Accuracy of percutaneous pedicle screws for thoracic and lumbar spine fractures: a prospective trial

Purpose

The percutaneous insertion technique requires surgical skill and experience. However, there have been few clinical reports evaluating the accuracy of minimally invasive pedicle screw placement using the conventional fluoroscopy method. The purpose of this study was to evaluate the accuracy of percutaneous pedicle screw placement in the treatment of thoracic and lumbar spine fractures using two-plane conventional fluoroscopy.

Methods

A prospective clinical trial was performed. A total of 502 percutaneous pedicle screws in 111 patients, all inserted with the assistance of conventional fluoroscopy, were evaluated. The safety and accuracy of pedicle screw placement were based on the evaluation of postoperative axial 3-mm slice computed tomography scans using the scoring system described by Zdichavsky et al. [Eur J Trauma 30:234–240, 2004; Eur J Trauma 30:241–247, 2004].

Results

427/502 pedicle screws (85 %) were classified as good and excellent concerning the best possible screw length and 494/502 (98 %) were found to have good or excellent position. One screw had to be revised due to medial position with a neurological deficit.

Conclusions

This study demonstrates the feasibility of placing percutaneous posterior thoracolumbar pedicle screws with the assistance of conventional fluoroscopy. Minimally invasive transpedicular instrumentation is an accurate, reliable and safe method to treat a variety of spinal disorders, including thoracic and lumbar spine fractures.     

An anatomic consideration of C2 vertebrae artery groove variation for individual screw implantation in axis

Study design

Retrospective case series.

Objectives

To identify the variation of C2 vertebral artery groove (VAG) based on the thin-slice computed tomography (CT) scan and choose an individual screw placement method to decrease risk of malposition.

Background

C2 pedicle screws can be successful anchors for a variety of cervical disorders. However, variations of VAG may cause malposition and breach when C2 transpedicle screw was inserted. Recognizing the variations of vertebrae artery groove (VAG) in C2 and choosing an individual screw placement method (transpedicle or translaminar) may be helpful for avoiding violation and decreasing the operation risk in upper cervical surgery.

Methods

From January 2009 to December 2010, a total 45 patients with upper cervical disorders underwent 1–mm-thin-slice CT scans along the C2 pedicle direction to obtain the consecutive spectrum of C2 VAG were included in this study. The C2 VAG (types I, II, III, and IV) was subgrouped based on parameter e (the vertical distance from the apex of VAG to the upper facet joint surface) and parameter a (horizontal distance from the entrance of VAG to the vertebrae canal). Subsequently, individual strategy was used to avoid the VAG violation.

Results

The variations of C2 VAG in these 45 patients include the following: type I 53 (58.9 %), type II 16 (17.8 %) type III 13 (14.4 %), and type IV 8 (8.9 %). Transpedicle screws of C2 were used in types I, III, and IV VAGs (n = 74); translaminar screws were inserted in type II subgroup (n = 16). Postoperative CT scans showed that there were two pedicle screws violated into the artery groove, and no translaminar screw breached into the vertebrae canal. All the other screws were in right position. None of the 45 patients had severe complications such as spinal cord injury, dura tear, and infection.

Conclusion

Thin-slice CT scan along the C2 pedicle direction to analysis the variations of C2 VAG can help choose an individual screw placement method (transpedicle or translaminar) with minimal complication for C2 screw fixation.     

A CT-based study investigating the relationship between pedicle screw placement and stimulation threshold of compound muscle action potentials measured by intraoperative neurophysiological monitoring

Purpose

Neurophysiological monitoring aims to improve the safety of pedicle screw placement, but few quantitative studies assess specificity and sensitivity. In this study, screw placement within the pedicle is measured (post-op CT scan, horizontal and vertical distance from the screw edge to the surface of the pedicle) and correlated with intraoperative neurophysiological stimulation thresholds.

Methods

A single surgeon placed 68 thoracic and 136 lumbar screws in 30 consecutive patients during instrumented fusion under EMG control. The female to male ratio was 1.6 and the average age was 61.3 years (SD 17.7). Radiological measurements, blinded to stimulation threshold, were done on reformatted CT reconstructions using OsiriX software. A standard deviation of the screw position of 2.8 mm was determined from pilot measurements, and a 1 mm of screw—pedicle edge distance was considered as a difference of interest (standardised difference of 0.35) leading to a power of the study of 75 % (significance level 0.05).

Results

Correct placement and stimulation thresholds above 10 mA were found in 71 % of screws. Twenty-two percent of screws caused cortical breach, 80 % of these had stimulation thresholds above 10 mA (sensitivity 20 %, specificity 90 %). True prediction of correct position of the screw was more frequent for lumbar than for thoracic screws.

Conclusion

A screw stimulation threshold of >10 mA does not indicate correct pedicle screw placement. A hypothesised gradual decrease of screw stimulation thresholds was not observed as screw placement approaches the nerve root. Aside from a robust threshold of 2 mA indicating direct contact with nervous tissue, a secondary threshold appears to depend on patients’ pathology and surgical conditions.     

Freehand technique for C2 pedicle and pars screw placement: is it safe?

Background Context

During placement of C2 pedicle and pars screws, intraoperative fluoroscopy is used so that neurovascular complications can be avoided, and screws can be placed in the proper position. However, this method is time consuming and increases radiation exposure. Furthermore, it does not guarantee a completely safe and accurate screw placement.

Outcomes of posterior facet versus pedicle screw fixation of circumferential fusion: a cohort study

Purpose

To compare single-level circumferential spinal fusion using pedicle (n = 27) versus low-profile minimally invasive facet screw (n = 35) posterior instrumentation.

Method

A prospective two-arm cohort study with 5-year outcomes as follow-up was conducted. Assessment included back and leg pain, pain drawing, Oswestry disability index (ODI), pain medication usage, self-assessment of procedure success, and >1-year postoperative lumbar magnetic resonance imaging.

Results

Significantly less operative time, estimated blood loss and costs were incurred for the facet group. Clinical improvement was significant for both groups (p < 0.01 for all outcomes scales). Outcomes were significantly better for back pain and ODI for the facet relative to the pedicle group at follow-up periods >1 year (p < 0.05). Postoperative magnetic resonance imaging found that 20 % had progressive adjacent disc degeneration, and posterior muscle changes tended to be greater for the pedicle screw group.

Conclusion

One-level circumferential spinal fusion using facet screws proved superior to pedicle screw instrumentation.     

Pedicle screw diameter selection for safe insertion in the thoracic spine

Objective

Many thoracic pedicles are too small for the safe acceptance of a transpedicular screw. However, few studies have so far reported on the methods to select a proper pedicle screw size and to confirm the morphologic changes for such a small thoracic spine pedicle. The objective of this work was to determine the potential limits of a pedicle screw diameter for transpedicular screw placement in the thoracic spine.

Methods

T2–T9 vertebrae from eleven patients that underwent posterior thoracic instrumentation with the use of fluoroscopically assisted insertion method were analyzed. The outcome measures were the pedicle widths, the gap between the outer pedicle width and the selected pedicle screw diameter, and the penetration length of the pedicle screws using computed tomography. The screws were distributed into two groups according to the pedicle width and screw diameter, and the screw perforation rate of the two groups was compared. The relationships of the gap and the distance of the screw penetration were compared and investigated in regard to the pedicle screw diameter selection.

Results

A total of 16 screws demonstrated a smaller diameter than the inner pedicle widths, while 22 screws had a larger diameter than the inner pedicle widths. One screw (6.3%) perforated the pedicle cortex in the smaller screw group, and twelve screws (54.5%) perforated the pedicle cortex in the larger screw group (P?=?0.006). A linear regression analysis in the larger screw group revealed that when the gap was less than 0.5?mm, a risk of a pedicle wall violation was observed.

Conclusions

When the screws with a larger diameter than the inner pedicle width are selected, the screw perforation rate increases. Therefore, the size of the screw diameter must be at least 0.5?mm less than the outer pedicle width to ensure safe transpedicular screw placement.     

Biomechanical advantage of C1 pedicle screws over C1 lateral mass screws: a cadaveric study

Purpose

The established technique for posterior C1 screw placement is via the lateral mass. Use of C1 monocortical pedicle screws is an emerging technique which utilizes the bone of the posterior arch while avoiding the paravertebral venous plexus and the C2 nerve root. This study compared the relative biomechanical fixation strengths of C1 pedicle screws with C1 lateral mass screws.

Methods

Nine human C1 vertebrae were instrumented with one lateral mass screw and one pedicle screw. The specimens were subjected to sinusoidal, cyclic (0.5 Hz) fatigue loading. Peak compressive and tensile forces started from ±25 N and constantly increased by 0.05 N every cycle. Testing was stopped at 5 mm displacement. Cycles to failure, displacement, and initial and end stiffness were measured. Finally, CT scans were taken and the removal torque measured.

Results

The pedicle screw technique consistently and significantly outperformed the lateral mass technique in cycles to failure (1,083 ± 166 vs. 689 ± 240 cycles), initial stiffness (24.6 ± 3.9 vs. 19.9 ± 3.2 N/mm), end stiffness (16.6 ± 2.7 vs. 11.6 ± 3.6 N/mm) and removal torque (0.70 ± 0.78 vs. 0.13 ± 0.09 N m). Only 33 % of pedicle screws were loose after testing compared to 100 % of lateral mass screws.

Conclusions

C1 pedicle screws were able to withstand higher toggle forces than lateral mass screws while maintaining a higher stiffness throughout and after testing. From a biomechanical point of view, the clinical use of pedicle screws in C1 is a promising alternative to lateral mass screws.     

CT-navigation versus fluoroscopy-guided placement of pedicle screws at the thoracolumbar spine: single center experience of 4,500 screws

Purpose

Single center evaluation of the placement accuracy of thoracolumbar pedicle screws implanted either with fluoroscopy or under CT-navigation using 3D-reconstruction and intraoperative computed tomography control of the screw position. There is in fact a huge variation in the reported placement accuracy of pedicle screws, especially concerning the screw placement under conventional fluoroscopy most notably due to the lack of the definition of screw misplacement, combined with a potpourri of postinstrumentation evaluation methods.

Methods

The operation data of 1,006 patients operated on in our clinic between 1995 and 2005 is analyzed retrospectively. There were 2,422 screws placed with the help of CT-navigation compared to 2,002 screws placed under fluoroscopy. The postoperative computed tomography images were reviewed by a radiologist and an independent spine surgeon.

Results

In the lumbar spine, the placement accuracy was 96.4 % for CT-navigated screws and 93.9 % for pedicle screws placed under fluoroscopy, respectively. This difference in accuracy was statistically significant (Fishers Exact Test, p = 0.001). The difference in accuracy became more impressing in the thoracic spine, with a placement accuracy of 95.5 % in the CT-navigation group, compared to 79.0 % accuracy in the fluoroscopy group (p < 0.001).

Conclusion

This study underlines the relevance of CT-navigation-guided pedicle screw placement, especially when instrumentation of the middle and upper thoracic spine is carried out.     

Risk-benefit analysis of navigation techniques for vertebral transpedicular instrumentation: a prospective study

Background Context

Pedicle screws in spinal surgery have allowed greater biomechanical stability and higher fusion rates. However, malposition is very common and may cause neurologic, vascular, and visceral injuries and compromise mechanical stability.

How Does a Novel Monoplanar Pedicle Screw Perform Biomechanically Relative to Monoaxial and Polyaxial Designs?

Background

Minimally invasive spinal fusions frequently require placement of pedicle screws through small incisions with limited visualization. Polyaxial pedicle screws are favored due to the difficulty of rod insertion with fixed monoaxial screws. Recently, a novel monoplanar screw became available that is mobile in the coronal plane to ease rod insertion but fixed in the sagittal plane to eliminate head slippage during flexion loads; however, the strength of this screw has not been established relative to other available screw designs.

Questions/purposes

We compared the static and dynamic load to failure in polyaxial, monoaxial, and monoplanar pedicle screws.

Methods

Six different manufacturers’ screws (42 total) were tested in three categories (polyaxial, n = 4; monoaxial, n = 1; monopolar, n = 1) utilizing titanium rods. An additional test was performed using cobalt-chromium rods with the monopolar screws only. Screws were embedded into polyethylene blocks and rods were attached using the manufacturers’ specifications. Static and dynamic testing was performed. Dynamic testing began at 80% of static yield strength at 1 Hz for 50,000 cycles.

Results

In static testing, monoaxial and monoplanar screws sustained higher loads than all polyaxial screw designs (range, 37%–425% higher; p < 0.001). The polyaxial screws failed at the head-screw interface, while the monoaxial and monoplanar screws failed by rod breakage in the static test. The dynamic loads to failure were greater with the monoplanar and monoaxial screws than with the polyaxial screws (range, 35%–560% higher; p < 0.001). With dynamic testing, polyaxial screws failed via screw-head slippage between 40% and 95% of static yield strength, while failures in monoaxial and monoplanar screws resulted from either screw shaft or rod breakage.

Conclusions

All polyaxial screws failed at the screw-head interface in static and dynamic testing and at lower values than monoaxial/monoplanar screw designs. Monoplanar and monoaxial screws failed at forces well above expected in vivo values; this was not the case for most polyaxial screws.

Clinical Relevance

Polyaxial screw heads slip on the screw shank at lower values than monoaxial or monoplanar screws, and this results in angular change between the rod and pedicle screw, which could cause loss of segmental lordosis. The novel monoplanar screw used in this study may combine ease of rod placement with sagittal plane strength.     

Screw perforation features in 129 consecutive patients performed computer-guided cervical pedicle screw insertion

Study design

A cross-sectional study of the data retrospectively collected by chart review.

Objectives

This study aimed to clarify screw perforation features in 129 consecutive patients treated with computer-assisted cervical pedicle screw (CPS) insertion and to determine important considerations for computer-assisted CPS insertion.

Summary of background data

CPS fixation has been criticized for the potential risk of serious injury to neurovascular structures. To avoid such serious risks, computed tomography (CT)-based navigation has been used during CPS insertion, but screw perforation can occur even with the use of a navigation system.

Methods

The records of 129 consecutive patients who underwent cervical (C2–C7) pedicle screw insertion using a CT-based navigation system from September 1997 to August 2013 were reviewed. Postoperative CT images were used to evaluate the accuracy of screw placement. The screw insertion status was classified as grade 1 (no perforation), indicating that the screw was accurately inserted in pedicle; grade 2 (minor perforation), indicating perforation of less than 50 % of the screw diameter; and grade 3 (major perforation), indicating perforation of 50 % or more of the screw diameter. We analyzed the direction and rate of screw perforation according to the vertebral level.

Results

The rate of grade 3 pedicle screw perforations was 6.7 % (39/579), whereas the combined rate of grades 2 and 3 perforations was 20.0 % (116/579). No clinically significant complications, such as vertebral artery injury, spinal cord injury, or nerve root injury, were caused by the screw perforations. Of the screws showing grade 3 perforation, 30.8 % screws were medially perforated and 69.2 % screws were laterally perforated. Of the screws showing grades 2 and 3 perforation, 21.6 % screws were medially perforated and 78.4 % screws were laterally perforated. Furthermore, we evaluated screw perforation rates according to the vertebral level. Grade 3 pedicle screw perforation occurred in 6.1 % of C2 screws; 7.5 % of C3 screws; 13.0 % of C4 screws; 6.5 % of C5 screws; 3.2 % of C6 screws; and 4.0 % of C7 screws. Grades 2 and 3 pedicle screw perforations occurred in 12.1 % of C2 screws, 22.6 % of C3 screws, 31.5 % of C4 screws, 22.2 % of C5 screws, 14.4 % of C6 screws, and 12.1 % of C7 screws. C3–5 screw perforation rate was significantly higher than C6–7 (p = 0.0024).

Conclusions

Careful insertion of pedicle screws is necessary, especially at C3 to C5, even when using a CT-based navigation system. Pedicle screws tend to be laterally perforated.     

Percutaneous pedicle screw placement under single dimensional fluoroscopy with a designed pedicle finder—a technical note and case series

Background Context

Minimally invasive spine surgery has become increasingly popular in clinical practice, and it offers patients the potential benefits of reduced blood loss, wound pain, and infection risk, and it also diminishes the loss of working time and length of hospital stay. However, surgeons require more intraoperative fluoroscopy and ionizing radiation exposure during minimally invasive spine surgery for localization, especially for guidance in instrumentation placement. In addition, computer navigation is not accessible in some facility-limited institutions.

Lumbar pedicle screw placement: Using only AP plane imaging

Background:

Variations in the pedicle morphology and presence of spinal deformities can make pedicle screw placement challenging. Recently, computerized tomography (CT) guided screw placement has reportedly improved the surgical accuracy of pedicle screw insertion. However, it is time consuming and expensive. We combined single-plane fluoroscopy in AP projection alone with tactile guidance for placing pedicle screws more efficiently and accurately. This report presents our results with this technique.

Materials and Methods:

An Institutional Review Board (IRB) approved retrospective study was carried out on 308 patients who underwent lumbar spinal fusion with 1806 pedicle screws placed using fluoroscopy only in the AP plane. There were 182 patients with two-level fusion, 79 with single-level fusion, 26 with three-level fusion, and 21 with more than three-level fusions. The indications of surgery included spondylolisthesis, adult scoliosis, revision surgery, lumbar canal stenosis, and discogenic pain. Pedicle screws were inserted under fluoroscopic guidance in the AP plane alone with a final lateral image after completion of implant placement. Radiographs were performed postoperatively in all patients and CT scans were obtained on 78 patients with 588 screws.

Results:

Twenty nine (5%) cortical wall perforations were noted amongst the 588 screws that were evaluated with a CT scan and did not result in postoperative vascular or neural complications. Anterior cortical vertebral violation was noted in 14 patients, while in 9 patients the screws penetrated the lateral wall of the pedicle. The medial wall of the pedicle was encroached in six patients with no frank perforations.

Conclusion:

Placement of pedicle screws under fluoroscopic guidance using AP plane imaging alone with tactile guidance is safe, fast, and reliable. However, a good understanding of the radiographic landmarks is a prerequisite.     

Computer tomography assessment of pedicle screw placement in thoracic spine: comparison between free hand and a generic 3D-based navigation techniques

Introduction

Although pedicle screw fixation is a well-established technique for the lumbar spine, screw placement in the thoracic spine is more challenging because of the smaller pedicle size and more complex 3D anatomy. The intraoperative use of image guidance devices may allow surgeons a safer, more accurate method for placing thoracic pedicle screws while limiting radiation exposure. This generic 3D imaging technique is a new generation intraoperative CT imaging system designed without compromise to address the needs of a modern OR.

Aim

The aim of our study was to check the accuracy of this generic 3D navigated pedicle screw implants in comparison to free hand technique described by Roy-Camille at the thoracic spine using CT scans.

Material and methods

The material of this study was divided into two groups: free hand group (group I) (18 patients; 108 screws) and 3D group (27 patients; 100 screws). The patients were operated upon from January 2009 to March 2010. Screw implantation was performed during internal fixation for fractures, tumors, and spondylodiscitis of the thoracic spine as well as for degenerative lumbar scoliosis.

Results

The accuracy rate in our work was 89.8 % in the free hand group compared to 98 % in the generic 3D navigated group.

Conclusion

In conclusion, 3D navigation-assisted pedicle screw placement is superior to free hand technique in the thoracic spine.     

A customized modular reference array clamp for navigated spine surgery

Introduction

The current authors have developed a modular system of reference array fixation which is tailored specifically to the spinal level being operated upon. They believe that this system may further increase the precision and accuracy of pedicle screw placement.

Materials and methods

Two formalin-fixed whole body cadavers were used for this study. For cervical spine evaluation of the reference clamp, four odontoid screws (two per cadaver) for C1/C2-fusion and four lateral mass screws (two per cadaver) were implanted. Following navigated screw placement with 2D and 3D fluoroscopic verification, insertion of two lateral mass screws was performed. In the same way, lumbar and thoracic pedicle screws were implanted. Two pedicle screws were placed at two levels of the lumbar and two levels of the thoracic areas giving an overall of 16 screws implanted (8 cervical, 4 thoracic, and 4 lumbar). Postoperative evaluation involved comparison of postoperative 3D scans and preoperative planning images. A simple classification system was used for evaluation of any deviation from the planned trajectory.

Results

All pedicle screw placements were performed as planned without any technical problems. The reference array clamps remained in position at all the spinal levels at which they were employed with no loosening or displacement and no secondary damage to any of the spinous processes. Manual manipulation was performed but no displacement or slippage was observed. Image artefacts caused by the reference clamp were not significant as to obscure the area of interest. Both imaging modalities (Iso-C 3D and Vario 3D) generated sufficiently precise 3D images. There was no substantial difference in quality when those two systems were compared.

Discussion

Insufficient fixation of the reference clamp can lead to failure and complications. To date, no reference clamp systems have been developed specifically for navigated spine surgery.

Conclusions

Stable reference array fixation is a critical step in navigated surgery. To date, the same reference clamps have been applied to the spinal anatomy as have been developed originally for the appendicular skeleton. The current investigators have developed a novel modular clamp and have demonstrated its efficacy in a cadaveric model.     

Pedicle screw placement accuracy in thoracic and lumbar spinal surgery with a patient-matched targeting guide: a cadaveric study

Purpose

Pedicle screw placement is an increasingly common procedure for the correction of spine degenerative disease, deformity and trauma. However, screw placement is demanding, with complications resulting from inaccurate screw placement. While several different techniques have been developed to improve accuracy, they all have their limitations.

Methods

We examined the MySpine (Medacta International SA, Castel San Pietro, CH) patient-matched pedicle targeting guide in three cadaveric spine specimens operated on by three surgeons. A three-dimensional (3D) preoperative plan was constructed from spinal computed tomography scans, from which individualised guides were developed for the placement of Medacta Unconstrained Screw Technology pedicle screws. Following screw placement, the 3D positioning of the screws was compared to the preoperative plan against a series of pre-defined criteria.

Results

Of 46 inserted screws eligible for assessment, 91.3 % were fully inside the pedicle. There were no cases of Grade B (2–4 mm) or C (>4 mm) pedicle perforation. The mean deviation between the planned and actual screw position at the midpoint of the pedicle was 0.70 mm, the mean horizontal deviation was 0.60 mm and the mean vertical deviation was 0.77 mm. The mean angular deviation in the sagittal plane was 1.74°, versus 1.32° in the transverse plane. The mean deviation in screw depth was 1.55 mm. On all measures, the accuracy of screw placement was within the predefined criteria.

Conclusions

Our cadaver study indicates that pedicle screw placement with the system is accurate and should be investigated in larger in vitro and in vivo studies.

     

Spinal intraoperative three-dimensional navigation: correlation between clinical and absolute engineering accuracy

Background Context

Spinal intraoperative computer-assisted navigation (CAN) may guide pedicle screw placement. Computer-assisted navigation techniques have been reported to reduce pedicle screw breach rates across all spinal levels. However, definitions of screw breach vary widely across studies, if reported at all. The absolute quantitative error of spinal navigation systems is theoretically a more precise and generalizable metric of navigation accuracy. It has also been computed variably and reported in less than a quarter of clinical studies of CAN-guided pedicle screw accuracy.