Ebook: Research into Spinal Deformities 9

In January 2021 the International Research Society of Spinal Deformities (IRSSD) held its bi-annual meeting in Milwaukee, Wisconsin, USA. Originally the meeting was scheduled in Milwaukee at an iconic Milwaukee hotel, the Pfister, but the pandemic intervened and necessitated the transition of the meeting to a virtual format. Even so, the meeting allowed interaction and open discussion amongst practitioners from around the world.

The IRSSD is an outgrowth of a group of researchers who met in 1980 to discuss surface topography and other techniques for assessment of trunk deformity. The society has always been multi-disciplinary in nature, and over the years there was seen to be a need to broaden the scope of the meeting, which led to the formation of the IRSSD.

Initially the groups emphasis was on surface topography but the society now studies a variety of methods to assess the 3D deformity of scoliosis, including EOS 3D reconstruction.

The IRSSD concentrates on research in spinal deformity with clinical applications. In addition to 3D assessment of the spine, researchers also explore spinal biomechanics, etiopathogenesis, and innovative conservative and surgical therapies. The goal is to integrate basic science with clinical care to improve patient care.

The first IRSSD meeting was held in 1996 in Sweden, hosted by John Sevastick. The second meeting was held in 1998 in Vermont and was hosted by Ian Stokes. The third meeting was held in 2000 in Clermont Ferrand, France, hosted by Alain Tanguy and Bernard Peuchot. The fourth in 2002 in Athens, Greece, organized by Dr. Theodoros B. Grivas.

Since then, the society has met in multiple countries around the world.

For the meeting we were lucky to have four keynote speakers of international note…

Patrick Cahill, MD; The Children’s Hospital of Philadelphia

Pulmonary Outcomes in Pediatric Spinal Deformity Surgery

Stefan Parent, MD, PhD; Sainte-Justine Hospital

Optimizing Surgical Results of Vertebral Body Tethering

Brandon Rebholz, MD; Froedtert & the Medical College of Wisconsin

Adaptation of Emerging Technologies in Adult Spinal Deformity Surgery

Carol Wise, PhD; Texas Scottish Rite Hospital for Children

What Causes AIS? Ask the Genome!

We also hosted 4 symposia on current controversies with experts in the field…

Eliminating 2D Spinal Assessments and Embracing 3D and 4D

Patrick Knott, PhD, PA-C, Xue-Cheng Liu, MD, PhD, and Saba Pasha, PhD

Gait and Posture Analysis in Scoliosis-Implications for Clinical Practice

Nachi Chockalingham, PhD, Ram Haddas, PhD, Robert Needham, PhD, and Thomas Shannon, PhD

Future Generation of Brace

Carl-Eric Aubin, PhD, PE, Man-Sang Wong, PhD, and Luke Stikeleather, CO

Bracing for the Early Onset Scoliosis

Timothy Hresko, MD, Channing Tassone, MD, John Thometz, MD, and Jim Wynne, CO

We are grateful to have had the opportunity to host this meeting. I would especially like to thank my co-chairman, Dr. Xue-Cheng Liu. His excellent skills in both the clinical and basic science research arena, along with his tireless efforts and outstanding productivity, made this meeting a success. The book is meant to further the mission of the IRSSD in expanding the scope of scoliosis research.

John Thometz

Milwaukee, Wisconsin

USA

March 16, 2021

The most common developmental disorder of the spine is scoliosis, a rotated, lateral deformity in the shape of the spinal column. Scoliosis may be part of the clinical spectrum that is observed in many developmental disorders, but typically presents as an isolated symptom in otherwise healthy adolescent children. Adolescent idiopathic scoliosis (AIS) has defied pathogenic understanding in part due to its genetic complexity, and to the lack of well-defined animal models. The disease is also remarkable in its sexual dimorphism, where girls are at more than five times greater risk of progressive deformity than boys. Breakthroughs have come from recent genome wide association studies (GWAS) and next generation sequencing (NGS) of human AIS cohorts. Post-hoc gene set and pathway-level analyses of genetic datasets have highlighted a role for cartilage biogenesis and the development of the intervertebral disc (IVD) in disease susceptibility. Moreover, next generation sequencing in AIS families, as well as modeling in vertebrate systems, has revealed that rare deficiencies in proteins of the cartilaginous extracellular matrix (ECM) collectively contribute to AIS. Thus, as in a jigsaw puzzle, the pieces coming together from multiple biologic studies suggest that deficiencies in the structural integrity and homeostasis of spinal cartilages are culprits in AIS susceptibility. Here, we update progress in understanding the genetic, biochemical, and cellular determinants of AIS. We also suggest a molecular model in which interaction of the hormonal environment with genetic susceptibility may increase risk of this common disorder of childhood.

The etiology of the adolescent idiopathic scoliosis (AIS) remains unknown. Variations in the sagittal profile of the spine between the early stage scoliotic and non-scoliotic pediatric patients have been shown. However, no quantitative study has shown the link between the sagittal profile and 3D deformity of the spine. 126 right thoracic scoliosis with spinal and 3D reconstructions were included. A 2D finite element model was developed for each of the sagittal curve types without any deformity in the frontal or axial planes. Physiological loadings were determined from the literature and were applied in the finite element model. The 3D deformation patterns of the models were compared to the 3D spinal patterns of the AIS with the same sagittal type. A significant correlation was found between the 3D deformity of the scoliotic curves and the numerical finite element simulation of the corresponding sagittal profile as determined by pattern correlation, p<0.001. The sagittal curve deformation patterns corresponded to the spinal deformities in the patients with the same sagittal curvature. Finite element models of the spines, representing different sagittal types in 126 AIS patients showed that deformation pattern of the sagittal types changes as a function of the spine curvature and associates with the patterns of 3D spinal deformity in AIS patients with the same sagittal curves. This finding provided evidence that the sagittal curve of the spine can determine the deformity patterns in AIS.

AIS is three-dimensional spinal deformity with unclear etiopathogenesis. LBX1 is so far the only multi-centers validated AIS predisposing gene. The imbalance of posterior paraspinal muscles is an important factor in AIS etiopathogenesis. It is poorly understood how LBX1 contributes to the abnormal paraspinal muscles and onset/progression of AIS. We aimed to evaluate the expression of LBX1 in paraspinal muscles at the concave and convex side in AIS, and whether alternation of LBX1 expression could affect myoblastsactivities and potentially influence muscle-bone interaction via myokines expression. Paraspinal muscles from AIS and age- and curvature-matched congenital scoliosis (CS) patients were collected for fiber types analysis. Biopsies were also subjected to qPCR to validate expression of myogenic markers, selected myokines and LBX1. Human skeletal muscle myoblast (HSMM) was used for LBX1 loss-of-function study in vitro. Muscle fiber types analysis showed type I and type IIX/IIAX fibers proportion were significantly different between AIS concave and convex but not in two sides of CS. LBX1, myogenic markers and one myokine were significantly imbalanced in AIS but not in CS. Loss-of-function study showed knockdown of LBX1 could inhibit myogenic markers expression and myokines as well. This study provides new insight into the association between imbalanced paraspinal muscle and potential muscle-bone crosstalk in AIS patients and the biological function of predisposing gene LBX1. Further investigation with appropriate animal models is warranted to explore if asymmetric expression of LBX1 could result in distinct muscle phenotypes and bone qualities thus affect the progression of spine curvature in AIS.

Idiopathic scoliosis in man is believed to be related to the unique human sagittal profile. Patients with a thoracic scoliosis have a longer, more proximal, posteriorly inclined segment of the spine as compared to lumbar scoliosis and controls, whereas patients with a lumbar scoliosis have a more caudal, shorter and steeper posteriorly inclined segment. In 22q11.2 deletion syndrome, half of the patients develop a scoliosis that is very similar to idiopathic scoliosis and may serve as a model for the general population. In our center, all patients with 22q11.2 deletion syndrome older than 6 years receive standardized radiographic spine imaging every 2 years to screen for scoliosis. In this prospective proof-of-principle study the goal was to determine whether there are differences in sagittal alignment between patients that develop scoliosis vs. controls before the onset of scoliosis, and obtain data to perform a power calculation for future studies. To capture the sagittal shape of the spine into one risk factor for development for scoliosis, we combined relative length and magnitude of dorsal inclination into a new parameter: the posterior inclined triangle surface (PITS). We included 31 patients with initially straight spines, five developed a thoracic scoliosis and seven developed a (thoraco)lumbar scoliosis after a mean follow-up of 3.4 years. The PITS was considerably higher in the group that developed scoliosis as compared to the controls (59 vs 43). Based on this pilot study, we have identified a potential overall sagittal profile risk parameter for the development of idiopathic scoliosis.

Adolescent Idiopathic Scoliosis (AIS) occurs during pubertal rapid growth period and is closely associated with low bone mass. The underlying mechanisms for systemic low bone mass in AIS remains unclear. Wnt signalling pathway is one of the important pathways regulating bone metabolism and influencing bone strength, its family member Wnt16 associates with lower bone mineral density (BMD) in late adulthood, and plays key regulatory role in determining cortical bone quality in adult mice. Our randomized control trial have reported vitamin D (VitD) supplementation significantly improved bone mass and reduced the risk of curve progression in AIS. A case-control study and animal study were employed to answer if WNT16 is associated with the abnormal bone quality in AIS and if the effect of VitD supplementation is associated with Wnt16, respectively. A cohort of 161 AIS and control female subjects were recruited for measurement of anthropometric parameters, bone qualities, and circulating Wnt16 level. In animal study, WT and Wnt16 gKO mice were both subjected to special VitD diet from week 4 and terminated at week 7 and 10 for samples harvesting. AIS showed significantly lower BMD, circulating WNT16 level, and elevated serum level of type I procollagen N-terminal propeptide. Wnt16 gKO mice demonstrated lower cortical bone density compared with WT mice from week 7 of age and Wnt16 gKO were less prone to cortical bone loss induced by high dosage VitD diet. Further study on the biological role of WNT16 and crosstalk with VitD metabolism on bone qualities is warranted which might shed light on prognostic gene of osteopenia and new perspectives for potential target to prevent curve progression.

Adolescent idiopathic scoliosis (AIS) is associated with osteopenia which could persist into adulthood affecting attainment of Peak Bone Mass thus resulting in osteoporosis in late adulthood. We previously reported a randomized double-blinded placebo-controlled trial(the Cal study) showing significant bone health improvement with 2-year calcium(Ca)+Vit-D supplementation for AIS girls. This study addressed the important issue whether bone health improvement from the initial 2-year Ca+Vit-D supplementation could persist as subjects approached towards Peak Bone Mass at 6-year ie after 4-year of supplement discontinuation. This was an extension of the Cal study on AIS girls (11–14 years old, mean age=12.9 years, Tanner stage<IV) with femoral neck aBMD Z-score<0 and Cobb angle≥15^∘. 330 subjects were randomized to Group1(placebo), Group2(600mgCa+400-IU-Vit-D₃/day) or Group3(600mgCa+800-IU-Vit-D₃/day) for 2-year supplementation after which supplementation was stopped. Investigations at baseline, 2-year and 6-year included High-resolution Peripheral Quantitative Computed Tomography(HR-pQCT) at distal radius and Dual Energy X-ray Absorptiometry(DXA) at both hips. 270(81.8%) subjects completed 2-year supplementation when changes in left femoral neck aBMD, trabecular vBMD, Trabecular BV/TV, Trabecular Number and Trabecular Separation indicated significant bone health improvement with Ca+Vit-D supplementation(p<0.05). At 6-year(mean age=19.2 years), no between-group difference on bone parameters was noted except increase in Cortical Thickness being greater only in Group3 than in Group1. After 4-year supplement discontinuation, the treatment effect from the initial 2-year supplementation mostly dissipated indicating the need of continued supplementation in AIS girls to sustain therapeutic improvement on bone health as subjects approach towards Peak Bone Mass.

The purpose of this study was to evaluate the morphological changes of intervertebral discs (IVD) and vertebral bodies (VB) in AIS girls according to the subgroups with different curve severity by magnetic resonance imaging (MRI). This study included 33 age-matched female controls and 76 AIS girls with a right-sided thoracic curvature. Wedge angle, height ratio and distance ratio of VB and IVD were measured on the best midline coronal and sagittal planes from reformatted MRI spine. Volumes of VB, IVD and nucleus pulposus (NP) were evaluated on volumetric images. One-way ANOVA with Bonferroni correction was used. There was significant difference in wedge angle and height ratio of VB and IVD between AIS and controls. In severe-AIS, the position of NP was significantly shifted to the convexity when compared with non-severe AIS and controls. Whereas, the volume of IVD and NP in severe-AIS was found to be significantly smaller. On top of coronal wedging of VB and IVD, there was significantly reduced volume of IVD and NP in severe-AIS patients, despite T2 signal of IVD was preserved. The current findings indicate that early mechanical effects on the discs and vertebrae in adolescent scoliotic spine is evident on quantitative imaging. Importantly, these patients may be vulnerable to disc degeneration if no operative treatment is prescribed.

Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional (3D) deformity, and the plane of maximum curvature (PMC) is proposed to reflect these clinical features, which refers to a vertical plane presenting the maximum projected spinal curvature and its parameters include the PMC Cobb and orientation (angle between PMC and sagittal planes). This study aimed to develop a computational method (CM) for PMC estimation. Twenty-nine patients with AIS and computed tomography (CT) images were recruited. For CT, PMC was determined by rotating a vertical plane about its vertical axis with 5° increment until the maximum Cobb angle was measured. For CM, PMC was estimated via identifying the eight points (the corner points of the superior and inferior endplates of the upper and lower end-vertebrae respectively) in the coronal and lateral CT images. Two experienced raters repeated the PMC estimation three times with one-week interval. The intra-class correlation coefficient (ICC) and Bland-Altman method were used for statistical analysis. Twenty-seven right thoracic curves (RTs) (mean Cobb: 46.1°±12.4°) and 23 left thoracolumbar/lumbar (LTLs/LLs) (mean Cobb: 30.6°±11.1°) were analysed. The intra- and inter-rater ICC values were >0.91 and 0.84 in RTs and LTLs/LLs, respectively. The PMCs obtained from the CM and CT were showed good agreement was also observed between the PMCs obtained from the two methods according to ICC (>0.90) and Bland-Altman method assessments. This purpose-design computational method could provide reliable and valid estimation of PMCs for AIS, which has potential to be used as an alternative for 3D assessment.

Prospective, concurrent-cohort study. To establish the relationship between radiographic alignment parameters and functional CoE measurements at one week before and at three months after realignment surgery in ADS patients. Adult degenerative scoliosis (ADS) represents a significant healthcare burden with exceedingly high and increasing prevalence, particularly among the elderly. Radiographic alignment measures and patient-reported outcomes currently serve as the standard means to assess spinal alignment, deformity, and stability. Neurological examinations have served as qualitative measures for indicating muscle strength, motor deficits, and gait abnormalities. Three-Dimensional motion analysis is increasingly being used to identify and measure gait and balance instability. Recently, techniques have been established to quantify balance characteristics described by Dubousset as the “cone of economy” (CoE). The relationship between radiographic alignment parameters and CoE balance measures of ADS patients before and after realignment surgery is currently unknown. 29 ADS patients treated with realignment surgery. Patients were evaluated at one week before realignment surgery and at their three-month follow-up examination. During each evaluation, patients completed self-reported outcomes (visual analog scales for pain, Oswestry Disability Index, SRS22r) and a functional balance test. Mean changes in dependent measures from before to after surgery were compared using paired t-tests. Pearson correlations were used to test for significant correlations between changes in radiographic and CoE measures. Significant improvements were found for all patient-reported outcomes, in several radiographic measures, and in CoE measures. Improvements of scoliosis Cobb angle, coronal pelvic tilt, lumbar lordosis, and thoracic kyphosis showed significant correlations with CoE sway and total distance measures at both the center of mass and center of the head. Improved radiographic alignment measures significantly correlated with improved CoE balance measures among ADS patients treated with realignment surgery at their three-month follow-up. These findings indicate that functional balance evaluations when used in conjunction with radiographic measurements, may provide a more robust and improved patient-specific sensitivity for postoperative assessments. CoE balance may represent a new measure of added value for surgical intervention of ADS.

The pathomechanism of spinal deformity development in adolescent idiopathic scoliosis (AIS) has been related to the sagittal curvature of the spine. It is not known how the variations in the sagittal profile relates to the coronal deformity patterns in AIS. A total of 70 Lenke 1 and 50 Lenke 5 AIS patients were included retrospectively. A finite element (FE) model was developed for each spine where the sagittal spinal curvatures were modeled as 2D S shaped elastic rods. Transverse plane deformation patterns of these rods under physiological loading were determined and clustered based on their similarities. The patients’ characteristics, including the Lenke type, and the spinal measurements in these deformation pattern clusters were statistically compared. Three different axial deformation patterns were determined from the FE simulations of the 120 sagittal curves. Two axial groups were looped shaped in opposing directions (Group I and III) and one was lemniscate shaped (Group II). 94% of the patients in Groups I and II were Lenke 1 and 100% of Group III was Lenke 5. The position of the sagittal inflection point moved downward from Group I-III resulting in significantly different ratio of the arc lengths above and below the sagittal inflection points for Groups I, II and III (0.49±0.59, 1.15±0.44, and 3.22±1.8). A classification of idiopathic scoliosis, based on the biomechanics of S-shaped flexible rods deformation could distinguish between different coronal curve types. The geometrical parameters of the sagittal profiles in the axial deformation pattern groups were significantly different.

Relative anterior spinal overgrowth (RASO) was proposed as a generalized growth disturbance and a potential initiator of adolescent idiopathic scoliosis (AIS). However, anterior lengthening was also observed in neuromuscular (NM) scoliosis, was shown to be restricted to the apical areas and to be located in the intervertebral discs, not in the bone. In this study the goal was to determine if other scoliotic curves of known origin exhibit the similar mechanism of anterior lengthening without changes in the vertebral body. Therefore CT-scans of 18 patients in whom a short segment congenital malformation had led to a long thoracic compensatory curve without bony abnormality were included. Of each vertebral body and intervertebral disc in the compensatory curve, the anterior and posterior length was measured on CT-scans in the exact mid-sagittal plane, corrected for deformity in all three planes. The total AP% of the compensatory curve in congenital scoliosis showed a lordosis (+1.8%) that differed from the kyphosis in non-scoliotic controls (-3.0%; p<0.001), and was comparable to AIS (+1.2%) and NM scoliosis (+0.5%). This anterior lengthening was not located in the bone; the vertebral body AP% showed a kyphosis (-3.2%), similar to non-scoliotic controls (-3.4%), as well as AIS (-2.5%) and NM scoliosis (-4.5%; p=1.000). However, the disc AP% showed a lordosis (+24.3%), which sharply contrasts to the kyphotic discs of controls (-1.5%; p<0.001), but was similar to AIS (+17.5%) and NM scoliosis (+20.5%). The results demonstrate that anterior lengthening is part of the three-dimensional deformity in different types of scoliosis and is exclusively located in the intervertebral discs. The bony vertebral bodies maintain their kyphotic shape, which indicates that there is no active bony overgrowth. Anterior lengthening appears to be a passive result of any scoliotic deformity, rather than being related to the specific cause of AIS.

The aim of the study is to evaluate the morphology of the intervertebral discs visible in the magnetic resonance image in patients with sudden severe low back pain (with or without radiation of pain to the lower limb). The second goal of the study is to perform a digital three-plane reconstruction of the intervertebral disc and to compare this technique with a standard magnetic resonance imaging test. Twenty-five patients, mean age 35.5 years, all with acute low back pain, were examined. We compared the 3D MR models with standard MRI scans by measuring seven MRI parameters. In patients with sudden, severe low back pain, with clinical symptoms suggesting an etiology within the intervertebral disc, changes in a standard MRI are found consisting of the presence of a hernia / protrusion of the intervertebral disc and lowering the height of the intervertebral disc – with lowering the disc height occurs to a greater extent in the rear section. The 3D reconstruction is a reliable 3D representation of the intervertebral disc and adjacent vertebral bodies.

To establish the age- and sex-related normative values of sagittal alignment in asymptomatic Chinese adults, and to investigate the changes and possible associated compensation mechanisms across age groups. 584 asymptomatic Chinese adults aged 20–89 years were recruited. Subjects were grouped according to age and gender. Whole-body standing radiographs were acquired for evaluating sagittal alignment from spine to lower limb. Sagittal parameters between gender in different age groups were compared via independent t test. Pearson correlation analysis was used to demonstrate relationships between parameters. Thoracic kyphosis (TK) increased steadily while lumbar lordosis decreased gradually in both genders. Pelvic tilt (PT) in male is greater than in female across all age groups with age related gradual increase. There were significant differences between male and female from 20s to 60s in terms of knee flexion angle (KA) and ankle dorsiflexion angle (AA), but the differences were not significant after 60s. T1 pelvic angle (TPA) was significantly correlated with spinal, pelvic and lower-limb alignment. The older group (≥50 years) had a stronger correlation of TPA with PT and KA, whereas the younger (<50 years) had stronger correlation with TK. This study comprehensively presented the normative sagittal alignment based on a large asymptomatic population, which could serve as an age- and gender-specific reference value for spine surgeons when planning for correction surgery. Age can influence the recruitment of compensation mechanism that involve more pelvic and lower limb mechanisms for elderly people.

The Adams Forward Bend Test recognizes the rotational aspect of the curve with the spine in flexion, and the AP X-ray measures the coronal plane deviation by using the Cobb Angle. However, modern techniques including CT-scan, biplanar radiograph, ultrasound, and surface topography allow the clinician to better evaluate and visualize the true 3-D nature of the spine. Surface Topography imaging uses the surface of the trunk to estimate the spine position using a mathematical algorithm that has been found to be accurate when compared to the radiologic Cobb Angle. The sagittal balance of the spine measured by surface topography is compared in three different situations, namely, “standing up straight,” “standing relaxed,” and “walking,” which will help to best assess posture and risk of proximal junctional kyphosis before and after the treatment. Coronal imbalance (lateral deviation) and a range of maximal vertebral surface rotation (amplitude in either direction) are considered as the parameters with an excellent to good reproducibility. COP displacement or symmetry from the midline is used to measure the stability of the trunk. Therefore, those selected spine shape parameters and COP deviation would be considered as the best descriptors in the assessment of postural sway and outcome of PSSE in children with AIS.

The aims of this study were to evaluate the effect of a thoracoplasty procedure in addition to a posterior spinal fusion and instrumentation on an Adolescent Idiopathic Scoliosis (AIS) patient’s 3D back contour as measured by surface topography. We performed a retrospective review to identify patients who were treated with posterior spinal fusion with spinal instrumentation and those who were treated with an additional thoracoplasty procedure. We analyzed changes in surface topography measurements between these two groups using t-test and ANCOVA statistical analyses. Although there were no statistically significant differences in 11 of 12 variables, thoracoplasty-posterior spinal fusion (n=10) group had a mean 6.6 unit reduction in trunk asymmetry while the posterior spinal fusion group (n=26) had a mean 22.8 unit reduction in trunk asymmetry (p-value<0.05). The posterior spinal fusion group and thoracoplasty-posterior spinal fusion group were not shown to have clinically significant differences in 3D back contour correction. An additional thoracoplasty procedure does not provide better correction in the transverse plane and in fact had a smaller degree of trunk asymmetry correction. This supports the current trends of decreasing use of thoracoplasty in AIS patients to address severe rib hump deformities given concerns for decreased post-operative lung function and alternative methods of vertebral body derotation, such as thoracic pedicle screws.

A sexual dimorphism (SD) of the “vertebra prominens” was found, namely the 7th cervical vertebra (C7) spinous process (SP) is more frequently longer in men and the 1st thoracic (T1) SP in women.[1] We assume that the cause of this SD is the different anatomy of the anterior upper thoracic region (AUTR) between men and women, due to the presence of the breast. One-hundred forty-two women aged 48.1Âś17 years old, who visited the OPD for neck complaints, were studied. Measures included the age, the relationship of C7 and T1 SP length, documented in three types (type 1= [C7>T1], 2 = [C7 = T1], 3 = [C7 < T1]), the breast size, (small, medium and large), the length ratio of C7/T1 SP and the BMI. Breast size and SP length relationship between C7 and T1 was found to be significantly correlated. The results confirm that the cause of the SD of the SP length of C7 and T1 seems to be the different female AUTR anatomy due to the presence of the breast and it is probably the result of the need of the posterior cervical anatomical structures to compensate for the higher torque created by the female AUTR anatomy. These original findings are useful in clinical examination, in breast oncology, for the plastic surgeons, in terms of implantation of the proper breast size implant, after mastectomies for malignancies but also for aesthetic reasons and the software of all surface topography devices should be adjusted accordingly.

Severe adolescent idiopathic scoliosis (AIS) requires surgery to halt curve progression. Accurate insertion of pedicle screws is important. This study reports a newly developed 3D ultrasound (3DUS) to localize pedicles intraoperatively and register a pre-op 3D vertebral model to the surface to be displayed for navigation. The objective was to determine speed of the custom 3DUS navigator and accuracy of pedicle probe placement. The developed 3DUS navigator integrated an ultrasound scanner with motion capture cameras. Two adolescent 3D printed spine models T2-T8 and T7-T11 were modified to include pedicle holes with known trajectory and be mounted on a high precision LEGO pegboard in a water bath for imaging. Calibration of the motion cameras and the 3DUS were conducted prior to the study. A total of 27 scans from T3 to T11 vertebrae with 3 individual scans were performed to validate the repeatability. Three accuracy tests that varied vertebral a) orientation, b) position and c) a combination of location and orientation were completed. Based on all experiments, the acquisition-to-display time was 18.9±3.1s. The repeatability of the trajectory error and positional error were 0.5±0.2° and 0.3±0.1mm, respectively. The a) center orientation, b) position and c) orientation/position on trajectory and positional error were for a) 1.4±0.9° and 0.5±0.4mm, b) 1.4±0.8° and 0.3±0.3mm and c) 2.0±0.8° and 0.5±0.5mm, respectively. These results demonstrated that a high precision real-time 3DUS navigator for screw placement in scoliosis surgery is feasible. The next step will study the effect of surrounding soft tissues on navigation accuracy.

Use of 3D ultrasound (US) scanners to detect and monitor scoliosis have been validated. The Cobb angle, axial vertebral rotation, spinal flexibility, curvatures in the sagittal profile and the Cobb angle on the plane of maximum curvature (PMC) can be measured from coronal, transverse and sagittal planes of ultrasound images. However, traditional 3D ultrasound scanners are relatively bulky and expensive. 2D US handheld and low-cost scanners are widely available. To adapt the 2D scanners for scoliosis applications, a position and orientation system is integrated with the scanner. The objective of this study was to validate a newly developed 3D handheld US system to image the spine. The wireless handheld US scanner (C3-HD, Clarius, Canada) was selected because of its high resolution and availability of raw data. A wireless tracking system based on electromagnetic (G4 system, Polhemus, USA) was integrated with the Clarius ultrasound. During scanning, the ultrasound information was synchronized with the scanner’s position and orientation by using custom developed software. Both information were streamed wirelessly to a laptop. Custom software reconstructed and displayed the 3D spinal image in real-time. A single 3D printed vertebra, two full plastic spine phantoms from T1-T12 vertebrae and a non-scoliotic volunteer were scanned. The 3D reconstruction process of a spine image was less than 3 seconds. The dimensional and the angle errors were 1 mm and 3°, respectively. This study demonstrated that a low-cost ($11,000 USD) handheld 3D ultrasound system was developed and validated. Clinical trials on subjects attending will be the next step.

Scoliosis screening is important for timely initiation of brace treatment to mitigate curve progression in skeletally immature children. Scoliosis screening programs frequently include the protocol of referring children screened positive with Scoliometer and Moiré Topography for confirmatory standard radiography. Despite being highly sensitive (88%) for detecting those who require specialist referral, the screening program was found to have more than 50% false positive rate that leads to unnecessary radiation exposure. Radiation-free ultrasound has been reported to be reliable for quantitative assessment of scoliosis curves. The aim of this prospective diagnostic accuracy study was to determine the accuracy of ultrasound in determining the referral status for children initially screened positive for scoliosis. 442 schoolchildren with a mean Cobb angle of 14.0 ± 6.6° were recruited. Using x-ray as the gold standard, the sensitivity and specificity of ultrasound in predicting the correct referral status were 92.3% and 51.6% respectively. ROC curve analysis revealed an area under curve of 0.735 for ultrasound alone and 0.832 for ultrasound plus scoliometer measurement. The finding provided strong evidences on the accuracy of ultrasound in determining the referral status that could result in more than 50% reduction of unnecessary radiation exposure for children undergoing scoliosis screening.