (A) Insertion angle (α) and screw length (β) were measured by subtracting the angle between the line passing through the centre of the pedicle before surgery, using axial CTs. (B) Obliquity of fluoroscopy was adjusted to be equal to the measured insertion angle (α). (C) Radiographs obtained in the patients who underwent L3–4 minimally invasive surgery-transpedicular lumbar interbody fusion. The true pedicle axis and the cephalad facet complex can be clearly seen, and the accurate insertion of pedicle screws was possible.

Fig. 2. The relative positions of the screws to the pedicles were assessed and classified using axial and reconstructed sagittal or coronal computed tomography as: A, completely within the pedicle; B, pedicle wall breach <2 mm; C, pedicle wall breach of 2–4 mm; or D, pedicle wall breach >4 mm.

Fig. 3. (A) Computed tomography obtained for a 58-year-old male patient who underwent L4–5 minimally invasive surgery-transpedicular lumbar interbody fusion using anterior-posterior and lateral fluoroscopic views (group M-1). Postoperatively medial grade D malposition of left L5 pedicle screw was revealed from his left L5 radiculopathy. (B) This screw was re-inserted in an additional surgery.