Complications associated with pedicle screws

Robot-assisted percutaneous screw placement combined with pelvic internal fixator for minimally invasive treatment of unstable pelvic ring fractures

Purpose

The purpose of this study was to investigate the safety and efficacy of the combination of robot‐assisted percutaneous screw placement and pelvic internal fixator (INFIX) for minimally invasive treatment of unstable anterior and posterior pelvic ring injuries.

Methods

From September 2016 to June 2017, twenty‐four patients with unstable anterior and posterior pelvic ring injuries were treated with TiRobot‐assisted percutaneous sacroiliac cannulated screw fixation on the posterior pelvic ring combined with robot‐assisted pedicle screw placement in the anterior inferior iliac spine along with INFIX on the anterior pelvic ring. The results of the treatment, including surgery duration, fluoroscopy frequency, total drilling, amount of blood loss, fracture healing time, and postoperative functional outcomes were recorded and compared with another 21 similar patients who underwent conventional manual positioning surgery.

Results

The TiRobot group incurred significantly shorter duration of surgery; less fluoroscopy frequency, intraoperative bleeding, and total drilling than in the conventional group (P < 0.05). Postoperative radiological follow‐up showed that all screws were in the safe area and no screw penetrated the cortex. All wounds healed by primary intention and no iatrogenic damage to the blood vessels, nerves, and organs occurred. Patients showed good tolerance to INFIX and reported no discomfort. The mean follow‐up duration was 5.4 months; the fractures were all healed, no loss of reduction occurred, and the mean Majeed score at the last follow‐up did not show any difference.

Conclusion

TiRobot‐assisted percutaneous screw placement combined with INFIX for the anterior and posterior pelvic ring injuries is accurate, safe, less invasive, and shows satisfactory efficacy, suggesting it is a better method for minimally invasive treatment of unstable pelvic ring fractures.

Virtual surgery simulation versus traditional approaches in training of residents in cervical pedicle screw placement

INTRODUCTION

The cervical screw placement is one of the most difficult procedures in spine surgery, which often needs a long period of repeated practices and could cause screw placement-related complications. We performed this cadaver study to investigate the effectiveness of virtual surgical training system (VSTS) on cervical pedicle screw instrumentation for residents.

MATERIALS AND METHODS

A total of ten novice residents were randomly assigned to two groups: the simulation training (ST) group (n = 5) and control group (n = 5). The ST group received a surgical training of cervical pedicle screw placement on VSTS and the control group was given an introductory teaching session before cadaver test. Ten fresh adult spine specimens including 6 males and 4 females were collected, and were randomly allocated to the two groups. The bilateral C3-C6 pedicle screw instrumentation was performed in the specimens of the two groups, respectively. After instrumentation, screw positions of the two groups were evaluated by image examinations.

RESULTS

There was significantly statistical difference in screw penetration rates between the ST (10%) and control group (62.5%, P < 0.05). The acceptable rates of screws were 100 and 50% in the ST and control groups with significant difference between each other (P < 0.05). In addition, the average screw penetration distance in the ST group (1.12 ± 0.47 mm) was significantly lower than the control group (2.08 ± 0.39 mm, P < 0.05).

CONCLUSIONS

This study demonstrated that the VSTS as an advanced training tool exhibited promising effects on improving performance of novice residents in cervical pedicle screw placement compared with the traditional teaching methods.

Increased Radiation but No Benefits in Pedicle Screw Accuracy With Navigation versus a Freehand Technique in Scoliosis Surgery

BACKGROUND

The clinical value of pedicle screws in spinal deformity surgery is well known; however, screw insertion is demanding and sometimes associated with complications. Navigation systems based on intraoperatively obtained three-dimensional (3-D) images were developed to minimize pedicle screw misplacements. However, there is a lack of data confirming superiority of navigation above other techniques. There are also concerns regarding increased radiation used during the procedure.

QUESTIONS/PURPOSES

The purposes of this study were (1) to compare accuracy of the two methods of pedicle screws placement: intraoperative 3-D image navigation versus a freehand technique in patients with idiopathic scoliosis; and (2) to assess the radiation dose received by patients with both methods.

METHODS

Between 2014 and 2016, 49 patients underwent posterior spinal fusion with all pedicle screw constructs for idiopathic scoliosis performed by two surgeons. The study design involved alternating the use of the freehand technique and navigation to position pedicle screws in consecutive patients, forming groups of 27 patients with 451 navigated screws and 22 patients with 384 screws positioned freehand. The two groups did not differ in age, sex, or magnitude of deformity. Two observers not involved in the treatment evaluated the position of the screws. The pedicle breach was assessed on intraoperatively obtained 3-D O-arm® scans according to a grading system: Grade 0 = no pedicle wall violation; Grade 1 = perforation ≤ 2 mm; Grade 2 = 2 to 4 mm; and Grade 3 = perforation > 4 mm. Grades 0 and 1 were considered properly positioned and Grades 2 and 3 represented malposition.

RESULTS

In terms of accuracy, we found no differences, with the numbers available, between the freehand and navigated groups in terms of the proportion of screws that were properly positioned (96% freehand and 96% in the navigation group, respectively; p = 0.518). Grade 3 pedicle screws were observed only in the freehand group and were all located in the upper thoracic spine. Patients undergoing navigated pedicle screw placement received a greater mean radiation dose than those whose screws were placed freehand (1071 ± 447 mGy-cm versus 391 ± 53 mGy-cm; mean difference, 680 mGy-cm; 95% confidence interval, 217-2053 mGy-cm; p < 0.001).

CONCLUSIONS

In patients with moderate idiopathic scoliosis undergoing primary surgery, we did not observe benefits of pedicle screw placement with CT-based navigation, but the patients experienced greater exposure to radiation.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Comparative Prospective Study Reporting Intraoperative Parameters, Pedicle Screw Perforation, and Radiation Exposure in Navigation-Guided versus Non-navigated Fluoroscopy-Assisted Minimal Invasive Transforaminal Lumbar Interbody Fusion

Study Design

Prospective cohort study.

Purpose

To compare intraoperative parameters, radiation exposure, and pedicle screw perforation rate in navigation-guided versus non-navigated fluoroscopy-assisted minimal invasive transforaminal lumbar interbody fusion (MIS TLIF).

Overview of Literature

The poor reliability of fluoroscopy-guided instrumentation and growing concerns about radiation exposure have led to the development of navigation-guided instrumentation techniques in MIS TLIF. The literature evaluating the efficacy of navigation-guided MIS TLIF is scant.

Methods

Eighty-seven patients underwent navigation- or fluoroscopy-guided MIS TLIF for symptomatic lumbar/lumbosacral spondylolisthesis. Demographics, intraoperative parameters (surgical time, blood loss), and radiation exposure (sec/mGy/Gy.cm² noted from C-arm for comparison only) were recorded. Computed tomography was performed in patients in the navigation and non-navigation groups at postoperative 12 months and reviewed by an independent observer to assess the accuracy of screw placement, perforation incidence, location, grade (Mirza), and critical versus non-critical neurological implications.

Results

Twenty-seven patients (male/female, 11/16; L4–L5/L5–S1, 9/18) were operated with navigation-guided MIS TLIF, whereas 60 (male/female, 25/35; L4–L5/L5–S1, 26/34) with conventional fluoroscopy-guided MIS TILF. The use of navigation resulted in reduced fluoroscopy usage (dose area product, 0.47 Gy.cm² versus 2.93 Gy.cm²), radiation exposure (1.68 mGy versus 10.97 mGy), and fluoroscopy time (46.5 seconds versus 119.08 seconds), with p-values of <0.001. Furthermore, 96.29% (104/108) of pedicle screws in the navigation group were accurately placed (grade 0) (4 breaches, all grade I) compared with 91.67% (220/240) in the non-navigation group (20 breaches, 16 grade I+4 grade II; p=0.114). None of the breaches resulted in a corresponding neurological deficit or required revision.

Conclusions

Navigation guidance in MIS TLIF reduced radiation exposure, but the perforation status was not statistically different than that for the fluoroscopy-based technique. Thus, navigation in nondeformity cases is useful for significantly reducing the radiation exposure, but its ability to reduce pedicle screw perforation in nondeformity cases remains to be proven.

Highlights from the First Annual Spinal Navigation, Emerging Technologies and Systems Integration Meeting

This paper provides a detailed report of the "First Annual Spinal Navigation, Emerging Technologies and Systems Integration" meeting held December 3, 2016 at the Seattle Science Foundation.

Sagittal orientation and uniform entry for thoracic pedicle screw placement with free-hand technique: A retrospective study on 382 pedicle screws

BACKGROUND

One of the most important factors in obtaining a successful outcome in spinal surgery is appropriate placement of the pedicle screw. A number of different techniques are used to achieve successful pedicle screw placement. The free-hand technique has the advantage of no requirement for radiation exposure, but its success is highly dependent on surgeon experience. Here, we describe our entry point and perioperative sagittal orientation method, and evaluate postoperative sagittal alignment of pedicle screws with the free-hand pedicle screw placement technique.

MATERIALS AND METHODS

Eighty-two patients undergoing spinal surgery between 2015 and 2016 were included in this study. Pedicle screw placement was evaluated retrospectively on postoperative anterior-posterior (A-P) and lateral load-bearing radiographs of the entire spinal column. The vertebral body was divided into five areas in the lateral plane. Sagittal orientation of the pedicle screws on lateral radiographs was evaluated by two spine surgeons with 3 years of experience and one radiologist experienced in musculoskeletal radiology, with each observer evaluating the image twice according to a 1-month interval.

RESULTS

A total of 382 pedicle screws were evaluated. There was no statistically significant difference between the first and second measurements, performed by individual observers, and there was good concordance among the three observers.

CONCLUSIONS

Use of a uniform entry point at all levels may increase the effectiveness of the free-hand technique and decrease the pedicle screw misplacement rate. Our technique may standardize the free-hand technique, which does not require radiation exposure, and make it more practical to apply uniformly.

Safety and Efficacy of Percutaneous Pedicle Screw Placement Using a Power Tool

Introduction

This study compared traditional manual methods and power tool use with regard to the speed and accuracy of percutaneous pedicle screw (PPS) placement and determined the advantages associated with the use of power tools.

Although the indication of PPS placement in minimally invasive spine stabilization (MISt) procedures has been recently expanded, there are no reports on PPS insertion using a power tool.

Methods

We evaluated 35 patients who underwent PPS insertion using a power tool during MISt procedures. On one side, PPS insertion was performed using the manual (M) method, whereas on the contralateral side, insertion was performed using the power tool (P) method. We assessed the number of implanted PPSs, time taken to implant PPSs after guidewire insertion, and accuracy of PPS placement as ranked postoperatively using computed tomography images.

Results

A total of 294 PPSs were inserted (147 using the M method and 147 using the P method). The mean PPS insertion time was 10.5 s using the P method and 27.4 s using the M method. The time required for inserting a screw using the P method remained consistent in the range of 10-15 s, whereas the time using the M method tended to increase from the second screw onward, with a range of 25-30 s. With regard to PPS insertion accuracy, a 2 mm or more pedicle breach was noted in 2 (1.4%) case after the P method and in 2 (1.4%) case after the M method.

Conclusions

PPS placement using power tools has the potential to save the surgical time during MISt procedures.

Pedicle Screw With Increased Cortical Purchase Can Be Inserted With Same Accuracy as the Screw in Straightforward Trajectory Using 3D Modeling Landmarks

STUDY DESIGN

Comparison, in terms of insertion accuracy and biomechanical performance, between an increased cortical purchase and straightforward pedicle screw trajectory.

OBJECTIVE

This study aims to compare a trajectory with increased cortical purchase to the more common straightforward trajectory in terms of strength and insertion accuracy using real-time navigation.

SUMMARY OF BACKGROUND DATA

In previous studies, it was suggested that pedicle screw pullout strength is strongly correlated with bone mineral density, and using a more cortical tract allows a greater portion of the denser bone, the cortex, to be in contact with the screw. In light of this advantage, an insertion technique has been proposed more recently, to increase the cortical purchase to maximize screw thread contact with cortical bone. It is performed inserting the screw with reduced transverse inclination and results in cortical bone purchase in the lateral portion of the pedicle.

METHODS

Eight T1 and eight T3 vertebra models were reconstructed in Mimics Suite (Materialise, Leuven, Belgium) using CT data obtained with a Medtronic O-arm. Using a previously developed computer algorithm, we calculated all achievable safe trajectories for pedicle screw placement ensuring a minimal distance of 0.5 mm between screw and pedicle edges. For both vertebrae, among these, the straightest and the most convergent trajectories with the calculated insertion region greater than 15% of the total were selected to safely instrument the vertebrae, respectively, as ICP and straightforward techniques. The straightforward technique was planned with a transverse angle of 22.50° in both vertebrae whereas the ICP was planned with a transverse angle of 12.50° for T1 and 2.5° for T3. The screws were implanted by a surgeon experienced in straightforward insertion, and other independent investigators measured placement accuracy and mechanical performance.

RESULTS

The transverse screw angles for T1 and T3 with straightforward technique had average values of 24.93° ± 2.96° and 23.53° ± 2.70°, respectively. For the ICP technique, the average values were 15.60° ± 2.95° for T1 and 2.29° ± 1.55° for T3. The resultant errors associated with screw placement for T1 and T3 were not significantly different (p > .05). The pullout failure loads with straightforward techniques ranged from 756 ± 164 N in T1 to 703 ± 74 N in T3 and were not significantly different (p > .05) from the values of 699 ± 84 N for T1 and of 732 ± 113 N measured for the ICP.

CONCLUSIONS

For the upper thoracic vertebrae tested, despite the use of shorter screws, the insertion technique with increased cortical purchase, in biomechanical terms, is comparable with the straightforward trajectory. Using guidance, the proposed ICP technique was performed with the same accuracy as the popular straightforward technique.

LEVEL OF EVIDENCE

Level V.

Adjacent-segment disease after thoracic pedicle screw fixation

OBJECTIVE Pedicle screw fixation is a technique widely used to treat conditions ranging from spine deformity to fracture stabilization. Pedicle screws have been used traditionally in the lumbar spine; however, they are now being used with increasing frequency in the thoracic spine as a more favorable alternative to hooks, wires, or cables. Although safety concerns, such as the incidence of adjacent-segment disease (ASD) after cervical and lumbar fusions, have been reported, such issues in the thoracic spine have yet to be addressed thoroughly. Here, the authors review the literature on ASD after thoracic pedicle screw fixation and report their own experience specifically involving the use of pedicle screws in the thoracic spine. METHODS Select references from online databases, such as PubMed (provided by the US National Library of Medicine at the National Institutes of Health), were used to survey the literature concerning ASD after thoracic pedicle screw fixation. To include the authors' experience at Rutgers New Jersey Medical School, a retrospective review of a prospectively maintained database was performed to determine the incidence of complications over a 13-year period in 123 consecutive adult patients who underwent thoracic pedicle screw fixation. Children, pregnant or lactating women, and prisoners were excluded from the review. By comparing preoperative and postoperative radiographic images, the occurrence of thoracic ASD and disease within the surgical construct was determined. RESULTS Definitive radiographic fusion was detected in 115 (93.5%) patients. Seven incidences of instrumentation failure and 8 lucencies surrounding the screws were observed. One patient was observed to have ASD of the thoracic spine. The mean follow-up duration was 50 months. CONCLUSIONS This long-term radiographic evaluation revealed the use of pedicle screws for thoracic fixation to be an effective stabilization modality. In particular, ASD seems to be less of a problem in the relatively immobile thoracic spine than in the more mobile cervical and lumbar spines.

Contribution to FE modeling for intraoperative pedicle screw strength prediction

Although the use of pedicle screws is considered safe, mechanical issues still often occur. Commonly reported issues are screw loosening, screw bending and screw fracture. The aim of this study was to develop a Finite Element (FE) model for the study of pedicle screw biomechanics and for the prediction of the intraoperative pullout strength. The model includes both a parameterized screw model and a patient-specific vertebra model. Pullout experiments were performed on 30 human cadaveric vertebrae from ten donors. The experimental force-displacement data served to evaluate the FE model performance. μCT images were taken before and after screw insertion, allowing the creation of an accurate 3D-model and a precise representation of the mechanical properties of the bone. The experimental results revealed a significant positive correlation between bone mineral density (BMD) and pullout strength (Spearman ρ = 0.59, p < 0.001) as well as between BMD and pullout stiffness (Spearman ρ = 0.59, p < 0.001). A high positive correlation was also found between the pullout strength and stiffness (Spearman ρ = 0.84, p < 0.0001). The FE model was able to reproduce the linear part of the experimental force-displacement curve. Moreover, a high positive correlation was found between numerical and experimental pullout stiffness (Pearson ρ = 0.96, p < 0.005) and strength (Pearson ρ = 0.90, p < 0.05). Once fully validated, this model opens the way for a detailed study of pedicle screw biomechanics and for future adjustments of the screw design.

Effect of Pedicle Fill on Axial Pullout Strength in Spinal Fixation After Rod Reduction

Rod reduction to pedicle screws is used for a variety of spinal fixation procedures; however, it can alter the integrity of the screw-bone interface. The authors investigated the effect of pedicle fill (ratio of pedicle screw diameter to pedicle diameter) on the strength of the screw-bone interface after simulated rod reduction on 17 vertebrae (3 thoracolumbar spine specimens). Pedicle diameter was measured with standard clinical computed tomography scan protocols. The authors determined the minimum pedicle diameter for each level. Polyaxial pedicle screws were surgically placed bilaterally with a freehand technique with standard clinical anatomic landmarks. The pedicle pairs were instrumented with pedicle screws of predetermined diameter, 1 with greater than 80% fill and 1 with less than 80% fill. A simulated reduction maneuver was performed with a 5-mm gap followed by an axial pullout test to assess screw interface strength. Comparison of insertion torque between less than 80% fill and greater than 80% fill did not show significant increases. A significant difference in pullout load (P=.043) occurred with greater than 80% fill (791±637 N) compared with less than 80% fill (636±492 N). No significant difference in stiffness was noted (P=.154) with pedicle fill of greater than 80% (427±134 N/mm) compared with less than 80% (376±178 N/mm). The current findings support the use of greater than 80% pedicle fill for optimal screw anchoring in pedicle screw-based constructs involving rod reduction. Surgeons should consider placing screws that can safely fill vertebral pedicles, especially at the apex of the curve and the proximal and distal levels of constructs, where excessive forces are imparted to the screws. [Orthopedics. 2017; 40(6):e990-e995.].

Accuracy of 837 pedicle screw positions in degenerative lumbar spine with conventional open surgery evaluated by computed tomography

BACKGROUND

The spatial and directional accuracy of the positioning of pedicle screws in the lumbosacral spine with conventional open surgery assessed by computed tomography (CT) has been published in several studies, systematic reviews and meta-analyses with a short-term follow-up. Inaccurate pedicle screw insertion may cause neurologic symptoms and weakens the construct.

METHODS

The data of 147 patients operated on with transpedicular screw fixation based on anatomical landmarks, supported by fluoroscopy, by a senior neurosurgeon in our clinic between 2000 and 2010 were analyzed retrospectively. The accuracy of the pedicle screw position was assessed by using postoperative CT images and graded in 2-mm increments up to 6 mm by two independent surgeons and partly by an independent radiologist.

RESULTS

A total of 837 lumbosacral pedicle screws were inserted in 147 randomly selected patients by a senior neurosurgeon. A mean accuracy of 85.7% of the screws being inside the pedicles was identified by the surgeon observers, with 3.3% being perforated 4 mm or more outside the pedicles. Postoperative neurologic symptoms were observed on the side corresponding to the breach in an average of 25.9% of patients with pedicle perforations, and 89.2% of the misplaced screws were either medially or inferiorly inserted.

CONCLUSIONS

Screw application reached a mean accuracy of 85.7% based on anatomical landmarks supported by fluoroscopy, warranting computer-assisted navigation for increased accuracy. Our results of 24 patients (16.3%) with the breached screws indicate that the direction of the breach may be more important than the absolute deviation in causing new neurologic symptoms.

Revision Rate of Misplaced Pedicle Screws of the Thoracolumbar Spine-Comparison of Three-Dimensional Fluoroscopy Navigation with Freehand Placement: A Systematic Analysis and Review of the Literature

BACKGROUND

Recent studies have shown higher accuracy rates of image-guided pedicle screw placement compared to freehand (FH) placement. However, data focusing on the impact of spinal navigation on the rate of revision surgeries caused by misplaced pedicle screws (PS) are scarce.

OBJECTIVE

This study is aimed at identifying the rate of revision surgeries for misplaced PS comparing three-dimensional (3D) fluoroscopy navigation (3DFL) with FH PS placement.

METHODS

A retrospective analysis was conducted of 2232 patients (mean age, 65.3 ± 13.5 years) with 13,703 implanted PS who underwent instrumentation of the thoracolumbar spine between 2007 and 2015. Group 1 received surgery with use of 3DFL (January 2011 to December 2015), group 2 received surgery in the FH technique (April 2007 to December 2015). Because the use of 3DFL was initiated in January 2011, the examined period for 3DFL-navigated surgeries is shorter. Patients routinely received postoperative computed tomography scans and/or intraoperative control 3D scans.

RESULTS

There was an overall rate of revision surgeries for malpositioned PS of 2.9%. In the 3DFL group, the rate of secondary revision surgeries was significantly lower with 1.35% (15/1112 patients) compared to 4.38% (49/1120 patients) in the FH group, respectively (odds ratio, 3.35; P < 0.01). Of all PS in the 3DFL group (30/7548 PS), 0.40% needed revision surgery (P < 0.01) compared to 1.14% in the FH group (70/6155 PS).

CONCLUSIONS

We were able to show that the use of 3DFL-navigated PS placement significantly reduces the rate of revision surgeries after posterior spinal instrumentation compared to freehand PS placement.

Approach to interpret images produced by new generations of multidetector CT scanners in post-operative spine

OBJECTIVE

To reach a practical approach to interpret MDCT findings in post-operative spine cases and to change the false belief of CT failure in the setting of instruments secondary to related artefacts.

METHODS

We performed observational retrospective analysis of premier, early and late MDCT scans in 68 post-operative spine patients, with emphasis on instruments related complications and osseous fusion status. We used a grading system for assessment of osseous fusion in 35 patients and we further analysed the findings in failure of fusion, grade (D).

RESULTS

We observed a variety of instruments related complications (mostly screws medially penetrating the pedicle) and osseous fusion status in late scans. We graded 11 interbody and 14 posterolateral levels as osseous fusion failure, showing additional instruments related complications, end plates erosive changes, adjacent segments spondylosis and malalignment.

CONCLUSION

Modern MDCT scanners provide high quality images and are strongly recommended in assessment of the instruments and status of osseous fusion. In post-operative imaging of the spine, it is essential to be aware for what you are looking for, in relevance to the date of surgery. Advances in knowledge: Modern MDCT scanners allow assessment of instruments position and integrity and osseous fusion status in post-operative spine. We propose a helpful algorithm to simplify interpreting post-operative spine imaging.

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.

PURPOSE

This study aimed to demonstrate a method for percutaneous screws placement using only the anterior-posterior (AP) trajectory of intraoperative fluoroscopy.

STUDY DESIGN

A technical report (a retrospective and prospective case series) was carried out.

PATIENT SAMPLE

Patients who received posterior fixation with percutaneous pedicle screws for thoracolumbar degenerative disease or trauma comprised the patient sample.

METHOD

We retrospectively reviewed the charts of consecutive 670 patients who received 4,072 pedicle screws between December 2010 and August 2015. Another case series study was conducted prospectively in three additional hospitals, and 88 consecutive patients with 413 pedicle screws were enrolled from February 2014 to July 2016. The fluoroscopy shot number and radiation dose were recorded. In the prospective study, 78 patients with 371 screws received computed tomography at 3 months postoperatively to evaluate the fusion condition and screw positions.

RESULTS

In the retrospective series, the placement of a percutaneous screw required 5.1 shots (2-14, standard deviation [SD]=2.366) of AP fluoroscopy. One screw was revised because of a medialwall breach of the pedicle. In the prospective series, 5.8 shots (2-16, SD=2.669) were required forone percutaneous pedicle screw placement. There were two screws with a Grade 1 breach (8.6%), both at the lateral wall of the pedicle, out of 23 screws placed at the thoracic spine at T9-T12. Forthe lumbar and sacral areas, there were 15 Grade 1 breaches (4.3%), 1 Grade 2 breach (0.3%), and 1 Grade 3 breach (0.3%). No revision surgery was necessary.

CONCLUSION

This method avoids lateral shots of fluoroscopy during screw placement and thus decreases the operation time and exposes surgeons to less radiation. At the same time, compared with the computer-navigated procedure, it is less facility-demanding, and provides satisfactory reliability and accuracy.

Retrospective Review on Accuracy: A Pilot Study of Robotically Guided Thoracolumbar/Sacral Pedicle Screws Versus Fluoroscopy-Guided and Computerized Tomography Stealth-Guided Screws

Introduction Pedicle screw insertion is the mainstay of thora-cic and lumbosacral posterior spinal instrumentation. However, it may be associated with complications such as screw mal-positioning. The purpose of this study was to develop a pilot study to compare the accuracy of robot-guided screw insertion versus hand-guided screw placement for spinal instrumentation. The hand-guided screws were placed with assistance from computerized tomography (CT) stealth guidance or fluoroscopy. Materials and methods A retrospective analysis of medical records was done for all patients that had pedicle screw insertion for instrumentation between the dates of December 2013 and January 2016 with post-screw placement CT imaging. The analysis was conducted on screw accuracy between the two categories based on the Gertzbein-Robbins classification. Results A total of 49 screws were analyzed for accuracy in six patients. There was no statistically significant difference between the accuracy of hand-placed pedicle screws versus the robotically placed screws (p = 0.311). There was no statistically significant difference in blood loss (p = 0.616), length of procedure (p = 0.192), or post-operative length of stay (p = 0.587). Conclusion The findings of our pilot study agree with most prior studies that there was no statistically significant difference in the accuracy of pedicle screw placement between the two methods of screw placement. Therefore, the techniques are equivocal in accuracy. The new technology (robotic-guidance) is as safe as conventional techniques for screw placement. Just like in any surgery, the technique preference should remain surgeon dependent. The results are only from a small sample size in the development of a pilot study so a strong reliance on the data would not be suggested. The study was a preliminary study that will be used as a template and learning process to create a future prospective study to investigate CT stealth and robotically guided screw placement versus "free hand" guided screws.

How Does Patient Radiation Exposure Compare With Low-dose O-arm Versus Fluoroscopy for Pedicle Screw Placement in Idiopathic Scoliosis?

BACKGROUND

Intraoperative C-arm fluoroscopy and low-dose O-arm are both reasonable means to assist in screw placement for idiopathic scoliosis surgery. Both using pediatric low-dose O-arm settings and minimizing the number of radiographs during C-arm fluoroscopy guidance decrease patient radiation exposure and its deleterious biological effect that may be associated with cancer risk. We hypothesized that the radiation dose for C-arm-guided fluoroscopy is no less than low-dose O-arm scanning for placement of pedicle screws.

METHODS

A multicenter matched-control cohort study of 28 patients in total was conducted. Fourteen patients who underwent O-arm-guided pedicle screw insertion for spinal fusion surgery in 1 institution were matched to another 14 patients who underwent C-arm fluoroscopy guidance in the other institution in terms of the age of surgery, body weight, and number of imaged spine levels. The total effective dose was compared. A low-dose pediatric protocol was used for all O-arm scans with an effective dose of 0.65 mSv per scan. The effective dose of C-arm fluoroscopy was determined using anthropomorphic phantoms that represented the thoracic and lumbar spine in anteroposterior and lateral views, respectively. The clinical outcome and complications of all patients were documented.

RESULTS

The mean total effective dose for the O-arm group was approximately 4 times higher than that of the C-arm group (P<0.0001). The effective dose for the C-arm patients had high variability based on fluoroscopy time and did not correlate with the number of imaged spine levels or body weight. The effective dose of 1 low-dose pediatric O-arm scan approximated 85 seconds of the C-arm fluoroscopy time. All patients had satisfactory clinical outcomes without major complications that required returning to the operating room.

CONCLUSIONS

Radiation exposure required for O-arm scans can be higher than that required for C-arm fluoroscopy, but it depends on fluoroscopy time. Inclusion of more medical centers and surgeons will better account for the variability of C-arm dose due to distinct patient characteristics, surgeon's preference, and individual institution's protocol.

LEVEL OF EVIDENCE

Level III-case-control study.

Posterior Lumbar Interbody Fusion with Interspinous Fastener Provides Comparable Clinical Outcome and Fusion Rate to Pedicle Screws

OBJECTIVE

To investigate the clinical feasibility and validity of interspinous fastener (ISF) for lumbar degenerative diseases.

METHODS

From October 2013 to March 2014, a total of 46 patients suffering from lumbar degenerative diseases underwent posterior lumbar interbody fusion (PLIF) randomly augmented by ISF or pedicle screws. The clinical outcome was primarily measured by Oswestry Disability Index (ODI) score. The minimal clinical important difference (MCID) was defined as an eight-point decrease in ODI. The second clinical outcome measurement was Japanese Orthopedic Association (JOA) score. Interbody fusion rates were evaluated by lumbar plain radiograph and computed tomography (CT) scan. Complications were also compared between groups. Statistical analyses were performed by SPSS version 13.0. Sample size calculation was performed before the study. The type I error α was set at 0.05 and the type II error β at 0.1. Based on these assumptions and adding 10% for possible drop-outs, sample size calculations indicated that a total of 46 patients were required for the study. Parametric data was compared by independent t-test and categorical variables were compared using χ² -tests or Fisher exact tests depending on the sample size. A P-value of less than 0.05 was considered significantly statistically different. Fleiss kappa coefficients were calculated for intra-observer and inter-observer reliability.

RESULTS

A total of 43 patients completed the follow-up, with 22 cases in the ISF group and 21 patients in the pedicle screws group, respectively. Less intraoperative blood loss and shorter operation time were observed in the ISF group. The mean ODI significantly declined in both groups, with the ISF group's decreasing from preoperative 43.3 ± 8.2 to 21.4 ± 3.5 at 24-month follow-up and the pedicle screws group's decreasing from preoperative 42.9 ± 7.9 to 22.5 ±3.8 at 24-month follow-up, respectively. The ODI changes between groups had no statistical difference (P > 0.05). Of the 43 patients, 33 patients achieved an MCID. The bone fusion rate was 77.3% according to X-rays and 68.2% according to CT scans in the ISF group, and 81.0% according to X-rays and 76.2% according to CT scans in the pedicle screws group at the final follow-up. The intra-observer and inter-observer reliability assessed by the kappa value were 0.93 and 0.89, respectively. One patient in the pedicle screws group demonstrated screw loosening at the 6-month follow-up but was asymptomatic. One patient with spondylolisthesis in the ISF group demonstrated cage subsidence during the follow-up but also without related symptoms.

CONCLUSION

The less invasive ISF combined with PLIF provided comparable clinical outcome and a similar bone fusion rate to pedicle screws. The ISF could potentially serve as a new alternative for lumbar degenerative diseases.

Intraosseous monitoring of drilling in lumbar vertebrae by ultrasound: An experimental feasibility study

The rationale for this project is to evaluate the efficiency of a novel sonographic method for measurements of interosseous distances. The method utilizes a propagating ultrasonic beam through aqueous milieu which is directed as a jet into a drilled tract. We used a plastic model of human L5 vertebra and ex vivo specimen of L5 porcine vertebra and generated 2 mm in diameter tracts in vertebral pedicles. The tracts were created in the "desired" central direction and in the "wrong" medial and lateral directions. The drilled tracts and the residual, up to opposite cortex, distances were measured sonographically and mechanically and compared statistically. We show that "true" mechanical measurements can be predicted from sonographic measurements with correction of 1-3 mm. The correct central route can be distinguished from the wrong misplaced routes. By using the sonographic measurements, a correct direction of drilling in the pedicle of lumbar L5 vertebra can be efficiently monitored.

Comparison of Effective Dose of Radiation During Pedicle Screw Placement Using Intraoperative Computed Tomography Navigation Versus Fluoroscopy in Children With Spinal Deformities

BACKGROUND

We compared the effective dose of radiation associated with pedicle screw placement in posterior spinal fusion in children using intraoperative computed tomography (CT) navigation versus intraoperative fluoroscopy (C-arm).

METHODS

In this review of posterior spinal fusion patients, height, weight, local density function, dose area product, body region, number of views, and part of the body were used to calculate the effective dose to the patient in millisieverts (mSv) in 37 children in whom pedicle screw placement was aided by intraoperative CT versus 44 children in whom pedicle screw placement was aided by C-arm. Both groups had posterior spinal fusions during the same time period by 3 surgeons between November 2012 and August 2013. Calculation of the radiation dose was made by the following method: for the C-arm, and the fluoroscopic/digital acquisitions part of the CT examinations, we estimated the effective dose using the program PCXMC 2.0. For the cross-sectional imaging part of the CT examinations, we used the dose-length product from the radiation dose reports of the CT unit and published dose-length product to effective dose conversion factors. The overall effective dose for the CT group was the total of the cross-sectional imaging dose and the fluoroscopic/digital acquisition imaging dose. An unpaired T test was used to determine significant difference between the C-arm and CT navigation groups.

RESULTS

The average effective dose was 1.48±1.66 mSv for the CT patients and 0.34±0.36 mSv for the C-arm patients. These values for the 2 groups are significantly different (P=0.0012). Obese children had very high mSv values in the CT group.

CONCLUSIONS

Intraoperative CT for navigational instrumentation placement associated with spinal fusion in children results in significantly more radiation to the child than C-arm. Families need to be counseled about radiation exposure associated with intraoperative CT, especially in obese children. Intraoperative CT use should be tailored to placing instrumentation where the benefit is the highest.

LEVEL OF EVIDENCE

Level II.

Biomechanical properties of posterior transpedicular-transdiscal oblique lumbar screw fixation with novel trapezoidal lateral interbody spacer: an in vitro human cadaveric model

PURPOSE

To investigate biomechanical properties of posterior transpedicular-transdiscal (TPTD) oblique lumbar screw fixation whereby the screw traverses the inferior pedicle across the posterior disc space into the super-adjacent body and lateral trapezoidal interbody spacer.

METHODS

Eight fresh-frozen osteoligamentous human cadaveric spines (L1-S1) were tested in flexion-extension (FE), lateral bending (LB), and axial rotation (AR), with pure bending moment set at 7.5 Nm. Surgical constructs included (1) intact spine; (2) bilateral pedicle screw (BPS) fixation at L3-L4; (3) TPTD screw fixation at L3-L4; (4) lateral L3-L4 discectomy; (5) TPTD screw fixation with lateral interbody spacer (TPTD+S); and (6) BPS fixation with lateral interbody spacer (BPS+S). Peak range of motion (ROM) at L3-L4 was normalized to intact for statistical analysis.

RESULTS

In FE and LB, all posterior fixation with or without interbody spacers significantly reduced motion compared with intact and discectomy. BPS and BPS+S provided increased fixation in all planes of motion; significantly reducing FE and LB motion relative to TPTD (p = 0.005, p = 0.002 and p = 0.020, p = 0.004, respectively). In AR, only BPS significantly reduced normalized ROM to intact (p = 0.034); BPS+S provided greater fixation compared with TPTD+S (p = 0.005).

CONCLUSIONS

Investigators found less stiffness with TPTD screw fixation than with BPS regardless of immediate stabilization with lateral discectomy and spacer. Clinical use should be decided by required biomechanical performance, difficulty of installation, and extent of paraspinal tissue disruption.

The Safety and Strength of a Novel Medial, Partial Nonthreaded Pedicle Screw: A Cadaveric and Biomechanical Investigation

STUDY DESIGN

Cadaveric and biomechanical study.

OBJECTIVE

The aim of this study was to assess the safety and pullout strength of medial, partial nonthreaded thoracic pedicle screws compared with conventional screws.

SUMMARY OF BACKGROUND DATA

The perforation rate of the pedicle screws has been reported as high as 41%. Nerve injury and irritation can result from the compression of malpositioned screw on neural structures.

METHODS

Ten fresh cadavers were studied. Screws, 5.0 and 6.0 mm, were inserted from T1 to T6 and T7 to T12, respectively. Pedicle perforations and fractures were recorded upon screw insertion and final positioning (nonthreaded portion facing medially) after a wide laminectomy. Pullout strength of novel and conventional screws were then tested using an Instron machine in an artificial bone substitute.

RESULTS

A total of 240 thoracic pedicle screws were inserted. Of them, 88.8% (213 screws) were fully contained during screw insertion. There were 5.0% (12 screws) grade 1 medial perforations and 6.2% (15 screws) grade 1 lateral perforations during screw insertion. Upon final positioning, 93.8% (225 screws) were fully contained. All grade 1 medial perforations, which occurred during insertion, were converted to grade 0. No dural or nerve root injuries occurred. Pedicle split fractures were noted in 6.7% (16 screws). The use of medial, partial nonthreaded screws reduced the overall perforation rate from 11.2% to 6.2%. The mean pullout load for the 5 mm fully threaded screw versus medial, partial nonthreaded was 1419.3±106.1 N (1275.8-1538.8 N) and 1336.6±44.2 N (1293.0-1405.1 N) respectively, whereas 6 mm pullout load averaged 2126.0±134.8 N (1986.3-2338.3 N) and 2036.5±210.0 N (1818.4-2355.9 N). The difference was not statistically significant.

CONCLUSIONS

The use of medial, partial nonthreaded pedicle screws reduced the medial perforation rate from 5.0% to 0%; however, the pullout strength was not significantly reduced. The use of this novel screw can potentially reduce the incidence of nerve injury or irritation after medial pedicle perforations.

Accuracy of pedicle screw placement in patients with Marfan syndrome

BACKGROUND

There is no study concerning safety and accuracy of pedicle screw placement in Marfan syndrome. The objective of this study is to investigate accuracy and safety of pedicle screw placement in scoliosis associated with Marfan syndrome.

METHODS

CT scanning was performed to analyze accuracy of pedicle screw placement. Pedicle perforations were classified as medial, lateral or anterior and categorized to four grades: ≤ 2 mm as Grade 1, 2.1-4.0 mm as Grade 2, 4.1-6.0 mm as Grade 3, ≥6.1 mm as Grade 4. Fully contained screws or with medial wall perforation ≤ 2 mm or with lateral wall perforation ≤ 6 mm and without injury of visceral organs were considered acceptable, otherwise were unacceptable.

RESULTS

976 pedicle screws were placed, 713 screws (73.1%) were fully contained within the cortical boundaries of the pedicle. 924 (94.7%) screws were considered as acceptable, and 52 (5.3%) as unacceptable. The perforation rate was higher using free-hand technique than O-arm navigation technique (30.8% VS. 11.4%, P < 0.05), higher in lumbar region than in thoracic region (34.1% VS. 22.3%, P < 0.05) and higher in concave side than in convex side (33.5% VS. 21.9%, P < 0.05). No injury of visceral organs especially aorta erosion was noted in the series. 7 cases of dural tear caused by misplaced screws occurred, and 4 cases developed cerebro-spinal fluid leak. Drainage and pressure dressings were applied for these patients, and no infection was observed. Leg pain was observed in 7 cases, and 2 cases simultaneously complained of leg weakness. Revision surgery was conducted to remove the misplaced screws for these 2 patients. Conservative treatment was applied for the 5 patients without leg weakness. Symptoms of leg weakness and pain resolved in all patients.

CONCLUSION

Placement of pedicle screw in Marfan syndrome is accuracy and safe. O-arm navigation was an effective modality to ensure the safety and accuracy of screw placement. Special attention should be paid when screws were placed at the lumber spine and the concave side of spine deformity to avoid the higher rate of complications.

Traumatic dislocation of the S1 polyaxial pedicle screw head: a case report

Polyaxial screw head dislocation in the absence of a manufacture defect is extremely rare and represents a biomechanical overload of the screw, leading to early failure. A 58-year-old gentleman underwent instrumented fusion using polyaxial pedicle screws-titanium rod construct with interbody cage for spondylolytic spondylolisthesis at the L5/S1 level. He attempted to bend forward ten days after the surgery which resulted in a dislocation of the right S1 polyaxial screw head from the screw shank with recurrence of symptoms. He underwent revision surgery uneventfully. This case highlights the need to pay particular attention to the strength of fixation and the amount of release to avoid such a complication.

Temporary Iliac Fixation to Salvage an Acute L4 Chance Fracture: Following Pedicle Screw Fixation for Adolescent Idiopathic Scoliosis

STUDY DESIGN

A case report.

OBJECTIVE

The aim of this study was to describe a technique of temporary distal fixation to the ilium to salvage an acute L4 fracture following a T3-L4 kyphoscoliosis correction.

SUMMARY OF BACKGROUND DATA

Pedicle fracture is a possible complication in pedicle screw fixation for scoliosis, which may lead to postoperative instability, resulting in loss of fixation and pseudoarthrosis. This report highlights the salvage treatment of a chance fracture that occurred in the lower instrumented vertebra following deformity correction for adolescent idiopathic scoliosis (AIS) without sacrificing further distal motion segments.

METHODS

A retrospective chart and radiograph review of a 13-year-old female who underwent surgical treatment for correction of AIS was performed.

RESULTS

Following a T3-L4 correction with apical posterior column releases, an L4 Chance fracture with loss of distal fixation occurred on post-op day 3. Following an unsuccessful salvage with an infralaminar hook, a second revision was performed replacing the hook and adding bilateral temporary fixation to the ilium connected to the distal ends of the main rods through side-to-side connectors. The temporary fixation was removed 6 months later with successful healing of the fracture maintenance of the scoliosis correction at 2-year follow-up.

CONCLUSION

Temporary extension of the construct to the ilium was successfully utilized in this case to salvage an acute L4 Chance fracture that occurred following a T3 to L4 construct for kyphoscoliosis. With this technique, successful reduction and healing of the fracture occurred with maintenance of the deformity correction without the need to fuse further distal segments.

LEVEL OF EVIDENCE

4.

Could the Topping-Off Technique Be the Preventive Strategy against Adjacent Segment Disease after Pedicle Screw-Based Fusion in Lumbar Degenerative Diseases? A Systematic Review

The "topping-off" technique is a new concept applying dynamic or less rigid fixation such as hybrid stabilization device (HSD) or interspinous process device (IPD) for the purpose of avoiding adjacent segment disease (ASD) proximal to the fusion construct. A systematic review of the literature was performed on the effect of topping-off techniques to prevent or decrease the occurrence of ASD after lumbar fusion surgery. We searched through major online databases, PubMed and MEDLINE, using key words related to "topping-off" technique. We reviewed the surgical results of "topping-off" techniques with either HSD or IPD, including the incidence of ASD at two proximal adjacent levels (index and supra-adjacent level) as compared to the fusion alone group. The results showed that the fusion alone group had statistically higher incidence of radiographic (52.6%) and symptomatic (11.6%) ASD at the index level as well as higher incidence (8.1%) of revision surgery. Besides, the HSD (10.5%) and fusion groups (24.7%) had statistically higher incidences of radiographic ASD at supra-adjacent level than the IPD (1%). The findings suggest that the "topping-off" technique may potentially decrease the occurrence of ASD at the proximal motion segments. However, higher quality prospective randomized trials are required prior to wide clinical application.

Biomechanical characteristics of pedicle screws in osteoporotic vertebrae-comparing a new cadaver corpectomy model and pure pull-out testing

Currently, evaluation of the stability of spinal instrumentations often focuses on simple pull-out or cyclic loading. However, the loading characteristics and the specimen alignment rarely simulate physiological loading conditions, or the clinical situation itself. The purpose of this study was to develop an alternative setup and parameters to compare static and dynamic characteristics of pedicle screws at the bone-implant interface in lumbar osteoporotic cadavers. A corpectomy model development was based on ASTM-1717 standard, allowing a deflection of the cranial and caudal element under loading. Twelve human osteoporotic vertebrae (L1-L4) were analyzed for morphological CT-data and T-Score. For group A (n = 6) loads were simulated as in vivo measurements during walking, representing 2 months postoperatively. A subsequent pull-out was performed. Group B (n = 6) was tested with pure pull-out. Screw loosening at the tip/head was optically measured and analyzed with respect to clinical patterns. Correlations between CT-data, T-Score, and in vitro parameters were determined. For group A, the subsidence for the head/tip was measured towards the upper/lower endplate, resulting in visible deflections. The progress of the subsidence was greatest within the first and last cycles until failure. The predominant patterns were pure rotation and toggling. However, the pull-out between groups was not significantly different. Pedicle-angle and cyclic-subsidence correlated with R = 0.806/0.794. T-Score and pull-out correlated only in group A. With the corpectomy setup, clinically observed wipe effects and a loss of correction could be simulated. The presented parameters facilitate analysis of the complex changing load distributions and interactions between the left and right bone-implant interface. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:167-174, 2017.

Preliminary application of a multi-level 3D printing drill guide template for pedicle screw placement in severe and rigid scoliosis

PURPOSE

Accurate implantation of pedicle screw in spinal deformity correction surgeries is always challenging. We have developed a method of pedicle screw placement in severe and rigid scoliosis with a multi-level 3D printing drill guide template.

METHODS

From November 2011 to March 2015, ten patients (4 males and 6 females) with severe and rigid scoliosis (Cobb angle >70° and flexibility <30%)were included. Multi-level template was designed and manufactured according to the part (two or three levels) of the most severe deformity. The drill template was then placed on the corresponding vertebral surface. Then, pedicle screws were carefully inserted along the trajectories. The other screws were placed in free hand. After surgery, the positions of the pedicle screws were evaluated by CT scan and graded for validation.

RESULTS

48 screws were implanted using templates, other 104 screws in free hand, and the accuracies were 93.8 and 78.8%, respectively, with significant difference. The deformity correction ratio was 67.1 and 41.2% in coronal and sagittal plane post-operatively, respectively. The average operation time was 234.0 ± 34.1 min, and average blood loss was 557 ± 67.4 ml.

CONCLUSIONS

With the application of multi-level template, the incidence of cortex perforation in severe and rigid scoliosis decreased and this technology is, therefore, potentially applicable in clinical practice.

Anatomical Location of the Common Iliac Veins at the Level of the Sacrum: Relationship between Perforation Risk and the Trajectory Angle of the Screw

Purpose. To determine the safety of transarticular surface screw (TASS) insertion and the anatomical location of the common iliac veins (CIVs) at the level of the promontorium. Materials and Methods. The locations of the CIVs on 1 mm computed tomography-myelography slices of 50 patients at the level of the promontorium and 20 human cadavers were investigated. Results. Among the patients, the left CIV was closer to the S1 anterior wall than the right CIV (mean distance: 5.0 ± 3.0 and 7.0 ± 4.2 mm, resp.). The level of the inferior vena cava (IVC) formation varied among the cadavers. The mean distance between the IVC formation and promontorium tip was 30.2 ± 12.8 mm. The height of the IVC formation and distance between the right and the left CIVs at the level of the promontorium were significantly correlated (P < 0.001). Conclusion. The TASS trajectory is safe as long as the screw does not penetrate the anterior cortex of S1. The level of the IVC formation can help to predict the distance between the right and the left CIVs at the level of the promontorium. The CIVs do not have a uniform anatomical location; therefore, preoperative computed tomography is necessary to confirm their location.

Biomechanical arrangement of threaded and unthreaded portions providing holding power of transpedicular screw fixation

BACKGROUND

Failure of pedicle screw is a major concern in spinal surgery. The threaded and unthreaded portions of the pedicle screw provide the ability to anchor and squeeze the surrounding bone, respectively. This study aimed to investigate the anchoring and squeezing effects of different design of the threaded/unthreaded portions of a pedicle screw to vertebrae.

METHODS

Four variations (one fully and three partially threaded, with a 1/3, 1/2, and 2/3 unthreaded designs at the proximal portion) of screws were used to measure pullout strength and withdrawn energy using synthetic and porcine specimens. The tests were conducted in static and dynamic fashions, in that the screws were axially extracted directly and after 150,000cycles of lateral bending. The load-displacement curves were recorded to gain insight into the peak load (pullout strength) and cumulative work (withdrawn energy).

FINDINGS

The two testing results of the synthetic and porcine specimens consistently showed that the 1/3 unthreaded screw provides significantly higher pullout strength and withdrawn energy than the fully threaded screw. The withdrawn energy of the three unthreaded screws was significantly higher than that of the threaded counterpart.

INTERPRETATION

The holding power of a pedicle screw was the integration of the anchoring (cancellous core) and squeezing (compact pedicle) effects within the threaded and unthreaded portions. The current study recommends the 1/3 unthreaded screw as an optimal alternative for use as a shank-sliding mechanism to preserve the holding power within the pedicle isthmus.

Reliability of the Planned Pedicle Screw Trajectory versus the Actual Pedicle Screw Trajectory using Intra-operative 3D CT and Image Guidance

BACKGROUND

Technological advances, including navigation, have been made to improve safety and accuracy of pedicle screw fixation. We evaluated the accuracy of the virtual screw placement (Stealth projection) compared to actual screw placement (intra-operative O-Arm) and examined for differences based on the distance from the reference frame.

METHODS

A retrospective evaluation of prospectively collected data was conducted from January 2013 to September 2013. We evaluated thoracic and lumbosacral pedicle screws placed using intraoperative O-arm and Stealth navigation by obtaining virtual screw projections and intraoperative O-arm images after screw placement. The screw trajectory angle to the midsagittal line and superior endplate was compared in the axial and sagittal views, respectively. Percent error and paired t-test statistics were then performed.

RESULTS

Thirty-one patients with 240 pedicle screws were analyzed. The mean angular difference between the virtual and actual image in all screws was 2.17° ± 2.20° on axial images and 2.16° ± 2.24° on sagittal images. There was excellent agreement between actual and virtual pedicle screw trajectories in the axial and sagittal plane with ICC = 0.99 (95%CI: 0.992-0.995) (p<0.001) and ICC= 0.81 (95%CI: 0.759-0.855) (p<0.001) respectively. When comparing thoracic and lumbar screws, there was a significant difference in the sagittal angulation between the two distributions. No statistical differences were found distance from the reference frame.

CONCLUSION

The virtual projection view is clinically accurate compared to the actual placement on intra-operative CT in both the axial and sagittal views. There is slight imprecision (~2°) in the axial and sagittal planes and a minor difference in the sagittal thoracic and lumbar angulation, although these did not affect clinical outcomes. In general, we find that pedicle screw placement using intraoperative cone beam CT and navigation to be accurate and reliable, and as such have made it a routine part of our spine practice. This study was approved by the University of Minnesota IRB (#1303E30544).

Pedicle screw position changing policy for nerve injury problems during screw insertion on thoracolumbar compression fractures

Introduction

Intraoperative neurophysiologic monitoring (IONM) had important role related to the complications in spinal surgery. Somatosensory Evoked Potential (SSEP), Transcranial electric Muscle Evoked Potentials (tceMEPs), and free run EMG are parameters used to asses functional integrity of the nervous system during surgical procedures. Once warning signal was recognized, surgeon have to make a precise decision to overcome that problem.

Presentation of case

We present a 47-year old male with back pain due to compression fracture of thoracic vertebra T12 and lumbar vertebrae L1. While stabilizing through the posterior approach on the T11 and 12 as well as L2 and L3, the SSEP monitor showed 50% reduction in the waveform as the pedicle screw was inserted at the left side of T12. The instrumentation was changed into vertebra thoracal T10, T11, and vertebrae lumbar L2, L3. The SSEP normalized and post operatively pain decreased. After surgery there was no neurological deficit.

Discussion

Acute trauma as a result of spine instrumentation may provoke significant edema, with mass effect causing neurophysiological dysfunction. Administration of intravenous steroid would do at this stage, followed by constant infusion for following 24–48 h, may help ameliorating the mass effect and improving the neurologic outcome. Alternatively, immediate pedicle screw changing policy showed absolute recovery of nerve injury.

Conclusion

Insertion of pedicle screw in spinal surgery has a risk of complication that could be treated by pedicle screw changing policy.

Switching to a Pediatric Dose O-Arm Protocol in Spine Surgery Significantly Reduced Patient Radiation Exposure

BACKGROUND

Intraoperative computed tomography and image-guided navigation improve the accuracy of screw placement. Radiation exposure to the patient remains a primary drawback. The objective of the present study was to compare the total intraoperative radiation dose and assess the resultant image quality for O-arm-assisted pedicle screw insertion, among 3 protocols: default (manufacturer recommended), institutional (reduced dose utilized in our institution), and pediatric (new protocol with lowest dose).

METHODS

Thirty-seven consecutive patients under the age of 18 years underwent posterior instrumentation of the spine and underwent an intraoperative O-arm scan. Techniques (kV and mAs) for default and institutional dose settings were manually adjusted based on spinal level and body weight. Pediatric dose techniques were 80 kV/80 mAs with no adjustment for level or weight. The number of scans repeated because of inadequate imaging was assessed, and the mean estimated effective dose between the 3 protocols was compared.

RESULTS

Sixty-eight scans were performed in 37 consecutive patients with mean age of 14 years and mean weight of 55 kg. For reference, the effective radiation dose of a chest x-ray is approximately 0.10 mSv. Use of the default protocol resulted in higher mean effective dose per scan of 4.65 mSv, whereas institutional protocol resulted in 2.37 mSv. The pediatric protocol reduced the mean dose to 0.65 mSv. The total effective dose per surgery was: 1.17 mSv (pediatric), 3.83 mSv (institutional), and 12.79 mSv (default) (P<0.0001 each). All scans lead to satisfactory image quality except in 1 patient >100 kg with stainless steel implants. There were no neurological or other implant-related complications. The pediatric protocol resulted in satisfactory image quality with the lowest total radiation dose, only 1/10 of that of the default protocol.

CONCLUSIONS

We successfully switched to a pediatric low-dose O-arm protocol in clinical practice, reducing the dose to <1/4 of the mean annual natural background radiation. This may allow use of intraoperative computed tomography and navigation for pedicle screw placement without excessive radiation exposure to young patients.

LEVEL OF EVIDENCE

Level III-retrospective comparative study.

Biomechanical Comparison of Expansive Pedicle Screw and Polymethylmethacrylate-augmented Pedicle Screw in Osteoporotic Synthetic Bone in Primary Implantation: An Experimental Study

STUDY DESIGN

Expansive pedicle screws (EPS) and polymethylmethacrylate-augmented pedicle screws (PMMA-PS) were inserted into osteoporotic synthetic bones, which were then tested by radiographic and biomechanical examinations.

OBJECTIVE

To compare the stability of EPS and PMMA-PS with that of a conventional pedicle screw (CPS) in an osteoporotic synthetic bone.

SUMMARY OF BACKGROUND DATA

It is a significant challenge for orthopedic surgeons performing transpedicular fixation in the osteoporotic spine. Prior studies have suggested that both EPS and PMMA-PS can increase the screw stability effectively. However, there are no biomechanical comparisons of EPS and PMMA-PS, especially in primary spinal surgery in osteoporosis.

METHODS

Thirty osteoporotic synthetic bone blocks were divided into 3 groups randomly. A pilot hole was prepared in advance in all samples by the same method. Then, the CPS was inserted directly into the pilot hole in the CPS group; the hole in the PMMA-PS group was first filled with polymethylmethacrylate (PMMA; 2.5 mL) and then inserted with CPS, and the EPS was inserted directly into the blocks in the EPS group. Twenty-four hours later, x-ray and computed tomography examination and axial pullout tests were performed on all samples; the block destructions were then recorded, and the hole diameters were measured.

RESULTS

In the CPS group, the screw was surrounded directly by the synthetic bone without any other materials, whereas in the PMMA-PS group, the screw was totally wrapped up by PMMA, and the PMMA was evenly distributed in the synthetic bone around the screw, indicating obvious improvement of the local density around the track. In the EPS group, the anterior part of the EPS presented an obvious expansion in synthetic bone and formed an unguiform structure pressing the surrounding synthetic bone. Screw stabilities in both the PMMA-PS and the EPS groups were significantly enhanced compared with those in the CPS group, and the screw stability in the PMMA-PS group was significantly higher than that in the EPS group. After the pullout tests, the block destructions were the most severe in the PMMA-PS group and the lightest in the CPS group. Hole diameters in the PMMA-PS and the EPS groups were significantly larger than that in the CPS group, whereas the diameter of the hole in the PMMA-PS group was significantly greater than that in the EPS group.

CONCLUSIONS

EPS can significantly increase the strength of screw fixation compared with CPS in osteoporotic synthetic bone. Although EPS shows a weaker fixation strength compared with PMMA-PS in the osteoporotic synthetic bone, it may still provide an alternative option to prevent screw loosening in the clinical treatment of osteoporosis.

Percutaneous Lumbar Transfacet Screw Fixation: A Technique Analysis of 176 Screws in 83 Patients With Assessment of Radiographic Accuracy, Hardware Failure, and Complications

Supplemental Digital Content Is Available in the Text.

Minimally invasive screw fixation of fractures in the thoracic spine: CT-controlled pre-surgical guidewire implantation in routine clinical practice

AIM

To evaluate the feasibility and accuracy of minimally invasive, transpedicular screw placement in cervicothoracic fractures with the help of computed tomography (CT)-controlled guidewires.

MATERIALS AND METHODS

Two hundred and ninety-three guidewires were inserted in 35 patients (42.9±21.2 years) under CT fluoroscopy (286 thoracic, seven cervical). There were 28 traumatic cases, three pathological fractures, three fractures due to infectious infiltrations, and one osteoporotic fracture. In 151 pedicles, screw placement was performed in the CT room. CT images were reviewed regarding accuracy and cortical violations using the popular 2 mm increment deviation classification of Gertzbein and Robbins.

RESULTS

Guidewire implantation resulted in only 28 cortical contacts. Minor encroachments of the pedicle wall by inserted screws occurred in 39.1% (59 of 151) and in 23.8% if taking unavoidable encroachments into account (30 of 59). Pedicular isthmus width correlated to cortical guidewire contacts (r=-0.449; p=0.077) and pedicle violations (all graded "A") by the inserted screws (r=-0.581; p=0.049). Total procedural duration was 138.6±44.2 minutes, representing 14.5±11.6 minutes for each pedicle, while showing a significant correlation against higher vertebral levels (r=-0.849; p=0.0002) and the occurrence of pedicle violations (r=-0.641; p=0.027).

CONCLUSIONS

The treatment of vertebral fractures with a guidewire-based pedicle screw insertion technique under CT imaging results in very high accuracy and a low complication rate.

Emerging Techniques for Posterior Fixation of the Lumbar Spine

Pedicle screw fixation is the preferred method of posterior fusion in lumbar spinal surgery. The technique provides three-column support of the vertebrae, contributing to the biomechanical strength of the construct. However, open pedicle screw fixation often necessitates wide posterior exposure and dissection with soft-tissue disruption of the facet joint. Alternative posterior fixation techniques have been developed to reduce surgical time, soft-tissue dissection, disruption of the adjacent facet joint capsule, neurologic risk, and implant cost. Results of these techniques are comparable to those of standard pedicle screw fixation systems. Certain patients, especially those at a lower risk of nonunion or those who require posterior fixation only as an adjunct to anterior column support, may benefit from the shorter surgical time and limited posterior exposure of the alternative techniques. However, the decreased rigidity of these alternative constructs can result in excessive motion, which can lead to nonunion and early hardware failure.

Anterior approach with expandable cage implantation in management of unstable thoracolumbar fractures: Results of a series of 93 patients

INTRODUCTION

Anterior approach indications in unstable thoracolumbar fractures (UTLF) are debated. The aim of this study was to evaluate the results of anterior fixation and expandable prosthetic vertebral body cage (EPVBC) implantation alone or combined with a posterior approach in the management of UTLF.

MATERIALS AND METHODS

Ninety-three patients underwent anterior fixation with implantation of an EPVBC for UTLF from T7 to L5. Long-term kyphosis and vertebral height loss reduction, functional outcomes including visual analogical scale and Oswestry disability index were evaluated.

RESULTS

Anterior fixation led to a significant increase of vertebral body height with a gain of 13% after a previous posterior approach, 38% after a single anterior approach and 65% after combined posterior and anterior approaches (P=0.0001). However, anterior fixation did not significantly enhance the vertebral regional kyphosis angle (P=0.08), except in cases of single anterior approach for thoracic fractures (P=0.03). No significant difference was found between early, 3 months and 1 year postoperative vertebral regional kyphosis angle and vertebral body height (P=0.6). Complete fusion was routinely observed at 1 year postoperatively. rhBMP2 implantation in selected cases appears to be a safe and reliable strategy. No infections or surgical revisions were observed after the anterior approach.

CONCLUSION

Anterior approach and EPVBC implantation, in UTLF, is a safe and effective procedure, providing long-term vertebral body height and kyphosis correction. Adverse effects of anterior approach remain acceptable. Single anterior fixation is a reliable surgical alternative in thoracic fractures without posterior spine segment injury or spinal cord compression. These results prompted us to extend anterior approach indications in oncology and infectious diseases.

Assessing the Intraoperative Accuracy of Pedicle Screw Placement by Using a Bone-Mounted Miniature Robot System through Secondary Registration

Introduction

Pedicle screws are commonly employed to restore spinal stability and correct deformities. The Renaissance robotic system was developed to improve the accuracy of pedicle screw placement.

Purpose

In this study, we developed an intraoperative classification system for evaluating the accuracy of pedicle screw placements through secondary registration. Furthermore, we evaluated the benefits of using the Renaissance robotic system in pedicle screw placement and postoperative evaluations. Finally, we examined the factors affecting the accuracy of pedicle screw implantation.

Results

Through use of the Renaissance robotic system, the accuracy of Kirschner-wire (K-wire) placements deviating <3 mm from the planned trajectory was determined to be 98.74%. According to our classification system, the robot-guided pedicle screw implantation attained an accuracy of 94.00% before repositioning and 98.74% after repositioning. However, the malposition rate before repositioning was 5.99%; among these placements, 4.73% were immediately repositioned using the robot system and 1.26% were manually repositioned after a failed robot repositioning attempt. Most K-wire entry points deviated caudally and laterally.

Conclusion

The Renaissance robotic system offers high accuracy in pedicle screw placement. Secondary registration improves the accuracy through increasing the precision of the positioning; moreover, intraoperative evaluation enables immediate repositioning. Furthermore, the K-wire tends to deviate caudally and laterally from the entry point because of skiving, which is characteristic of robot-assisted pedicle screw placement.

The Biomechanical Properties of Pedicle Screw Fixation Combined With Trajectory Bone Cement Augmentation in Osteoporotic Vertebrae

STUDY DESIGN

The biomechanics of pedicle screw fixation combined with trajectory cement augmentation with various filling volumes were measured by pull-out, periodic antibending, and compression fatigue tests.

OBJECTIVE

To investigate the biomechanical properties of the pedicle screw fixation combined with trajectory bone cement (polymethylmethacrylate) augmentation in osteoporotic vertebrae and to explore the optimum filling volume of the bone cement.

SUMMARY OF BACKGROUND DATA

Pedicle screw fixation is considered to be the most effective posterior fixation method. The decrease of the bone mineral density apparently increases the fixation failure risk caused by screw loosening and displacement. Trajectory bone cement augmentation has been confirmed to be an effective method to increase the bone intensity and could markedly increase the stability of the fixation interface.

METHODS

Sixteen elderly cadaveric 1-5 lumbar vertebral specimens were diagnosed with osteoporosis. The left and right vertebral pedicles were alternatively randomized for treatment in all groups, with the contralateral pedicles as control. The study groups included: group A (pedicle screw fixation with full trajectory bone cement augmentation), group B (75% filling), group C (50% filling), and group D (25% filling). Finally, the bone cement leakage and dispersion were assessed and the mechanical testing was conducted.

RESULTS

The bone cement was well dispersed around the pedicle screw. The augmented bone intensity, pull-out strength, periodic loading times, and compression fatigue performance were markedly higher than those of the control groups. With the increase in trajectory bone cement, the leakage was also increased (P<0.05). The pull-out strength of the pedicle screw was increased with an increase in bone mineral density and trajectory bone cement. It peaked at 75% filling, with the largest power consumption.

CONCLUSIONS

The optimal filling volume of the bone cement was 75% of the trajectory volume (about 1.03 mL). The use of excessive bone cement did not increase the fixation intensity but increased the risk of leakage.

Iliac vein compression syndrome from anterior perforation of a pedicle screw

May-Thurner syndrome is an anatomic variant where the right common iliac artery compresses the left common iliac vein. The variant exists in a significant portion of the population, but is usually asymptomatic; however, clinically significant stenosis can occur by iatrogenic means. In this report, we describe a patient who presents with left lower extremity pain and swelling. Initial workup for deep vein thrombosis was negative. After being referred to our venous clinic, a magnetic resonance angiography revealed narrowing of the left common iliac vein with a tortuous right common iliac artery crossing over the constriction. During left iliac vein stent placement, a pedicle screw from a prior L2-S1 spinal fusion was noted to be perforated through L5 vertebral body impinging the posterior aspect of the vein. This case demonstrates that increased scrutiny must be applied when dealing with pathology in close proximity to any implanted medical device.

Unplanned revision spinal surgery within a week: a retrospective analysis of surgical causes

Background

The need for revision surgery after a spinal surgery can cause a variety of problems, including reduced quality of life for the patient, additional medical expenses, and patient-physician conflicts. The purpose of this study was to evaluate the causes of unplanned revision spinal surgery within a week after the initial surgery in order to identify the surgical issues most commonly associated with unplanned revision surgery.

Methods

We retrospectively reviewed the medical records of all patients at who received a spinal surgery at a regional medical center from July 2004 to April 2011 in order to identify those who required a revision surgery within one week of their initial surgery. Patients were excluded if they received a vertebroplasty, kyphoplasty, or nerve block surgery, because those surgeries are one-day surgeries that do not require hospital admission. In addition, patients with a primary diagnosis of wound infection were also excluded since reoperations for infection control can be expected.

Results

The overall incidence of unplanned revision spinal surgery during the time period covered by this review was 1.12 % (116/10,350 patients). The most common surgical causes of reoperation were screw malposition (41 patients), symptomatic epidural hematoma (27 patients), and inadequate decompression (37 patients). Screw malposition was the most common complication, with an incidence rate of 0.82 %. Screw instrumentation was significantly associated with revision surgery (p = 0.023), which suggests that this procedure carried a greater risk of requiring revision. The mean time interval to reoperation for epidural hematomas was significantly shorter than the intervals for other causes of revision spinal surgery (p < 0.001), which suggests that epidural hematoma was more emergent than other complications. Also, 25.93 % of patients who underwent hematoma removal experienced residual sequelae; this percentage was significantly higher than for other surgical causes of revision spinal surgery (p = 0.013).

Conclusions

The results suggest that to avoid the need for reoperation, screw malposition, inadequate decompression, and epidural hematoma are the key surgical complications to be guarded against. Accordingly, adequate decompression, epidural hematoma prevention, and proper pedicle screw placement may help reduce the incidence of revision surgery.

What would be the annual cost savings if fewer screws were used in adolescent idiopathic scoliosis treatment in the US?

OBJECT

There is substantial heterogeneity in the number of screws used per level fused in adolescent idiopathic scoliosis (AIS) surgery. Assuming equivalent clinical outcomes, the potential cost savings of using fewer pedicle screws were estimated using a medical decision model with sensitivity analysis.

METHODS

Descriptive analyses explored the annual costs for 5710 AIS inpatient stays using discharge data from the 2009 Kids’ Inpatient Database (Healthcare Cost and Utilization Project, Agency for Healthcare Research and Quality), which is a national all-payer inpatient database. Patients between 10 and 17 years of age were identified using the ICD-9-CM code for idiopathic scoliosis (737.30). All inpatient stays were assumed to represent 10-level fusions with pedicle screws for AIS. High screw density was defined at 1.8 screws per level fused, and the standard screw density was defined as 1.48 screws per level fused. The surgical return for screw malposition was set at $23,762. A sensitivity analysis was performed by varying the cost per screw ($600–$1000) and the rate of surgical revisions for screw malposition (0.117%–0.483% of screws; 0.8%–4.3% of patients). The reported outcomes include estimated prevented malpositioned screws (set at 5.1%), averted revision surgeries, and annual cost savings in 2009 US dollars, assuming similar clinical outcomes (rates of complications, revision) using a standard- versus high-density pattern.

RESULTS

The total annual costs for 5710 AIS hospital stays was $278 million ($48,900 per patient). Substituting a high for a standard screw density yields 3.2 fewer screws implanted per patient, with 932 malpositioned screws prevented and 21 to 88 revision surgeries for implant malposition averted, and a potential annual cost savings of $11 million to $20 million (4%–7% reduction in the total cost of AIS hospitalizations).

CONCLUSIONS

Reducing the number of screws used in scoliosis surgery could potentially decrease national AIS hospitalization costs by up to 7%, which may improve the safety and efficiency of care. However, such a screw construct must first be proven safe and effective.

Control of Pedicle Screw Placement with an Electrical Conductivity Measurement Device: Initial Evaluation in the Thoracic and Lumbar Spine

Aim. Transpedicular screw fixation is widely used in spinal surgery. But the insertion of pedicle screws can sometimes be challenging because of the variability in pedicle size and the proximity of nerve roots. Methods. We detected intraoperatively the sensitivity for iatrogenic pedicel perforation with a hand-held electronic conductivity measurement device (ECD) that measures electrical conductivity of tissue-medium surrounding the instrument tip. ECD was used to guide the placement of 84 pedicle screws in 15 patients undergoing surgery for tumor or degenerative spinal disease at various spinal levels from T8 to L5. Additionally a CT-scan controlled screw positioning postoperatively. Results. The placement was "correct" (no mediocaudal pedicle wall penetration) for 78 of 84 (92,8%) screws, "suboptimal but acceptable" (0-2 mm penetration) for 4 of 84 (4,8%) screws, and "misplaced" (penetration > 2 mm) for 2 of 84 (2,4%) screws. Conclusion. Although this study was not designed to compare electronic conductivity technique to other guidance methods, such as fluoroscopy or navigation, a convincing "proof of concept" for ECD use in spinal instrumentation could be demonstrated. Advantages include easy handling without time-consuming setup and reduced X-ray exposure. However, further investigations are necessary to evaluate i.a. the economic aspects for this single-use developed instrument.

Is removal of the implants needed after fixation of burst fractures of the thoracolumbar and lumbar spine without fusion?

Methods

In this study of patients who underwent internal fixation without fusion for a burst thoracolumbar or lumbar fracture, we compared the serial changes in the injured disc height (DH), and the fractured vertebral body height (VBH) and kyphotic angle between patients in whom the implants were removed and those in whom they were not. Radiological parameters such as injured DH, fractured VBH and kyphotic angle were measured. Functional outcomes were evaluated using the Greenough low back outcome scale and a VAS scale for pain.

Results

Between June 1996 and May 2012, 69 patients were analysed retrospectively; 47 were included in the implant removal group and 22 in the implant retention group. After a mean follow-up of 66 months (48 to 107), eight patients (36.3%) in the implant retention group had screw breakage. There was no screw breakage in the implant removal group. All radiological and functional outcomes were similar between these two groups. Although solid union of the fractured vertebrae was achieved, the kyphotic angle and the anterior third of the injured DH changed significantly with time (p < 0.05).

Discussion

The radiological and functional outcomes of both implant removal and retention were similar. Although screw breakage may occur, the implants may not need to be removed. Take home message: Implant removal may not be needed for patients with burst fractures of the thoracolumbar and lumbar spine after fixation without fusion. However, information should be provided beforehand regarding the possibility of screw breakage. Cite this article: Bone Joint J 2016;98-B:109–16.