Navigated, percutaneous, three-step technique for lumbar and sacral screw placement: a novel, minimally invasive, and maximally safe strategy

Abstract

Background: Minimally invasive spine surgery is a field of active and intense research. Image-guided percutaneous pedicle screw (PPS) placement is a valid alternative to the standard free-hand technique, thanks to technological advancements that provide potential improvement in accuracy and safety. Herein, we describe the clinical results of a surgical technique exploiting integration of neuronavigation and intraoperative neurophysiological monitoring (IONM) for minimally invasive PPS.

Materials and methods: An intraoperative-computed tomography (CT)-based neuronavigation system was combined with IONM in a three-step technique for PPS. Clinical and radiological data were collected to evaluate the safety and efficacy of the procedure. The accuracy of PPS placement was classified according to the Gertzbein-Robbins scale.

Results: A total of 230 screws were placed in 49 patients. Only two screws were misplaced (0.8%); nevertheless, no clinical sign of radiculopathy was experienced by these patients. The majority of the screws (221, 96.1%) were classified as grade A according to Gertzbein-Robbins scale, seven screws were classified as grade B, one screw was classified as grade D, and one last screw was classified as grade E.

Conclusions: The proposed three-step, navigated, percutaneous procedure offers a safe and accurate alternative to traditional techniques for lumbar and sacral pedicle screw placement. Level of Evidence Level 3. Trial registration Not applicable.

Keywords: Lumbo–sacral instrumentation; Minimally invasive spine surgery; Navigated drill guide; Percutaneous navigated screw placement.

Fig. 1

Orange square: the tip of the drill is set to 2.5 cm depth from the entry point. Red square: the navigated guide with hand holder. Green square: the safe screw to set the depth of the drill tip. Yellow square: the low-speed/high-torque power drill

Fig. 2

A While screwing the pedicle, a red light (red circle) indicates that we are too close to nerve roots. B The green light (green circle) indicates no radicular conflicts. C The monitor with visual confirmation of the neuromonitoring

Fig. 3

A Calibration of the navigated drill guide; B calibration of the pedicle screw

Fig. 4

Step 1: Placement of the navigated drill guide on the appropriate entry point. A Red square: the assistant is holding the navigated drill guide in place while the surgeon inserts the low-speed/high-torque power drill to screw the pedicle. Yellow square: navigation reference clamp of the L5 spinous process. B Neuronavigation monitor confirming adequate screw positioning

Fig. 5

Step 2: drilling a hole with the navigated drill guide. The surgeon will handle the drill while the assistant will hold the navigated drill guide. A Yellow square: neuronavigated projection we follow with the low-speed/high-torque power drill. Red circle: the length of the drill tip that will enter the pedicle (as seen in B, green circle)

Fig. 6

Step 2.1: After the drill hole, a k-wire is placed following the same navigated guide direction. A The surgeon is placing the K-wire following the navigated drill guide. B The surgeon holds the K-wire while the assistant removes the navigated dill guide. C Following the K-wire with a navigated screw, the surgeon inserts a screw in the vertebra

Fig. 7

Step 3: placement of the pedicle screw. The surgeon will screw the pedicle and vertebral body while the assistant will handle the intraoperative monitoring and will remove the K-wire once the screw enters the vertebral body. A Yellow square: real time projection of the screw while it is entering the vertebra. Green circle: Klemmer forceps on the K-wire to be sure that it does not enter together with the screw. Red circle: intraoperative monitoring. B Orange circle: the neuromonitoring indicates a green light, meaning no radicular conflict exist