The relationship between hip flexion/extension and the sagittal curves of the spine.

The objective of this study was to develop a finite element model (FEM) in order to study the relationship between hip flexion/extension and the sagittal curves of the spine. A previously developed FEM of the spine, rib cage and pelvis personalized to the 3D reconstructed geometry of a patient using biplanar radiographs was adapted to include the lower limbs including muscles. Simulations were performed to determine: the relationship between hip flexion / extension and lumbar lordosis / thoracic kyphosis, the mechanism of transfer between hip flexion / extension and pelvic rotation, and the influence that knee bending, muscle stiffness, and muscle mass have on the degree to which sagittal spinal curves are modified due to lower limb positioning. Preliminary results showed that the model was able to accurately reproduce published results for the modulation of lumbar lordosis due to hip flexion; which proved to linearly decrease 68% at 90 degrees of flexion. Additional simulations showed that the hamstrings and gluteal muscles were responsible for the transmission of hip flexion to pelvic rotation with the legs straight and flexed respectively, and the important influence of knee bending on lordosis modulation during lower limb positioning. The knowledge gained through this study is intended to be used to improve operative patient positioning.

A novel system for thE 3-D reconstruction of the human spine and rib cage from biplanar X-ray images.

The main objective of this study was to develop a 3-D X-ray reconstruction system of the spine and rib cage for an accurate 3-D clinical assessment of spinal deformities. The system currently used at Sainte-Justine Hospital in Montreal is based on an implicit calibration technique based on a direct linear transform (DLT), using a sufficiently large rigid object incorporated in the positioning apparatus to locate any anatomical structure to be reconstructed within its bounds. During the time lapse between the two successive X-ray acquisitions required for the 3-D reconstruction, involuntary patient motion introduce errors due to the incorrect epipolar geometry inferred from the stationary object. An approach using a new calibration jacket and explicit calibration algorithm is proposed in this paper. This approach yields accurate results and compensates for involuntary motion occurring between X-ray exposures.

Semi-automatic detection of scoliotic rib borders using chest radiographs.

Stereoradiography is a well known technique to obtain 3D reconstructions of the rib cage. However, clinical applications are limited by the associated 2D rib detection method. Either this detection is widely supervised and time-consuming for the user, or it is fully automatic and not accurate enough for proper 3D reconstruction or clinical indices extraction. To address these issues, we propose a novel, semi-automated technique for detecting scoliotic rib borders in PA-0 degrees and PA-20 degrees chest X-ray images, using a modified edge-following approach. The novelty consists in following multiple promising edges simultaneously. Detections are initiated from starting points (input by the user) along the upper and lower rib edges and the final rib border is obtained by finding the most parallel pair among the detected edges. Promising results show the superiority of this approach over classical rib detection in terms of accuracy. Moreover, the proposed method is of great relevancy in the scoliotic context since scoliotic ribs present very few shape priors, due to their irregularities, and hence, standard rib detection techniques become unsuitable.

Androgenetic/biparental mosaicism causes placental mesenchymal dysplasia.

BACKGROUND: Placental mesenchymal dysplasia (PMD) is a distinct syndrome of unknown aetiology that is associated with significant fetal morbidity and mortality. Intrauterine growth restriction is common, yet, paradoxically, many of the associated fetuses/newborns have been diagnosed with Beckwith-Wiedemann syndrome (BWS). METHODS: We report two cases of PMD with high levels of androgenetic (complete paternal uniparental isodisomy) cells in the placenta and document, in one case, a likely androgenetic contribution to the fetus as well. RESULTS: The same haploid paternal complement found in the androgenetic cells was present in coexisting biparental cells, suggesting origin from a single fertilisation event. CONCLUSIONS: Preferential allocation of the normal cells into the trophoblast explains the absence of trophoblast overgrowth, a key feature of this syndrome. Interestingly, the distribution of androgenetic cells appears to differ from that reported for artificially created androgenetic mouse chimeras. Androgenetic mosaicism for the first time provides an aetiology for PMD, and may be a novel mechanism for BWS and unexplained intrauterine growth restriction.

Accuracy assessment of human trunk surface 3D reconstructions from an optical digitising system.

The lack of reliable techniques to follow up scoliotic deformity from the external asymmetry of the trunk leads to a general use of X-rays and indices of spinal deformity. Young adolescents with idiopathic scoliosis need intensive follow-ups for many years and, consequently, they are repeatedly exposed to ionising radiation, which is hazardous to their long-term health. Furthermore, treatments attempt to improve both spinal and surface deformities, but internal indices do not describe the external asymmetry. The purpose of this study was to assess a commercial, optical 3D digitising system for the 3D reconstruction of the entire trunk for clinical assessment of external asymmetry. The resulting surface is a textured, high-density polygonal mesh. The accuracy assessment was based on repeated reconstructions of a manikin with markers fixed on it. The average normal distance between the reconstructed surfaces and the reference data (markers measured with CMM) was 1.1 +/- 0.9 mm.

Personalized biomechanical simulations of orthotic treatment in idiopathic scoliosis.

OBJECTIVES: To analyse patient-specific bracing biomechanics in the treatment of scoliosis. DESIGN: Two complementary computer tools have been developed to quantify the brace action on scoliotic spine from pressure measurements, and to simulate its effect on patient-adapted finite element model. BACKGROUND: Brace pad forces and brace effect on spine deformities have been reported. However, the brace mechanisms still need to be better understood to obtain more effective treatments. METHODS: The 3D geometry of the spine and rib cage of three scoliotic adolescents treated by the Boston brace was obtained using a multiview radiographic reconstruction technique. A personalized biomechanical model was constructed for each patient. Pressures generated by the brace on the thorax were measured using pressure sensors. For each zone with a threshold pressure higher than 30 mmHg, a total equivalent force was calculated and applied to the corresponding model nodes. RESULTS: The pressure were generally scattered on the overall torso, with the highest pressures measured on five distinct regions: right thoracic, left lumbar, abdominal, right and left sides of the pelvis. The equivalent forces were of 18-73 N. Differences between simulated deformed shapes and real in-brace geometry of the patients were less than 6 and 9.8 mm for the vertebral positions in the coronal and sagittal planes, and 7.7 degrees for the Cobb angles. CONCLUSION: The results supported the feasibility of such approach to analyse patient-specific bracing biomechanics, which may be useful in the design of more effective braces.

Biomechanical simulations of the spine deformation process in adolescent idiopathic scoliosis from different pathogenesis hypotheses.

It is generally recognized that progressive adolescent idiopathic scoliosis (AIS) evolves within a self-sustaining biomechanical process involving asymmetrical growth modulation of vertebrae due to altered spinal load distribution. A biomechanical finite element model of normal thoracic and lumbar spine integrating vertebral growth was used to simulate the progression of spinal deformities over 24 months. Five pathogenesis hypotheses of AIS were represented, using an initial geometrical eccentricity (gravity line imbalance of 3 mm or 2 degrees rotation) at the thoracic apex to trigger the self-sustaining deformation process. For each simulation, regional (thoracic Cobb angle, kyphosis) and local scoliotic descriptors (axial rotation and wedging of the thoracic apical vertebra) were evaluated at each growth cycle. The simulated AIS pathogeneses resulted in the development of different scoliotic deformities. Imbalance of 3 mm in the frontal plane, combined or not with the sagittal plane, resulted in the closest representation of typical scoliotic deformities, with the thoracic Cobb angle progressing up to 39 degrees (26 degrees when a sagittal offset was added). The apical vertebral rotation increased by 7 degrees towards the convexity of the curve, while the apical wedging increased to 8.5 degrees (7.3 degrees with the sagittal eccentricity) and this deformity evolved towards the vertebral frontal plane. A sole eccentricity in the sagittal plane generated a non-significant frontal plane deformity. Simulations involving an initial rotational shift (2 degrees ) in the transverse plane globally produced relatively small and non-typical scoliotic deformations. Overall, the thoracic segment predominantly was sensitive to imbalances in the frontal plane, although unidirectional geometrical eccentricities in different planes produced three-dimensional deformities at the regional and vertebral levels, and their deformities did not cumulate when combined. These results support the hypothesis of a prime lesion involving the precarious balance in the frontal plane, which could concomitantly be associated with a hypokyphotic component. They also suggest that coupling mechanisms are involved in the deformation process.

Assessment of the 3-d reconstruction and high-resolution geometrical modeling of the human skeletal trunk from 2-D radiographic images.

This paper presents an in vivo validation of a method for the three-dimensional (3-D) high-resolution modeling of the human spine, rib cage, and pelvis for the study of spinal deformities. The method uses an adaptation of a standard close-range photogrammetry method called direct linear transformation to reconstruct the 3-D coordinates of anatomical landmarks from three radiographic images of the subject's trunk. It then deforms in 3-D 1-mm-resolution anatomical primitives (reference bones) obtained by serial computed tomography-scan reconstruction of a dry specimen. The free-form deformation is calculated using dual kriging equations. In vivo validation of this method on 40 scoliotic vertebrae gives an overall accuracy of 3.3 +/- 3.8 mm, making it an adequate tool for clinical studies and mechanical analysis purposes.

Simulation of progressive deformities in adolescent idiopathic scoliosis using a biomechanical model integrating vertebral growth modulation.

While the etiology and pathogenesis of adolescent idiopathic scoliosis are still not well understood, it is generally recognized that it progresses within a biomechanical process involving asymmetrical loading of the spine and vertebral growth modulation. This study intends to develop a finite element model incorporating vertebral growth and growth modulation in order to represent the progression of scoliotic deformities. The biomechanical model was based on experimental and clinical observations, and was formulated with variables integrating a biomechanical stimulus of growth modulation along directions perpendicular (x) and parallel (y, z) to the growth plates, a sensitivity factor beta to that stimulus and time. It was integrated into a finite element model of the thoracic and lumbar spine, which was personalized to the geometry of a female subject without spinal deformity. An imbalance of 2 mm in the right direction at the 8th thoracic vertebra was imposed and two simulations were performed: one with only growth modulation perpendicular to growth plates (Sim1), and the other one with additional components in the transverse plane (Sim2). Semi-quantitative characterization of the scoliotic deformities at each growth cycle was made using regional scoliotic descriptors (thoracic Cobb angle and kyphosis) and local scoliotic descriptors (wedging angle and axial rotation of the thoracic apical vertebra). In all simulations, spinal profiles corresponded to clinically observable configurations. The Cobb angle increased non-linearly from 0.3 degree to 34 degrees (Sim1) and 20 degrees (Sim2) from the first to last growth cycle, adequately reproducing the amplifying thoracic scoliotic curve. The sagittal thoracic profile (kyphosis) remained quite constant. Similarly to clinical and experimental observations, vertebral wedging angle of the thoracic apex progressed from 2.6 degrees to 10.7 degrees (Sim1) and 7.8 degrees (Sim2) with curve progression. Concomitantly, vertebral rotation of the thoracic apex increased of 10 degrees (Sim1) and 6 degrees (Sim2) clockwise, adequately reproducing the evolution of axial rotation reported in several studies. Similar trends but of lesser magnitude (Sim2) suggests that growth modulation parallel to growth plates tend to counteract the growth modulation effects in longitudinal direction. Overall, the developed model adequately represents the self-sustaining progression of vertebral and spinal scoliotic deformities. This study demonstrates the feasibility of the modeling approach, and compared to other biomechanical studies of scoliosis it achieves a more complete representation of the scoliotic spine.

A new X-ray calibration/reconstruction system for 3D clinical assessment of spinal deformities.

The main objective of this study was to develop a 3D X-ray reconstruction system of the spine and rib cage for an accurate clinical assessment of spinal deformities. The proposed system uses an explicit calibration technique and a new calibration object composed of: (1) a set of radiopaque markers embedded in a jacket worn by the patient during the X-ray exposures; (2) six control markers to define a reference vertical plane. Computer simulations were performed to evaluate the accuracy of the 3D reconstruction procedure when different kind of displacements were applied on a reference model. Clinical indices computed from the 3D X-ray reconstruction of the spine for 24 scoliotic subjects were compared to those obtained with the DLT method. The results of the evaluation study showed that the new system allows the patient to adopt a normal attitude without any constraint, compensating for its displacement between exposures.

Personalized biomechanical modeling of Boston brace treatment in idiopathic scoliosis.

The aim of this study was to describe how the Boston brace modify the scoliotic curvatures using a finite element (FE) model and experimental measurements. The experimental protocol, applied on 12 scoliotic girls, was composed of the pressure measurement at the brace-torso interface followed by two radiographic acquisitions of the patient's torso with and without brace. A 3D FE model of the trunk was built for each unbraced patient. The brace treatment was represented by two different modeling approaches: 1) using equivalent forces calculated from the measured pressures; 2) by an explicit personalized FE model of the brace (hexahedral elements) and its interface with the torso (contact elements). In the first model, measured brace forces less than 40N and up to 113N induced respectively less than 21% and up to 87% of real correction. Thoracic forces induced the main correction, affecting partially both lumbar and thoracic curves, in agreement with the literature. In the second model, the brace closing reduced the curves up to 35% of real correction. Contact reaction forces (16-79N) were similar to real brace forces (11-72N). The results suggested that other mechanisms than brace pads contribute to the equilibrium of the patients. Postural control by the muscular system remains a problem to address in a future study. The second model represented more realistically the load transfer from the brace to the spine than external forces application. With such model, it is expected to predict the effect of a brace before its design and manufacturing, and also to improve its design.

Evaluation of the efficiency of patient stabilization devices for 3D X-ray reconstruction of the spine and rib cage.

Four devices designed to stabilize the patient's position and/or posture between X-ray exposures were investigated in order to obtain accurate 3-D reconstruction of their spine: a pelvis support, two elbow supports with handlebars, a back neck contact system and a device with three divergent laser beams pointing on subject body targets. Stability and the bearing of natural posture on a group of 10 adults without scoliosis was evaluated for the different devices using a statistical experimental design (Plackett-Burman plan of resolution IV). Small displacements of subjects were obtained by an Optotrak system with 11 infrared diodes placed on the subject's back. Results showed that the elbow supports with handlebars and pelvis support improved the subject's stability while the pelvis support was the device that produces more changes in the subject's natural posture. The elbow and back neck supports were retained for further evaluation.

Biomechanical modelling of spinal growth modulation for the study of adolescent scoliotic deformities: a feasibility study.

A model of growth modulation was formulated with variables integrating a biomechanical stimulus of growth modulation, a sensitivity factor to the stimulus and time. It was integrated into a finite element model of the thoracic and lumbar spine using an iterative procedure. A simulation on the personalized geometry of a mild scoliotic patient allowed qualitative investigation of scoliotic deformities over 12 cycles (months) in response to a load variation due to an eccentricity of the patient's gravity line in the frontal plane. Resulting frontal, sagittal and transverse spinal views correspond to clinically observable scoliotic configurations. The simulation adequately reproduces a progressing thoracic scoliotic curve while the slight increasing kyphosis represents a possible condition although a thoracic hypokyphosis is frequently reported in the literature. At the thoracic apex, increased wedging as well as axial rotation evolving towards curve convexity are in agreement with clinical and experimental observations reported with curve progression. This study demonstrates the feasibility of the approach and, compared to other biomechanical models, it achieves a more complete representation of the scoliotic spine by incorporating vertebral growth modulation.

Evolution of 3D deformities in adolescents with progressive idiopathic scoliosis.

The objective of this study was to conduct an intrasubject longitudinal study quantifying the evolution of two- and three-dimensional geometrical scoliotic descriptors. The evolution of regional and local scoliotic descriptors was analyzed between two scoliotic visits on a cohort of 28 adolescents with progressive idiopathic scoliosis. Mean age at the first visit was 12.7 +/- 1.7 years old and averaged time interval between two assessments reached 22.8 +/- 10.8 months. Scoliotic descriptors were obtained from three-dimensionally reconstructed spines. The initial thoracic Cobb angle was on average 35.3 degrees +/- 8.4 degrees (range, 14 degrees-54 degrees). The evolution of spinal curvatures and vertebral deformities was assessed statistically in terms of descriptor absolute variations, and of descriptor variations normalized with respect to time and to the increase in Cobb angle. At the thoracic level, vertebral wedging increased with curve severity in a relatively consistent pattern for most scoliotic patients and axial rotation mainly increased towards curve convexity with scoliosis severity. No consistent evolution was associated with the angular orientation of the maximum wedging. Thoracic kyphosis changes (increase and decrease) were observed in important proportions. Results of this study challenge the existence of a typical scoliotic evolution pattern and suggest that the scoliotic evolution is quite variable and patient-specific.

Study of patient positioning on a dynamic frame for scoliosis surgery.

The goal of this clinical trial was to measure patient geometry on a dynamic positioning frame in various prone positions. Fourteen subjects (2 males and 12 females) were recruited from the scoliosis clinic at Ste-Justine Hospital on a volunteer basis. The subjects were AIS patients who were potential candidates for surgery. The Cobb angle, averaged 50 degrees (32 degrees-64 degrees). The mean age was 14.1 years (11-17). A Polaris system (Northern Digital inc, Canada) with 10 passive reflective markers was used to measure various indices of the patient's trunk geometry. Acquisitions were made while the unanaesthetized patient was in five different prone positions: I similar to the standard positioning on a Relton-Hall frame; II addition of a force applied to the ribcage at the apex of the curve; III application of a force at the apex of the curve in the lumbar region; IV, the shoulder pads were elevated to increase the patient's kyphosis; V adjustment of each pad and the application of thoracic and lumbar forces to obtain an optimal correction. The measurements of trunk geometry at each position were compared using position I as a base. A paired student t-test determined a significant difference between positions. When comparing position I to position II there was a significant difference and correction of the rib hump. There was also a significant change in shoulder angle that resulted in over correction. Position III had a significantly negative change in the rib hump. During position IV, there was a measurable increase in kyphosis. During the optimal correction, position V, a significant increase in spine length was observed as well as a significant correction in rib hump and shoulder angle. Patient trunk geometry can be improved by the application of different forces on a dynamic positioning frame. Caution is necessary as over correction and unintended negative effects were observed. The optimal patient position has not yet been found and future studies are directed at determining this.

Idiopathic scoliosis in three dimensions: a succession of two-dimensional deformities?

STUDY DESIGN: A geometric analysis of computerized three-dimensional (3-D) reconstructions of the spine of adolescents with idiopathic scoliosis. OBJECTIVES: To analyze and describe the 3-D location of scoliotic curves with respect to the global frontal, sagittal, and transverse planes of each subject. SUMMARY OF BACKGROUND DATA: Clinical two-dimensional (2-D) measurements cannot fully describe the 3-D deformity of a scoliotic spine because they are done in the 2-D frontal or sagittal plane projection of a subject and do not correspond to the actual deformity. METHODS: The spinal deformity from T1 to L5 of 50 adolescents with thoracic idiopathic scoliosis was reconstructed in 3-D using a multiplanar digital radiographic technique allowing the visualization of the vertebral line of the spine in any projection using auto CAD software. The curvature was segmented in three distinct curves for each subject: a high thoracic, a thoracic, and a lumbar. A regional plane passing through the two end-vertebrae and the apical vertebra was defined, and a series of geometric manipulations were performed to realign each regional plane with the global axis system of each subject. RESULTS: A total of 91% of the 147 curves studied were found to be entirely contained within its 2-D regional plane, and all scoliotic curves were found to be oriented in a 3-D location different from the classic frontal, sagittal, and transverse orthogonal planes of each subject. CONCLUSION: In thoracic idiopathic scoliosis the deformity of the spine is 3-D, but the regional deformity of each high thoracic, thoracic, or lumbar curve is almost always 2-D. The orientation in space of each 2-D plane is such that it cannot be seen in its true frontal or sagittal projection using standard frontal or sagittal radiologic views of the subject.

Geometric torsion in idiopathic scoliosis: three-dimensional analysis and proposal for a new classification.

STUDY DESIGN: Three-dimensionally reconstructed spines of 62 subjects with idiopathic scoliosis were reviewed for three-dimensional pattern classification based on the measurement of geometric torsion. OBJECTIVES: To evaluate the relevance of geometric torsion as a three-dimensional index of scoliosis, and to develop a three-dimensional classification of deformity for idiopathic scoliosis as opposed to the current classifications based on two-dimensional frontal views. SUMMARY OF BACKGROUND DATA: Attempts have been made to measure the geometric torsional shape of scoliotic curves represented curvilinearly. However, the geometric torsion phenomenon has never been properly analyzed and thus has never been precisely defined. METHODS: Standardized stereoradiographs of 62 patients with idiopathic scoliosis were obtained and used to generate three-dimensional reconstructions. A continuous parametric form of the curved line that passes through the vertebrae was created by least square fitting of Fourier series functions. Frenet's formulas then were used to calculate the geometric torsion. RESULTS: Analysis of geometric torsion associated with 94 major scoliotic curves allowed three basic categories of torsion curve patterns to be identified. Scoliotic spines with multiple major curves are described by a combination of basic torsion patterns, one for each curve. CONCLUSIONS: A three-dimensional analysis of the spine in terms of geometric torsion has defined three distinct patterns of torsion in a group of scoliotic curves. Geometric torsion had extreme values at the levels of upper and lower vertebrae, but zero or nearly zero values at the levels of the apices. The torsional phenomenon can be unidirectional or bidirectional in both single and double major curves.

Progression of vertebral and spinal three-dimensional deformities in adolescent idiopathic scoliosis: a longitudinal study.

STUDY DESIGN: The evolution of scoliotic descriptors was analyzed from three-dimensionally reconstructed spines and assessed statistically in a group of adolescents with progressive idiopathic scoliosis. OBJECTIVES: To conduct an intrasubject longitudinal study quantifying evolution of two- and three-dimensional geometrical descriptors characterizing the scoliotic spine and vertebral deformities. SUMMARY OF BACKGROUND DATA: The data available on geometric descriptors usually are based on cross-sectional studies comparing scoliotic configurations of different individuals. The literature reports very few longitudinal studies that evaluated different phases of scoliotic progression in the same patients. METHODS: The evolution of regional and local descriptors between two scoliotic visits was analyzed in 28 adolescents with scoliosis. Several statistical analyses were performed to determine how spinal curvatures and vertebral deformities change during scoliosis progression. RESULTS: At the thoracic level, vertebral wedging increases with curve severity in a relatively consistent pattern for most patients with scoliosis. Axial rotation mainly increases toward curve convexity with scoliosis severity, worsening the progression of vertebral body deformities. No consistent evolution is associated with the angular orientation of the maximum wedging. Thoracic kyphosis varies considerably among subjects. Both increasing and decreasing kyphosis are observed in nonnegligible proportions. A decrease in kyphosis is associated with a shift in the plane of maximum deformity toward the frontal plane, which worsens the three-dimensional shape of the spine. CONCLUSIONS: The results of this study challenge the existence of a typical scoliotic evolution pattern and suggest that scoliotic evolution is quite variable and patient specific.

Analysis of pressure distribution at the body-seat interface in able-bodied and paraplegic subjects using a deformable active contour algorithm.

In this paper, a semi-automatic method for segmenting pressure distribution image-based data at the body-seat interface is presented. The purpose of this work was to estimate the surface and the load supported by the ischial tuberosity (IT) region. The proposed method involves three steps: (1) detecting the IT region using a pressure-distribution image gradient; (2) estimating the contour of the IT region by an iterative active contour algorithm and finally (3) estimating the percentage of the surface and the weight-bearing of the IT region in a group of able-bodied (AB) and spinal-cord injury (SCI) subjects. It was found in this study that the weight bearing on the IT for the spinal-cord injured group is distributed on half the surface in comparison with the AB group or the powered wheelchair users groups. The findings of this study provide insights concerning pressure distribution in sitting for the paraplegic and able-bodied.

Analysis of sliding and pressure distribution during a repositioning of persons in a simulator chair.

This study was undertaken to investigate the effect of system tilt and back recline angles on sliding and pressure distribution of seated subjects. Ten able-bodied subjects adopted successively 12 postures on a multiadjustable simulator chair. The system tilt angle was varied from 0 degrees to 45 degrees posterior tilt, while the seat to back angle varied from 90 degrees to 120 degrees. A maximum of 40.2% of weight shift was found when combining a system tilt angle of 45 degrees to a seat to back angle of 120 degrees. Maximum value of 74 mm of sliding was observed for the acromion marker during repositioning. Significant weight shift at the level of the seat is obtained only when the system tilt angle exceeds 15 degrees in a posterior direction. We can put forward here that a small tilt < or =15 degrees can be used to adjust back pressure distribution, whereas large posterior tilts are used for an effective weight shift at the seat level. The peak pressure gradient remains in general in the interval of +/-30% from the neutral posture for the able-bodied subjects and is fairly constant at 15 degrees of tilt. A significant amount of displacement along the back and seat reference plane were found for the shoulder and hip markers, but this displacement does not necessarily correspond to a pure translation motion of the pelvic segment.