Intraosseous ultrasonography to determine the accuracy of drill hole positioning prior to the placement of pedicle screws: an experimental study

Feasibility of Endoscopic Inspection of Pedicle Wall Integrity in a Live Surgery Model

Background

Perforations of the pedicle wall during cannulation can occur with experienced surgeons. Direct endoscopic visualization has not been used to inspect pedicles previously due to bone bleeding obscuring the camera visualization. The hypothesis of this study was that endoscopic visualization of pedicle wall integrity was technically feasible and would enable identification of clinically significant pedicle breaches.

Methods

A live porcine model was used. Eight lumbar pedicles were cannulated. Clinically significant breaches were created. An endoscope was introduced and was used to inspect the pedicles.

Results

All lumbar pedicles were endoscopically visible at a systolic pressure of 100 mm Hg. Clinically relevant anatomic structures and iatrogenic pathology, such as medial, lateral, and anterior breaches, were identified. There were no untoward events resulting from endoscopic inspection of the pedicle endosteal canal.

Conclusions

Endoscopic inspection of lumbar pedicles was safe and effective. The findings on endoscopic inspection corresponded with the ball-tip probe palpation techniques. Additional techniques, such as selection between 2 tracts, was possible with the endoscopic technique.

Guided pedicle screw insertion: techniques and training

BACKGROUND CONTEXT

In spinal fusion surgery, the accuracy with which screws are inserted in the pedicle has a direct effect on the surgical outcome. Accurate placement generally involves considerable judgmental skills that have been developed through a lengthy training process. Because the impact of misaligning one or more pedicle screws can directly affect patient safety, a number of navigational and trajectory verification approaches have been described and evaluated in the literature to provide some degree of guidance to the surgeon.

PURPOSE

To provide a concise review to justify the need and explore the current state of developing navigational or trajectory verification techniques for ensuring proper pedicle screw insertion along with simulation methods for better educating the surgical trainees.

STUDY DESIGN

Recent literature review.

METHODS

To justify the need to develop new methods for optimizing pedicle screw paths, we first reviewed some of the recent publications relating to the statistical outcomes for different types of navigation along with the conventional freehand (unassisted) screw insertion. Second, because of the importance of providing improved training in the skill of accurate screw insertion, the training aspects of relevant techniques are considered. The third part is devoted to the description of specific navigational assist methods or trajectory verification techniques and these include computer-assisted navigation, three-dimensional simulations, and also electric impedance and optical and ultrasonic image-guided methods.

CONCLUSIONS

This article presents an overview of the need and the current status of the guidance methods available for improving the surgical outcomes in spinal fusion procedures. It also describes educational aids that have the potential for reducing the training process.

Ultrasonic measurement of bone thickness for spinal surgery

We measured the thickness of the transverse structures associated with the bovine coccygeal transverse processes (bone specimen) by using ultrasonic waves and examined the reliability of this measurement for use in spinal surgery. We first measured the velocity of ultrasonic waves propagating in the spinous process. We then made a hole in the transverse process with an air drill and placed an ultrasonic transducer with a center frequency of 10 MHz in the hole. The time of reflection of the ultrasonic wave from the underside of the transverse process was detected to estimate the remaining bone thickness. The thickness estimated by using ultrasound was compared with the thickness measured by microscopic examination. We could detect reflection waves from the underside of the transverse process in 91.7% of cases (i.e., 22 of 24 measurements using 6 bones from 3 cows). The thickness of the transverse processes in which we detected the waves varied from 0.24 to 6.8 mm. The 95% limit of agreement between ultrasonic and histological measurement was 0.71 mm. Pearson's correlation coefficient showed a strong and positive relationship between the two measurements (r = 0.97, n = 22, P <0.0001).

On ultrasound imaging for guided screw insertion in spinal fusion surgery

Spinal fusion surgery generally involves the insertion of screws in the pedicle, a three-dimensional (3-D) process that requires great skill if serious consequences are to be avoided. This article describes an image guidance technique based on generating B‑mode images from within a small bore hole in the pedicle's trabecular bone. The purpose is to determine the viability and safety of the hole placement for subsequent insertion of the screw. Toward this end, this article endeavours to understand the factors that govern B-mode image quality. Specifically, the results of numerical simulations on the effects of transducer frequency and bone volume on image quality are presented along with demonstrations of B-mode image formation obtained in vitro on human pedicles using a 3.2 MHz probe. The results of the numerical simulations suggest that high frequency and high bone volume generally reduce the image quality. The in vitro experiments showed that the trabecular and cortical bone can be detected in the B-mode images.