Elsevier

World Neurosurgery

Volume 115, July 2018, Pages e360-e365
World Neurosurgery

Original Article
Transmuscular Ultrasonography of the Placement of Thoracolumbar Pedicle Screws: A Cadaveric Study

https://doi.org/10.1016/j.wneu.2018.04.057Get rights and content

Highlights

  • A transpedicular screw protruding >2 mm can cause damage to nearby blood vessels, spinal cord, or nerve roots.

  • US can detect the pedicle screw protruding from the cortical bone of the vertebra.

  • Pins protruding >1 mm from the cortical bone of the vertebra can be detected by US.

  • The sensitivity of US for detecting perforation was greater in the lateral wall than in the anterior wall.

Background

Transpedicular screw fixation has a biomechanical advantage of improving fusion rates. In posterior thoracolumbar immobilization, a large number of screws cause perforation to the pedicle or vertebral body. Radiography and computed tomography (CT) have been used to minimize this complication. The ability of ultrasound (US) to detect the pedicle breach during placement of the screw is unknown. The aim of this study was to evaluate the sensitivity of US for detecting breaches.

Methods

A B-type transducer was used to scan 216 titanium pins inserted into cadaveric pedicles. Of the pins, 180 were intentionally misplaced: 90 pins breached the lateral wall of the pedicle, and 90 pins pierced the anterior wall of the vertebral body. US images were reviewed by 3 examiners blinded to both the procedure and the corresponding CT findings. The perforation length of pins was measured by 3 radiologists on CT images.

Results

CT data were divided into 2 groups. In group 1 (perforation length 0–2 mm), sensitivity of US for detecting lateral wall and anterior wall perforation was 80.95% and 76.42%, respectively; in group 2 (perforation length 2–4 mm), sensitivity was 94.79% and 91.93%. Overall sensitivity of US to detect lateral wall and anterior wall perforation was 89.63% and 86.30%, respectively. The sensitivity of US for detecting perforation was greater in the lateral wall than in the anterior wall. Sensitivity of US was greater in group 2 than group 1 for both lateral and anterior perforation.

Conclusions

US can be applied to detect perforation of ≤4 mm. Use of US may improve patient safety.

Introduction

Transpedicular screws have the advantage of enhancing joint stability and are widely used in thoracolumbar spine surgery. Complications often occur during the insertion of pedicle screws, with reported misplacement rates of 5%–41% at the lumbar level and 3%–55% at the thoracic level.1, 2, 3, 4 Specifically, accidental breaching of the cortical bone of the pedicle can lead to impingement on nearby blood vessels, spinal cord, or nerve roots. The rate of screw malposition has been the subject of much investigation. In the literature, variation of perforation rates depended on the technique used to determine the perforation. Some researchers indicated that postoperative computed tomography (CT) scan showed a higher rate of breach than plain radiography obtained during spine surgery. Brooks et al.,5 in a study of cadaveric human lumbar spine, found that plain radiographs correctly identified screw positions in 79.4% of specimens compared with CT, which correctly identified screw positions in 84.4% of specimens; the 2 techniques combined could correctly identify screw positions in 90%. However, radiation exposure and the dose delivered to surgeons and patients with combined imaging can be significant as well.

No article can give surgeons a guarantee of no perforation of the pedicle, and repeated use of CT or radiography during surgery to ensure the pedicle screws are correctly inserted into the pedicle is harmful to the patients and the medical staff in the operating room. Ultrasound (US) is radiation-free, is portable, and provides real-time imaging. Thus, US can be applied to prevent or detect potential pedicle screw breaching of the cortical bone before serious damage occurs. Moreover, a positive US scan gives the surgeon the opportunity to change a screw length while still in the operating room. The aim of the present study was to evaluate the sensitivity of US in detecting the perforation of titanium pins inserted through the thoracolumbar pedicle by identifying correlations between CT and US findings (i.e., a pin penetrating the cortical bone appears as a comet artifact, whereas a smooth curve represent the pin with no penetration of the cortical bone). To our knowledge, no studies to date have demonstrated whether US can detect the perforation of pedicle screws as well as its sensitivity.

Section snippets

Clinical Materials

Approval for this study was received from the Second Hospital of Wenzhou Medical College Research Ethics Committee. Six cadaveric thoracolumbar specimens (4 men and 2 women; mean age 48.33 ± 12.55 years; age range, 30–63 years) were used. Cadavers with obvious congenital conditions, trauma, neoplasia, deformities, or previous surgery as determined by radiographs were excluded. The thoracolumbar specimens were scanned by a 256-slice iCT scanner (Philips Medical Systems, Eindhoven, The

Results

All 216 pins inserted into the pedicles were scanned by CT. There were 90 pins perforating the lateral wall and 90 pins perforating the anterior wall. The mean lengths of perforation are shown in Table 1. Perforating pins 0–4 mm in size were detected by US (Figure 2). There were no false-positives findings in our study. However, false-negative findings occurred in 10.37% of lateral walls and 14.70% of anterior walls. This was mainly due to the length of the pins being too short to be detected

Discussion

Few studies have assessed the sensitivity of US in identifying a screw perforation to the pedicle or vertebral body. This is the first study to our knowledge to assess the sensitivity of transmuscular US for detecting a lateral perforation to the pedicle and a surface perforation to the vertebral body. In this study, as a new method to detect the accuracy of pedicle screw placement, we investigated the accuracy and sensitivity of US for detecting pin (instead of screw) placement.

Conclusions

US could reasonably be applied to detect perforation of ≤4 mm. The sensitivity of US for detecting lateral wall and anterior wall perforation in group 1 was 80.95% and 76.42%, respectively, and in group 2 was 94.79% and 91.93%. The overall sensitivity of US to detect lateral wall and anterior wall perforation was 86.30% and 89.63%, respectively. The sensitivity of US for detecting perforation was greater in the lateral wall than in the anterior wall. Also, perforation was more easily detected

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Conflict of interest statement: This work was supported by the National Natural Science Foundation of China (Grant No. 80215108).

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