Novel MIS 3D NAV Single Step Pedicle Screw System (SSPSS): Workflow, Accuracy and Initial Clinical Experience

Abstract

Study design: Prospective case series.

Objective: SSPSS (single step pedicle screw system) was developed for minimally invasive spine surgery. We performed this study to report on safety, workflow, and our initial clinical experience with this novel technique.

Methods: The prospective study was conducted on patients who underwent pedicle screw fixation between October 2017 and April 2018 using a novel single step 3D navigated pedicle screw system for MIS. Outcome measurements were obtained from intraoperative computerized tomography. The images were evaluated to determine pedicle wall penetration. We used a grading system to assess the severity of the pedicle wall penetration. Breaches were classified as grade 1 (<2 mm), grade 2 (2-4 mm), or grade 3 (<4 mm),¹ and as cranial, caudal, medial, and lateral.

Results: Our study includes 135 screws in 24 patients. SSPSS eliminated K-wires and multiple steps traditionally necessary for MIS pedicle screw insertion. The median time per screw was 2.45 minutes. 3 screws were corrected intraoperatively. Pedicle wall penetration occurred in 14 screws (10%). Grade 1 breaches occurred in 4 screws (3%) and grade 2 breaches occurred in 10 screws (7%). Lateral breaches were observed more often than medial breaches. The accuracy rate in our study was 90% (Grade 0 breach). No revision surgeries were needed and no complications occurred.

Conclusions: Our study suggests that SSPSS could be a safe, accurate, and efficient tool. Our accuracy rate is comparable to that found in the literature.

Keywords: 3D-NAV; MIS; MISS; SSPSS; accuracy; minimally invasive; navigation; pedicle screw; screw placement; thoracolumbosacral pedicle screw system; time.

Figure 1.

A, Picture showing a SSPSS navigated screw inserter. B and C, The navigated stylet can be extended to a maximum of 5 mm beyond the tip of the screw.

Figure 2.

Drawing showing the OR setup with patient positioning, intraoperative CT, anesthesia, and navigation unit.

Figure 3.

Flow chart illustrating the typical steps of traditional pedicle screw insertion in comparison to SSPSS.

Figure 4.

A, Drawing showing the measuring technique of a medial and lateral breach. B, The breach measurement techniques in the axial, coronal and sagittal plane. Axial CT scan: breach grade 2 right T9 screw. Coronal CT scan: breach grade 2 right T10 screw. Sagittal CT scan: without any breach in the sagittal scan.

Figure 5.

Drawing illustrating the 4 type of breaches (cranial, caudal, medial, and lateral) on the left side. Medial and caudal breaches are more likely to impinge the exiting nerve root. The screw on the ride side is correctly placed.

Figure 6.

The approaches performed by the senior author in percent.

Figure 7.

A, Intraoperative CT scan of 66-year-old female patient with very slim L3 pedicle on the right side due to tumor growth. B, Postoperative X-ray showing correct placement of instrumentation.

Figure 8.

Navigated awl-tip tap penetrate hard sclerotic bone.

Figure 9.

A, Intraoperative revision of misplaces SSPSS pedicle screw: Intraoperative control CT scan showed laterally misplaces right L1 pedicle screw. Decision was made to revise screw. The image shows planning of correct screw trajectory. B, Correct medial trajectory has been planned (blue screw). The navigated awl-tip tap is used to prepare screw hole. C, The placement of correct SSPSS screw. D and E, Control CT showing correctly placed screw in L1. The misplaced lateral screw has been removed.