Low-dose helical computed tomography (CT) in the perioperative workup of adolescent idiopathic scoliosis

Change of vertebral orientation, between the supine position and the prone position

PURPOSE

Our aim was to assess the change of vertebral orientation, expressed in the sagittal plane, in the transversal plane and in the frontal plane, at each level from T1 to S1 between the supine position (like in in a CT scan) and the prone position lying on bolsters like in an OR.

METHODS

Thirty-six patients were selected and included for a total number of one hundred and forty-eight vertebral levels. There were 30 females and 6 males. The mean age was 15 years and 9 months. A semi-automatic image processing technique and software (3D slicer), with a custom-made python script add-on, was used for each patient: paired preoperative CT scan and intraoperative cone beam computed tomography (CBCT) scan were processed to acquire complete spinal reconstructions in a consistent 3D coordinate system. The aim was to automatically compute a set of sagittal, transversal, and frontal rotations of each vertebral level of the same patient describing the 3D vertebral rotation between the supine position and the prone position lying on bolsters.

RESULTS

For sagittal analysis, the results showed a behavior in the evolution of rotation depending on the level. Between T01 and T10, the rotation was between - 14° and - 8°. Between T10 and L05, the sagittal rotation increased from - 10° up to + 10°. For frontal and transversal analysis, the rotations were under 6.5°.

CONCLUSION

These results could be valuable to perform a safe virtual templating: the information given by the virtual templating seems to be more accurate in the transversal plane than in the sagittal plane.

Spontaneous induced bone fusion in minimally invasive fusionless bipolar fixation in neuromuscular scoliosis: a computed tomography analysis

PURPOSE

Posterior spinal fusion (PSF) at skeletal maturity is still the gold standard in children with neuromuscular scoliosis (NMS) who underwent fusionless surgery. The aim of this computed tomography (CT) study was to quantify the spontaneous bone fusion at the end of a lengthening program by minimally invasive fusionless bipolar fixation (MIFBF), that could avoid PSF.

METHODS

NMS operated on with MIFBF from T1 to the pelvis and at final lengthening program were included. CT was performed at least five years postoperatively. The autofusion was classified as completely or not fused at the facets joint (on both coronal and sagittal plane, right and left side, from T1 to L5), and around the rods (axial plane, right and left side, from T5 to L5). Vertebral body heights were assessed.

RESULTS

Ten patients were included (10.7y ± 2 at initial surgery). Mean Cobb angle was 82 ± 20 preoperatively and 37 ± 13 at last follow-up. CT were performed on average 6.7y ± 1.7 after initial surgery. Mean preoperative and last follow-up thoracic vertebrae height were respectively 13.5 mm ± 1.7 and 17.4 mm ± 1.7 (p < 0.001). 93% facets joints were fused (out of 320 analyzed joints), corresponding to 15/16 vertebral levels. Ossification around the rods was observed in 6.5±2.4 levels out of 13 in the convex side, and 4.2 ± 2.2 in the concave side (p = 0.04).

CONCLUSIONS

This first computed quantitative study showed MIFBF in NMS preserved spinal growth, while it induced 93% of facet joints fusion. This could be is an additional argument when questionning the real need for PSF at skeletal maturity.

Computed Tomography of the Spine

The introduction of the first whole-body CT scanner in 1974 marked the beginning of cross-sectional spine imaging. In the last decades, the technological advancement, increasing availability and clinical success of CT led to a rapidly growing number of CT examinations, also of the spine. After initially being primarily used for trauma evaluation, new indications continued to emerge, such as assessment of vertebral fractures or degenerative spine disease, preoperative and postoperative evaluation, or CT-guided interventions at the spine; however, improvements in patient management and clinical outcomes come along with higher radiation exposure, which increases the risk for secondary malignancies. Therefore, technical developments in CT acquisition and reconstruction must always include efforts to reduce the radiation dose. But how exactly can the dose be reduced? What amount of dose reduction can be achieved without compromising the clinical value of spinal CT examinations and what can be expected from the rising stars in CT technology: artificial intelligence and photon counting CT? In this article, we try to answer these questions by systematically reviewing dose reduction techniques with respect to the major clinical indications of spinal CT. Furthermore, we take a concise look on the dose reduction potential of future developments in CT hardware and software.

How often does the preoperative plan for freehand pedicle screw placement match the actual surgical execution in adolescent idiopathic scoliosis?

PURPOSE

To provide a baseline for comparison with future advancements, this study determined the accuracy of preoperative planning of pedicle screw placement using standard radiographs for posterior fusion (PSF) for adolescent idiopathic scoliosis (AIS).

METHODS

Ninety-five patients with AIS planned for PSF were prospectively enrolled. Preoperative planning was based upon standard upright posteroanterior and lateral radiographs. The planned number of screws to be placed at each level was recorded. Intraoperatively, all screws were placed by freehand technique. The number of successfully placed screws and the reasons for abandoning screw placement were documented.

RESULTS

There were a total of 1783 pedicle screws planned preoperatively. The average planned implant density was 2.0 implants/vertebra. A total of 1723 (96.6%) of the planned screws were placed successfully. Fourteen (0.8%) screws were abandoned after attempted placement (range 0-2 screws/case). Of 241 screws planned in pedicles noted to be "hypoplastic," 13 resulted in the use of a hook or no instrumentation. The placement was not attempted for 49 (range 0-7/case) planned screws due to intraoperative decision-making and a sense that the curve was flexible enough not to require every screw. Three cases (3.2%) required instrumentation of an additional level.

CONCLUSIONS

Standard spine radiographs allow for accurate preoperative planning for freehand pedicle screw placement in AIS. Ninety-seven percent of planned screws were placed successfully. The primary reason for deviation from the preoperative plan was intraoperative surgeon decision-making rather than difficulty with screw placement. This study will serve as a baseline when considering the utilization of navigation in PSF for AIS.

Increased proximal vertebral rotation is associated with shoulder imbalance after posterior spinal fusion for severe adolescent idiopathic scoliosis

PURPOSE

Residual shoulder imbalance is associated with suboptimal outcomes following the surgical correction of adolescent idiopathic scoliosis (AIS) including poor patient satisfaction. In this retrospective study, we evaluate the radiographic parameters and the relationship between the global and local indices of spinal alignment with shoulder balance pre- and postoperatively utilizing EOS imaging and 3D reconstruction.

METHODS

A retrospective radiographic analysis was performed on patients with AIS, treated with posterior spinal fusion. Postoperative radiographs were obtained immediately following surgery, at 6 months and final follow-up over 2 years postoperatively. 3D Radiographic measurements included in the coronal plane radiographic shoulder height difference (RSHD), proximal thoracic Cobb angle (PT) and main thoracic Cobb (MT), in the sagittal plane T4-T12 kyphosis, T12-L5 lordosis, in the axial plane proximal thoracic (PT AVR) and main thoracic apical vertebral rotation (MT AVR).

RESULTS

Sixty-six patients were included (63 females) with an average main thoracic curvature of 76 degrees. RSHD averaged 14 mm ± 14 preoperatively, -15 mm ± 12 postoperatively, -8.5 mm ± 11 at 6 months, and -8.3 mm ± 8.7 at final follow-up, respectively. Statistical analysis revealed a significant correlation between RSHD and proximal thoracic Cobb angle, between RSHD and proximal thoracic apical vertebral rotation (PTAVR) (r > 0.20, p < 0.05).

CONCLUSION

The significant correlation presented in this study suggests that PT Cobb angle and PT AVR are involved in postoperative shoulder imbalance.

THE LEVEL OF EVIDENCE

Level 4.

Radiation dose levels of thoracic-lumbar spine CT in pediatric trauma patients and assessment of scan parameters for dose optimization

BACKGROUND

CT is frequently used for assessing spinal trauma in children.

OBJECTIVE

To establish the local diagnostic reference levels of spine CT examinations in pediatric spinal trauma patients and analyze scan parameters to enable dose optimization.

MATERIALS AND METHODS

In this retrospective study, we included 192 pediatric spinal trauma patients who underwent spine CT. Children were divided into two age groups: 0-10 years (group 1) and 11-17 years (group 2). Each group was subdivided into thoracic, thoracolumbar and lumbar CT groups. CT acquisition parameters (tube potential, in kilovoltage [kV]; mean tube current-time product, in milliamperes [mAs]; reference mAs; collimated slice width; tube rotation time; pitch; scan length) and radiation dose descriptors (volume CT dose index [CTDI_vol] and dose-length product [DLP]) were recorded. The CTDI_vol and DLP values of spine CTs obtained with different tube potential and collimated slice width values were compared for each group.

RESULTS

CTDI_vol and DLP values of thoracolumbar spine CTs in group 1 and lumbar spine CTs in group 2 were significantly lower in CTs acquired with low tube potential levels (P<0.05). CTDI_vol and DLP values of thoracolumbar spine CTs in both groups and lumbar spine CTs in group 2 acquired with high collimated slice width values were significantly lower than in corresponding CTs acquired with low collimated slice width values (P<0.05).

CONCLUSION

Pediatric spine CT radiation doses can be notably reduced from the manufacturers' default protocols while preserving image quality.

Deep Learning-based Reconstruction for Lower-Dose Pediatric CT: Technical Principles, Image Characteristics, and Clinical Implementations

Optimizing the CT acquisition parameters to obtain diagnostic image quality at the lowest possible radiation dose is crucial in the radiosensitive pediatric population. The image quality of low-dose CT can be severely degraded by increased image noise with filtered back projection (FBP) reconstruction. Iterative reconstruction (IR) techniques partially resolve the trade-off relationship between noise and radiation dose but still suffer from degraded noise texture and low-contrast detectability at considerably low-dose settings. Furthermore, sophisticated model-based IR usually requires a long reconstruction time, which restricts its clinical usability. With recent advances in artificial intelligence technology, deep learning-based reconstruction (DLR) has been introduced to overcome the limitations of the FBP and IR approaches and is currently available clinically. DLR incorporates convolutional neural networks-which comprise multiple layers of mathematical equations-into the image reconstruction process to reduce image noise, improve spatial resolution, and preserve preferable noise texture in the CT images. For DLR development, numerous network parameters are iteratively optimized through an extensive learning process to discriminate true attenuation from noise by using low-dose training and high-dose teaching image data. After rigorous validations of network generalizability, the DLR engine can be used to generate high-quality images from low-dose projection data in a short reconstruction time in a clinical environment. Application of the DLR technique allows substantial dose reduction in pediatric CT performed for various clinical indications while preserving the diagnostic image quality. The authors present an overview of the basic concept, technical principles, and image characteristics of DLR and its clinical feasibility for low-dose pediatric CT. ^©RSNA, 2021.

Deep Learning Algorithm for Simultaneous Noise Reduction and Edge Sharpening in Low-Dose CT Images: A Pilot Study Using Lumbar Spine CT

Objective

The purpose of this study was to assess whether a deep learning (DL) algorithm could enable simultaneous noise reduction and edge sharpening in low-dose lumbar spine CT.

Materials and Methods

This retrospective study included 52 patients (26 male and 26 female; median age, 60.5 years) who had undergone CT-guided lumbar bone biopsy between October 2015 and April 2020. Initial 100-mAs survey images and 50-mAs intraprocedural images were reconstructed by filtered back projection. Denoising was performed using a vendor-agnostic DL model (ClariCT.AI™, ClariPI) for the 50-mAS images, and the 50-mAs, denoised 50-mAs, and 100-mAs CT images were compared. Noise, signal-to-noise ratio (SNR), and edge rise distance (ERD) for image sharpness were measured. The data were summarized as the mean ± standard deviation for these parameters. Two musculoskeletal radiologists assessed the visibility of the normal anatomical structures.

Results

Noise was lower in the denoised 50-mAs images (36.38 ± 7.03 Hounsfield unit [HU]) than the 50-mAs (93.33 ± 25.36 HU) and 100-mAs (63.33 ± 16.09 HU) images (p < 0.001). The SNRs for the images in descending order were as follows: denoised 50-mAs (1.46 ± 0.54), 100-mAs (0.99 ± 0.34), and 50-mAs (0.58 ± 0.18) images (p < 0.001). The denoised 50-mAs images had better edge sharpness than the 100-mAs images at the vertebral body (ERD; 0.94 ± 0.2 mm vs. 1.05 ± 0.24 mm, p = 0.036) and the psoas (ERD; 0.42 ± 0.09 mm vs. 0.50 ± 0.12 mm, p = 0.002). The denoised 50-mAs images significantly improved the visualization of the normal anatomical structures (p < 0.001).

Conclusion

DL-based reconstruction may enable simultaneous noise reduction and improvement in image quality with the preservation of edge sharpness on low-dose lumbar spine CT. Investigations on further radiation dose reduction and the clinical applicability of this technique are warranted.

Evaluation of correlation between sagittal balance and plantar pressure distributions in adolescent idiopathic scoliosis: A pilot study

BACKGROUND

To evaluate the correlation between baropodometric parameters and sagittal parameters for adolescent idiopathic scoliosis.

METHODS

44 volunteers (7 males and 37 females) were recruited. All participants were diagnosed as adolescent idiopathic scoliosis by X-ray before baropodometric study. Sagittal parameters included thoracic kyphosis, lumbar lordosis, sagittal vertical axis, pelvic tilt, sacral slope and pelvic incidence. A static baropodometry was performed for each patient. The foot area was divided into four quadrants. The contact surface and weight percentage were measured.

FINDINGS

Lumbar lordosis was positively correlated to pelvic incidence, sacral slope and (P < 0.001, P < 0.001, respectively). On the major curve side, pelvic tilt showed a positive correlation with all baropodometric parameters (P < 0.05) except forefoot weight percentage. Thoracic kyphosis showed negative correlations with contact surface and weight percentage of the forefoot (P = 0.04, 0.02 respectively) but no correlation with any rearfoot feature. Lumbar lordosis, sagittal vertical axis, pelvic incidence and sacral slope were not in correlation with plantar pressure. On the opposite side, sagittal profile showed no obvious correlation with any baropodometric parameter.

INTERPRETATION

In scoliosis, sagittal balance is closely correlated to plantar pressure distributions. Baropodometry is a feasible method to assess sagittal balance.

Correlation between spinal coronal balance and static baropodometry in children with adolescent idiopathic scoliosis

BACKGROUND

Scoliosis is accepted as a 3-dimensional deformity involving axial, sagittal and frontal planes.

RESEARCH QUESTION

To evaluate the correlation between baropodometric parameters and coronal balance status for idiopathic scoliosis.

METHODS

44 patients (7 males and 37 females) of Adolescent Idiopathic Scoliosis (AIS) were recruited. All participants should have scoliosis confirmed by a spine X-ray performed less than one month ahead of the baropodometric study. Radiographic studies including Cobb angle, offset between Central Sacral Vertical Line (CSVL) and C7 Vertebra Plumb Line (C7PL) (considered as global coronal balance, GCB), Apical Translation of the major curve (AT, considered as regional coronal balance) as well as Lateral Pelvic Tilt (LPT) were examined. A static baropodometry was performed for each patient. The contact surface and load ratio (to the entire load of both feet) were measured.

RESULTS

On both sides, the surface of the forefoot was significantly larger than that of the rearfoot (P < 0.001) and the load ratio of the forefoot was significantly smaller than that of the rearfoot (P < 0.001). On the major curve side, GCB showed a positive correlation with the contact surface of the forefoot (r = 0.36, P = 0.019), as well as the load ratio (r = 0.40, P = 0.008). AT also showed a positive correlation with the load ratio of the forefoot (r = 0.331, P = 0.03) but no correlation with contact surface.

SIGNIFICANCE

In scoliosis, coronal balance is correlated to plantar pressure distribution. Apical translation of the major curve and offset between CSVL and C7PL are the best describers of coronal balance.

Surgical Outcomes of Anterior Versus Posterior Fusion in Lenke Type 1 Adolescent Idiopathic Scoliosis

STUDY DESIGN

Retrospective study.

OBJECTIVE

To describe surgical results in two and three dimensions and patient-reported outcomes of scoliosis treatment for Lenke type 1 idiopathic curves with an open anterior or posterior approach.

SUMMARY OF BACKGROUND DATA

Different surgical techniques have been described to prevent curve progression and to restore spinal alignment in idiopathic scoliosis. The spine can be accessed via an anterior or a posterior approach. However, the surgical outcomes, especially in three dimensions, for different surgical approaches remain unclear.

METHODS

Cohorts of Lenke curve type 1 idiopathic scoliosis patients, after anterior or posterior spinal fusion were recruited, to measure curve characteristics on conventional radiographs, before and after surgery and after 2 years follow-up, whereas the vertebral axial rotation, true mid-sagittal anterior-posterior height ratio of individual structures, and spinal height differences were measured on 3D reconstructions of the pre- and postoperative supine low-dose computed tomography (CT) scans. Additionally, the intraoperative parameters were described and the patients completed the Scoliosis Research Society outcomes and the 3-level version of EuroQol Group questionnaires postoperatively.

RESULTS

Fifty-three patients with Lenke curve type 1 idiopathic scoliosis (26 in the anterior cohort and 27 in the posterior cohort) were analyzed. Fewer vertebrae were instrumented in the anterior cohort compared with the posterior cohort (P < 0.001), with less surgery time and lower intraoperative blood loss (P < 0.001). The Cobb angle correction of the primary thoracic curve directly after surgery was 57 ± 12% in the anterior cohort and 73 ± 12% in the posterior cohort (P < 0.001) and 55 ± 13% and 66 ± 12% (P = 0.001) at 2 years follow-up. Postoperative 3D alignment restoration and questionnaires showed no significant differences between the cohorts.

CONCLUSION

This study suggests that Lenke type 1 curves can be effectively managed surgically with either an open anterior or posterior approach. Each approach, however, has specific advantages and challenges, as described in this study, which must be considered before treating each patient.

LEVEL OF EVIDENCE

3.

Low-dose CT of postoperative pelvic fractures: a comparison with radiography

BACKGROUND

Computed tomography (CT) is superior to conventional radiography (CR) for assessing internal fixation of pelvic fractures, but with a higher radiation exposure. Low-dose CT (LDCT) could possibly have a sufficient diagnostic accuracy but with a lower radiation dose.

PURPOSE

To compare postoperative diagnostic accuracy of LDCT and CR after open reduction and internal fixation of pelvic fracture.

MATERIAL AND METHODS

Twenty-one patients were examined with LDCT and CR 0-9 days after surgery. The examinations were reviewed by two musculoskeletal radiologists. Hardware, degree of fracture reduction, image quality, and reviewing time were assessed, and effective radiation dose was calculated. Inter-reader agreement was calculated.

RESULTS

LDCT was significantly better than CR in determining whether hardware positioning was assessable ( P < 0.001). Acetabular congruence was assessable in all fractured patients with LDCT. In 12 of the 32 assessments with CR of patients with an acetabular fracture, joint congruence was not assessable due to overlapping hardware ( P = 0.001). Image quality was significantly higher for LDCT. Median time to review was 240 s for LDCT compared to 180 s for CR. Effective dose was 0.79 mSv for LDCT compared to 0.32 mSv for CR ( P < 0.001).

CONCLUSION

LDCT is more reliable than CR in assessing hardware position and fracture reduction. Joint congruency is sometimes not possible to assess with CR, due to overlapping hardware. The image quality is higher, but also the effective dose, with LDCT than with CR.

Perspective review on applications of optics in spinal surgery

Optical technologies may be applied to multiple facets of spinal surgery from diagnostics to intraoperative image guidance to therapeutics. In diagnostics, the current standard remains cross-sectional static imaging. Optical surface scanning tools may have an important role; however, significant work is required to clearly correlate surface metrics to radiographic and clinically relevant spinal anatomy and alignment. In the realm of intraoperative image guidance, optical tracking is widely developed as the current standard of instrument tracking, however remains compromised by line-of-sight issues and more globally cumbersome registration workflows. Surface scanning registration tools are being refined to address concerns over workflow and learning curves, and allow real-time update of tissue deformation; however, the line-of-sight issues plaguing instrument tracking remain to be addressed. In therapeutics, optical applications exist in both visualization, in the form of endoscopes, and ablation, in the form of lasers. Further work is required to extend the feasibility of laser ablation to multiple tissues, including disc, bone, and tumor, in a safe and time-efficient manner. Finally, we postulate some of the short- and long-term opportunities for future growth of optical techniques in the context of spinal surgery. Particular emphasis is placed on intraoperative image guidance, the area of the authors' primary expertise.

Three-dimensional EOS Analysis of Apical Vertebral Rotation in Adolescent Idiopathic Scoliosis

BACKGROUND

Apical vertebral rotation (AVR) is increasingly recognized as one of the important radiographic parameters in adolescent idiopathic scoliosis (AIS). EOS enables us to precisely measure AVR by 3-dimensional reconstruction. The objective of the present study was to describe the postoperative correction and the long-term follow-up of AVR in posterior spinal fusion with direct vertebral rotation and elucidate the factors that affected the correction.

METHODS

We retrospectively reviewed 153 consecutive posterior spinal fusion surgeries for AIS performed between 2009 and 2012. Among them, 55 patients who fulfilled the study inclusion criteria with complete preoperative, immediate postoperative, and last follow-up (>1 y) EOS images were included in the present study. EOS 3-dimentional reconstructions were undertaken for each patient. Postoperative AVR correction and the loss of correction were calculated.

RESULTS

Preoperative AVR of the major curve averaged 19 degrees (SD=7 degrees), and AVR on immediate postoperative images averaged 9 degrees (SD=6 degrees, P<0.001). AVR at final follow-up averaged 11 degrees (SD=6 degrees, P=0.06). Postoperative correction was larger in all-screw construct than in hybrid construct (55% vs. 36%, P=0.03).

CONCLUSIONS

The present study is the first study to measure AVR in a large population of AIS patients using EOS 3-dimensional reconstruction. We report the correction magnitude was significantly affected by the construct.

LEVEL OF EVIDENCE

Level IV-therapeutic study (case series).

Organ doses and lifetime attributable risk evaluations for scoliosis examinations of adolescent patients with the EOS imaging system

PURPOSE

The goal of this work is to evaluate organ doses and lifetime attributable risk of cancer incidence and mortality in scoliosis examinations of adolescent patients performed with EOS imaging system, in order to optimize patient dose and protocols.

METHODS

An anthropomorphic phantom of a normal patient, with thermoluminescent dosimeters in correspondence with the main organs at risk, was imaged with both EOS and computed radiography (CR). For each modality, effective dose was calculated from the measured organ doses. Lifetime attributable risk was computed accordingly to the Committee on the Biological Effects of Ionizing Radiation (BEIR VII) and Public Health England (HPA) publications.

RESULTS

Except for testes and eyes, which were excluded from the scan in CR protocol, for all the other organs the doses delivered with CR examination were higher than these delivered by EOS system. The effective dose in EOS examination (0.43 ± 0.04 mSv) is about two times less than the dose in computed radiography with anti-scatter grid examination (0.87 ± 0.09 mSv), and, consequently, also the cancer probability is lower (5.4 vs 9.7 number of any cancers induction cases per 100,000 person examined, for a 20-year-old male patient).

CONCLUSIONS

The EOS system is efficient in limiting patient dose. The shielding of testes and the exclusion of eyes from the scan could allow to further reduce the dose.

Effective dose in low-dose CT compared with radiography for templating of total hip arthroplasty

Background Recently, total hip arthroplasty (THA) has come to focus on restoration of individual anatomy including femoral neck anteversion and global offset (femoral and acetabular offset). Three-dimensional (3D) computed tomography (CT) data could provide a better basis for preoperative templating. The use of CT has been hampered by high radiation dose. Purpose To evaluate the effective dose used in pelvis and hip CT for THA templating. Material and Methods CT data from two clinical trials of THA were evaluated for CT scan length and volume CT dose index (CTDI_vol). The effective doses from hip-knee-ankle CT and pelvis and hip radiography were compared. Conversion factors for effective dose for radiography were calculated using the PCXMC software. Results A reduced dose CT protocol for pelvis imaging gave a substantial dose reduction compared with standard CT, while maintaining sufficient image quality. Between the two clinical trials there was a significant reduction in effective CT dose corresponding to changes in the CT protocol ( P < 0.01). The CT dose for the latter group was similar to, but nevertheless significantly higher than for, radiography ( P < 0.01). However, in the latter group the theoretical minimum dose for CT, using the minimum scan length required by the templating software, was equal to the dose from radiography. Conclusion Although the CT dose remained higher than for radiography, potential reductions in scan length could reduce the dose further so that CT would have a comparable level of risk to radiography with the added benefit of 3D templating.

CT Radiation Dose Reduction in Robot-assisted Pediatric Spinal Surgery

STUDY DESIGN

Retrospective consecutive cohort series.

OBJECTIVE

The aim of this study was to develop a low-dose computed tomography (CT) protocol for use in robot-assisted pediatric spinal surgery.

SUMMARY OF BACKGROUND DATA

CT scans are utilized preoperatively for preoperative planning, by navigation software during robot-assisted surgery, and postoperatively to assess surgical implant placement. Traditionally high radiation doses produced by CT scanning are a concern in the highly radiosensitive pediatric population.

METHODS

We developed a low-dose protocol using phantom scans. A cohort of patients undergoing CT scanning using the low-dose protocol was collected. Further, a matching cohort of patients who underwent standard scanning was collected. Image quality was assessed by observer ratings. Radiation doses and image quality metrics were compared for the standard and low-dose protocol patients.

RESULTS

Effective dose significantly decreased 84% to 91% depending on patient size and whether the scan was preoperative or postoperative. All scans were compatible with the navigation software. No clinically significant differences in image quality were observed between low-dose and standard patient cohorts.

CONCLUSIONS

Task-based CT protocol optimization can produce acceptable image quality with dose comparable to standard two-view radiography.

LEVEL OF EVIDENCE

2.

3D-modeling of the spine using EOS imaging system: Inter-reader reproducibility and reliability

Objectives

To retrospectively assess the interreader reproducibility and reliability of EOS 3D full spine reconstructions in patients with adolescent idiopathic scoliosis (AIS).

Methods

73 patients with mean age of 17 years and a moderate AIS (median Cobb Angle 18.2°) obtained low-dose standing biplanar radiographs with EOS. Two independent readers performed “full spine” 3D reconstructions of the spine with the “full-spine” method adjusting the bone contour of every thoracic and lumbar vertebra (Th1-L5). Interreader reproducibility was assessed regarding rotation of every single vertebra in the coronal (i.e. frontal), sagittal (i.e. lateral), and axial plane, T1/T12 kyphosis, T4/T12 kyphosis, L1/L5 lordosis, L1/S1 lordosis and pelvic parameters. Radiation exposure, scan-time and 3D reconstruction time were recorded.

Results

Interclass correlation (ICC) ranged between 0.83 and 0.98 for frontal vertebral rotation, between 0.94 and 0.99 for lateral vertebral rotation and between 0.51 and 0.88 for axial vertebral rotation. ICC was 0.92 for T1/T12 kyphosis, 0.95 for T4/T12 kyphosis, 0.90 for L1/L5 lordosis, 0.85 for L1/S1 lordosis, 0.97 for pelvic incidence, 0.96 for sacral slope, 0.98 for sagittal pelvic tilt and 0.94 for lateral pelvic tilt. The mean time for reconstruction was 14.9 minutes (reader 1: 14.6 minutes, reader 2: 15.2 minutes, p<0.0001). The mean total absorbed dose was 593.4μGy ±212.3 per patient.

Conclusion

EOS “full spine” 3D angle measurement of vertebral rotation proved to be reliable and was performed in an acceptable reconstruction time. Interreader reproducibility of axial rotation was limited to some degree in the upper and middle thoracic spine due the obtuse angulation of the pedicles and the processi spinosi in the frontal view somewhat complicating their delineation.

Reliability and Usefulness of Intraoperative 3-Dimensional Imaging by Mobile C-Arm With Flat-Panel Detector

STUDY DESIGN

Reliability and agreement study.

OBJECTIVE

To assess the reliability of intraoperative 3-dimensional imaging with a mobile C-arm (3D C-arm) equipped with a flat-panel detector.

SUMMARY OF BACKGROUND DATA

Pedicle screws are widely used in spinal surgery. Postoperative computed tomography (CT) is the most reliable method to detect screw misplacement. Recent advances in imaging devices have enabled surgeons to acquire 3D images of the spine during surgery. However, the reliability of these imaging devices is not known.

METHODS

A total of 203 screws were used in 22 consecutive patients who underwent surgery for scoliosis. Screw position was read twice with a 3D C-arm and twice with CT in a blinded manner by 2 independent observers. Screw positions were classified into 4 categories at every 2 mm and then into 2 simpler categories of acceptable or unacceptable. The degree of agreement with respect to screw positions between the double readings was evaluated by κ value. With unanimous agreement between 2 observers regarding postoperative CT readings considered the gold standard, the sensitivity of the 3D C-arm for determining screw misplacement was calculated.

RESULTS

A total 804 readings were performed. For the 4-category classification, the mean κ value for the 2 interobserver readings was 0.52 for the 3D C-arm and 0.46 for CT. For the 2-category classification, the mean κ value for the 2 interobserver readings was 0.80 for the 3D C-arm and 0.66 for CT. The sensitivity, specificity, positive predictive value, and negative predictive value of intraoperative imaging with the 3D C-arm were 70%, 95%, 44%, and 98%, respectively. With respect to screws with perforation ≥4 mm, the sensitivity was 83%. No revision surgery was performed.

CONCLUSIONS

Intraoperative imaging with a 3D C-arm was reliable for detecting screw misplacement and helpful in decreasing the rate of revision surgery for screw misplacement.

A Comparison of Cobb Angle: Standing Versus Supine Images of Late-Onset Idiopathic Scoliosis

Background

Scoliosis is traditionally evaluated by measuring the Cobb angle in radiograph images taken while the patient is standing. However, low-dose computed tomography (CT) images, which are taken while the patient is in a supine position, provide new opportunities to evaluate scoliosis. Few studies have investigated how the patient’s position, standing or supine, affects measurements. The purpose of this study was to compare the Cobb angle in images from patients while standing versus supine.

Material/Methods

A total of 128 consecutive patients (97 females and 21 males; mean age 15.5 [11–26] years) with late-onset scoliosis requiring corrective surgery were enrolled. One observer evaluated the type of curve (Lenke classification) and measured the Cobb angle in whole-spine radiography (standing) and scout images from low-dose CT (supine) were taken on the same day.

Results

For all primary curves, the mean Cobb angle was 59° (SD 12°) while standing and 48° (SD 12°) while in the supine position, with a mean difference of 11° (SD 5°). The correlation between primary standing and supine images had an r value of 0.899 (95% CI 0.860–0.928) and an intra-class correlation coefficient value of 0.969. The correlation between the difference in standing and supine images from primary and secondary curves had an r value of 0.340 (95% CI 0.177–0.484).

Conclusions

We found a strong correlation between the Cobb angle in images obtained while the patient was standing versus supine for primary and secondary curves. This study is only applicable for patients with severe curves requiring surgical treatment. It enables additional studies based on low-dose CT.

Low dose CT of the lumbar spine compared with radiography: a study on image quality with implications for clinical practice

BACKGROUND

Lumbar spine radiography is often performed instead of CT for radiation dose concerns.

PURPOSE

To compare image quality and diagnostic information from low dose lumbar spine CT at an effective dose of about 1 mSv with lumbar spine radiography.

MATERIAL AND METHODS

Fifty-one patients were examined by both methods. Five reviewers scored all examinations on eight image quality criteria using a five-graded scale and also assessed three common pathologic changes.

RESULTS

Low dose CT scored better than radiography on the following: sharp reproduction of disc profile and vertebral end-plates (odds ratio [OR], 1.8; 95% confidence interval [CI], 1.3-2.5), intervertebral foramina and pedicles (OR, 4.3; 95% CI, 3.1-5.9), intervertebral joints (OR, 139; 95% CI, 59-326), spinous and transverse processes (OR, 7.0; 95% CI, 4.3-11.2), sacro-iliac joints (OR, 4.2; 95% CI, 3.2-5.7), reproduction of the adjacent soft tissues (OR, 2.9; 95% CI, 2.1-4.0), and absence of any obscuring superimposed gastrointestinal gas and contents (OR, 188; 95% CI, 66-539). Radiography scored better on sharp reproduction of cortical and trabecular bone (OR, 0.3; 95% CI, 0.2-0.4). The reviewers visualized disk degeneration, spondylosis/diffuse idiopathic skeletal hyperostosis (DISH) and intervertebral joint osteoarthritis more clearly and were more certain with low dose CT. Mean time to review low dose CT was 204 s (95% CI, 194-214 s.), radiography 152 s (95% CI, 146-158 s.). The effective dose for low dose CT was 1.0-1.1 mSv, for radiography 0.7 mSv.

CONCLUSION

Low dose lumbar spine CT at about 1 mSv has superior image quality to lumbar spine radiography with more anatomical and diagnostic information.

Intraoperative computed tomography navigation for transpedicular screw fixation to treat unstable thoracic and lumbar spine fractures: clinical analysis of a case series (CARE-compliant)

Transpedicular screw (TPS) fixation in unstable thoracic and lumbar (TL) spine fractures remains technically difficult because of destroyed anatomical landmarks, unstable gross segments, and discrepancies in anatomic orientation using conventional anatomic landmarks, fluoroscopic guidance, or computed tomography (CT)-based navigation. In this study, we evaluated the safety and accuracy of TPS placement under intraoperative computed tomography (iCT) navigation in managing unstable TL spine fractures.From 2010 to 2013, we retrospectively reviewed the Spine Operation Registry records of patients who underwent posterior instrumented fusion to treat unstable TL spine fractures via the iCT navigation system. An unstable spine fracture was identified as AO/Magerl classification type B or type C.In all, 316 screws in 37 patients with unstable TL spine fractures were evaluated and involved 7 thoracic, 23 thoracolumbar junctional, and 7 lumbar fractures. The accuracy of TPS positioning in the pedicle without breach was 98% (310/316). The average number of iCT scans per patient was 2.1 (range 2-3). The average total radiation dose to patients was 15.8 mSv; the dose per single level exposure was 2.7 mSv. The TPS intraoperative revision rate was 0.6% (2/316) and no neurovascular sequela was observed. TPS fixation using the iCT navigation system obtained a 98% accuracy in stabilizing unstable TL spine fractures. A malplaced TPS could be revised during real-time confirmation of the TPS position, and no secondary operation was required to revise malplaced screws.The iCT navigation system provides accurate and safe management of unstable TL spine fractures. In addition, operating room personnel, including surgeons and nurses, did not need to wear heavy lead aprons as they were not exposed to radiation.

Pedicle screw loosening: a clinically relevant complication?

PURPOSE

Literature studies showed a very wide range of pedicle screw loosening rates after thoracolumbar stabilization, ranging from less than 1 to 15 % in non-osteoporotic patients treated with rigid systems and even higher in osteoporotic subjects or patients treated with dynamic systems. Firstly, this paper aims to investigate how much this complication is affecting the success rate of pedicle screw fixation, in both non-osteoporotic and osteoporotic patients, and to discuss the biomechanical reasons which may be related to the variability of the rates found in the literature. The secondary aim was to summarize and discuss the published definitions and conventions about screw loosening from a clinical and radiological point of view.

METHODS

Narrative literature review.

RESULTS

Screw loosening appears to be a minor problem for fixation and fusion of healthy, non-osteoporotic bone. Pedicle screw fixation in osteoporotic bone is believed to be at risk of loosening, but clinical data are actually scarce. Both expandable and augmented screws may be a viable option to reduce the risk of loosening, but clinical evidence is missing. Posterior motion-preserving implants seems to have a significant risk of screw loosening. Standardization appears to be lacking regarding the radiological assessment. Marked differences in the loosening rates found based either on planar radiography or on CT scanning were observed.

CONCLUSIONS

Reported loosening rates primarily depended on the protocol used for the clinical examination during follow-up and on the conventions used for the radiological assessment. Aiming to a better comparability of published data, we recommend the authors of clinical studies to describe which criteria were used to assess a loosened screw, as well as the protocol of the clinical follow-up examination. Low-dose CT should be used for the assessment of screw loosening whenever possible.

Intraoperative image-guided spinal navigation: technical pitfalls and their avoidance

Spinal instrumentation has made significant advances in the last two decades, with transpedicular constructs now widely used in spinal fixation. Pedicle screw constructs are routinely used in thoracolumbar-instrumented fusions, and in recent years, the cervical spine as well. Three-column fixations with pedicle screws provide the most rigid form of posterior stabilization. Surgical landmarks and fluoroscopy have been used routinely for pedicle screw insertion, but a number of studies reveal inaccuracies in placement using these conventional techniques (ranging from 10% to 50%). The ability to combine 3D imaging with intraoperative navigation systems has improved the accuracy and safety of pedicle screw placement, especially in more complex spinal deformities. However, in the authors' experience with image guidance in more than 1500 cases, several potential pitfalls have been identified while using intraoperative spinal navigation that could lead to suboptimal results. This article summarizes the authors' experience with these various pitfalls using spinal navigation, and gives practical tips on their avoidance and management.

Low-dose computed tomography of the lumbar spine: a phantom study on imaging parameters and image quality

BACKGROUND

Lumbar spine radiography has limited diagnostic value but low radiation dose compared with computed tomography (CT). The average effective radiation dose from lumbar spine radiography is about 1.1 mSv. Low-dose lumbar spine CT may be an alternative to increase the diagnostic value at low radiation dose, around 1 mSv.

PURPOSE

To determine the optimal settings for low-dose lumbar spine CT simultaneously aiming for the highest diagnostic image quality possible.

MATERIAL AND METHODS

An ovine lower thoracic and lumbar spine phantom, with all soft tissues around the vertebrae preserved except the skin, was placed in a 20 L plastic container filled with water. The phantom was scanned repeatedly with various technical settings; different tube potential, reference mAs, and with different convolution filters. Five radiologists evaluated the image quality according to a modification of the European guidelines for multislice computed tomography (MSCT) quality criteria for lumbar spine CT 2004. In a visual comparison the different scans were also ranked subjectively according to perceived image quality. Image noise and contrast were measured.

RESULTS

A tube potential of 120 kV with reference mAs 30 and medium or medium smooth convolution filter gave the best image quality at a sub-millisievert dose level, i.e. with an effective dose comparable to that from lumbar spine radiography.

CONCLUSION

Low-dose lumbar spine CT thus opens a possibility to substitute lumbar spine radiography with CT without obvious increase in radiation dose.

Evaluation of implant loosening following segmental pedicle screw fixation in adolescent idiopathic scoliosis: a 2 year follow-up with low-dose CT

Background

The long term radiological status of screw fixation following scoliosis surgery with all pedicle screw construct is not previously studied.

Aim

To evaluate the incidence of loosening (implant failure) evaluated with low-dose CT two years following scoliosis surgery.

Study design

Retrospective study.

Methods

81 consecutive patients with adolescent idiopathic scoliosis (AIS), aged 18 ± 3 years at 2 years follow-up (83% were female), subjected for scoliosis corrective surgery with all pedicle screw construct (total of 1666 screws) has been examined with plain radiography and with low dose CT 6 weeks and 2 years postoperatively.

Results

In 26 out of 81 (32%) patients there were signs of loosening of one or more screws, a maximum 3 screws. 47 out of 1666 (2.8%) screws showed evidence of loosening. Preoperative Cobb angle was 56° among patients with loosening compared with 53° among patients with no evidence of loosening (P = 0.288). In males there were signs of loosening in 8 out of 14 (57%) and in females 18 out of 67 (27%), (P = 0.027). Among cases with loosening, 14% had suboptimal screw placement at the first postoperative CT compared with 11% among patients with no evidence of loosening (P = 0.254). One patient with a loosened L4 screw had neurological deficit and subjected for revision of the construct. Out of 26 patients with evidence of loosening, 5 patients reported minor pain or discomfort, 1 patient had a minor proximal junctional kyphosis of about 15° and 3 patients showed evidence of pull-out of 3–5 mm at the upper end of the construct but no clinical complaint. With plain radiography loosening could be observed only in 11 out of 26 cases, 5 were in the lumbar region.

Conclusions

In a consecutive series of 81 cases with AIS who had underwent scoliosis surgery, one third showed, 2 years after the intervention, minor screw loosening. Males were more prone to develop screw loosening. In CT system that enables low-dose protocol, CT is recommended for the evaluation of evidence of screw loosening.

Three-dimensional imaging of the spine using the EOS system: is it reliable? A comparative study using computed tomography imaging

The aim of this study was to evaluate the precision of three-dimensional geometry compared with computed tomography (CT) images. This retrospective study included patients who had undergone both imaging of the spine using the EOS imaging system and CT scanning of the spine. The apical vertebral orientation was also measured using the EOS imaging system and by CT. Other measures such as the Cobb angle and apical vertebral rotation and translation were used as the control variables to evaluate the potential discrepancy between the standing position in EOS imaging and the supine position in CT scanning. The apical vertebral orientations were 8.7° for the first measurement and 8.4° for the second measurement made by the first author, and 10.3° for the measurement made by the second author. The average of these measurements was 9.3° compared with 6.6° (P=0.65) obtained on CT scanning. The precision of EOS-based measurements of vertebral rotation has never been tested in clinical practice. Although it has limitations, this study suggests that the results obtained using EOS are comparable to those obtained on CT.

Adolescent idiopathic scoliosis treated with posteromedial translation: radiologic evaluation with a 3D low-dose system

PURPOSE

Computed tomography can be used for three-dimensional (3D) evaluation of adolescent idiopathic scoliosis (AIS) patients, but at the expense of high radiation exposure, and with the limitation of being performed in the supine position. These drawbacks can now be avoided with low-dose stereoradiography, even in routine clinical use. The purpose of this study was to determine the 3D postoperative correction of AIS patients treated by posteromedial translation.

METHODS

Forty-nine consecutive patients operated for AIS (Lenke 1-4) using posteromedial translation were included. Corrections were evaluated preoperatively, postoperatively and after at least 2 years using the EOS imaging system. 3D angles were measured in the plane of maximum deformity.

RESULTS

Mean number of levels fused and operative time were 13.5 ± 1 and 215 ± 25 min, respectively. Main thoracic, proximal thoracic, and lumbar curves corrections averaged 64.4 ± 18, 31 ± 10 and 69 ± 20 %, respectively. Mean T4-T12 kyphosis increased 18.8° ± 9° in the subgroup of hypokyphotic patients. Mean apical vertebral rotation reduction was 48.3 ± 20 %. Trunk height gain averaged 27.8 ± 14 mm. There was no pseudarthrosis or significant loss of correction in any plane during follow-up. Two patients (4 %) developed asymptomatic proximal junctional kyphosis, despite having normal thoracic kyphosis. Their sagittal balance was shifted posteriorly by 36 and 47 mm, respectively, by the operation, but revision surgery was not performed.

CONCLUSIONS

Low-dose stereoradiography provided 3D reconstructions of the fused and unfused spine in routine clinical use. Postoperative 3D analysis showed that posteromedial translation enhanced sagittal balance correction, without sacrificing frontal or axial correction of the deformity.

Whole spine CT for evaluation of scoliosis in children: feasibility of sub-milliSievert scanning protocol

BACKGROUND

Optimization of CT radiation dose is important for children due to their higher risk of radiation-induced adverse effects. Anatomical structures with high inherent contrast, such as bones can be imaged at very low radiation doses by optimizing scan parameters.

PURPOSE

To assess feasibility of sub-milliSievert whole spine CT scanning protocol for evaluation of scoliosis in children.

MATERIAL AND METHODS

With approval of the ethical board, we performed whole spine CT for evaluation of scoliosis in 22 children (age range, 3-18 years; mean age, 13 years; 13 girls, 9 boys) on a 128-slice dual source multidetector-row CT scanner. Lowest possible quality reference mAs value (image quality factor for xy-z automatic exposure control or xyz-AEC, CARE Dose 4D) was selected on a per patient basis. Remaining parameters were held constant at 3.0:1 pitch, 128 × 0.6 mm detector collimation, 115.2 mm table feed per gantry rotation, 100 kVp, and 1 and 3 mm reconstructed sections. Average mAs, projected estimated dose savings with AEC, computed tomography dose index volume (CTDI vol), and dose length product (DLP) were recorded. Artifacts were graded on a four-point scale (1, no artifacts; 4, severe artifacts). Ability to identify vertebral and pedicular contours, and measure pedicular width and degree of vertebral rotation was graded on a three-point scale (1, unacceptable; 3, excellent).

RESULTS

All CT examinations were deemed as reliable for identifying vertebral and pedicular contours as well as for measuring pedicular width (5.9 ± 1.6 mm) and degree of vertebral rotation (28.7 ± 23.4°). Mean objective image noise and signal to noise ratio (SNR) were 57.5 ± 21.5 and 4.7 ± 2.3, respectively. With a mean quality reference mAs of 13, the scanner employed an average actual effective mAs of 10 ± 3.8 (range, 6-18 mAs) with an estimated radiation dose saving of 43.5 ± 16.3% with xyz-AEC compared with fixed mAs. The mean CTDI, DLP, and estimated effective doses were 0.4 ± 0.1 mGy (0.2-0.7 mGy), 21 ± 10 mGy.cm (8-41 mGy.cm), and 0.3 ± 0.1 mSv (0.12-0.64 mSv), respectively.

CONCLUSION

Radiation dose for whole spine CT for evaluation of scoliosis in children can be minimized to less than one-third of a milliSievert while maintaining diagnostic image quality.

Preoperative templating before spinal fusion using a fluoroscopic multiplanar imaging system is as accurate as CT scan and uses substantially less radiation

BACKGROUND

Many surgeons utilize preoperative multiplanar imaging for surgical planning before fusion surgery using pedicle screw instrumentation. Computed tomographic (CT) scan is often used but limited by non-weight-bearing images and high-ionizing radiation. The purpose of this study was to compare pedicle length and width measurements using a multiplanar fluoroscopic imaging system and CT with gross measurements to validate the accuracy of multiplanar fluoroscopic imaging and compare relative radiation exposure between techniques.

METHODS

Thirteen intact cadaveric lumbar spine segments were imaged using multiplanar fluoroscopic imaging and conventional CT scan using a low-dose pediatric protocol. At each level and each imaging modality, the 26 pedicles were measured digitally for width and pedicle screw length in accordance with typical presurgical planning procedures. All images were independently measured by 3 observers. After measurement, the specimens were sectioned using a microsurgical saw to facilitate anatomic measurements using calipers. Measurements of the multiplanar fluoroscopic imaging and CT were compared with direct anatomic measurements to quantitate and compare measurement accuracy of CT and fluoroscopic imaging. At the time of image acquisition, radiation exposure from each modality was quantified to allow for comparison of radiation exposures.

RESULTS

CT and multiplanar fluoroscopy had similar agreement with gross measurements with respect to pedicle width and length, with κ values for comparison of CT and fluoroscopy with gross measurements falling between 0.61 and 0.73. Both modalities underestimated pedicle width (by 1.9 mm for both modalities) and length (5.5 mm for CT, 6.6 mm for fluoroscopy). Interobserver reliability was higher for fluoroscopy versus CT. High-dose fluoroscopic imaging used 31% of the radiation exposure for CT.

CONCLUSIONS

Multiplanar fluoroscopic imaging provides comparable diagnostic preoperative planning to CT scan in an experimental cadaveric model. The use of multiplanar fluoroscopic imaging resulted in between 69% and 85% less radiation exposure than conventional CT scan using pediatric settings.

CLINICAL EVIDENCE

This study demonstrates similar results from simulated preoperative templating using fluoroscopic imaging compared with CT scan but with less radiation exposure.

Early onset scoliosis: current concepts and controversies

Early Onset Scoliosis (EOS) may be associated with long-term pulmonary morbidity, which is not commonly seen in Adolescent Idiopathic Scoliosis. Initial evaluation is based on determining any underlying etiology related to congenital or syndromic conditions. Assessing the impact of scoliosis on thoracic development may help guide treatment, which is often required at a young age in these children to prevent irreversible pulmonary insufficiency. Treatment is based on multiple factors but may include non-surgical strategies, such as casting or bracing, along with growth-sparing surgical procedures using growing rods or chest wall expansion. Definitive fusion is rarely indicated in young patients. This chapter will cover the diagnosis, evaluation, and treatment of children with EOS.

Accuracy of image-guided pedicle screw placement using intraoperative computed tomography-based navigation with automated referencing. Part II: thoracolumbar spine

BACKGROUND

Image-guided spinal instrumentation may reduce complications in spinal instrumentation.

OBJECTIVE

To assess accuracy, time efficiency, and staff radiation exposure during thoracolumbar screw instrumentation guided by intraoperative computed tomography (iCT)-based neuronavigation (iCT-N).

METHODS

In 55 patients treated for idiopathic and degenerative deformities, 826 screws were inserted in the thoracic (T2-T12; n = 243) and lumbosacral (L1-S1; n = 545) spine, as well as ilium (n = 38) guided by iCT-N. Up to 17 segments were instrumented following a single automated registration sequence with the dynamic reference arc (DRA) uniformly attached to L5. Accuracy of iCT-N was assessed by calculating angular deviations between individual navigated tool trajectories and final implant positions. Final screw positions were also graded according to established classification systems. Clinical and radiological outcome was assessed at 12 to 14 months.

RESULTS

Additional intraoperative fluoroscopy was unnecessary, eliminating staff radiation exposure. Unisegmental K-wire insertion required 4.6 ± 2.9 minutes. Of the thoracic pedicle screws 98.4% were assigned grades I to III according to the Heary classification, with 1.6% grade IV placement. In the lumbar spine, 94.4% of screws were completely contained (Gertzbein classification grade 0), 4.6% displayed minor pedicle breaches <2 mm (grade 1), and 1% of lumbar screws deviated by >2 to <4 mm (grade 2). The accuracy of iCT-N progressively deteriorates with increasing distance from the DRA, but allows safe instrumentation of up to 12 segments.

CONCLUSION

iCT-N using automated referencing allows for safe, highly accurate multilevel instrumentation of the entire thoracolumbosacral spine and ilium, rendering additional intraoperative imaging dispensable. In addition, automated registration is time-efficient and significantly reduces the need for re-registration in multilevel surgery.

Patients with adolescent idiopathic scoliosis of Lenke type-1 curve exhibit specific pedicle width pattern

INTRODUCTION

Study aim was to find out if patients with Lenke type 1 curve exhibit smaller pedicles and specific pedicle width pattern compared with individuals with no scoliosis.

MATERIALS AND METHODS

4,828 pedicle width measurements (T1-L5) in 61 consecutive patients with adolescent idiopathic scoliosis of Lenke type 1 curve, 61 control subjects, and 20 patients with Lenke type 5 curve, were retrospectively performed by an experienced neuroradiologist.

RESULTS

Among patients with Lenke type 1 curve, the differences between the width of right and left upper thoracic pedicles were statistically significant; smallest at right T4 (2.6 mm). At scoliotic apex, the pedicles on the concave (left) side were significantly smaller than those on the convex (right) side; smallest at left T7 (3.2 mm). Among patients with Lenke type 1 curve, 97% had pedicle width <4 mm.

CONCLUSIONS

Our study showed that patients with Lenke type 1 curve exhibit smaller pedicles and asymmetric pedicle width compared with control subjects.

Reducing patient radiation dose during CT-guided procedures: demonstration in spinal injections for pain

BACKGROUND AND PURPOSE

CT guidance may improve precision for diagnostic and therapeutic spinal injections, but it can increase patient radiation dose. This study examined the impact of reducing tube current on patient radiation exposure and the technical success for these procedures, by using axial acquisitions for short scan lengths and eliminating nonessential imaging.

MATERIALS AND METHODS

Our institutional review board approved retrospective analysis of records from 100 consecutive outpatients undergoing spinal injections for pain before and after the CT protocol modification to reduce radiation dose. Data collected included patient age and sex, response to injection, number of sites and spinal levels treated, injection type, performing physician, CT acquisition method, number of imaging series, tube current, scan length, and DLP.

RESULTS

Image contrast was reduced with the low-dose protocol, but this did not affect technical success or immediate pain relief. Mean DLP for all procedures decreased from 1458 ± 1022 to 199 ± 101 mGy · cm (P < .001). The range of radiologist-dependent DLP per procedure also was reduced significantly with the modified protocol. Selective nerve root blocks, lumbar injections, multiple injection sites, and the lack of prior imaging were each associated with a slightly higher DLP (<50 mGy · cm).

CONCLUSIONS

Radiation to patients undergoing CT-guided spinal injections can be decreased significantly without affecting outcome by reducing tube current, using axial acquisitions for short scan lengths, and eliminating nonessential imaging guidance. These measures also decrease variability in radiation doses between different practitioners and should be useful for other CT-guided procedures in radiology.

Angle measurement reproducibility using EOS three-dimensional reconstructions in adolescent idiopathic scoliosis treated by posterior instrumentation

STUDY DESIGN

A reproducibility study was conducted in preoperative and postoperative three-dimensional (3D) measurements for patients operated for adolescent idiopathic scoliosis (AIS).

OBJECTIVE

To assess the reliability of preoperative and postoperative 3D reconstructions using EOS in patients operated for AIS.

SUMMARY OF BACKGROUND DATA

No prior reliability study of 3D measurements has been performed in the literature for severe scoliosis and for operated patients.

METHODS

This series included 24 patients (62° ± 11) operated for Lenke 1 or 2 AIS, using either all-pedicle screw constructs (group 1) or hybrid constructs, with universal clamps at thoracic levels (group 2). All patients underwent low-dose standing biplanar radiographs, pre- and postoperatively. Three operators performed the 3D reconstruction process two times preoperatively and two times postoperatively (total 288 reconstructions). Intraoperator repeatability and interoperator reproducibility were calculated and compared between groups.

RESULTS

The preoperative reproducibility was between 4° and 6.5° for parameters dedicated to scoliosis (Cobb and apical vertebral rotation), between 4° and 7° for kyphosis and lordosis values, and between 1° and 5° for pelvic measurements. The postoperative reproducibility was between 5° and 8° for values of kyphosis and lordosis, between 1° and 5.5° for pelvic parameters, and between 6.5° and 10.5° for the scoliotic parameters. The reproducibility of the scoliotic parameters was slightly better in the hybrid construct group, but the difference was not significant (P = 0.8). No difference was found between groups for the other parameters.

CONCLUSION

3D postoperative reconstructions are as reproducible as preoperative ones. The reproducibility is not influenced by the type of implant used for correction. Mean difference between operator was higher than previously reported for the apical rotation measurement, but this difference can be explained by the severity of the curves and the lower visibility of the anatomical landmarks due to the implants.

Increased rod stiffness improves the degree of deformity correction by segmental pedicle screw fixation in adolescent idiopathic scoliosis

Background

There are limited reports in literature studying the impact of rod diameter and stiffness on the degree of deformity correction in patients with AIS.

Aims

The aims of this study were to evaluate the 3-dimentional deformity correction achieved by segmental pedicle screw fixation in patients with adolescent idiopathic scoliosis, and to find out if learning or the change to stiffer rods had any positive impact on deformity correction.

Study design

Retrospective study.

Methods

Plain radiographs and low-dose spine CTs of 116 consecutive patients (aged 15.9 ± 2.8 years) operated during the period 2005-2009 (group 1: patients operated autumn 2005-2006; group 2: 2007; group 3: 2008; group 4: 2009) were retrospectively evaluated.

Results

There was no statistically significant difference between the correction of the Cobb angle (P = 0.425) or lower end vertebra tilt (P = 0.298) in patients operated during the first versus the remaining periods of the study. No restoration of the sagittal kyphosis was reported in the first period compared with 5.9° in the last study period (P < 0.001). The correction of vertebral rotation was also improved from 4.2° to 7.8° (P < 0.001) for the same periods. For the whole study population, there was statistically significant correlation between the order of the operation (patient number) and the restoration of sagittal kyphosis (r = -0.344, P = 0.001), and the correction of vertebral rotation (r = 0.370, P < 0.001), but not for the Cobb angle or LEVT. However, there was no significant difference in restoration of sagittal kyphosis and the vertebral rotation in the first 17 patients compared with the last 17 patients operated with rods of 5.5 mm diameter (P = 0.621, and 0.941, respectively), indicating that rod stiffness had more impact on the deformity correction than did learning.

Conclusions

This study showed that rod stiffness had more impact on the deformity correction than did learning.

Accuracy of Image-Guided Pedicle Screw Placement Using Intraoperative Computed Tomography-Based Navigation With Automated Referencing, Part I: Cervicothoracic Spine

BACKGROUND:

Image-guided spinal instrumentation reduces the incidence of implant misplacement.

OBJECTIVE:

To assess the accuracy of intraoperative computed tomography (iCT)-based neuronavigation (iCT-N).

METHODS:

In 35 patients (age range, 18-87 years), a total of 248 pedicle screws were placed in the cervical (C1-C7) and upper and midthoracic (T1-T8) spine. An automated iCT registration sequence was used for multisegmental instrumentation, with the reference frame fixed to either a Mayfield head clamp and/or the most distal spinous process within the instrumentation. Pediculation was performed with navigated drill guides or Jamshidi cannulas. The angular deviation between navigated tool trajectory and final implant positions (evaluated on postinstrumentation iCT or postoperative CT scans) was calculated to assess the accuracy of iCT-N. Final screw positions were also graded according to established classification systems. Mean follow-up was 16.7 months.

RESULTS:

Clinically significant screw misplacement or iCT-N failure mandating conversion to conventional technique did not occur. A total of 71.4% of patients self-rated their outcome as excellent or good at 12 months; 99.3% of cervical screws were compliant with Neo classification grades 0 and 1 (grade 2, 0.7%), and neurovascular injury did not occur. In addition, 97.8% of thoracic pedicle screws were assigned grades I to III of the Heary classification, with 2.2% grade IV placement. Accuracy of iCT-N progressively deteriorated with increasing distance from the spinal reference clamp but allowed safe instrumentation of up to 10 segments.

CONCLUSION:

Image-guided spinal instrumentation using iCT-N with automated referencing allows safe, highly accurate multilevel instrumentation of the cervical and upper and midthoracic spine. In addition, iCT-N significantly reduces the need for reregistration in multilevel surgery.

The rate of screw misplacement in segmental pedicle screw fixation in adolescent idiopathic scoliosis

BACKGROUND AND PURPOSE

There are no reports in the literature on the influence of learning on the pedicle screw insertion. We studied the effect of learning on the rate of screw misplacement in patients with adolescent idiopathic scoliosis treated with segmental pedicle screw fixation.

METHOD

We retrospectively evaluated low-dose spine computed tomography of 116 consecutive patients (aged 16 (12-24) years, 94 females) who were operated during 4 periods over 2005-2009 (group 1: patients operated autumn 2005-2006; group 2: 2007; group 3: 2008; and group 4: 2009). 5 types of misplacement were recorded: medial cortical perforation, lateral cortical perforation, anterior cortical perforation of the vertebral body, endplate perforation, and perforation of the neural foramen.

RESULTS

2,201 pedicle screws were evaluated, with an average of 19 screws per patient. The rate of screw misplacement for the whole study was 14%. The rate of lateral and medial cortical perforation was 7% and 5%. There was an inverse correlation between the occurrence of misplacement and the patient number, i.e. the date of operation (r = -0.35; p < 0.001). The skillfulness of screw insertion improved with reduction of the rate of screw misplacement from 20% in 2005-2006 to 11% in 2009, with a breakpoint at the end of the first study period (34 patients).

INTERPRETATION

We found a substantial learning curve; cumulative experience may have contributed to continued reduction of misplacement rate.

Technical aspects of CT imaging of the spine

This review article discusses technical aspects of computed tomography (CT) imaging of the spine. Patient positioning, and its influence on image quality and movement artefact, is discussed. Particular emphasis is placed on the choice of scan parameters and their relation to image quality and radiation burden to the patient. Strategies to reduce radiation burden and artefact from metal implants are outlined. Data acquisition, processing, image display and steps to reduce artefact are reviewed. CT imaging of the spine is put into context with other imaging modalities for specific clinical indications or problems. This review aims to review underlying principles for image acquisition and to provide a rough guide for clinical problems without being prescriptive. Individual practice will always vary and reflect differences in local experience, technical provisions and clinical requirements.

Curve length, curve form, and location of lower-end vertebra as a means of identifying the type of scoliosis

PURPOSE

To determine if the curve length, curve form, and location of the lower-end vertebra can identify the type of scoliosis.

METHODS

Standing posteroanterior and lateral radiographs of 78 women and 27 men with scoliosis aged 8 to 32 years were retrospectively analysed. Parameters measured were (1) the curve length (the number of vertebrae in the main curve), (2) the curve form (C-form, inverted C-form, or S-form), (3) the curve apex (the vertebral body at the apex of each curve), (4) the site of the scoliosis (thoracic, thoracolumbar, or lumbar), and (5) the location of the lower-end vertebra.

RESULTS

Only 3 (4%) of 77 patients with idiopathic scoliosis had a curve length of >8 vertebrae, compared with 19 (90%) of 21 patients with neuromuscular/neuropathic scoliosis (p<0.001, Fisher's exact test). 14 (18%) of the patients with idiopathic scoliosis had an S-form curve, compared with none in those with neuromuscular/neuropathic or congenital/osteogenic scoliosis (p=0.035, Fisher's exact test). No patient with idiopathic scoliosis had the lower- end vertebra located at L5, compared with 8 (38%) patients with neuromuscular scoliosis (p<0.001, Fisher's exact test). The criteria for neuromuscular/neuropathic scoliosis (a curve length of >8 vertebrae, a C-form or inverted C-form curve, and a lower-end vertebra located at L4 or L5) had 81% specificity, 76% sensitivity, 100% positive and 93% negative predictive values.

CONCLUSION

These criteria may help identify patients with neuromuscular/neuropathic scoliosis for further investigation by magnetic resonance imaging or computed tomography before they undergo corrective surgery.

Low-dose spine CT: optimisation and clinical implementation

Spinal deformities affect young individuals predominantly girls who are usually subjected to regular and intensive radiological investigation especially before and after corrective surgery. Optimisation of spine computed tomography (CT) and the implementation of the low-dose CT in the work-up of spinal deformities were presented. The presented low-dose CT here means providing the operating surgeons with essential information about 15 vertebral bodies (almost 36-cm long region of the vertebral column). The mean effective dose of the low-dose CT was 0.37 mSv without any negative impact on image quality with regard to answering the clinical questions at issue. Tube current modulation (angular and longitudinal) has contributed to 19 % of the total dose reduction and soft tissue algorithm has helped to reduce the artefacts from the metal implants in the postoperative CTs.