Use of a Novel Computerized Drill for Pedicle Screw Insertion in the Thoracic and Lumbar Spine: A Cadaveric Study

INTRODUCTION

Roy-Camille is credited with popularizing pedicle screw fixation in North America with his presentation at the American Academy of Orthopaedic Surgeons in 1979 and his subsequent reports regarding the use of pedicle screw stabilization in the lumbar and thoracic spine.^1,2 This technique has since evolved, with pedicle screws being successfully used in cases of deformity correction, fractures, arthrodesis, and neoplasms.^3–7 Specifically, the use of pedicle screws in scoliosis has now become the accepted standard replacing previously described techniques for instrumented fusion, including the Harrington rod system, sublaminar hooks and wires, and hybrid instrumentation. This is due in part to improved curve correction with the use of pedicle screw constructs.^8,9 Proponents of this technique also cite the possibility of 3-column fixation with minimal risk to adjacent structures and the ability to achieve better coronal balance and derotation.¹⁰

However, this technique is not without complications. The most commonly reported complication is screw malposition, with reported rates ranging widely in the literature from 1.2% to 65%.^10–16 Major complications can also occur, including pulmonary, vascular, and catastrophic neurologic injury.^13,17–20 Various techniques have been described to minimize these complications and prevent aberrant pedicle screw placement. These include modified freehand techniques, computer-assisted navigation, and fluoroscopic guidance.

Potential drawbacks of these newer systems include the need for preoperative computed tomographic (CT) imaging, additional cost, and higher doses of radiation to the surgeon and patient.²¹ Additional technologies that are less reliant on fluoroscopy and do not require additional preoperative imaging include modified drill templates and computerized drill technology. One example is a novel handheld computerized drill system that utilizes integrated software to detect cortical density, thereby helping to improve drill accuracy. The IntelliSense Drill Technology (McGinley Orthopedics, Casper, Wyoming) consists of 2 functional modes: (1) freehand and (2) bicortical mode. In freehand mode, the drill functions similar to that of a standard handheld drill but detects when cortical perforation occurs and reports on the depth of the bone tunnel created. In bicortical mode, the drill software stops the drill's motor when it detects an impending cortical breach, thereby preventing perforation or plunging. Although its application in spine surgery has never been described, the computerized drill may be effective in optimizing accurate pedicle screw placement. The aim of this study is to assess the ability of this technology to identify and create accurate pedicle trajectories in the thoracic and lumbar spine in comparison to a standard freehand technique.

MATERIALS AND METHODS

RESULTS

Comparison of Accuracy

A total of 134 pedicle screws were placed, including 70 by surgeon 1 (35 freehand and 35 computerized drill) and 64 by surgeon 2 (32 freehand and 32 computerized drill). One screw placed by surgeon 2 using the computerized drill was excluded from analysis due to inadequate CT imaging. Overall, there were no significant differences in incidence of pedicle screw perforation between the freehand and computerized drill techniques on CT analysis before (19.4% versus 19.7%, P = .553) and after screw placement (22.4% versus 18.2%, P = .767) (Table 1 and Figure 1). Surgeon 1 had 7 lateral and no medial screw perforations using a freehand technique and 9 lateral and 2 medial breaches with the computerized drill (P = .492) (Figure 2). Surgeon 2 had 6 lateral and 2 medial breaches using a freehand technique and 2 lateral and no medial breaches with the computerized drill (P = .108) (Figure 3). For both surgeons, the majority of pedicle screw perforations occurred in the upper thoracic spine from T2 to T6 regardless of technique.

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Table 1

Comparison of pedicle violations between drill techniques on computed tomographic imaging.

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Figure 1

Pedicle violations using freehand and computerized drill techniques (A) before and (B) after screw placement.

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Figure 2

Accuracy of senior surgeon using the freehand and computerized drill techniques (A) before and (B) after screw placement.

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Figure 3

Accuracy of junior surgeon using the freehand and computerized drill techniques (A) before and (B) after screw placement.

DISCUSSION

With increasing use of pedicle screw constructs for a variety of spinal pathology, efforts have been focused on improving accuracy and reducing complications associated with aberrant screw placement. This is the first study assessing the use of a novel computerized handheld drill for pedicle screw placement in the thoracic and lumbar spine. Our overall screw malposition rates of 22.4% and 18.2% with a freehand and motorized drill technique, respectively, is comparable with other rates reported in the literature. While there is significant variability, a systematic review by Hicks et al¹³ noted screw malposition in 518 of 4570 screws (4.2%) on plain films placed in the thoracic spine for pediatric deformity. These lower rates are influenced by the method of assessment of screw perforation. When CT was used postoperatively to assess screw position, rates were significantly higher occurring at 15.7% per screw inserted. This is similar to those findings by Kwan et al,¹⁴ who noted a 20.3% perforation rate in 2020 pedicle screws used in adolescent idiopathic scoliosis (AIS) with a 0.1% rate of symptomatic screw perforation.

While there were a total of 12 perforations after screw placement using the computerized drill, only 1 (1.5%) medial perforation occurred. This may be due in part to overcompensation laterally in an effort to avoid medial perforation into the dural sheath. This is consistent with other series that note higher rates of lateral perforation compared to medial breach.^22–24 Clinically, neurologic deficits as the result of screw malposition are exceedingly rare but occur more commonly with medial perforation.^15,25,26 Dede et al²⁵ reported on their complications in 591 patients with AIS. They noted a 0.6% reoperation rate and 0.14% rate of symptomatic misplaced pedicle screws, all of which were medial.

Once the computerized drill technique had been optimized, including removal of a portion of the superior articular process, significant improvements in the perforation rates between the first and second specimens were noted for both surgeons. This included a significant reduction in overall perforation rates from 31.3% to 5.9% (P = .027). In addition, both had an approximately 50% decrease in time per pedicle screw in the second specimen using the computerized drill. The short learning curve associated with this device may be due to increased familiarity with the tactile feedback offered by the computerized drill as well as a better understanding of the unique surgical technique. These findings were suggestive of a short learning curve for both a senior-level and a junior-level attending surgeon, after which time accuracy and speed were similar to that of a standard freehand technique. This is in contrast to longer learning curves that have been associated with other methods of pedicle screw placement.^27,28

There were several limitations to this study. First, there was limited sample size consisting of 4 cadavers with 134 pedicle screws. If a larger sample was used, discrepancies in accuracy between the 2 techniques may have become more apparent, or the learning curve for the IntelliSense drill may have become more pronounced. Second, all cadavers used in this study were free of deformity, and therefore the use of this technique in AIS or other technically challenging cases warrants further examination.

CONCLUSIONS

After a brief initial learning curve, use of a novel automated computerized drill technology for placement of pedicle screws in the thoracic and lumbar spine is comparable to a freehand technique by both a senior-level and a junior-level attending surgeon in a cadaveric model. Further investigation is needed to identify the clinical role of this technology in spine surgery.