Thoracic Pedicle Screw Placement Research Articles

Pedicle Screw Placement in the Thoracic Spine

A cadaveric study comparing image guidance technology to fluoroscopic guidance as a means of pedicle screw placement in the thoracic spine, using a unique starting point for screw placement. To assess accuracy of thoracic pedicle screw placement using image guidance versus fluoroscopic guidance for screw insertion. While use of pedicle screws in the thoracic spine has been increasing, its adoption has been slower than for the lumbar spine, reflecting concern regarding possible vascular or spinal cord injury due to screw malplacement. Given these risks, efforts to improve the accuracy of thoracic pedicle screw placement remain appropriate. Stereotactic guidance has been applied in other aspects of spinal surgery to improve the accuracy of instrumentation placement. Pedicle screws were placed in the thoracic spines of eight cadavers, using either a stereotactic guidance or a manual, fluoroscopically guided technique. A slightly more superior and lateral starting point from prior descriptions was used. Each cadaver was instrumented with pedicle screws in the upper thoracic (T1-T2), middle thoracic (T4-T7), and lower thoracic (T9-T10) regions. In the upper and middle thoracic regions, screws with a 4.0-mm shank diameter were used while in the lower thoracic region a shank diameter of 4.5 mm was used. Postinstrumentation CT scans, followed by anatomic dissections, were used to evaluate screw exit rates and orientation relative to the pedicle axis. Exit rates for the two techniques and the effect of vertebral level on exit rate were compared using a chi analysis. The effect of pedicle diameter was tested using a Pearson correlation coefficient. No significant differences in the overall exit rates or orientation were found between the two techniques. There were significant differences in exit rates between the middle (47%), compared with the upper (9%) and lower (16%) thoracic regions, respectively (P < 0.001). A significant correlation between pedicle diameter and exit rate was also found (P < 0.0001). Our study showed no significant differences in the overall exit rates between the two techniques. Image guidance may increase confidence of surgeons with limited experience in thoracic pedicle screw placement. Successful placement of screws within the pedicle varies with the anatomic diameter of the pedicle itself. Concerns regarding accuracy of screw placement should be greatest in the middle thoracic vertebrae (T4-T7), where pedicle diameters are smallest and proximity of the great vessels is nearest.

Thoracic pedicle screw placement: Free-hand technique

Thoracic pedicle screws provide a number of advantages over other methods of spinal fixation in treating a variety of conditions including: better pull-out strength and greater control in the sagittal, coronal and rotational planes due to increased stability to axial, bending and rotational forces by three-column fixation, fewer vertebral motion segments arthrodesed, no or lessened need for postoperative bracing and secure fixation after laminectomy or incompetent posterior elements. In patients with spinal deformity, segmental pedicle fixation has demonstrated greater three-dimensional correction with decreased rates of curve progression and higher fusion rates, the ability to treat the rigid scoliosis between 70 and 100 curves without anterior release with smaller total hospital cost and direct apical vertebral derotation to enhance correction and potentially obviate the need for a thoracoplasty. Also, the flexibility of multiple screw types allows easier connection to rods, especially in patients with deformity. Despite the potential benefits, many surgeons have avoided placing thoracic pedicle screws because of their concern on neurologic, vascular and visceral complications. 26] The purpose of this manuscript is to delineate the “Free-Hand” thoracic pedicle screw placement with respect to the pertinent anatomy, placement technique, confirmation of the accurate screw placement, salvage, reported complications and several methods to help avoid such complications.

Posterior thoracic segmental pedicle screw instrumentation: Evolving methods of safe and effective placement

The use of pedicle screw instrumentation in the spine has evolved over the last two decades. The initial use of pedicle screws began in the lumbar spine. As surgeons have become more comfortable with the complex anatomy required for accurate screw placement, the use of pedicle instrumentation has evolved to include their use in the thoracolumbar and thoracic spine. The impetus behind their increased use is a result of the many advantages that pedicle screw anchorage offers over traditional hook and rod constructs. Improved deformity correction and overall construct rigidity are two important advantages of pedicle screw instrumentation due its three-column control over the spinal elements. First, pedicle screw instrumentation obviates the need to place instrumentation within the spinal canal with its inherent risk of neurologic injury. Second, the placement of pedicle screws is independent of facet or laminar integrity and thus has been extremely useful in traumatic, neoplastic, and degenerative conditions. The benefits of pedicle screws in the thoracic spine has been tempered by the potential for catastrophic neurological or soft tissue injuries due to the close proximity of these structures. The narrow and inconsistent shape of the thoracic pedicles, especially in spinal deformity, makes their placement technically challenging. As a result, surgeons have employed a number of techniques to ensure the safe and efficacious placement of thoracic pedicle screws. Detailed anatomic landmarks used to determine pedicle location, intraoperative imaging including navigation, and neurophysiological monitoring are some of the techniques currently used by surgeons. The implementation of these techniques and a thorough understanding of the complex three-dimensional anatomy have allowed surgeons to successfully place thoracic and thoracolumbar pedicle screws.

Technique of thoracic pedicle screw fixation for trauma

Thoracic fractures after trauma can lead to devastating neurological injury because of the close relationship among spinal cord, nerve roots, and their bony surroundings. Transpedicular fixation using pedicle screws in the thoracic spine is technically challenging but can be done safely and effectively if surgeons understand the complex anatomy of the region and adhere to biomechanical principles. This article discusses different approaches for placing pedicle screws in the thoracic spine and presents some case examples that demonstrate the technique. Surgeons involved with the operative management of spine trauma should become familiar with the placement of thoracic pedicle screws. The technique requires a thorough understanding of the anatomy of the region and the techniques used for placing instrumentation.

Free hand pedicle screw placement in the thoracic spine: is it safe?

A retrospective study. To evaluate the safety of a free hand technique of pedicle screw placement in the thoracic spine at a single institution over a 10-year experience. Thoracic pedicle screw fixation techniques are still controversial for thoracic deformities because of possible complications including neurologic. Three hundred ninety-four consecutive patients who underwent posterior stabilization utilizing 3204 transpedicular thoracic screws by 2 surgeons from 1992 to 2002 were analyzed. The mean age was 27 + 10 years (range 5 + 3-87 + 0 years) at the time of surgery. Etiologic diagnoses were: scoliosis in 273, kyphosis in 53, other spinal disease in 68. Pedicle screws were inserted using a free hand technique similar to that used in the lumbar spine in which anatomic landmarks and specific entry sites were used to guide the surgeon. A 2-mm tip pedicle probe was carefully advanced free hand down the pedicle into the body. Careful palpation of all bony borders (floor and four pedicle walls) was performed before and after tapping. Next, the screw was placed, followed by neurophysiologic (screw stimulation with rectus abdominus muscle recording) and radiographic (anteroposterior and lateral) confirmation. An independent spine surgeon using medical records and roentgenograms taken during treatment and follow-up reviewed all the patients. The number of the screws inserted at each level were as follows (total n = 3204): T1, n = 13; T2, n = 60; T3, n = 192; T4, n = 275; T5, n = 279; T6, n = 240; T7, n = 230; T8, n = 253; T9, n = 259; T10, n = 341; T11, n = 488; T12, n = 572. Five hundred seventy-seven screws inserted into the deformed thoracic spine were randomly evaluated by thoracic computed tomography scan to assess for screw position. Thirty-six screws (6.2%) were inserted with moderate cortical perforation, which meant the central line of the pedicle screw was out of the outer cortex of the pedicle wall and included 10 screws (1.7%) that violated the medial wall. There were no screws (out of the entire study group of 3204) with any neurologic, vascular, or visceral complications with up to 10 years follow-up. The free hand technique of thoracic pedicle screw placement performed in a step-wise, consistent, and compulsive manner is an accurate, reliable, and safe method of insertion to treat a variety of spinal disorders, including spinal deformity.

The accuracy of pedicle screw placement in the thoracic spine using the "Funnel Technique": part 1. A cadaveric study.

A cadaveric study using the "funnel technique" to probe thoracic pedicles was conducted. The results (location, level, and perforation rate) of three spine surgeons of varying experience were compared. The objectives were to evaluate the reliability and accuracy of the funnel technique for the placement of thoracic pedicle screws and to describe the technique. Nine fresh cadavers (216 thoracic pedicles) were used for pedicle screw placement using the funnel technique. The study was conducted by three spine surgeons with a significantly different level of experience in thoracic pedicle screw placement (72 thoracic pedicles each). Critical and noncritical perforations were recorded. The perforation rate was 6% (13 of 216 pedicles). Of this, only 0.4% (1 of 216) was a critical perforation (a contact with T8 nerve root). The junior spine surgeon who had no previous experience with thoracic pedicle screw placement had a 12.5% (9 of 72) perforation rate, the surgeon very familiar with the technique had a 5.5% (4 of 72) perforation rate, and the senior author who originated this technique had a 1.4% (1 of 70) perforation rate. All perforations made by the junior spine surgeon occurred in his first 24 pedicles; none occurred in his last 48 pedicles. The reliability of the funnel technique in placement of thoracic pedicle screws was proven in our cadaveric study. It provided even an entry-level surgeon with a safe way to identify and place thoracic pedicle screws. The funnel technique is a simple, safe, and cost-effective alternative to any other currently recommended techniques for pedicle screw placement.

3:41 Transcranial electric motor-evoked potential monitoring as an early indicator of emerging thoracic spinal cord ischemic injury

Purpose of study: Somatosensory evoked potential (SSEP) monitoring has enjoyed widespread application for assessing global spinal cord function during corrective thoracic spine surgery for scoliosis and trauma. Because the SSEP is dorsal column mediated, however, it can be insufficiently sensitive to identifying inadequate perfusion or impending ischemia to the anterior spinal cord. Transcranial electric motor-evoked potentials (TCEMEPs), on the other hand, permit real-time monitoring of the corticospinal tracts and, as such, provide instantaneous assessment of changes in spinal cord function secondary either to surgical insult or inadequate spinal cord blood flow from hypotension. The purpose of this study was to determine the sensitivity of TCEMEP monitoring as an early indicator of impending spinal cord injury during corrective thoracic spine surgery.Methods used: A retrospective chart review was performed for all adult patients who underwent thoracic or thoracolumbar spine surgery between January 2000 and December 2001 at a single institution. Perioperative neurophysiological monitoring included recording of posterior tibial nerve SSEPs and TCEMEPs (Digitimer, Ltd., Garden City, UK) recorded from hand, leg and foot muscles. Monitoring commenced after intubation and continued throughout the entire operative procedure. All patients who experienced a significant (greater than 75%) intraoperative TCEMEP or SSEP amplitude loss were identified. Hospital and office charts were also reviewed to obtain diagnosis, preoperative, immediate postoperative and follow-up neurologic data.of findings: Of 125 cases reviewed, significant intraoperative TCEMEP amplitude decreases that prompted surgical alert were noted in seven (5.6%). A concomitant significant SSEP amplitude loss was noted in only one of these patients and lagged behind the loss of TCEMEPs by 20 minutes. Of the remaining six patients, TCEMEP amplitude diminished by greater than 75% during placement of corrective hardware in four, whereas that for the two patients was secondary to acute hypotension (MAP < 50 mm Hg). SSEP amplitudes never changed across all six of these patients. When TCEMEP amplitude was significantly depressed, intraoperative intervention included reversal of corrective forces or complete hardware removal, increasing mean arterial blood pressure to al least 90 torr and administering high-dose methylprednisolone (NASCIS-2 protocol). Improvement in spinal cord motor function occurred in seven of the eight patients after surgical and/or medical intervention. None of these presented with postoperative neurologic deficit. The one patient who lost transcranial motor-evoked potentials after placement of thoracic pedicle screws, followed 20 minutes later by complete SSEP loss, never regained neurophysiological function and awoke with dense paraplegia as predicted.Relationship between findings and existing knowledge: These data suggest that TCEMEPs are a more sensitive and earlier indicator of impending spinal cord ischemic injury then somatosensory evoked potentials.Overall significance of findings: This study highlights the feared limitation of SSEPs for spinal cord monitoring; namely, the potential for false-negative results in the presence of impending spinal cord ischemic injury. As a result, TCEMEPs are recommended as the primary monitoring modality with SSEPs serving adjunctively.Disclosures: Device or drug: Digitimer D-185 Multi-pulse Motor Evoked Potential Stimulator. Status: investigational.Conflict of interest: No conflicts.

2:26 Safety of thoracic pedicle screw insertion with and without computer assistance: a cadaveric study

Purpose of study: The placement of pedicle screws is technically demanding and poses potential hazards related mainly to penetration of the anterolateral vertebral body or medial pedicle. To investigate safety, we undertook an in vitro analysis of thoracic pedicle screw placement by two senior spine surgeons using standard fluoroscopy, virtual fluoroscopy and computed tomography image guidance.Methods used: In a simulated OR environment, cadaveric thoracic spines with the posterolateral rib cage intact were mounted in foam. Pedicle screws were placed from T1 up to T11 in 20 cadaveric thoracic spines using standard anatomic landmarks and fluoroscopic guidance (Group 1), FluoroNav with one reference (Group 2) or multiple reference points (Group 3), and Stealth (Group 4). Radiation exposure to the surgeon's torso, hands and specimen were measured. The specimens were then dissected, sagittally split and examined for evidence of pedicle or vertebral body cortical screw perforations. Any cortical violation except the costovertebral junction was considered out. The cortical perforations were then graded by 2-mm increments. Statistical analysis was performed.of findings: There were 94, 99, 70 and 74 screws placed in the four groups. There was significantly more average radiation exposure to the specimen in Group 3 (27 mREM) and less in Group 4 (0 mREM) than in Group 1 (7.8 mREM). Radiation exposure to the surgeon was minimal, measuring less than 1 mREM to the surgeon's torso per specimen in all groups except 4 (0 mREM). Average time per screw was significantly longer in Group 4 (6.8 minutes) compared with Group 1 (2.4 minutes). Cortical violations were significantly less in Group 3 (11.4%) and Group 4 (5.4%) compared with Group 1 (20.2%). The only medial cortical violations were in Group 1, and none were greater than 2 mm.Relationship between findings and existing knowledge: Anatomic landmarks and standard fluoroscopy have been shown to have approximately 20% thoracic screw malpositioning. The current study confirms this and demonstrates greater accuracy with image guidance.Overall significance of findings: Although the time for screw placement was longer with Stealth and FluoroNav, the percentage of screws with cortical violations was significantly less. Computer-assisted thoracic pedicle screw placement may provide more accurate placement and less risk to critical structures.Disclosures: Device or drug: pedicle screws. Status: approved. Device or drug: FluoroNav. Status: approved. Device or drug: Stealth. Status: approved.Conflict of interest: Christopher Shaffrey, grant research support; Jens Chapman, grant research support Syntles USAAO/ASIF International Sofamor Danek; Jens Chapman, CHAIR, Surgical Dynamics.

Comparison of FlouroNav and standard fluoroscopy for placement of thoracic pedicle screws

Andrew T. Dailey, MD, Darrel S. Brodke, MD, Matthew Rondina, BS, Kent N. Bachus, PhD, Salt Lake City, UT, USA; Thomas H. Jansen, MS, Memphis, TN, USAIntroduction: Despite its wide use in the lumbar spine, pedicle screw fixation has not been universally accepted in the thoracic spine. Morphometric data have shown the thoracic pedicles to be very narrow in transverse diameter, particularly in the T4–T7 region. However, studies have appeared in the literature illustrating the use of pedicle screws for trauma and deformity correction with pedicle perforation rates of 15% to 25%. Recently, the combination of image-guided surgery and fluoroscopy or virtual fluoroscopy has been introduced to improve the ease and accuracy of pedicle screw placement and reduce radiation exposure to the surgeon. This study is an in vitro comparison of a freehand fluoroscopically guided technique with that using virtual fluoroscopy (FlouroNav) in the placement of thoracic pedicle screws.Methods: Eight cadaveric spines with ribs intact were instrumented from T1 to T12. Preoperative computed tomography (CT) scans were performed to assess pedicle size and orientation. Pedicles larger than 5.5 mm were instrumented with 5.5 mm diameter screws, and those ranging from 4.5 to 5.5 mm had 4.5-mm screws placed. Any pedicles less than 4.5 mm were not instrumented. The freehand technique was performed using fluoroscopic images (OEC 9600) in the lateral and anteroposterior (AP) planes to guide the pedicle finder. An entry point at the intersection of the superior border of the transverse process and the lateral two thirds of the facet was used to start the pedicle finder. In the spines instrumented with FlouroNav, the dynamic reference arc was applied to the spinous process of the vertebrae, AP and lateral fluoroscopy images were acquired (OEC 9600 with calibration device attached), and then three adjacent vertebrae were instrumented using the image-guided pedicle awl and finder. Postoperatively, CT scans were performed using 3-mm cuts with 1 mm overlap through the entire vertebral body to assess accuracy of screw placement. Results were compared using chi-squared tests with significance set at p <.05.Results: A total of 158 pedicles were instrumented in both groups (n = 84, freehand; n = 74, FlouroNav). Screw placement was graded on CT as follows: Grade 0, no pedicle perforation; Grade 1, threads out only (less than 2 mm); Grade 2, core screw diameter outside the pedicle (2 to 4 mm) and Grade 3, screw entirely outside the pedicle. Accuracy was confirmed with visual inspection of the dissected spine. In the freehand spines, 16% of screws had Grade 2 perforations, 24% had Grade 1 perforations and 60% were Grade 0. With FlouroNav guidance, there were no Grade 2 perforation, 16% Grade 1 perforations and 84% were Grade 0 (p <.05). Combining Grade 0 and 1 perforations, accuracy was 84% with freehand versus 100% with FlouroNav (p <.05). Only 5% of perforations using either technique were medial perforations, and all were Grade 1 perforations. The amount of fluoroscopy time was reduced by more than 60% using the FlouroNav technique (FlouroNav, 1.2 seconds/screw; freehand, 3.1 seconds/screw).Discussion: Virtual fluoroscopy significantly improved accuracy of screw placement in the thoracic spine and reduced the amount of radiation exposure secondary to C-arm fluoroscopy. Although the biomechanical strength of thoracic pedicle screws that do not have an ideal trajectory remains to be determined, the avoidance of neurological and vascular complications is clinically relevant. Further studies will reveal the utility of these systems in the clinical setting.

Use of a transpedicular drill guide for pedicle screw insertion in the thoracic spine

A transpedicular drill guide (TDG) was designed to assist in the safe placement of pedicle screws in the thoracic spine. In a preliminary study, pilot holes were drilled into the pedicles (T1 to T12) of eight anatomical models in order to compare the conventional anatomical technique to the TDG. Visual inspection of the drilled pedicles was performed. Subsequently in a cadaveric study, pilot holes were made using the TDG in the thoracic spine (T1 to T11) of one human cadaver before inserting 4.5 mm diameter screws. CT scan followed by visual inspection of the cadaveric spine was performed to evaluate the position of the screws. With the anatomical models, 19 of 96 (19.8%) holes drilled using the TDG and 64 of 96 (66.7%) holes drilled using the anatomical technique violated the pedicle wall (p<0.001). The TDG reduced the rate of medial perforation. Ninety-nine percent of the pilot holes made with the TDG were within 2 mm from the pedicle wall compared to 79.2% for the anatomical technique. In the cadaveric study, one of the 22 (4.5%) screws violated the medial wall of the right T1 pedicle by less than 1 mm. No screw penetrated the anterior vertebral cortex, nor the lateral, superior or inferior pedicle wall. The TDG is easy to use and can decrease the incidence of misplaced thoracic pedicle screws. The TDG could be used alone as an alternative to navigation systems in certain applications or with fluoroscopy during thoracic pedicle screw placement, especially for training surgeons.

Triggered electromyographic threshold for accuracy of thoracic pedicle screw placement in a porcine model.

A porcine model of thoracic pedicle screw insertion was used to determine the effect of screw position on triggered electromyographic response. To develop a model of intraoperative detection of misplaced thoracic pedicle screws. Triggered electromyographic stimulation has been a valuable aid in determining appropriate placement of lumbar pedicle screws. The use of pedicle screws is increasing in the thoracic spine. Misplaced thoracic pedicle screws may have significant implications if the spinal cord is injured. This study was an attempt to determine whether the established lumbar model can be used for thoracic pedicle screws. Five 120- to 150-lb domestic pigs had 85 pedicle screws placed bilaterally in the thoracic spine at each level from T6 to T15. Screws were inserted entirely in the pedicle (Group A). After removal of the medial pedicle wall, the screws were reinserted in the pedicle with no neural contact (Group B). The screws were then placed with purposeful contact with the neural elements (Group C). The screws were stimulated, eliciting an electromyographic response in the intercostal muscles for each instrumented level. The type of response noted was classified as either primary (response from appropriate nerve root), secondary (response at different root) or no response (response at different root, no response at appropriate root). Two hundred fifty responses were recorded. A primary response was noted in 72% of recordings. There was a relatively consistent decrease in the triggered electromyographic response from Group A (mean 4.15 +/- 1.80 mA) to Group C (mean 3.02 +/- 2.53 mA) screws (P = 0.0003). There was little difference in the response obtained from Group A to Group B (mean 4.37 +/- 2.48 mA) screws (P > 0.05). When a primary response was recorded, the mean threshold electromyographic response recorded was significantly lower than recordings with secondary and no response recordings (P < 0.05). Even though there was a consistent decrease between the A and C screws that was more definitively separated when a primary response was elicited, it was not possible to determine a cutoff trigger electromyographic level that would consistently differentiate intraosseous from epidural pedicle screw placement. Furthermore, this method could not differentiate screws clearly in the pedicle from screws with medial pedicle wall breakthrough. A more direct method of spinal cord monitoring must be established to provide the surgeon with early warning of the potential of neural injury in the placement of thoracic pedicle screws.

Use of a guide device to place pedicle screws in the thoracic spine: a cadaveric study. Technical note.

In this cadaveric study, the safety and accuracy of a specially designed guide device for the placement of thoracic pedicle screws was investigated in a normal anatomical situation. Five embalmed human cadaveric thoracic spines (T1-12) were used for the study of transpedicular screw placement in the thoracic spine. Overall 120 screws were placed at all thoracic levels. The screws were inserted bilaterally in the thoracic pedicles by using a specially designed guide device. No radiographs or other imaging studies were obtained. Following screw placement, computerized tomography scans were performed to evaluate the accuracy of the pedicle screw positioning. Seven (5.8%) of the screws penetrated the pedicle wall or the vertebral body (VB) cortex. Two screws (1.7%) penetrated the medial wall of the pedicle. Two screws (1.7%) penetrated the lateral wall of the pedicle, and one screw (0.8%) penetrated the lateral wall of the pedicle and the anterior VB cortex simultaneously. Two screws (1.7%) penetrated the anterior VB cortex. Compared with the results of other studies, the findings here indicate that using this device to guide the placement of thoracic pedicle screws can significantly reduce the incidence of pedicle penetration, particularly in the medial wall.

Image-guid ed thoracic pedicle screw placement: a technical study in cadavers and preliminary clinical experience

Thoracic pedicle screw fixation is effective and reliable in providing short-segment stabilization. Although the procedure is becoming more widely used, accurate insertion of the screws is difficult due to the small dimensions of thoracic pedicles, and the associated risk is high due to the proximity of the spinal cord. In previous studies authors have shown the accuracy of image-guided lumbar pedicle screw placement, but there have been no reported investigations into the accuracy of image-guided thoracic pedicle screw placement. The authors report their experience with such an investigation. To evaluate the accuracy of image-guided thoracic pedicle screw placement in vitro and in vivo, thoracic pedicle screws were placed with an image-guidance system in five human cadavers and 10 patients. In cadavers, the accuracy of screw placement was assessed by postoperative computerized tomography and visual inspection and in patients by postoperative imaging studies. Of the 120 pedicle screws placed in five cadavers pedicle violation occurred in 23 cases (19.2%); there was one pedicle violation (4.2%) in each of the last two cadavers. Of the 45 pedicle screws placed in 10 patients, pedicle violations occurred in three (6.7%). In comparison with historical controls, the accuracy of thoracic pedicle screw placement is improved with the use of an image-guidance system. It allows the surgeon to visualize the thoracic pedicle and the surrounding structures that are normally out of the surgical field of view. The surgeon, however, must be aware of the limitations of an image-guidance system and have a sound basic knowledge of spinal anatomy to avoid causing serious complications.

Computer-assisted thoracic pedicle screw placement: an in vitro feasibility study.

In this cadaveric study, a computer-assisted image guidance system was tested for accuracy of thoracic pedicle screw placement. Evaluate the system's accuracy for thoracic pedicle screw placement in vitro. The effective use and reliability of pedicle screw instrumentation in providing short-segment stabilization and correction of deformity is well known in the lumbar spine. Pedicle screw placement in the thoracic spine is difficult because of the small dimensions of the thoracic pedicles and risk to the adjacent spinal cord and neurovascular structures. Investigators have shown the improved accuracy of computer-assisted lumbar pedicle screw placement; but the accuracy of computer-assisted thoracic pedicle screw placement, which is becoming more widely used, has not been shown. In five human cadavers, 120 thoracic pedicle screws were placed with computer-assisted image guidance. The largest clinically feasible screw was used based on the cross-sectional dimensions of each pedicle. The accuracy was assessed by postoperative computed tomography and visual inspection. The overall pedicle cortex violation was 23 of 120 pedicles (19.2%). Nine violations (7.5%) were graded as major and 14 (11.7%) as minor. A marked and progressive learning curve was evident with the perforation rates that decreased from 37.5% in the first cadaver to 4.2% in the last two cadavers. Accurate thoracic pedicle screw placement is feasible with computer-assisted surgery. However, as with any other new surgical technology, the learning curve must be recognized and incorporated into the necessary fundamental knowledge and experience for these procedures.

804 Comparison of FluoroNav and Standard Fluoroscopy for Placement of Thoracic Pedicle Screws

Dailey, Andrew T. MD; Brodke, Darrel S. MD; Rondina, Matthew T. BS; Jansen, Thomas H. MSc; Bachus, Kent N. PhD

807 Thoracic Pedicle Screws Are a Safe and Effective Alternative for Thoracic Spinal Stabilization

Screws placed in the pedicles of the thoracic spine provide a biomechanically superior form of stabilization when compared to standard posterior stabilization techniques. Tranditional thoracic stabilization techniques (hooks, rods, cables) immobilize the posterior column of the spine. Thoracic pedicle screws provide for stabilization of the posterior, middle, and anterior columns of the spine. Twenty one patients (8 males, 13 females) with a mean age of 42 years (range 22–76 years) had placement of thoracic pedicle screws over a 2 year period. Surgery was performed for trauma (12), infection (5), congenital (2), degenerative (1), and neoplastic (1) conditions. Revision surgery to correct an iatrogenic spinal deformity from a prior failed procedure was performed in 7 patients. Nine patients had ASIA class A spinal cord injuries and 12 had incomplete lesions (ASIA classes C-E). A total of 141 screws were placed (T1-T4: 43, T5- T8: 43, T9-T12: 55). Image guidance (Stealth) was...

Thoracic Pedicle Screw Placement Guided by Computed Tomographic Measurements

Cadaveric pedicle screw placement guided by the measurements from axial computed tomography (CT) scans in the thoracic spine was assessed in this study. Axial CT scans were performed on four cadaveric thoracic spines, and the measurements included the pedicle transverse angle, inner pedicle width, and distance between the midline of the vertebra and the pedicle axis on the dorsal aspect of the lamina. With utilization of the data from CT scans, screws were directly placed into the thoracic pedicle from T1 to T10. Screw penetration of the pedicle was determined by gross examination. The results showed that the largest pedicle transverse angle was found at the levels of T1-2, and the smallest occurred at the T3 through T8 levels. The value of the pedicle inner width was quite different between specimens with a minimum of 3.0 mm at T4 and a maximum of 9.2 mm at T10. Gross examination of the pedicle showed that 13 (16.3%) of 80 screws penetrated the pedicle wall, with a Grade I penetration in 11 pedicles and a Grade II penetration in 2 pedicles. Screw penetration of the medial wall was found in four pedicles and penetration of the lateral wall was noted in nine pedicles. No screw penetration of the superior and inferior walls of the pedicle was identified in any of the four specimens. Thoracic pedicle screw placement guided by the measurements from axial CT scans significantly reduced the incidence of pedicle penetration. Axial CT measurements of the pedicle inner diameter and transverse angle as well as the starting point for screw insertion are recommended if pedicle screw fixation is intended in the thoracic spine.

Thoracic Pedicle Screw Placement Guided by Computed Tomographic Measurements

Cadaveric pedicle screw placement guided by the measurements from axial computed tomography (CT) scans in the thoracic spine was assessed in this study. Axial CT scans were performed on four cadaveric thoracic spines, and the measurements included the pedicle transverse angle, inner pedicle width, and distance between the midline of the vertebra and the pedicle axis on the dorsal aspect of the lamina. With utilization of the data from CT scans, screws were directly placed into the thoracic pedicle from T1 to T10. Screw penetration of the pedicle was determined by gross examination. The results showed that the largest pedicle transverse angle was found at the levels of T1–2, and the smallest occurred at the T3 through T8 levels. The value of the pedicle inner width was quite different between specimens with a minimum of 3.0 mm at T4 and a maximum of 9.2 mm at T10. Gross examination of the pedicle showed that 13 (16.3%) of 80 screws penetrated the pedicle wall, with a Grade I penetration in 11 pedicles and a Grade II penetration in 2 pedicles. Screw penetration of the medial wall was found in four pedicles and penetration of the lateral wall was noted in nine pedicles. No screw penetration of the superior and inferior walls of the pedicle was identified in any of the four specimens. Thoracic pedicle screw placement guided by the measurements from axial CT scans significantly reduced the incidence of pedicle penetration. Axial CT measurements of the pedicle inner diameter and transverse angle as well as the starting point for screw insertion are recommended if pedicle screw fixation is intended in the thoracic spine.