Pedicle morphology of the lower thoracic and lumbar spine in a Chinese population

Pedicle screw placement with a free hand technique in thoracolumbar spine: is it safe?

STUDY DESIGN

Computerized tomography (CT) analysis of in vivo pedicle screw placement to determine their exact position in relation to the pedicle in thoracolumbar region (T10-L3).

OBJECTIVE

To evaluate the clinical accuracy of the placement of thoracolumbar pedicle screws with a free hand technique after reviewing preoperative imaging.

SUMMARY OF BACKGROUND DATA

CT scans have been used in research clinical settings to evaluate pedicle screw placement in thoracolumbar spine.

MATERIAL AND METHODS

Ninety-eight consecutive patients who underwent posterior stabilization using 640 transpedicular screws by 1 surgeon from T10 to L3 were analyzed. The mean age was 36.1+/-15.1 (13 to 73) years at the time of surgery. Pedicle screws were inserted using anatomic landmarks; specific entry sites, preoperative anteroposterior/lateral radiographs, and CT imaging were used to guide the surgeon. After preparation of entry point, a pedicle probe was carefully advanced free hand down the pedicle into the body. Careful palpation of all bony borders (flour and 4 pedicle walls) was performed before placement the screw. Postoperative CT scans were used to evaluate the position of all pedicle screws inserted. Screw cortical penetration was graded on the basis of anatomy (the wall penetrated) and distance of the penetration, with 2 mm of interval.

RESULTS

The number of screws inserted at each level were as follows: T10 (n=55), T11 (n=124), T12 (n=118), L1 (n=91), L2 (n=146), and L3 (n=106). Analysis of these pedicle screws using postoperative CT scans confirmed 37 (5.8%) violated screws, including 12 medial, 18 lateral, 2 superior, 1 inferior, and 4 anterolateral vertebral body penetrations. No neurologic, vascular, or pleural injuries occurred. No screws required postoperative repositioning.

CONCLUSIONS

Pedicle screw placement with a free hand technique after reviewing preoperative imaging seems to be accurate, reliable, and safe adjunct for the placement of thoracolumbar spine screws.

Pulse-train stimulation for detecting medial malpositioning of thoracic pedicle screws

STUDY DESIGN

Thoracic pedicle screw location and the current needed to stimulate adjacent neural tissue was evaluated using brief, high-frequency pulse trains and monitoring electromyography (EMG) from muscles in the lower limbs.

OBJECTIVE

To establish a safe and reliable method for detecting medial malpositioning of pedicle screws placed in the thoracic spine during instrumentation and fusion.

SUMMARY OF BACKGROUND DATA

Neurophysiologic studies for testing thoracic pedicle screw placement used single-pulse stimulation and monitored EMG from thoracic-innervated muscles. We propose that with this approach, stimulation fails to activate lower motor neurons innervated by spinal cord axons, such that medial malplacement of screws will go largely undetected.

METHODS

EMG was monitored from multiple lower-limb muscles. Pedicle tracks were created free-hand, using a curved pedicle finder. A ball-tipped probe-insulated along its shaft-was used to palpate the walls of the pedicle tracks. During probing, constant-current, high-frequency 4-pulse stimulus trains were delivered through the ball tip, and the minimum current (i.e., threshold) needed to evoke EMG was determined for each pedicle track. The threshold current for stimulation through each screw was also determined. Postoperative serial computed tomography scans of all implanted thoracic and L1 screws were rated with respect to screw position and the pedicle wall.

RESULTS

A total of 116 screws were implanted in 7 subjects. Two pedicle tracks were redirected during surgery because of particularly low thresholds to stimulation. Definite medial defects were found in 19 screws, 18 of which were detected by the experimental technique. For these screws, the average threshold to probe stimulation of their associated pedicle tracks was 7.9 +/- 4.6 mA, much lower than current thresholds for less medially placed pedicle tracks. Stimulation of these screws resulted in high thresholds (19.8 +/- 5.3 mA) when a response was evoked at all; stimulating 8 of these 19 medially malpositioned screws failed to elicit any lower-limb EMG at considerably higher (25 or 30 mA) stimulus intensities.

CONCLUSION

This preliminary study supports the hypothesis that high-frequency stimulus pulse trains areeffective at detecting defects in the medial wall of pedicles in the thoracic spine during instrumentation, thereby improving on techniques using single-pulse stimulus protocols.

CT evaluation of cervical pedicle in a Chinese population for surgical application of transpedicular screw placement

The lower cervical pedicle size differs between the Chinese and the non-Chinese population. Knowledge of pedicle dimensions and surface landmarks is crucial for the safe placement of screws, but few quantitative data concerning the lower cervical pedicle using CT scan and multiplanar reformations (MPR) in a Chinese population exist. The aim of this study was to evaluate lower cervical pedicle (C3-C7) dimensions in a Chinese population by computed axial tomography for surgical application. The dimensions of the pedicles (C3-C7) were determined in 60 patients from CT images of cervical spinal lesions. Measurements of pedicle height, width, pedicle axis length, effective length, and two angles of the pedicles, the distances from the projection point of the pedicle axis to the lateral edge of the lateral mass and to the inferior edge of the superior facet were measured. The smallest outer pedicle width was found at C3 among the female and C4 among the male. This measurement was significantly different between male and female patients in the outer pedicle width (P < 0.05; independent samples t test) at C3 and C4. The mean values of the outer pedicle width ranged from 5.4 to 6.7 mm in males, and 4.4 to 6.3 mm in females. The projection point of the pedicle axis in the lateral-superior area of the cervical lateral mass was the most important. There were significant correlations (P < 0.01; Kendall's W test) between the vertebral level and both pedicle angles (PTA and PSA). The smallest pedicle transverse angle was at C7 in males and females. The cervical spinal cord or vertebral artery may be at risk of injury if the angulation of the screw insert is over-medial or over-lateral in the transverse plane. Therefore, preoperative CT evaluation of pedicle transverse angle is very important. Considering the amount of variation among individuals, our data on CT measurements of pedicle in a Chinese population in conjunction with evaluation of the results of preoperative CT may enhance the safety of transpedicular screw fixation in the lower cervical spine.

Pedicle and spinal canal parameters of the lower thoracic and lumbar vertebrae in the achondroplast population

STUDY DESIGN

Retrospective morphometric population study.

OBJECTIVE

To characterize pedicle and spinal canal morphology of the achondroplastic lower thoracic and lumbar vertebrae and to suggest dimensions for improving pedicle screw selection and placement.

SUMMARY OF BACKGROUND DATA

Although morphometric population studies exist for various races, to our knowledge, no such analysis has been made in achondroplastic patients.

METHODS

With computer software, we measured pedicle parameters on the computed tomography images of 19 adult achondroplastic patients.

RESULTS

Pedicle and chord lengths ranged from 9.5-12.5 mm and 29.5-36.4 mm, respectively. Transverse pedicle diameter increased from T9 (5.5 mm) to L5 (14.2 mm). Sagittal pedicle diameter declined from L1 (11.6 mm) to L5 (7.8 mm). Transverse angulation was greatest at L5 (15.7 degrees ) and smallest at T12 (1.1 degrees ). Pedicles were directed cranially at all levels, ranging from 3.8 degrees -15.6 degrees . Interpedicular distance and cross-sectional area were smallest at L4 (14.9 mm and 119 mm, respectively). Pedicle starting points diverged from T9 (13.6 mm) to L5 (19.2 mm2).

CONCLUSION

Achondroplastic pedicle morphology differs markedly from those of the normal spine: chord lengths are substantially shorter, pedicles are inclined cranially, pedicle starting points diverge progressively in the lumbar spine, and pedicle shape transitions from vertically to horizontally oriented ellipsoids along the lumbar spine. Consideration of this variation could maximize the effectiveness and safety of pedicle instrumentation.

Is it safer to place pedicle screws in the lower thoracic spine than in the upper lumbar spine?

STUDY DESIGN

An anatomic study of 100 patients comparing the pedicle isthmic width of the lower thoracic spine and the upper lumbar spine using magnetic resonance imaging.

OBJECTIVES

To compare the lower thoracic pedicles and upper lumbar pedicles in nondeformity patients as a surrogate measure of safety of pedicle screw use.

SUMMARY OF BACKGROUND DATA

Pedicle isthmic width is the significant limiting factor in the safety and proper placement of transpedicular screws. The presumption in the past has been that the lumbar pedicles are larger than the thoracic pedicles. Few publications in the English-language literature specifically evaluate the association between the pedicle isthmic widths of the lower thoracic and upper lumbar.

METHODS

The study evaluates 100 patients, without coronal spinal deformities. MRIs were obtained of the pedicles from T10 to L2 and subsequently measured using the axial T2-weighted views. Lower thoracic and upper lumbar pedicle isthmus, the narrowest section of pedicle, was investigated and compared. The "medial pedicle to medial rib corridor" at T10-T12 was defined and measured as part of the methodology of the study. Statistical analysis included one-way analysis of variance with post hoc least significant difference pairwise comparisons.

RESULTS

The smallest pedicle isthmic width was at L1 (mean +/- SD, 6.0 +/- 1.6 mm), while T12 (mean +/- SD, 7.6 +/- 1.5 mm) had the largest pedicle width. Although smaller in diameter than T12, both T10 (mean +/- SD, 6.2 +/- 1.2 mm) and T11 (mean +/- SD, 7.5 +/- 1.6 mm) had larger pedicle width than L1 (P < 0.01). Pedicle widths were larger in males compared with females (P < 0.05).

CONCLUSIONS

The results show that the lower thoracic pedicles are larger than the upper lumbar pedicles. This may make it safer to place screws in the lower thoracic spine than in the upper lumbar spine. Upper lumbar may be so small (<5 mm) to preclude safe conventional screw placement.

Analysis of anatomic morphometry of the pedicles and the safe zone for through-pedicle procedures in the thoracic and lumbar spine

Posterior instrumentation through the pedicle is a common surgery. Understanding the morphometry of the pedicle and the anatomy of adjacent neural structures should help decrease the risk of postoperative complications. T1-L5 segments from 15 sets of human vertebrae were separated into individual vertebrae and the morphometric characteristics of the thoracic and lumbar spine and the safe zone of the pedicle were analyzed. T11-L5 segments from six human cadavers were dissected. Measurements were taken from the pedicle to the dura and nerve roots superiorly, inferiorly, medially, and laterally, and the transverse angles of the nerve roots were measured. Pedicles were widest in L5 and narrowest in T4 in the transverse plane, and widest in T11 or T12 and narrowest in T1 in the sagittal plane. In individual pedicle, the ranges of the safe zone width and height were 3.4-7.7 and 8.6-13.7 mm, respectively, in T1-T10; and 7.2-17.8 and 13.9-16.7 mm, respectively, in T11-L5. The transverse angle of the pedicle decreases progressively from T1 to T12, then increase from L1 to L5. In sagittal angle, the largest angle localized at T2 and the smallest at L5. The mean distances from pedicles to adjacent neural structures were greater superiorly and laterally than inferiorly and medially. The lateral distance between nerve root and the pedicle ranged from 2.4 to 9.6 mm in lumbar spine. This study provides potential safe zones for the application of through-pedicle procedures to help decrease the risk of postoperative complications.

Computer analysis of the safety of using three different pedicular screw insertion points in the lumbar spine in the Chinese population

To help decide the best starting point for lumbar spine pedicle screw insertion in the Chinese population using three different techniques (Roy-Camille, Magerl, and Du). Three-dimensional CT reconstructions were created from 40 adult lumbar vertebral segments. Three different starting points for lumbar pedicle screw insertion were used. The direction of the pedicle screw through each hole was simulated on three-dimensional reconstructed images. Precise CT measurements were made to assess the distance from the simulated screw and the medial and lateral pedicle walls at the smallest transverse section of each pedicle. To measure a pedicle transverse section angle (TSA) lines were drawn on a CT scan in the direct axis of the pedicle, tangential to the medial, and separately lateral, walls of the pedicles at the isthmus. The angle these lines made with an anterior to posterior line, which directly bisected the mid-portion of the vertebral body was called the TSA. The greater the difference between the TSA between the medial and lateral walls provides the greatest flexibility for the insertion angle of the pedicle screw. Additionally, the distance from a line drawn in the direct central axis of the pedicle was measured from the point of exit from the pedicle to the entry point of each of three insertion techniques (Du, Mageral, and Roy-Camille), to help understand potential risk factors. There were statistically significant differences between the distances from the entrance point to the direct pedicle axis among the three methods (P < 0.001). Du's insertion point was the shortest from L1 to L4. The distances measured following Magerl's technique were shortest at L5 (P < 0.05). There was no significant difference of the safe range of the TSA between the three methods from L1 and L2 (P > 0.05), but significant differences at L3, L4, and L5 (P < 0.05). At L3 and L4 the safe ranges of TSA using Du and Magerl's methods were significantly larger than those measured by Roy-Camille (P < 0.05). At L5 the safe ranges of TSA for the Magerl technique were the greatest among the three methods (P < 0.05). These results demonstrate that Du's method provides the safest starting point to place pedicle screws from L1 to L4, as its distance from the entrance point to the pedicle axis is the shortest and the safe range of TSA the largest of the three techniques. Magerl's technique can be safely used in the pedicles from L3 to L5, and is the safest choice at L5. Roy-Camille's technique is most applicable at L1 and L2, but has the highest risk when applied from L3 to L5.

Human osseous intervertebral foramen width

Alterations of the width of the human intervertebral foramen can play a pathophysiological role in low back pain. Osseous dimensions of the human intervertebral foramen are rarely recorded. Therefore, we present reference data obtained from skeletal samples of known lifestyle, population affinity, sex, and age at death. Cervical, thoracic, and lumbar vertebrae of functional transition zones of 71 macroscopically normal spines from early 19th century AD Swiss burial sites were selected. The intervertebral foramen widths (IFW) were analyzed with respect to possible lateralization and the impact of sex, individual age, and stature. Neither a significant side difference nor a correlation of IFW with individual age or stature could be found. Females show somewhat larger IFW than males, especially in the lumbar region. Data comparisons with earlier studies are limited due to methodological differences and possible interpopulational variations. Furthermore, the osseous intervertebral foramen only reveals a glimpse of the clinically relevant in vivo structure. Nevertheless, more focus on the osseous dimensions of the intervertebral foramen will provide baseline data of this important anatomical landmark. These data could also explore the peculiarities of the intervertebral foramen, such as its reverse sex dimorphism.

Computerized tomographic measurement of the cervical pedicles diameter in a Malaysian population and the feasibility for transpedicular fixation

STUDY DESIGN

The cervical pedicle diameter size differs between Asians and non-Asians. The authors studied the transverse pedicle diameter of the C2-C7 of the cervical spine in a Malaysian population using computerized tomography (CT) measurements. The transverse diameter of the pedicle is the determinant of the feasibility of this technique because the sagittal diameter of the pedicle has been wider than the transverse pedicle diameter.

OBJECTIVES

To study the average transverse pedicle diameter of the cervical spine in a Malaysian population, and evaluate the feasibility and safety of pedicle screw fixation in these patients.

SUMMARY OF BACKGROUND DATA

Cervical transpedicular screw fixation has been safe and is most probably going to be the gold standard for cervical spine fixation. However, its use in the Asian population should be considered cautiously because our cervical pedicle diameter may not be adequate to accommodate the standard pedicle screw size, which can be dangerous because there are vital structures located adjacent to the pedicles.

METHODS

The measurements of the cervical pedicles were performed on CT images using its measurement tools. CT cutting was made at 2.5-mm intervals. The pedicle transverse diameters were defined as the most outer diameter of the pedicle, taken perpendicular to the axis of the pedicle and measured in millimeters up to 0.1 mm.

RESULTS

The mean transverse diameters of the cervical pedicle of C2, C3, C4, C5, C6, and C7 in males were 5.4, 5.2, 5.1, 5.2, 5.5, and 6.5 mm, respectively, and ranged between 5.1 and 6.5 mm. In females, the mean transverse diameter of the cervical pedicle of C2, C3, C4, C5, C6, and C7 were 5.0, 4.6, 4.7, 4.9, 5.2, and 5.6 mm, respectively, and ranged between 4.6 and 5.6 mm. If the minimum transverse diameter required is 5.0 mm for 3.5-mm screw insertion, about 4.2% to 54.2% (male) of pedicles at different levels and 6.7% to 73.3% (females) of patients cannot have fixation with a 3.5-mm screw using this technique.

CONCLUSION

Transpedicular screw fixation for the cervical spine must not be attempted in the Malaysian population before the exact pedicle diameters are known.Therefore, preoperative CT evaluation is a must before transpedicular fixation is performed, especially in female patients. Because the margin for mistake is very narrow, it is best avoided in upper cervical spines.

Accuracy Over Space and Time of Computer-Assisted Fluoroscopic Navigation in the Lumbar Spine In Vivo

OBJECTIVE

The integration of digital image-guided surgical navigation with C-arm fluoroscopy, known as virtual fluoroscopy (VF), has been shown to enhance the safety of spine surgery in vitro. Few clinical studies have assessed the accuracy of VF during actual spinal surgery, and no studies have investigated variations in accuracy over the course of a series of measurements obtained during operative cases. We sought to study the intraoperative accuracy of VF over time and space during lumbar pedicle screw placement in human patients.

METHODS

Fluoroscopic images of the lumbar spine were obtained, calibrated, and saved to the Stealth Station (FluoroNav) on seven patients undergoing lumbar fusion surgery. The tracking arc was attached to an exposed lumbar spinous process, which was designated the index level. With use of anatomic surface irregularities in the laminae and spinous processes, several points were identified and registered on three different vertebrae directly adjacent to the index level vertebra. Every 15 minutes, throughout the operative case, the probe was brought to each point and the apparent distance from the original location recorded (as measured by the FluoroNav system). Measurements were collected from three vertebral levels adjacent to the index level over a time course of 120 minutes during the operation.

RESULTS

At the index, index +1, index +2, and index +3 levels, 89%, 81%, 92%, and 64% of measurements were within <2 mm, whereas 97%, 96%, 97%, and 91% were within <3 mm, respectively. At 15, 30, 45, 60, 75, 90, 105, and 120 minutes, 96%, 89%, 85%, 61%, 85%, 90%, 93%, and 50% of measurements were within <2 mm, whereas 100%, 93%, 100%, 83%, 100%, 90%, 100%, and 100% of measurements were within <3 mm, respectively. The error in millimeters tended to increase as the distance from the index level increased (R = 0.19, P < 0.05) and as operative time increased (R = 0.26, P < 0.01). Calibration studies of intraoperative VF (IoVF) in the lumbar spine documented a reasonable degree of accuracy. The majority of sequential measurements obtained during IoVF in the lumbar spine were within an error range of <3 mm.

CONCLUSIONS

Our results suggest that the use of VF is a reliable method of verifying the use of anatomic and/or radiographic landmarks for guidance during lumbar pedicle screw placement.

Pedicle dimensions of the thoracic and lumbar vertebrae in the Greek population

The aim of this study is to understand the magnitude of the pedicle's diameters for the use of pedicle screw fixation in spinal instrumentation. Pedicle dimensions from T1 to L5 were measured in 16 whole human cadaver spines (eight women and eight men). The mean age at the time of death was 67.2 (range: 59-84 years). The external transverse, the external sagittal, and the internal transverse diameter pedicle widths were measured with electronic calipers both on the right and left pedicles. The widest external transverse diameter was at the L5 level with a mean of 13.61 mm (range: 10.29-16.20 mm). The narrowest external transverse pedicle diameter was at the T5 level with a mean of 5.09 mm (range: 4.10-6.88 mm). The widest external sagittal pedicle diameter was at the T11 level with a mean of 17.02 mm (range: 14.84-19.57 mm), while the narrowest one was at T1 level with a mean of 8.90 mm (range: 7.18-11.37 mm). The maximum internal transverse pedicle diameter was at the L5 level with a mean 8.95 mm (range: 7.10-11.21 mm), while the minimum was at the T5 level with a mean 3.90 mm (range: 3.10-4.82 mm). Statistical significant greater pedicle dimensions were found in males at multiple levels. Pedicle dimensions at the levels from T3 to T8 need preoperative evaluation with computed tomography before the insertion of pedicle screws with diameter more than 5 mm. Pedicles at T12 to L5 levels may accommodate screws of 7 mm diameter.

Comparative assessment of pedicle morphology of the lumbar spine in various degenerative diseases

Measurement of the morphological dimensions of the pedicles of the lumbar spine was conducted using computed tomography (CT) to clarify the difference in pedicle morphology among different lumbar degenerative diseases. The subjects were 136 patients with lumbar spinal disorders who underwent myelography followed by CT scans. They were divided into four groups, that is a group of 25 patients with degenerative spondylolisthesis (DS group), a group of 54 patients with lumbar canal stenosis (LCS group), a group of 42 patients with lumbar disc herniation (LDH group), and a control group of 15 patients with spinal cord tumor in cervicothoracic region but without lumbar diseases (control group). Measurements of the transverse diameter, axial length, and axial angle of the pedicles were performed on CT slices obtained at the middle of the pedicle. The transverse diameter was the width of the isthmus, the axial length was the distance between the anterior of the vertebral body and the posterior of the vertebral arch on a line perpendicular to the line bisecting the isthmus, and the axial angle was the angle between the line perpendicular to the line bisecting the isthmus and the midline of the vertebral body. While there were no significant differences in the mean transverse diameter or axial length among the four groups, the mean axial angle was significantly smaller in the DS and LCS groups when compared to that in the LDH and control groups. In the DS and LCS groups, the pedicles were more sagitally oriented than in the LDH and control groups. Such difference in the axial angle of the pedicles in different lumbar diseases should be taken into consideration when placing at the insertion of pedicle screws, because precise orientation of screw insertion would scarcely allow penetration of the pedicle wall.

Morphometric analysis of the thoracic and lumbar spine in Japanese on the use of pedicle screws

The pedicle screw and hook have become popular instruments in treating spinal deformity and disease. This study gathered morphological data on thoracic and lumbar spines in a Japanese population that should serve as useful reference for posterior instrumentation surgery. One hundred and three dry bones were used to investigate the morphology of pedicle and facet in thoracic and lumbar spines. Measurements included the diameter and axial length of pedicle from T8 to L5, height and width of facets and thickness of articular processes from T1 to T12, and axial angle of pedicle from T1 to L5. The diameter and axial length of pedicle were smallest at T8, diameter was largest at L5 and axial length was largest at L3. Height of facets and thickness of articular processes were largest at T12. Men tended to have larger pedicles and facets than women. Transverse angle of pedicle was smallest at T12. These precise data may provide useful information when performing posterior instrumentation surgery and when developing new spinal implant systems for Asians.

Morphometric study of the thoracic vertebral pedicle in an Indian population

STUDY DESIGN

Morphometric study of the thoracic vertebral pedicular parameters and comparison with the previous studies in the literature.

OBJECTIVES

To define pedicular dimensions and screw placement in the Indian population.

SUMMARY OF THE BACKGROUND DATA

Pedicular morphometric characteristics vary in different population groups. Thoracic pedicular screw fixation is being used more frequently with the advent of better imaging methods. Because of the small size and close proximity to the neurovascular structures, thoracic pedicle fixation has little margin of safety.

METHODS

T1-T12 vertebral pedicles were studied in 18 cadavers by direct, roentgenographic, and computerized tomographic scan methods. The following parameters were studied: transverse diameter, transverse angle, sagittal diameter, sagittal angle, chord length, interpedicular distance, pedicle entrance point, and pedicle cortical thickness (medial and lateral). RESULTS.: Transverse diameter was more than 6 mm at both ends of the thoracic spine (T1, T2, T11, and T12). Between T3-T9 levels, it was less than 5 mm at some levels. The transverse angle was widest at T1 (30 degrees) and was less than 5 degrees from T5 to T12. Pedicles were directed cephalad in the sagittal plane at all thoracic levels. Sagittal angle was less than 12 degrees at all thoracic levels. Chord length was largest at T11 (37.3 mm) and smallest at T1 and T2 (29.9 mm). Interpedicular distance was 29 mm at T12 and 21.3 mm at T1. Medial pedicular cortex was thicker than lateral cortex at all levels.

CONCLUSIONS

These results suggest that even a 4-mm screw should be used carefully at the midthoracic level; 5-mm screw seems to be safe at upper and lower thoracic spine. Because of very small sagittal and transverse angle at mid and lower thoracic levels, the pedicular screw should be inserted along almost perpendicular line in these planes; 25-mm and 30-mm screw length appears to be safe at upper thoracic and lower thoracic levels, respectively. Pedicle entrance point lies along the midtrans-verse line at upper thoracic levels and along the upper border of transverse process at lower thoracic levels.

Measurements of the lumbar pedicles in the Eastern Anatolian population

Pedicle screw fixation of the spine has become one of the most stable and versatile methods of spine fixation, and knowledge of pedicle morphology is crucial for the safe application of these systems. We undertook this study because only a few reports have investigated Eastern populations. Lumbar pedicle anatomy, i.e., pedicle width (PW) and pedicle height (PH), transverse and sagittal pedicle angles (TPA, SPA), and pedicle length (PL), were assessed in the following two groups: (1) computed tomography scans of 29 normal adults, and (2) 16 dried lumbar spines obtained from the Anatomy Department. Interpedicular distance was different in each group. PW ranged from 4 mm to 14 mm. In both groups, the narrowest PH was 8.2 mm, the widest 19.7 mm. TPA ranged from 6(o) to 19(o) and increased from L1 to L5. In the sagittal plane, the pedicles angled caudally at L5. PL was longest at L1 and shortest at L5. In conclusion, pedicle dimensions and angles may show individual and structural differences. Our data were not significantly different from previous reported data. A detailed knowledge of these relationships is important for any surgery involving screw purchase via a pedicle, to prevent screw cutout and failure of fixation or neurological injury. Selection of the proper diameter of screw is an important issue for safe placement. Knowledge of the pedicle axis length is essential in choosing screw lengths but should always be checked intraoperatively with fluoroscopic control during screw insertion.

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.

Lumbar pedicle morphology in the immature spine: a three-dimensional study using spiral computed tomography

STUDY DESIGN

A cross-sectional study was conducted.

OBJECTIVE

To investigate the pediatric pedicle morphology with the help of modern computed tomography technology.

SUMMARY OF BACKGROUND DATA

The use of pedicular screws recently has gained popularity because of their ability to provide three-dimensional correction of spinal deformity. Extensive work has been published on the pedicle morphology of the adult and adolescent thoracolumbar spine. Less is known about the pedicle morphology of children.

METHODS

A total of 21 patients ages 5 to 10 years underwent standard spiral computed tomography of the abdomen. The patients were grouped according to age: Group 1 (5 to 8 years of age) and Group 2 (9 to 10 years of age). Images were reformatted, and multiplanar reconstructions were used to attain images of lumbar pedicles on sagittal, coronal, and transverse planes. The measurements included the inner and outer pedicle diameters on the transverse plane, the pedicle angle on both the transverse and sagittal planes, and pedicle length.

RESULTS

The smallest pedicle lengths were 24 mm for Group 1 and 25 mm for Group 2. When the average values were considered, the smallest lengths were at L5 and the longest at L3. The smallest diameter was at L1 (2.3 mm for Group 1 and 3 mm for Group 2), whereas L5 had the largest diameter (6.17 mm for Group 1 and 8.72 mm for Group 2). In the transverse plane, the pedicle angle increased from L1 to L5 in both groups. In the sagittal plane, the angulations followed an opposite trend.

CONCLUSIONS

The inner transverse diameter of the lumbar pedicle, particularly in young children, is smaller than previously reported. Insertion of screws currently available commercially screws seems to be safe in the L4-L5 pedicles of children ages 5 to 8 years, and in the L3-L5 pedicles of older children. Custom-made screws might be considered for upper levels for safe application.

Morphometric study of the lumbar pedicle in the Indian population as related to pedicular screw fixation

STUDY DESIGN

A morphometric study of lumbar vertebral pedicular parameters in cadavers and comparison with previous studies in the literature was conducted.

OBJECTIVES

To suggest dimensions for pedicular implants in the Indian population, and to improve the pedicular screw placement technique.

SUMMARY OF BACKGROUND DATA

Detailed knowledge of pedicle morphometry is critical for proper placement of a transpedicular screw. The size and shape of the vertebral pedicle vary between different races. Morphometric studies have been conducted in white and nonwhite populations (e.g., Chinese, Koreans).

METHODS

The vertebral pedicles at L1-L5 were studied in 20 cadavers by direct roentgenographic and computerized tomographic scan methods. The following parameters were studied: transverse diameter, transverse angle, sagittal diameter, sagittal angle, chord length, interpedicular distance, medial and lateral cortical thickness.

RESULTS

Transverse diameter was largest at L5 (16.19 mm) and smallest at L1 (7.05 mm). The transverse angle was largest at L5 (29 degrees) and smallest at L1 (9 degrees). The pedicles were directed cranially in the sagittal plane at all lumber levels except L5. The sagittal angle was largest at L5 (29 degrees) and smallest at L1 (9 degrees). Chord length was largest at L2 (47.5 mm) and smallest at L1 (46.01 mm). The values of linear measurements were smaller in females at all levels.

CONCLUSIONS

On the basis of this limited study in a subset of the Indian population, it appears that the transverse diameter and pedicle entrance point differ from those in the white population. The results suggest that a 5-mm screw would be safer in the upper lumbar levels (L1, L2), and 6-mm screw in the lower lumbar levels (L3-L5). The pedicle entrance point migrates laterally for lower lumbar levels, especially at L5. The medial pedicle cortex can be safely sounded while the pedicle is probed.

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.

The use of pedicle-screw internal fixation for the operative treatment of spinal disorders

Pedicle screws have dramatically improved the outcomes of spinal reconstruction requiring spinal fusion. Short-segment surgical treatments based on the use of pedicle screws for the treatment of neoplastic, developmental, congenital, traumatic, and degenerative conditions have been proved to be practical, safe, and effective. The Funnel Technique provides a straightforward, direct, and inexpensive way to very safely apply pedicle screws in the cervical, thoracic, or lumbar spine. Carefully applied pedicle-screw fixation does not produce severe or frequent complications. Pedicle-screw fixation can be effectively and safely used wherever a vertebral pedicle can accommodate a pedicle screw--that is, in the cervical, thoracic, or lumbar spine. Training in pedicle-screw application should be standard in orthopaedic training programs since pedicle-screw fixation represents the so-called gold standard of spinal internal fixation.

Placement of pedicle screws in the human cadaveric cervical spine: comparative accuracy of three techniques

STUDY DESIGN

This investigation was conducted in two parts. In the first part, a morphometric analysis of critical cervical pedicle dimensions were measured to create guidelines for cervical pedicle screw fixation based on posterior cervical topography. In the second part of the study, a human cadaver model was used to assess the accuracy and safety of transpedicular screw placement in the subaxial spine using three different surgical techniques: 1) using surface landmarks established in the first part of the study, 2) using supplemental visual and tactile cues provided by performing laminoforaminotomies, and 3) using a computer-assisted surgical guidance system.

OBJECTIVE

To assess the accuracy of transpedicular screw placement in the cervical spine using three surgical techniques.

SUMMARY OF BACKGROUND DATA

A three-column fixation device implanted to secure an unstable cervical spine can be a valuable tool with a biomechanical advantage in the spine surgeon's armamentarium. Despite this advantage, concerns over surgical neurovascular complications have surfaced. Cadaver-based morphometric measurements used to guide the surgeon in the placement of a pedicle screw show significant variability, raising legitimate concerns as to whether transpedicular fixation can be applied safely.

METHODS

Precise measurements of 14 human cadaveric cervical spines were made by two independent examiners of pedicle dimensions, angulation, and offset relative to the lateral mass boundaries. On the basis of this analysis, guidelines for pedicle screw placement relative to posterior cervical topography were derived. In the second part of the study, 12 human cadaveric cervical spines were instrumented with 3.5-mm screws placed in the pedicles C3-C7 according to one of three techniques. Cortical integrity and neurovascular injury were then assessed by obtaining postoperative computed tomography scans (1-mm cuts) of each specimen. Cortical breaches were classified into critical or noncritical breaches.

RESULTS

Linear measurements of pedicle dimensions had a wide range of values with only fair interobservercorrelation. Angular measurements showed similarangulation in the transverse plane (40 degrees ) at each level. With respect to the sagittal plane, both C3 and C4 pedicles were oriented superiorly relative to the axis of the lateral mass, whereas the C6 and C7 pedicles were oriented inferiorly. The dorsal entry point of the pedicle on the lateral mass defined by transverse and sagittal offset had similar mean values with wide ranges, although there often was excellent correlation between observers. There were no significant interlevel, right/left, or male/female differences noted with respect to offset. Using one of three techniques, 120 pedicles were instrumented. In group 1 (morphometric data): 12.5% of the screws were placed entirely within the pedicle; 21.9% had a noncritical breach; and 65. 5% had a critical breach. In group 2 (laminoforaminotomy), 45% of the screws were within the pedicle; 15.4% had a noncritical breach; and 39.6% had a critical breach. In group 3 (computer-assisted surgical guidance system), 76% of the screws were entirely within the pedicle; 13.4% had a noncritical breach; and 10.6% had a critical breach. Regardless of the technique used, the vertebral artery was the structure most likely to be injured.

CONCLUSIONS

On the basis of the morphometric data, guidelines for cervical spine pedicle screw placement at each subaxial level were derived. Although a statistical analysis of cadaveric morphometric data obtained from the cervical spine could provide guidelines for transpedicular screw placement based on topographic landmarks, sufficient variation exists to preclude safe instrumentation without additional anatomic data. Insufficient correlation between different surgeons' assessments of surface landmarks attests to the inadequacy of screw insertion techniques in the cervical spine based on such specific topographic guide

The radiologic anatomy of the lumbar and lumbosacral pedicles

STUDY DESIGN

An anatomic and radiologic study of lumbar and lumbosacral pedicle anatomy.

OBJECTIVES

To define the radiologic anatomy of the lumbar and first sacral pedicle in the coaxial projection.

SUMMARY OF BACKGROUND DATA

Fluoroscopic assistance for pedicle screw placement requires radiologic landmarks. The radiologic landmarks have previously been assumed. Detailed study of the correlation between anatomy and radiology is required.

METHODS

Lumbar vertebrae and sacra were marked with radiopaque material to demonstrate the pedicle cortical borders. The vertebrae were then imaged in the coaxial projection to determine the correlation between the pedicle cortex and the radiologic image. Pedicle dimensions were recorded.

RESULTS

Pedicle dimensions were consistent with known measurements, yet the long axis of the L4 and L5 pedicle ellipse was oblique to the vertical. Consequently, the minor diameter of the pedicle ellipse was considerably less than the measured pedicle width at L5. The radiologic pedicle image was consistently within the true pedicle cortex, by up to 3 mm, and probably represents the inner cortical border of the pedicle. The S1 pedicle has reliable anatomic landmarks, yet only the medial and superior borders were visualized.

CONCLUSIONS

The radiologic pedicle image in the lumbar and lumbosacral spine is a reliable guide to the true bony cortex of the pedicle. At S1 the pedicle image is less well correlated with the cortical borders of the pedicle, yet other reliable anatomic landmarks exist.

Anatomic considerations for anterior instrumentation of the lumbar spine

One hundred seventy lumbar vertebrae from L1-L4 were used to quantitatively evaluate the lumbar vertebral body and examine the relationship of the maximum posterior angles of screw placement to the spinal canal. Anatomic evaluation included dimensions of the vertebral body. Three entrance points on the lateral aspect of the vertebral body for screw insertion and an additional point 3 mm from the posterolateral corner of the spinal canal were defined and marked. The maximum posterior screw angles were determined as the angles between the line connecting the entrance point with the additional point and the coronal plane. Results showed that vertebral body dimensions increased from L1-L4. The average vertebral body depth, width, and height were approximately 26 mm, 36 mm, and 22 mm at L1, and 30 mm, 44 mm, and 23 mm at L4, respectively. The spinal canal may be penetrated if the screws are directed posteriorly 2 degrees-5 degrees at L1 - L2 and 9 degrees - 14 degrees at L3-L4 starting at the junction between the pedicle and vertebral body, 22 degrees - 32 degrees at L1-L4 from the level of 10 mm anterior to the junction, and 43 degrees -50 degrees from the level of 20 mm anterior to the junction. Therefore, mid-body screws should be directed perpendicular to the lateral plane of the vertebral body. For a more anteriorly placed screw, slightly posterior angulation is recommended.

Pedicle instrumentation in the thoracic spine. A morphometric and cadaveric study for placement of screws

STUDY DESIGN

In part 1 of the study, the morphometry of thoracic pedicles and bony landmarks for pedicle screw placement were evaluated. In part 2, pedicle screws were inserted in fresh cadavers, using a different entry point in the left and right pedicles.

OBJECTIVES

To identify the safest entry point and screw orientation for pedicle screws in the thoracic spine.

SUMMARY OF BACKGROUND DATA

A few morphometric investigations have been performed on thoracic vertebrae, but the safest technique for screw insertion in thoracic pedicles has not been analyzed.

METHODS

Mean, range, and standard deviations of pedicle transverse diameter and pedicle orientation were measured in 99 dried thoracic vertebrae. We evaluated the position of the bottom of the superior facet and that of the superior border of the transverse process in relation to the center of the pedicle. The relation between the pedicle axis and the superior facet in the frontal plane was also assessed. In part 2 of the study, pedicle screws were inserted in fresh cadavers at the intersection between the superior border of the transverse process and the middle of the superior facet (entry point A) and between the former and the lateral two thirds of the facet (entry point B).

RESULTS

The smallest transverse diameter was found at 16 (mean 4.3 mm) where pedicles measured less than 5 mm in 68% of the specimens. In the frontal plane, the pedicle axis intersected the middle of the superior facet in 15% of specimens, the lateral two-thirds in 62%, and the lateral border of the facet in 23%. Of the 126 screws inserted in fresh human cadavers, 15 (24%) of the screws inserted using entry point A and 10 (16%) of those inserted using entry point B violated the pedicle cortex (P > 0.05). Six (10%) of the screws inserted using entry point A compared with no screw inserted using entry point B penetrated the anterior vertebral cortex (P = 0.03).

CONCLUSIONS

Pedicles between T4 and T8 may not be wide enough for screw fixation. An entry point for pedicle screws located at the intersection between the superior border of the transverse process and the lateral two thirds of the superior facet seems more likely to be in line with the pedicle axis than do other entry points. In the lower thoracic vertebrae this entry point, in combination with insertion of the screws more medially oriented than the pedicle axis, significantly reduces the risk of violating the anterior vertebral cortex.

Pedicle screw fixation in spinal disorders: a European view

Continuing controversy over the use of pedicular fixation in the United States is promoted by the lack of governmental approval for the marketing of these devices due to safety and efficacy concerns. These implants have meanwhile become an invaluable part of spinal instrumentation in Europe. With regard to the North American view, there is a lack of comprehensive reviews that consider the historical evolution of pedicle screw systems, the rationales for their application, and the clinical outcome from a European perspective. This literature review suggests that pedicular fixation is a relatively safe procedure and is not associated with a significantly higher complication risk than non-pedicular instrumentation. Pedicle screw fixation provides short, rigid segmental stabilization that allows preservation of motion segments and stabilization of the spine in the absence of intact posterior elements, which is not possible with non-pedicular instrumentation. Fusion rates and clinical outcome in the treatment of thoracolumbar fractures appear to be superior to that achieved using other forms of treatment. For the correction of spinal deformity (i.e., scoliosis, kyphosis, spondylolisthesis, tumor), pedicular fixation provides the theoretical benefit of rigid segmental fixation and of facilitated deformity correction by a posterior approach, but the clinical relevance so far remains unknown. In low-back pain disorders, a literature analysis of 5,600 cases of lumbar fusion with different techniques reveals a trend that pedicle screw fixation enhances the fusion rate but not clinical outcome. The most striking finding in the literature is the large range in the radiological and clinical results. For every single fusion technique poor and excellent results have been described. This review argues that European spine surgeons should begin to back up the evident benefits of pedicle screw systems for specific spinal disorders by controlled prospective clinical trials. This may prevent forthcoming medical licensing authorities from restricting the use of pedicle screw devices and dictating the practice of spinal surgery in Europe in the near future.

Computer-aided pedicle screw placement using frameless stereotaxis

STUDY DESIGN

In vitro assessment of accuracy and reliability of frameless stereotaxis for insertion of pedicle screws in human cadaveric lumbar spine.

OBJECTIVES

To assess a new method of targeting and placing pedicle screws in a human cadaver study.

SUMMARY OF BACKGROUND DATA

Pedicle screw instrumentation is common. Complications may occur from improper placement of screws. Even when performed by experienced spinal surgeons, improper placement can occur in 5.2% of pedicles instrumented. Development of computer-guided methods of pedicle screw insertion may decrease this complication rate.

METHODS

The technique used preoperative computed tomography scans together with a commercial neurosurgical navigational computer system to assist in placing guidewires in the pedicles. A section of human cadaver spine was first scanned and the data transferred to the workstation. The image data set and physical specimen were then registered by using an instrumented articulated arm to identify selected points on the specimen and randomly sample surface points. Eight highly repeatable locations on each vertebral body were found to be suitable for registration, but better overall accuracy was obtained when surface matching was used in combination with these points. Under guidance of image on the computer, Kirschner wires were inserted into the pedicles of four vertebral bodies. The spine was rescanned, and the planned and resulting positions of the wires compared.

RESULTS

The average distance between the planned and resulting wire entry point was 1.2 mm, with an average difference in planned and resulting trajectories of 6.0 degrees.

CONCLUSIONS

Computer-aided pedicle screw instrumentation is feasible. Further technical points require clarification before widespread use is possible.

Anatomy of the thoracic pedicle

Thoracic pedicle anatomy (interpedicular distance, transverse and sagittal pedicle widths, transverse and sagittal pedicle angles, and the distance from the axis of the pedicle to the axis of the transverse process) was assessed in 11 cadavers of elderly people. The cadaveric spines were extensively dissected to augment the accuracy of the measurements via caliper and goniometer. The results were compared with those of previous studies that assessed pedicle anatomy with computed tomography, direct measurement, and three-dimensional morphometry. Between the studies, significant differences were found in transverse pedicle width and transverse and sagittal pedicle angles. These morphometric differences may reflect either the diversity of the techniques used to measure the pedicle anatomy or sampling variation. This article presents a previously unreported morphometric finding, the rostral-caudal distance from the thoracic pedicle to the midpoint of the base of the transverse process. At T1, the transverse process is 5.45 +/- 1.2 mm rostral to the pedicle. This relationship gradually changes as the thoracic spine is descended, so that at T12, the transverse process is 6.6 +/- 2.4 mm caudal to the pedicle. Crossover consistently occurs at the T6-T7 region. Although the transverse process is a reliable external landmark for the location of the pedicle in the lumbar spine, this relationship in the thoracic spine is variable and only moderately predictable.

Clinical evaluation of a system for precision enhancement in spine surgery

Most techniques in segmental spinal fixation surgery rely on the identification of predefined targets with the help of anatomical landmarks and on intraoperative use of image intensifiers. However, because there is no direct link between the image information, the accessible spinal anatomy, and the action of surgical instruments several potential problems and possible complications are still involved. A novel system for spinal surgery has been designed allowing for the real-time, intraoperative localization of surgical instruments in medical images. In practice this was achieved by combining image-guided stereotaxis with advanced optoelectronic position sensing techniques. Modules were developed for image data processing, surgical planning and simulation, and various intraoperative procedures. A detailed validation of the system was performed indicating an overall accuracy to be better than the slice distance of the spinal image used. In an in-vitro setting 20 pilot holes for pedicle screws were prepared in human cadaveric lumbar spines. An analysis in 77 histological cuts showed an ideal location in 70 and only minor cortex engagement in seven sections. In vivo the system has been successfully applied in three posterior low lumbar stabilizations with overall 15 transpedicular screws. RELEVANCE--:This article focuses on the clinical evaluation of a computer-assisted surgery system and its application to the operating theatre for transpedicular fixation of the spine. The given approach effectively keeps the surgeon 'in the loop' and requires only minor modifications of the established surgical techniques and associated instruments. The results of this study indicate that advanced computer-assisted techniques may significantly improve the accuracy and safety of surgical interventions of the spine. The proposed technique may in future be adapted to other applications in orthopaedic surgery.

Anatomy of the thoracic pedicle

Thoracic pedicle anatomy (interpedicular distance, transverse and sagittal pedicle widths, transverse and sagittal pedicle angles, and the distance from the axis of the pedicle to the axis of the transverse process) was assessed in 11 cadavers of elderly people. The cadaveric spines were extensively dissected to augment the accuracy of the measurements via caliper and goniometer. The results were compared with those of previous studies that assessed pedicle anatomy with computed tomography, direct measurement, and three-dimensional morphometry. Between the studies, significant differences were found in transverse pedicle width and transverse and sagittal pedicle angles. These morphometric differences may reflect either the diversity of the techniques used to measure the pedicle anatomy or sampling variation. This article presents a previously unreported morphometric finding, the rostral-caudal distance from the thoracic pedicle to the midpoint of the base of the transverse process. At T1, the transverse process is 5.45 +/- 1.2 mm rostral to the pedicle. This relationship gradually changes as the thoracic spine is descended, so that at T12, the transverse process is 6.6 +/- 2.4 mm caudal to the pedicle. Crossover consistently occurs at the T6-T7 region. Although the transverse process is a reliable external landmark for the location of the pedicle in the lumbar spine, this relationship in the thoracic spine is variable and only moderately predictable.