A computed tomography-based morphometric study of thoracic pedicle anatomy in a random United States trauma population

How to Optimize Pedicle Screw Parameters for the Thoracic Spine? A Biomechanical and Finite Element Method Study

STUDY DESIGN

Pedicle screw study.

OBJECTIVE

The selection of pedicle screw parameters usually involves the surgeon's analysis of preoperative CT imaging along with anatomical landmarks and tactile examination. However, there is minimal consensus on a standardized guideline for selection methods on pedicle screws. We aimed to determine the effects of thoracic screw diameter to pedicle width on pullout strength determined by cortical bone purchase.

METHODS

Biomechanical study performed with human cadaveric thoracic vertebrae and experimentally validated three-dimensional finite element model instrumented with pedicle screws of various diameters. We used a variable (SD/PW) ratio to express the screw selection. We hypothesized a positive correlation between the pullout load determined by the bone purchase and the SD/PW. This relationship was first investigated in a validated finite element model considering bone purchase related to the strength of an upper thoracic vertebra. Then, the correlation to the entire spine is evaluated.

RESULTS

The failure load ranged from 371.3 to 1601.0 N, respectively, for 3 and 6 mm screws. The determinant coefficient was increased to R2=.421 when a linear relationship between pullout load and the SD/PW ratio was used. The peak loads of 1216 and 1288N were found for an SD/PW ratio of .83.

CONCLUSION

We have found that the screw pullout load is more correlated to SD/PW than other pedicle measures for a maximized SD/PW ratio of .83. This particular value should be considered the upper limit of the indicated SD/PW ratio and a means to determine the optimal screw diameter to enhance pullout strength.

Performance evaluation of an AI-based preoperative planning software application for automatic selection of pedicle screws based on computed tomography images

Introduction

Recent neurosurgical applications based on artificial intelligence (AI) have demonstrated its potential in surgical planning and anatomical measurement. We aimed to evaluate the performance of an AI planning software application on screw length/diameter selection and insertion accuracy in comparison with freehand surgery.

Methods

A total of 45 patients with 208 pedicle screw placements on thoracolumbar segments were included in this analysis. The novel AI planning software was developed based on a deep learning model. AI-based pedicle screw placements were selected on the basis of preoperative computed tomography (CT) data, and freehand surgery screw placements were observed based on postoperative CT data. The performance of AI pedicle screw placements was evaluated on the components of screw length, diameter, and Gertzbein grade in comparison with the results achieved by freehand surgery.

Results

Among 208 pedicle screw placements, the average screw length/diameters selected by the AI model and used in freehand surgery were 48.65 ± 5.99 mm/7.39 ± 0.42 mm and 44.78 ± 2.99 mm/6.1 ± 0.27 mm, respectively. Among AI screw placements, 85.1% were classified as Gertzbein Grade A (no cortical pedicle breach); among free-hand surgery placements, 64.9% were classified as Gertzbein Grade A.

Conclusion

The novel AI planning software application could provide an accessible and safe pedicle screw placement strategy in comparison with traditional freehand pedicle screw placement strategies. The choices of pedicle screw dimensional parameters made by the model, including length and diameter, may provide potential inspiration for real clinical discretion.

Thoracolumbar Spine Trauma

Thoracolumbar spine trauma can result in potentially life-threatening consequences and requires careful management to ensure good outcomes. The purpose of this chapter is to discuss the anatomy, diagnostic tools, non-operative, and operative treatments important when addressing thoracolumbar trauma.

TOMOGRAPHIC ANALYSIS OF C7, T1 AND T2 VERTEBRAE ANATOMY IN CHILDREN

OBJECTIVE

To evaluate and compare anatomical measurements of C7, T1 and T2 vertebrae in children from 3 to 12 years of age to provide useful epidemiological data for determining the safe anatomical margin for transpedicular and translaminar fixation with screws in this population.

METHODS

This observational retrospective cross-sectional study evaluated 76 computed tomography scans obtained over 6 months, analyzing the following parameters: the angle of attack, length, thickness and diameter of the pedicle; and the angle of attack, length and thickness of the lamina.

RESULTS

The lamina length and thickness, as well as pedicle length varied in size according to age. Although the angle of attack was similar across different ages, age-dependent variation occurred in the T1 vertebra.

CONCLUSION

Screws with a 3.5 mm diameter are safe to use in the C7 and T2 pedicles, while the T1 pedicle allows the introduction of larger screws ranging from 3.5-4.5 mm in diameter. In the lamina, 3.5 mm screws are safe for use only in children older than 7 years. However, each case should be analyzed individually, with the present study not aiming to replace the preoperative use of CT. Level of Evidence III, Retrospective comparative study.

Morphology and growth of the pediatric lumbar vertebrae

BACKGROUND CONTEXT

The majority of existing literature describing pediatric lumbar vertebral morphology are limited to characterization of the vertebral bodies, pedicles, and spinal canal and no study has described the rates of growth for any lumbar vertebral structure. While it is known that growth of the lumbar vertebrae results in changes in vertebral shape, the dimension ratios used to quantify these shape changes do not represent the 3D morphology of the vertebral structures. Additionally, many of the previous evaluations of growth and shape are purely descriptive and do not investigate sexual dimorphism or variations across vertebral levels.

PURPOSE

This study aims to establish a database of pediatric lumbar vertebra dimension, growth, and shape data for subjects between and ages of 1 and 19 years.

STUDY DESIGN

A retrospective study of computed tomography (CT) data.

METHODS

Retrospective, abdominal, CT scans of 102 skeletally normal pediatric subjects (54 males, 48 females) between the ages of 1 and 19 years were digitally reconstructed and manually segmented. Thirty surface landmark points (LMPs), 30 vertebral measurements, the centroid size, centroid location, and the local orientation were collected for each lumbar vertebra along with the centroid size of the LMPs comprising each subject's full lumbar spine and their intervertebral disc (IVD) heights. Nonparametric statistics were used to compare dimension values across vertebral levels and between sexes. Linear models with age as the independent variable were used to characterize dimension growth for each sex and vertebral level. Age-dependent quadratic equations were fit to LMP distributions resulting from a generalized Procrustes analysis (GPA) of the vertebrae and fixed effects models were used to investigate differences in model coefficients across levels and between sexes.

RESULTS

Intervertebral level dimension differences were observed across all vertebral structures in both sexes while pedicle widths and IVDs heights were the only measurements found to be sexually dimorphic. Dimension growth rates generally varied across vertebral levels and the growth rates of males were typically larger than those of females. Differences between male and female vertebral shapes were also found for all lumbar vertebral structures.

CONCLUSIONS

To the authors' knowledge, this is the first study to report growth rates for the majority of pediatric lumbar vertebral structures and the first to describe the 3D age-dependent shapes of the pediatric lumbar spine and vertebrae. In addition to providing a quantitative database, the dimension, growth, and shape data reported here would have applications in medical device design, surgical planning, surgical training, and biomechanical modeling.

Thoracic and lumbar spine pedicle morphology in Japanese patients

PURPOSE

Pedicle morphology is important for intraoperative surgical anatomy and to define pedicle screw design and parameters. However, differences of pedicle size according to ethnicity and gender are not well studied. The purpose of this study is to investigate morphological characteristics of the pedicle in Japanese patients for determining adequate screw size and optimal surgical planning.

METHODS

We investigated thoracic and lumbar pedicle morphology in Japanese patients using computed tomography (CT) measurements and analyzed the standard size of pedicles on upper thoracic to lumbar spine CT images in 227 Japanese patients.

RESULTS

Gender had a larger impact on the shape and size of pedicles than racial differences. In the distribution of pedicle width, we calculated the ratio of values less than 4.5 mm, that in females resulted to be over 30% for the Th3-Th9 segment, and particularly high, above 60% at Th4 and Th5.

CONCLUSION

Our measurement analysis showed that pedicle morphological parameters in Japanese patients showed tendency to be smaller to those found in other studies, and particularly in female patients, they were statistically significantly smaller. Adequate transpedicular instrumentation for Japanese patients will require smaller size pedicle-related devices that will match our anatomical findings to achieve safe device placement. In addition, serving ethnically non-homogenous patient population can require further to spinal morphometric for precise device selection.

Currently Adopted Criteria for Pedicle Screw Diameter Selection

BACKGROUND

Transpedicular screw insertion has become widely accepted for the correction of spinal deformity as well as degenerative and traumatic injury, but adoption of this technique has remained less widespread in the thoracic compared to the lumbar spine. This is thought to be associated with the relative technical difficulty of screw insertion into the narrower widths of the thoracic pedicles and the neurologic and mechanical risks associated with breach of the pedicle wall. The surgical decision making involves determining the appropriate sized screw for maximum fixation strength while simultaneously respecting the structural integrity of the vertebral pedicles to prevent a breach and provide better fixation. This paper presents a systematic review of criteria for thoracic pedicle screw diameter (SD) selection in order to orient inexperienced surgeons on the impact of this selection on pedicle breaching and fixation strength.

METHODS

We performed a systematic literature review focused on studies reporting SD selection in relation to pedicle dimensions, measures of fixation strength, and breach rate.

RESULTS

Twenty-nine articles that measured fixation strength, breach rate, and/or provided SD in relation to pedicle width were selected for inclusion.

CONCLUSIONS

A commonly accepted criteria for pedicle SD selection has not yet been proposed. Screw diameters approximately 80% of the pedicle width have been adopted, but this proportion is rarely reported in the midthoracic vertebrae for which smaller pedicles and inadequate hardware specificity result in higher breach rates. Depending upon the insertion technique adopted, greater specificity in diameter selection by vertebral level should be pursued in order to maximally target cortical bone purchase.

CLINICAL RELEVANCE

Based on this review of the literature, we believe that proper selection of the SD for individual vertebral level directly affects the insertion technique and the potential breach.

Morphometric characteristics of the thoracοlumbar and lumbar vertebrae in the Greek population: a computed tomography-based study on 900 vertebrae-"Hellenic Spine Society (HSS) 2017 Award Winner"

Background

Vertebrae morphology appears to have genetic and ethnic variations. Knowledge of the vertebra and pedicle morphology is essential for proper selection and safe application of transpedicular screws. The aim of this study is to create a morphometric database for thoracolumbar and lumbar vertebrae (T9-L5) among individuals of both sexes in the Greek population.

Material and methods

The morphometric dimensions of T9-L5 vertebrae on computed tomography (CT) scan images were measured in 100 adults (79 males and 21 females), without spinal pathology, age from 33 to 87 years old (mean 70 ± 8.73 years). The anterior vertebral body height (AVBH), the posterior vertebral body height (PVBH), the angle formed by the upper end plate of vertebral body and the horizontal line in the sagittal plane, the inner cancellous and outer cortical pedicle height and width, the angle formed by the longitudinal trajectory of the right- and left-sided pedicles and the midline anteroposterior axis of the vertebra (pedicle axis angle (PAA)), and the postero-anterior trajectory's length of the pedicle from the entry point to the anterior cortex of the vertebra (PTLP), for the right- and left-sided pedicles, were calculated. The Mann-Whitney U tests were conducted to compare the differences in various morphometric characteristics between sexes. The collected data were statistically analyzed using the SAS/STAT software 3.1.3 and SPSS version 22. The statistical significance was set at the level of p < 0.05. The intra- and inter-observer reliability of the measured parameters was also calculated.

Results

The L5 vertebra had the maximum AVBH with a mean of 28.47 mm (SD ± 2.55 mm) in males and 26.48 mm (SD ± 1.61 mm) in females. The maximum PVBH in males was at L1 vertebra with a mean of 27.77 mm (SD ± 1.64 mm) and in females at L2 vertebral with a mean of 27.11 mm (SD ± 1.27 mm). Regarding the left pedicle dimensions, the maximum inner cancellous and outer cortical pedicle height was at T11 with a mean of 12.86 mm (SD ± 1.26 mm) and 18.82 mm (SD ± 1.37 mm) in males and 10.24 mm (SD ± 1.88 mm) and 16.19 mm (SD ± 3.27 mm) in females, respectively. The maximum inner cancellous and outer cortical pedicle width was at L5 with a mean of 11.57 mm (SD ± 1.97 mm) and 17.08 mm (SD ± 1.97 mm) in males and 10.24 mm (SD ± 1.88 mm) and 16.27 mm (SD ± 3.27 mm) in females, respectively. The largest PAA was found at the L5 with a mean angle of 26.23° (SD ± 2.65°) in males and 23.63° (SD ± 4.59°) in females, respectively. The maximum PTLP was found at the level of L4 with a mean of 55.31 mm (SD ± 4.52 mm) in males and 48.7 mm (SD ± 4.17 mm) in females, respectively. Regarding the right pedicle dimensions, the maximum inner cancellous and outer cortical pedicle height was found at T12 with a mean of 13.03 mm (SD ± 2.01 mm) and 18.01 mm (SD ± 1.56 mm) in males and 10.24 mm (SD ± 1.23 mm) and 16.14 mm (SD ± 1.23 mm) in females, respectively. The maximum inner cancellous and outer cortical pedicle width was at L5 with a mean of 11.3 mm (SD ± 2.86 mm) and 16.34 mm (SD ± 2.98 mm) in males and 12 mm (SD ± 3.18 mm) and 15.69 mm (SD ± 2.59 mm) in females, respectively. The greater PAA was at the L5 vertebral with a mean of 25.7° (SD ± 5.19°) in males and 25.56° (SD ± 5.31°) in females, respectively. The maximum PTLP was at the level of L3 with a mean of 54.86 mm (SD ± 3.18 mm) in males and 49.01 mm (SD ± 2.97 mm) in females, respectively. At all vertebrae, the only statistically significant difference (p < 0.0001) between the two sexes was the mean PTLP of the right and the left pedicle. The L5 vertebra was found to have the largest AVBH, PAA, and pedicle width in male and female populations.

Conclusions

This study provides a database of morphometric characteristics on thoracolumbar and lumbar vertebrae from T9 to L5 in the Greek population. This database may prove to be of great significance for forthcoming comparative studies. It can also serve as a basis in order to detect pathological changes in the spine and furthermore to plan operative interventions. It was found that the dimensions of thoracolumbar and lumbar vertebrae in the Greek population are sex-dependent. In the current study, vertebra and pedicle dimensions seem to have some similarities compared to other Western populations. However, in the thoracolumbar region, the pedicles of T9 and T10 may hardly accommodate a 4.00-mm pedicle screw given the narrow inner cancellous pedicle width. Importantly, the vertebra and pedicle dimensions measured in the current study can be used to guide the selection of transpedicular screws in the Greek population and to guide further research.

Evaluation of a more ventral starting point for thoracic pedicle screws: higher maximal insertional arc and more medial and safer screw angulation

OBJECTIVETo demonstrate that a more ventral starting point for thoracic pedicle screw insertion, produced by aggressively removing the dorsal transverse process bone down to the superior articular facet (SAF), results in a larger margin for error and more medial screw angulation compared to the traditional dorsal starting point (DSP). The margin for error will be quantified by the maximal insertional arc (MIA).METHODSThe study population included 10 consecutive operative patients with adult idiopathic scoliosis who underwent primary surgery. All measurements were performed using 3D visualization software by an attending spine surgeon. The screw starting points were 2 mm lateral to the midline of the SAF in the mediolateral direction and in the center of the pedicle in the cephalocaudal direction. The DSP was on the dorsal cortex. The ventral starting point (VSP) was at the depth of the SAF. Measurements included distance to the pedicle isthmus, MIA, and screw trajectories.RESULTSTen patients and 110 vertebral levels (T1-11) were measured. The patients' average age was 41.4 years (range 18-64 years). The pedicle isthmus was largest at T1 (4.04 ± 1.09 mm), and smallest at T5 (1.05 ± 0.93 mm). The distance to the pedicle isthmus was 7.47 mm for the VSP and 11.92 mm for the DSP (p < 0.001). The MIA was 15.3° for the VSP and 10.1° for the DSP (p < 0.001). Screw angulation was 21.7° for the VSP and 16.8° for the DSP (p < 0.001).CONCLUSIONSA more ventral starting point for thoracic pedicle screws results in increased MIA and more medial screw angulation. The increased MIA represents an increased tolerance for error that should improve the safety of pedicle screw placement. More medial screw angulation allows improved triangulation of pedicle screws.

Photoacoustic imaging of a human vertebra: implications for guiding spinal fusion surgeries

It is well known that there are structural differences between cortical and cancellous bone. However, spinal surgeons currently have no reliable method to non-invasively determine these differences in real-time when choosing the optimal starting point and trajectory to insert pedicle screws and avoid surgical complications associated with breached or weakened bone. This paper explores 3D photoacoustic imaging of a human vertebra to noninvasively differentiate cortical from cancellous bone for this surgical task. We observed that signals from the cortical bone tend to appear as compact, high-amplitude signals, while signals from the cancellous bone have lower amplitudes and are more diffuse. In addition, we discovered that the location of the light source for photoacoustic imaging is a critical parameter that can be adjusted to non-invasively determine the optimal entry point into the pedicle. Once inside the pedicle, statistically significant differences in the contrast and SNR of signals originating from the cancellous core of the pedicle (when compared to signals originating from the surrounding cortical bone) were obtained with laser energies of 0.23-2.08 mJ (p  <  0.05). Similar quantitative differences were observed with an energy of 1.57 mJ at distances  ⩾6 mm from the cortical bone of the pedicle. These quantifiable differences between cortical and cancellous bone (when imaging with an ultrasound probe in direct contact with each bone type) can potentially be used to ensure an optimal trajectory during surgery. Our results are promising for the introduction and development of photoacoustic imaging systems to overcome a wide range of longstanding challenges with spinal surgeries, including challenges with the occurrence of bone breaches due to misplaced pedicle screws.

Inserting pedicle screws in lumbar spondylolisthesis - The easy bone conserving way

BACKGROUND

Pedicle screw fixation in high grade lumbar listhetic vertebral body has been nightmare for Orthopaedic and spine surgeons. This is because of abnormally positioned listhetic pedicles and non-visualization of pedicle in conventional image intensifier (C-Arm). This results into increased surgical time, more blood loss, radiation exposure and more chances of infection. To overcome this problem, we have devised a new Technique of putting of pedicle screw fixation in listhetic vertebrae.

METHODS

Total 20 patients of average age of 42 (25-56) were included during 2010 to 2015. Listhesis was classified according to etiology, Meyerding grading and DeWald modification of Newman criteria used for assessment of severity for spondylolisthesis on standing X-ray lumbosacral spine. Patients satisfying following criteria were considered for surgery. Age more than 20 years, with single involvement of either L4-5/L5-S1, high grade spondylolisthesis (≥ 50% Meyerding grade), unresolving radiculopathy, cauda equina syndrome or pain with and without instability not relieved by 6 months of conservative treatment. According to Meyerding radiographic grading system,10 patients were of type II and 8 of type III and 2 of type IV. Treatment given was pedicle screw fixation, reduction of listhesis vertebra and spinal fusion with our technique. PLT was done in 10 cases and transforaminal lumbar interbody fusion (TLIF) in the other 10 cases.

RESULTS

Mean follow up duration was 2 years (range 1.3-3.3 year). The average preoperative LBP VAS of low back pain were 6.7 and average LP VAS for leg pain 5.7. Postoperatively at final follow up there was reduction of LBP VAS to 2.2 and LP VAS to 0.5. There was rapid reduction in their LBP VAS in first two visits at 4 weeks and in LP VAS in first three visits at 8 weeks. The pain-free walking distance improved significantly. The average pre-operative ODI score was 51.4, improved to 18.6 postoperatively. There was no difference in above scores between PLT and TLIF.

CONCLUSION

Our surgical technique used for high grade spondylolisthesis is safe, cost-effective, bone-preserving, reliable, and reproducible for high grade Lumber spondylolisthesis.

Are Traditional Radiographic Methods Accurate Predictors of Pedicle Morphology?

STUDY DESIGN

Cadaveric in vitro computed tomography (CT) imaging study.

OBJECTIVE

To examine minimum pedicle diameter from transverse and coronal CT reconstructions of thoracolumbar spine specimens and compare their degree of disparity, if any. Pedicle angulation in coronal and transverse planes was measured and their contribution to the disparity in minimum pedicle diameter was assessed.

SUMMARY OF BACKGROUND DATA

Spinal minimum pedicle diameter can be obtained from both transverse and coronal CT reconstructions; however, the degree of disparity in these measurements has not been described previously. Angulation of the pedicle in transverse and coronal planes may contribute to a disparity in minimum pedicle diameter acquired from reconstructions. This also has not been described previously. This study examined whether the disparity could be predicted by spinal level, as pedicle angulations vary in both coronal and transverse planes.

METHODS

Five thoracolumbar specimens (T1-L5, age 48-59 yrs, male) were CT scanned utilizing clinical protocols. Minimum pedicle diameters and pedicle angulations were acquired in transverse and coronal reconstructions. Disparities between minimum pedicle diameters were measured and the correlation between this disparity and spinal level was characterized.

RESULTS

A significant difference (P < 0.001) in minimum pedicle diameter existed between measures from coronal and transverse reconstructions. There was a significant correlation (P < 0.001) between the difference in minimal pedicle diameter and the transverse pedicle angle as well as the coronal pedicle angle.

CONCLUSION

An overestimation of minimum pedicle diameter in the transverse reconstruction occurs when the coronal pedicle angulation increases, and in the coronal reconstruction when the transverse pedicle angulation increases. Therefore, pedicle angle should be determined using both coronal and transverse reconstructions and utilized to reduce the risk of overestimation of the true pedicle diameter.

LEVEL OF EVIDENCE

NA.

Thoracic spine morphology of a pseudo-biped animal model (kangaroo) and comparisons with human and quadruped animals

PURPOSE

Based on the structural anatomy, loading condition and range of motion (ROM), no quadruped animal has been shown to accurately mimic the structure and biomechanical function of the human spine. The objective of this study is to quantify the thoracic vertebrae geometry of the kangaroo, and compare with adult human, pig, sheep, and deer.

METHODS

The thoracic vertebrae (T1-T12) from whole body CT scans of ten juvenile kangaroos (ages 11-14 months) were digitally reconstructed and geometric dimensions of the vertebral bodies, endplates, pedicles, spinal canal, processes, facets and intervertebral discs were recorded. Similar data available in the literature on the adult human, pig, sheep, and deer were compared to the kangaroo. A non-parametric trend analysis was performed.

RESULTS

Thoracic vertebral dimensions of the juvenile kangaroo were found to be generally smaller than those of the adult human and quadruped animals. The most significant (p < 0.001) correlations (Rho) found between the human and kangaroo were in vertebrae and endplate dimensions (0.951 ≤ Rho ≤ 0.963), pedicles (0.851 ≤ Rho ≤ 0.951), and inter-facet heights (0.891 ≤ Rho ≤ 0.967). The deer displayed the least similar trends across vertebral levels.

CONCLUSIONS

Similarities in thoracic spine vertebral geometry, particularly of the vertebrae, pedicles and facets may render the kangaroo a more clinically relevant human surrogate for testing spinal implants. The pseudo-biped kangaroo may also be a more suitable model for the human thoracic spine for simulating spine deformities, based on previously published similarities in biomechanical loading, posture and ROM.

Computed tomographic-based morphometric study of thoracic spine and its relevance to anaesthetic and spinal surgical procedures

BACKGROUND

To collect a baseline computer software aided normative morphometric data of thoracic spine in the Indian population and analyze it to give pre-procedural guidelines to clinicians for safe surgical and anaesthetic procedures in the thoracic spine.

METHODS

CT scans of thoracic spine of patients free from spinal disorders were reviewed in a total of 600 vertebrae in 50 patients. Parameters recorded with the help of computer software were pedicle width, length and height, transverse pedicle angles, chord length, canal dimensions, body width and height, spinous process angle and transverse process length.

RESULTS

Pedicle width decreased from T1 (9.27 ± 1.01) to T4 (4.5 ± 0.93) and increased to T12 (8.31 ± 1.83). At T4 76% and at T5 62% of the pedicles were smaller than 5 mm and would not accept 4 mm screw with 1.0-mm clearance. However, at T1 2%, at T11 7% and at T12 8% would not accept a 4 mm screw. Chord length gradually increased in upper thoracic vertebrae and was relatively constant in middle and decreased in lower thoracic vertebrae. Shortest estimated chord length was at T1 (30.30 ± 2.11). On an average, from T1 to T6 and at T11 and T12, a screw length of 25-30 mm could be accommodated and from T7 to T10, 30-35 mm screw length could be accommodated. Transverse pedicle angle decreased from T1 (35.4 ± 2.21) to T12 (-9.8 ± 2.39). Canal dimensions were narrowest at T4/T5 (20.02 ± 1.23) in anteroposterior and 21.12 ± 1.23 in interpedicular diameters. Spinous process angle increased from T1 (30.11 ± 6.74) to T6 (57.89 ± 9.31) and decreased to 16.21 ± 7.38 at T12. Transverse process length increased from T1 to T7 (23.54 + 2.12 to 31.21 + 1.91) and then decreased to 12.11 + 2.3 at T12. Vertebral body dimensions showed increasing trends from T1 to T12.

CONCLUSIONS

A thorough knowledge of anatomical and radiological characteristics of the spine and their variations is essential for the clinicians. Data collected in the present study provides baseline normative values in Indian population and will help in guiding safe and effective completion of both surgical and anaesthetic procedures in the thoracic spine. Computer software aided morphometric data can help in selecting appropriate size and optimal placement of the implant with minimal procedural difficulties and complications during spine surgery.

Cadaver training module for teaching thoracic pedicle screw placement to residents

Surgical training using simulators has been shown to be highly effective but is not available for some applications and is too expensive for many programs. The authors piloted a cadaver-based module with the goal of objectively measuring and significantly improving orthopedic residents' surgical skills in placing thoracic pedicle screws, an advanced procedure. An experienced spine surgeon placed thoracic pedicle screws in 7 cadavers (T1-T12) to establish the skilled accuracy rate. For this pilot study, 3 orthopedic residents unfamiliar with the procedure were given didactic training for safe thoracic pedicle screw insertion. Each resident instrumented alternating sides of 5 consecutive cadavers (T1-T12). Screw positions were graded by computed tomography in a blinded fashion, with accuracy defined as no shank breach of the pedicle or vertebral body. Results were reviewed with the residents, instruction was repeated, and alternating sides of 5 cadavers were instrumented by the residents. The experienced surgeon accurately placed 67 (82%) of 82 pedicle screws. Residents accurately placed 80 (44%) of 180 pedicle screws in the initial set of specimens and 105 (58%) of 180 pedicle screws in the second set of specimens (P=.01). Accuracy varied significantly among residents before but not after computed tomography review. The study's results show that a cadaver-based training module that resembles the clinical setting can be used to teach complex surgical skills to orthopedic residents.

The rib head as a landmark in the anterolateral approach to the thoracic spine: a computed tomography-based morphometric study

OBJECT

The rib head is an important landmark in the anterolateral approach to the thoracic spine. Resection of the rib head is typically the first step in gaining access to the underlying pedicle and ultimately the spinal canal. The goal of this work is to quantify the relationship of the rib head to the spinal canal and adjacent aorta at each thoracic level using CT-based morphometric measurements.

METHODS

One hundred thoracic spine CT scans (obtained in 50 male and 50 female subjects) were evaluated in this study. The width and depth of each vertebra body were measured from T-1 to T-12. In addition, the distance of each rib head to the spinal canal was determined by drawing a line connecting the rib heads bilaterally and measuring the distance to this line from the most ventral aspect of the spinal canal. Finally, the distance of the left rib head to the thoracic aorta was measured at each thoracic level below the aortic arch.

RESULTS

The vertebral body depth progressively increased in a rostral to caudal direction. The vertebral body width was at its minimum at T-4 and progressively increased to T-12. The rib head extended beyond the spinal canal maximally at T-1. This distance incrementally decreased toward the caudal levels, with the tip of the rib head lying approximately even with the ventral canal at T-11 and T-12. The distance between the aorta and the left rib head increased in a rostral to caudal direction as well.

CONCLUSIONS

The rib head is an important landmark in the anterolateral approach to the thoracic spine. At more cephalad levels, a larger portion of rib head requires resection to gain access to the spinal canal. At more caudad levels, there is a safer working distance between the rib head and aorta.

Reliability and consequences of intraoperative 3D imaging to control positions of thoracic pedicle screws

INTRODUCTION

The insertion of thoracic pedicle screws (T1-T10) is subject to a relevant rate of malplacement. The optimum implantation procedure is still a topic of controversial debate. Currently, a postoperative computed tomography is required to evaluate the screw positions. The present study was undertaken to clarify whether intraoperative 3D imaging is a reliable method of determining the position of thoracic pedicle screws.

METHODS

This prospective study involved 40 consecutive patients with thoracic spinal injuries, with intraoperative 3D scans being performed to determine the positions of 240 pedicle screws in T1-T10. The results of the 3D scans were compared with the findings of postoperative CT scans, using a clinical classification system.

RESULTS

The positions of 204 pedicle screws could be viewed by means of both 3D and CT scans and the results compared. The 3D scans achieved a sensitivity of 90.9 % and a specificity of 98.8 %. The rate of misclassification by the 3D scans was 2.5 %. Nine pedicle screws were classified as misplaced and their position corrected intraoperatively (3.8 %). No screws required postoperative revision.

CONCLUSIONS

Performing an intraoperative 3D scan enables the position of thoracic pedicle screws to be determined with sufficient accuracy. The rate of revision surgery was reduced to 0 %.

A PET/CT-based Morphometric Study of Spinal Canal in Korean Young Adults: Anteroposterior Diameter from Cervical Vertebra to Sacrum

Objective

To establish normative data for spinal canal AP diameter from cervical vertebra to sacrum in the Korean young and to assess the exposed spinal canal after laminectomy which was related with restenosis by post-laminectomy membrane formation.

Methods

From PET/CT, axial bone-window CT of 83 young adults (20-29 years) were obtained, and we measured AP diameters of C3, C5, C7, T1, T4, T8, T12, L1, L3, L5 and S1. We also measured exposed AP diameter of C3, C5, C7, T1 and T2 above imaginary line for laminectomy.

Results

The shortest mean AP diameter was at C5 (14.5±1.5 mm), and the longest was at S1 (17.4±2.3 mm). AP diameter increased from C3 (14.6±1.1 mm) to T1 (16.1±1.2 mm) at cervical spine. In the thoracic spine, the diameter gradually decreased from T1 (16.1±1.2 mm) to T8 (14.6±1.3 mm) and increased to T12 (16.7±1.2 mm). The diameter decreased from L1 (16.7±1.3 mm) to L3 (15.7±1.9 mm), and it increased to S1 (17.4±2.3 mm) at lumbar spine. Exposed AP diameter above imaginary line for laminectomy was the longest at C3 (4.8±1.2 mm) and gradually decreased to T1 (3.3±0.9 mm) and T2 (0 mm).

Conclusions

Spinal AP diameter was the shortest in the mid-cervical area (C5) and increased to the upper thoracic area. From the upper thoracic vertebra, the diameter gradually decreased to the mid-thoracic vertebra (T8) and then increased to the lower thoracic vertebra. Lumbar vertebra also was similar with thoracic vertebra. Below T2, there was no exposed dural sac after laminectomy. This means that restenosis by post-laminectomy membrane formation can occur above T1.