Radiographic verification of pedicle screw pilot hole placement using Kirshner wires versus beaded wires

Novel MIS 3D NAV Single Step Pedicle Screw System (SSPSS): Workflow, Accuracy and Initial Clinical Experience

STUDY DESIGN

Prospective case series.

OBJECTIVE

SSPSS (single step pedicle screw system) was developed for minimally invasive spine surgery. We performed this study to report on safety, workflow, and our initial clinical experience with this novel technique.

METHODS

The prospective study was conducted on patients who underwent pedicle screw fixation between October 2017 and April 2018 using a novel single step 3D navigated pedicle screw system for MIS. Outcome measurements were obtained from intraoperative computerized tomography. The images were evaluated to determine pedicle wall penetration. We used a grading system to assess the severity of the pedicle wall penetration. Breaches were classified as grade 1 (<2 mm), grade 2 (2-4 mm), or grade 3 (<4 mm),¹ and as cranial, caudal, medial, and lateral.

RESULTS

Our study includes 135 screws in 24 patients. SSPSS eliminated K-wires and multiple steps traditionally necessary for MIS pedicle screw insertion. The median time per screw was 2.45 minutes. 3 screws were corrected intraoperatively. Pedicle wall penetration occurred in 14 screws (10%). Grade 1 breaches occurred in 4 screws (3%) and grade 2 breaches occurred in 10 screws (7%). Lateral breaches were observed more often than medial breaches. The accuracy rate in our study was 90% (Grade 0 breach). No revision surgeries were needed and no complications occurred.

CONCLUSIONS

Our study suggests that SSPSS could be a safe, accurate, and efficient tool. Our accuracy rate is comparable to that found in the literature.

Accurate placement of cervical pedicle screws using 3D-printed navigational templates : An improved technique with continuous image registration

OBJECTIVE

Accurate placement of cervical pedicle screws remains a surgical challenge. This study aimed to test the feasibility of using a novel three-dimensional (3D-)printed navigational template to overcome this challenge.

METHODS

Cervical spines were scanned using computed tomography (CT). A 3D model of the cervical spines was created. The screw trajectory was designed to pass through the central axis of the pedicle. Thereafter, a navigational template was designed by removing the soft tissue from the bony surface in the 3D model. A 3D printer was used to print the navigational template. The screws were then placed in the cadavers following CT scanning. The 3D model of the designed trajectory and the placed screws were registered. The coordinates of the entry and exit points of the designed trajectory and the actual trajectory were recorded. The numbers of qualified points that met the different degrees of accuracy were compared using a χ² test.

RESULTS

A total of 158 screws were placed. Five screws breached the pedicle cortex with a distance <2 mm. There was no significant difference between the pre- and postoperative entry points with a degree of accuracy ≥1.7 mm (P = 0.131). Meanwhile, there was no significant difference between the pre- and postoperative exit points with degrees of accuracy ≥6.4 mm (P = 0.071).

CONCLUSION

A navigational template can be designed by removing the soft tissue from the bony surface in a CT-generated 3D model. This guiding tool may effectively prevent intraoperative drifting and accurately places cervical pedicle screws.

Spinal instrumentation in infants, children, and adolescents: a review

OBJECTIVEThe evolution of pediatric spinal instrumentation has progressed in the last 70 years since the popularization of the Harrington rod showing the feasibility of placing spinal instrumentation into the pediatric spine. Although lacking in pediatric-specific spinal instrumentation, when possible, adult instrumentation techniques and tools have been adapted for the pediatric spine. A new generation of pediatric neurosurgeons with interest in complex spine disorder has pushed the field forward, while keeping the special nuances of the growing immature spine in mind. The authors sought to review their own experience with various types of spinal instrumentation in the pediatric spine and document the state of the art for pediatric spine surgery.METHODSThe authors retrospectively reviewed patients in their practice who underwent complex spine surgery. Patient demographics, operative data, and perioperative complications were recorded. At the same time, the authors surveyed the literature for spinal instrumentation techniques that have been utilized in the pediatric spine. The authors chronicle the past and present of pediatric spinal instrumentation, and speculate about its future.RESULTSThe medical records of the first 361 patients who underwent 384 procedures involving spinal instrumentation from July 1, 2007, to May 31, 2018, were analyzed. The mean age at surgery was 12 years and 6 months (range 3 months to 21 years and 4 months). The types of spinal instrumentation utilized included occipital screws (94 cases); C1 lateral mass screws (115 cases); C2 pars/translaminar screws (143 cases); subaxial cervical lateral mass screws (95 cases); thoracic and lumbar spine traditional-trajectory and cortical-trajectory pedicle screws (234 cases); thoracic and lumbar sublaminar, subtransverse, and subcostal polyester bands (65 cases); S1 pedicle screws (103 cases); and S2 alar-iliac/iliac screws (56 cases). Complications related to spinal instrumentation included hardware-related skin breakdown (1.8%), infection (1.8%), proximal junctional kyphosis (1.0%), pseudarthroses (1.0%), screw malpositioning (0.5%), CSF leak (0.5%), hardware failure (0.5%), graft migration (0.3%), nerve root injury (0.3%), and vertebral artery injury (0.3%).CONCLUSIONSPediatric neurosurgeons with an interest in complex spine disorders in children should develop a comprehensive armamentarium of safe techniques for placing rigid and nonrigid spinal instrumentation even in the smallest of children, with low complication rates. The authors' review provides some benchmarks and outcomes for comparison, and furnishes a historical perspective of the past and future of pediatric spine surgery.

Transsacral transdiscal L5-S1 screws for the management of high-grade spondylolisthesis in an adolescent

The surgical management of high-grade spondylolisthesis in adolescents remains a controversial issue. Because the basic procedure, posterolateral fusion, is associated with a significant rate of pseudarthrosis and listhesis progression, there is a pressing need for alternative surgical techniques. In the present report, the authors describe the case of an adolescent patient with significant low-back pain who was found to have Grade IV spondylolisthesis at L5-S1 that was treated with transsacral transdiscal screw fixation. Bilateral pedicle screws were placed starting from the top of the S-1 pedicle, across the L5-S1 intervertebral disc space, and into the L-5 body. At 14 months after surgery, the patient had considerable improvement in his pain and radiographic fusion across L5-S1. The authors conclude that transsacral transdiscal pedicle screws may serve as an efficacious and safe option for the correction of high-grade spondylolisthesis in adolescent patients.

The mechanisms of medial pedicle wall violation: insertion method is as important as correct cannulation of the pedicle

A cadaver study aims to determine the mechanisms of medial pedicle wall violation after a correct cannulation of the pedicle. The study presents finding out the effect of insertion angle and insertion force on medial wall violation. We used 100 lumbar pedicles of cadavers. Special wooden blocks were produced to simulate a fixed angle fault after a correct pedicle cannulation. Pedicles were divided into 4 groups: 10-degree free drive (group 10), 15-degree free drive (group 15), 10-degree push drive (group 10P), and 15-degree push drive (group 15P). After insertion of pedicle screws, laminectomies were done and the pedicles were evaluated from the inside. Pedicle complications were more in group 10P than group 10 (P = 0.009). Medial wall fracture (P = 0.002) and canal penetration were more in group 15P than group 15 (P = 0.001). Groups 10P and 15P were similar regarding medial wall fractures but canal penetration was significantly higher in group 15P (P = 0.001). Medial wall breaches can happen after correct cannulation of pedicles. Change in insertion angle is one factor but the most important factor is the use of a pushing force while inserting a screw. The pedicle seems to be extremely tolerant to insertion angulation mistakes up to 10 degrees and tends to lead the screw into the correct path spontaneously.

Pathophysiological effects of lumbar instrumentation surgery on lumbosacral nerve roots in the vertebral foramen: measurement of local pressure of intervertebral foramen

STUDY DESIGN

Measurement of local pressure of the intervertebral foramina.

OBJECTIVE

To evaluate the pathophysiological effects of lumbar instrumentation surgery on lumbosacral nerve roots in the vertebral foramen.

SUMMARY OF BACKGROUND DATA

The physiological states of lumbosacral nerve roots in the vertebral foramen remain controversial.

METHODS

From 2000 to 2012, 11 of 710 patients with L4 degenerative spondylolisthesis failed to develop postoperative radiculopathy because of intraoperative pedicle screw malposition (L5: 10, L4: 1). We prospectively evaluated the local pressure at the L4-L5 and L5-LS vertebral foramina in 18 patients with L4 degenerative spondylolisthesis. All patients underwent L4-L5 posterolateral fusion (PLF) with L3-L4-L5 laminotomy. Intraoperatively, local pressure of the intervertebral foramen was measured using a catheter pressure transducer while changing the lumbar spine posture, and the measurement was performed before and after L4-L5 PLF.

RESULTS

The local pressures at the L4-L5 vertebral foramen were 29.74 ± 16.26 and 51.57 ± 23.18 mm Hg (before fixation), and 39.13 ± 17.69 and 41.71 ± 17.94 mm Hg (after fixation) in the lumbar spine neutral and extension postures, respectively. The local pressure before fixation increased significantly during lumbar spine extension (P < 0.001), although the value after fixation was almost identical. The local pressures at the L5-LS vertebral foramen were 26.91 ± 18.16 and 54.36 ± 26.67 mm Hg (before fixation), and 24.82 ± 17.1 and 58.46 ± 32.78 mm Hg (after fixation) in the lumbar spine neutral and extension postures, respectively. The local pressure before and after fixation increased significantly during lumbar spine extension (P < 0.001), and the values after fixation were higher than those before fixation.

CONCLUSION

The local pressure at the L4-L5 vertebral foramen did not change during lumbar extension after L4-L5 PLF, whereas the local pressure at the L5-LS vertebral foramen was significantly increased during lumbar extension after L4-L5 PLF. Our results suggested that the nerve roots caudal to the fixed segments may be exposed to higher external dynamic stresses after lumbar instrumentation surgery.

LEVEL OF EVIDENCE

4.

Intraoperative three-dimensional fluoroscopy after transpedicular positioning of Kirschner-wire versus conventional intraoperative biplanar fluoroscopic control: A retrospective study of 345 patients and 1880 pedicle screws

STUDY DESIGN

Retrospective study.

OBJECTIVE

The aim was to find out whether intraoperative three-dimensional imaging after transpedicular positioning of Kirschner wire (K-wire) in lumbar and thoracic posterior instrumentation procedures is of benefit to the patients and if this technique is accurately enough to make a postoperative screw position control through computer tomography (CT) dispensable.

PATIENTS AND METHODS

Lumbar and thoracic posterior instrumentation procedures conducted at our department between 2002 and 2012 were retrospectively reviewed. The patients were divided into two groups: group A, including patients who underwent intraoperative three-dimensional scan after transpedicular positioning of the K-wire and group B, including patients who underwent only intraoperative biplanar fluoroscopy. An early postoperative CT of the instrumented section was done in all cases to assess the screw position. The rate of immediate intraoperative correction of the K-wires in cases of mal-positioning, as well as the rate of postoperative screw revisions, was measured.

RESULTS

In general, 345 patients (1880 screws) were reviewed and divided into two groups; group A with 225 patients (1218 screws) and group B with 120 patients (662 screws). One patient (0.44%) (one screw [0.082%]) of group A underwent postoperative screw correction while screw revisions were necessary in 14 patients (11.7%) (28 screws [4.2%]) of group B. Twenty-three patients (10.2%) (28 K-wires [2.3%]) of group A underwent intraoperative correction due to primary intraoperative detected K-wire mal-position. None of the corrected K-wires resulted in a corresponding neurological deficit.

CONCLUSION

Three-dimensional imaging after transpedicular K-wire positioning leads to solid intraoperative identification of misplaced K-wires prior to screw placement and reduces screw revision rates compared with conventional fluoroscopic control. When no clinical deterioration emerges, a postoperative CT seems to be dispensable using this intraoperative three-dimensional control method.

Navigated guide tube for the placement of mini-open pedicle screws using stereotactic 3D navigation without the use of K-wires

Object

Three-dimensional spinal navigation increases screw accuracy, but its implementation in clinical practice has been difficult, mainly because of surgeons' concerns about increased operative times, disturbance of workflow, and safety. The authors present a custom-designed navigated guide that addresses some of these concerns by allowing for drilling, tapping, and placing the final screw via a minimally invasive approach without the need for K-wires. In this paper, the authors' goal was to describe the technical aspects of the navigated guide tube as well as pedicle screw accuracy.

Methods

The authors present the technical details of a navigated guide that allows drilling, tapping, and the placement of the final screw without the need for K-wires. The first 10 patients who received minimally invasive mini-open spinal pedicle screws are presented. The case series focuses on the immediate postoperative outcomes, pedicle screw accuracy, and pedicle screw–related complications. An independent board-certified neuroradiologist determined pedicle screw accuracy according to a 4-tiered grading system.

Results

The navigated guide allowed successful placement of mini-open pedicle screws as part of posterior fixation from L-1 to S-1 without the use of K-wires. Only 7-mm-diameter screws were placed, and 72% of screws were completely contained within the pedicle. Breaches less than 2 mm were seen in 23% of cases, and these were all lateral except for one screw. Breaches were related to the lateral to medial trajectory chosen to avoid the superior facet joint. There were no complications related to pedicle screw insertion.

Conclusions

A novel customized navigated guide tube is presented that facilitates the workflow and allows accurate placement of mini-open pedicle screws without the need for K-wires.

Surgeon's view of pedicle screw implantation for the monitoring neurophysiologist

Pedicle screws have become the gold standard of spinal instrumentation over the past decade owing to their biomechanical superiority. Despite their advantages, pedicle screw instrumentation is potentially dangerous, and surgeons wish to improve accuracy of screw placement to avoid complications associated with screw misplacement. The anatomy of the pedicles is variable throughout the spine, and several landmarks and trajectories have been suggested to aid safe placement of pedicle screws in the spine. Several techniques such as x-ray and computed tomography scan imaging coupled with computer-aided navigation are available to improve accuracy of screw insertion. Intraoperative neuromonitoring with the help of triggered electromyographic recordings has evolved as an objective evidence of assessing pedicle breach and proximity of the screw to neural structures. While all imaging and electrophysiological modalities should be applied on an individualized basis, finally no adjunctive technique can fully replace the need for surgical expertise and experience.

Alignment of pedicle screws with pilot holes: can tapping improve screw trajectory in thoracic spines?

Pedicle screws are placed using pilot holes. The trajectory of pilot holes can be verified by pedicle sounding or radiographs. However, a pilot hole alone does not insure that the screw will follow the pilot hole. No studies have characterized the risk of misalignment of a pedicle screw with respect to its pilot hole trajectory. The objective of this study was to measure the misalignment angles between pedicle screws and pilot holes with or without tapping. Six human cadaveric thoracic spines were used. One hundred and forty pilot holes were created with a straight probe. Steel wires were temporarily inserted and their positions were recorded with CT scans. The left pedicles were tapped with 4.5 mm fluted tap and the right pedicles remained untapped. Pedicle screws (5.5 mm) were inserted into the tapped and untapped pedicles followed by CT scans. The trajectories of pilot holes and screws were calculated using three-dimensional vector analysis. A total of 133 pilot holes (95%) were inside pedicles. For the untapped side, 14 out of 68 (20%) screws did not follow the pilot holes and were outside the pedicles. For the tapped side, 2 out of 65 (3%) did not follow and breached the pedicles. The average misalignment angles between the screw and pilot hole trajectory were 7.7 degrees +/- 6.5 degrees and 5.6 degrees +/- 3.2 degrees for the untapped side and tapped side, respectively (P < 0.05). Most pedicle screws had lateral screw breach (13 out of 16) whereas most pilot holes had medial pedicle breach (6 out of 7). Tapping of pilot holes (1 mm undertap) helps align pedicle screws and reduces the risk of screw malposition. Although most pedicle screws had lateral breach, the risk of medial pedicle breach of the pilot holes must be recognized.

Correlation between low triggered electromyographic thresholds and lumbar pedicle screw malposition: analysis of 4857 screws

STUDY DESIGN

A retrospective analysis of 1078 spinal surgical procedures with lumbar pedicle screw placement at a single institution.

OBJECTIVE

Based on previously established normative values, triggered electromyographic stimulation (TrgEMG) was re-examined to evaluate its efficacy in determining screw malposition.

SUMMARY OF BACKGROUND DATA

Threshold values for confirmation of intraosseous placement of pedicle screws with EMG stimulation is controversial.

METHODS

TrgEMG threshold values for 4857 pedicle screws placed from L2 to S1 from 1996 to 2005 were analyzed. An ascending method of constant current stimulation was applied to each pedicle screw to obtain a compound muscle action potential (CMAP) from lower extremity myotomes. Previously determined threshold value normative data from a published clinical series of 233 screws were as follows: 0 to 4 mA, high likelihood of pedicle wall breach; 4 to 8 mA, possible pedicle wall breach; >8 mA, no pedicle wall defect.

RESULTS

A total of 7.74% (376 of 4857) of all screws tested had threshold values <8.0 mA. A total of 19.1% (72 of 376) of these were <4.0 mA: 54% (39 of 72) were repositioned (26) or removed (13) while the remaining 33 screws were left in place following repalpation. A total of 80.9% (304 of 376) had thresholds between 4 and 8 mA: 17.4% (53) were repositioned (38) or removed (15). Nine screws had thresholds of <or=2.8 mA and were either repositioned or removed following confirmation of a medial wall breach. A total of 74.5% (280 of 376) of all screws with thresholds <8.0 mA were verified as correctly placed by repalpation/radiography and therefore left in place.

CONCLUSION

The probability of a medial breach pedicle screw detected by triggered EMG stimulation increases with decreasing triggered EMG thresholds: 0.31% for >8.0 mA, 17.4% for 4.0 to 8.0 mA, 54.2% for <4.0 mA, and 100% for <2.8 mA. At 2.8 mA, triggered EMG has a specificity of 100%, with sensitivity of 8.4%; at 4.0 mA, specificity of 99% and sensitivity of 36%; and at 8.0 mA, 94% specificity and 86% sensitivity. TrgEMG is an adjunct technique and should always be used in conjunction with palpation and radiography to optimize safe pedicle screw placement.

C-arm assessment of cervical pedicle screw: screw coaxial fluoroscopy and oblique view

STUDY DESIGN

Oblique view and screw coaxial fluoroscopy were used to assess cervical pedicle screw position in human cadaveric spine, results of which were compared with those of direct visual inspection by an anatomist.

OBJECTIVES

To determine whether clinicians can detect misplaced cervical pedicle screws with accurate sensitivity and specificity using conventional C-arm equipment.

SUMMARY OF BACKGROUND DATA

In the cervical region, pedicle screws have not been used so popularly as in lumbar or in thoracic regions. The reasons are related to the risk of inserting screw in small pedicle. So far, no method has been studied to assess the position of cervical pedicle screw during the operation.

METHODS

Ten human cadavers were prepared for this study. Headed and nonheaded pedicle screws were inserted bilaterally from C3-C7. Using C-arm oblique and screw coaxial fluoroscopy, the depth of penetration was recorded in 2-dimension scale (superoinferior and mediolateral direction) by 6 different observers. The vertebrae were all harvested, and the penetration depth was recorded by an anatomist under direct visualization. The accuracy of C-arm measurements was analyzed. The results of nonheaded and headed screws also were compared.

RESULTS

A total of 98 pedicle screw positions were finally enrolled into the study. The oblique view can verify screw position with the sensitivity of 86.1% and specificity of 64.5%. Coaxial fluoroscopy had a sensitivity of 89.8% and a specificity of 56.9% in superoinferior direction. Mediolaterally coaxial fluoroscopy had a sensitivity of 70.0% and a specificity of 51.3%.

CONCLUSION

C-arm assessment of pedicle position has acceptable accuracy. With C-arm swing motion of the coaxial fluoroscopy, headed screws were also inspected without any difference as nonheaded screws. Measurements for superoinferior direction showed better sensitivity than those for mediolateral direction, which are supposed to be related to be elliptical shape and thin lateral margin of cervical pedicle.

Pedicle screw placement accuracy: a meta-analysis

STUDY DESIGN

A meta-analysis of the published literature was conducted specifically looking at accuracy and the postoperative methods used for the assessment of pedicle screw placement in the human spine.

OBJECTIVES

This study specifically aimed to identify postoperative methods used for pedicle screw placement assessment, including the most common method, and to report cumulative pedicle screw placement study statistics from synthesis of the published literature.

SUMMARY OF BACKGROUND DATA

Safety concerns have driven specific interests in the accuracy and precision of pedicle screw placement. A large variation in reported accuracy may exist partly due to the lack of a standardized evaluation method and/or the lack of consensus to what, or in which range, is pedicle screw placement accuracy considered satisfactory.

METHODS

A MEDLINE search was executed covering the span from 1966 until 2006, and references from identified papers were reviewed. An extensive database was constructed for synthesis of the identified studies. Subgroups and descriptive statistics were determined based on the type of population, in vivo or cadaveric, and separated based on whether the assistance of navigation was employed.

RESULTS

In total, we report on 130 studies resulting in 37,337 total pedicle screws implanted, of which 34,107 (91.3%) were identified as accurately placed for the combined in vivo and cadaveric populations. The most common assessment method identified pedicle screw violations simply as either present or absent. Overall, the median placement accuracy for the in vivo assisted navigation subgroup (95.2%) was higher than that of the subgroup without the use of navigation (90.3%).

CONCLUSIONS

Navigation does indeed provide a higher accuracy in the placement of pedicle screws for most of the subgroups presented. However, an exception is found at the thoracic levels for both the in vivo and cadaveric populations, where no advantage in the use of navigation was found.

Probing for thoracic pedicle screw tract violation(s): is it valid?

BACKGROUND

Preparation of the thoracic pedicle screw tract is a critical step prior to the placement of screws. The ability to detect pedicle wall violation(s) by probing prior to insertion of thoracic pedicles screws, however, has not been studied. The purpose of this study was to evaluate the inter- and intraobserver agreement and the accuracy in detecting thoracic pedicle screw tract violation(s) among surgeons at various levels of training.

METHODS

With use of a straightforward trajectory, under direct visualization, 108 thoracic pedicle screw tracts (54 cadaveric thoracic vertebrae) were prepared in a standard fashion, followed by tapping with a 4.5-mm cannulated tap. A deliberate pedicle violation was randomly created by an independent investigator in either the anterior, the medial, or the lateral wall in 65 pedicles. Following this, four blinded, independent surgeons at various levels of training probed the specimens on three separate occasions to determine if a breach was present (1,296 discrete data points). Surgeon findings were then recorded as breach present or absent and, if present, breach location. The Cohen kappa correlation coefficient (kappa a) and 95% confidence interval were used to assess the accuracy of the observers and the inter- and intraobserver agreement.

RESULTS

The mean accuracy over three iterations, the validity in detecting the breach location, and the intraobserver agreement varied by level of training and experience, with the most experienced observer (observer 1) scoring the best and the least experienced observer (observer 4) scoring the worst. The three most senior surgeons had good intraobserver agreement. Interobserver agreement was low between the four observers.

CONCLUSIONS

An observer's ability to accurately detect the presence or absence of a pedicle tract violation and the breach location, if present, is dependent on the surgeon's level of training. Probing the pedicle tract prior to placement of pedicle screws in the thoracic spine is likely a learned skill that improves with repetition and experience.

Thoracic pedicle screws: postoperative computerized tomography scanning assessment

OBJECT

The authors evaluated the accuracy of placement of thoracic pedicle screws by performing postoperative computerized tomography (CT) scanning. A grading system is presented by which screw placement is classified in relation to neurological, bone, and intrathoracic landmarks.

METHODS

One hundred eighty-five thoracic pedicle screws were implanted in 27 patients with the assistance of computer image guidance or fluoroscopy. Postoperative CT scanning was conducted to determine a grade for each screw: Grade I, entirely contained within pedicle; Grade II, violates lateral pedicle but screw tip entirely contained within the vertebral body (VB); Grade III, tip penetrates anterior or lateral VB; Grade IV, breaches medial or inferior pedicle; and Grade V, violates pedicle or VB and endangers spinal cord, nerve root, or great vessels and requires immediate revision. Based on anatomical morphometry, the spine was subdivided into upper (T1-2), middle (T3-6), and lower (T7-12) regions. Statistical analyses were performed to compare regions. The mean follow-up period was 37.6 months. The following postoperative CT scanning-documented grades were determined: Grade I, 160 screws (86.5%); Grade II, 15 (8.1%); Grade III, six (3.2%); Grade IV, three (1.6%); and Grade V, one (0.5%). Among cases involving screw misplacements, Grade II placement was most common, and this occurred most frequently in the middle thoracic region.

CONCLUSIONS

The authors' grading system has advantages over those previously described; however, further study to determine its reliability, reproducibility, and predictive value of clinical sequelae is warranted. Postoperative CT scanning should be considered the gold standard for evaluating thoracic pedicle screw placement.

In vivo accuracy of thoracic pedicle screws

STUDY DESIGN

A retrospective observational study of 279 transpedicular thoracic screws using postoperative computed tomography (CT).

OBJECTIVE

To determine the accuracy of transpedicular thoracic screws.

SUMMARY OF BACKGROUND DATA

Previous studies have reported the importance of properly placed transpedicular thoracic screws. To our knowledge, the in vivo accuracy of pedicle screw placement throughout the entire thoracic spine by CT is unknown.

METHODS

The accuracy of thoracic screw placement within the pedicle and vertebral body and the resultant transverse screw angle (TSA) were assessed by postoperative CT. Cortical perforations of the pedicle were graded in 2-mm increments. Screws were regionally grouped for analysis.

RESULTS

Forty consecutive patients underwent instrumented posterior spinal fusion using 279 titanium thoracic pedicle screws of various diameters (4.5-6.5 mm). The regional distribution of the screws was 39 screws at T1-T4, 77 screws at T5-T8, and 163 screws at T9-T12. Fifty-seven percent of screws were totally confined within the pedicle. Although medial perforation of the pedicle wall occurred in 14% of screws, in <1% there was >2 mm of canal intrusion. Lateral pedicular perforation occurred in 68% of perforating screws and was significantly more common than medial perforation (P < 0.0005). Seventeen screws penetrated the anterior vertebral cortex by an average of 1.7 mm. Screws inserted between T1 and T4 had a decreased incidence of full containment within the pedicle (P < 0.0005) and vertebral body (P = 0.039) compared with T9-T12. The mean TSA for screws localized within the pedicle was 14.6 degrees and was significantly different from screws with either medial (mean 18.0 degrees ) or lateral (mean 11.5 degrees ) pedicle perforation (P < 0.0005). Anterior vertebral penetration was associated with a smaller mean TSA of 10.1 degrees (P = 0.01) and with lateral pedicle perforation (P < 0.0005). There were no neurologic or vascular complications.

CONCLUSIONS

Ninety-nine percent of screws were fully contained or were inserted with either < or =2 mm of medial cortical perforation or an acceptable lateral breech using the "in-out-in" technique. Anterior cortical penetration occurred significantly more often with lateral pedicle perforation and with a smaller mean TSA. The incidence of fully contained screws was directly correlated with the region of instrumented thoracic spine.