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.

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.

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.

Two-domain structure of the td intron-encoded endonuclease I-TevI correlates with the two-domain configuration of the homing site.

I-TevI, the T4 td intron-encoded endonuclease, catalyzes the first step in intron homing by making a double-strand break in the intronless allele within a sequence designated the homing site. The 28 kDa enzyme, which interacts with the homing site over a span of 37 bp, binds as a monomer, contacting two domains of the substrate. In this study, limited proteolysis experiments indicate that I-TevI consists of two domains that behave as discrete physical entities as judged by a number of functional and structural criteria. Overexpression clones for each domain were constructed and the proteins were purified. The carboxy-terminal domain has DNA-binding activity coincident with the primary binding region of the homing site and binds with the same affinity as the full-length enzyme. The isolated amino-terminal domain, contains the conserved GIY-YIG motif, consistent with its being the catalytic domain. Furthermore, site-directed mutagenesis of a conserved arginine residue within the extended motif rendered the full-length protein catalytically inactive, although DNA-binding was maintained. This is the first evidence that the GIY-YIG motif is important for catalytic activity. An enzyme with an N-terminal catalytic domain and a C-terminal DNA-binding domain connected by a flexible linker is in accord with the bipartite structure of the homing site.

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.

Corticosteroid therapy associated with ischemic necrosis of bone in systemic lupus erythematosus.

In this prospective study, 28 (52 percent) of 54 patients with systemic lupus erythematosus (SLE) had ischemic necrosis of bone in 93 sites. All but two of the patients had multiple sites of involvement, with hips, knees, and shoulders affected in decreasing order of frequency. Demographic, clinical, and laboratory features were comparable in patients with and without ischemic necrosis of bone except for cushingoid changes in 24 (86 percent) of the 28 patients with ischemic necrosis of bone versus four (15 percent) of the 26 patients without ischemic necrosis of bone (p less than 0.0001). The duration of steroid therapy, total cumulative steroid dose, and the mean daily prednisone dose for the first one, three, six, and 12 months of therapy were not significantly different between the two groups. Mean daily prednisone dose for the highest single month as well as the highest consecutive three, six, and 12 months of therapy was significantly higher in patients with ischemic necrosis of bone. The mean daily dose of prednisone for the highest month of therapy was greater than 40 mg per day in 93 percent and greater than 20 mg per day in all patients with ischemic necrosis of bone. In patients with ischemic necrosis of bone, there was a statistically significant correlation between higher mean prednisone dose at all time intervals and increased number of bony sites involved. A lower mean dose of prednisone was required to produce ischemic necrosis of bone in patients with Raynaud's phenomenon.

Tight glucose control results in normal perinatal outcome in 150 patients with gestational diabetes.

OBJECTIVE: To determine whether tight control of blood glucose is associated with normal outcomes in gestational diabetes. METHODS: We studied 150 consecutive patients with gestational diabetes referred to a diabetes in pregnancy clinic. Selection criteria were an abnormal glucose tolerance test, diabetic management by one physician, capillary blood glucose monitoring in the prenatal period, and delivery at Grace Hospital. Degree of glucose control during pregnancy and maternal and perinatal outcomes were determined by chart review. RESULTS: Overall average glucose levels were 4.9 mmol/L (89 mg/dL) before meals and 6.7 mmol/L (122 mg/dL) 1 hour after meals. Thirty-one percent of the patients were treated with insulin in the prenatal period. In this series, there was no perinatal mortality and no increased incidence of large or small for gestational age infants, cesarean delivery, preterm labor, pregnancy-induced hypertension, neonatal respiratory distress, hypoglycemia, polycythemia, symptomatic hyperbilirubinemia, symptomatic hypocalcemia, or congenital malformations. CONCLUSIONS: Tight glucose control is associated with normal perinatal outcome in gestational diabetes.

Rib cage asymmetry in idiopathic scoliosis.

Seventy-one patients attending a scoliosis clinic and 10 control subjects were studied by a stereoradiographic three-dimensional reconstruction of the spine and rib cage. The symmetry of each rib pair (at each anatomic level) was described by measurements of rib arc length, chord length, enclosed area, maximum curvature, and frontal and lateral angulations. Patients were divided into four groups: 19 with a single right thoracic curve, 15 with a single left lumbar or thoracolumbar curve, 22 with double curves, and 15 with a curve with less than 10 degrees Cobb angle. In the control group and the group with minimal scoliosis, there was no statistically significant rib asymmetry. Among the patients with scoliosis, 11 of 19 patients with right single thoracic curves had rib arc lengths greater on the right side at the curve apex, and nine of 15 patients with left lumbar scoliosis had longer ribs on the left side in the corresponding region of the thoracic spine. Eleven of 22 patients with double curves had symmetrical rib lengths (within +/- 3%), the other 11 had ribs longer on the left. These proportions should not have occurred by chance (p less than 0.001). The mean rib length difference in patients with single thoracic curves was 1.39% (right longer than left), in single lumbar curves it was 3.57% (left longer than right), and in double curves 3.18% (left longer than right). These differences between the groups of patients and control subjects were statistically significant (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Kinematic modeling for the assessment of wheelchair user's stability.

A computer kinematic model was developed to simulate the lateral and transverse stabilities of wheelchair users in order to compare the effect of different backrests. This model is composed of ellipsoids and parallelepipeds representing the main components of the human body, the seating devices and the wheelchair. A fifteen-segment three-dimensional (3-D) model linked by spherical and revolute joints was created using the ADAMS software (Mechanical Dynamics, Inc.). Torsional springs and dampers are used at the joints to represent four sets of articulation stiffness. Seating devices are represented with 45 rectangular surface patches. The interface between human body and seating devices is modeled by contact elements, which included the specification of stiffness, damping, and deformation of cushions and buttocks. Simulations of a user and his wheelchair moving at 1.4 m/s on a tilted pathway were performed. Different indexes [trunk lateral tilt (TLT) and trunk transverse rotation (TTR)] were measured and compared to those of a similar experimental study on four subjects. The effect of joint stiffness was quantified and a sensitivity study showed the importance of the hip, neck, lumbar, and thoracic joint stiffness on model response (between 16% and 68%). Two backrests (standard and highly contoured) were tested with the kinematic model and their stability compared. Overall, the coherence between the simulations and the experiments shows that this approach is appropriate to compare various seating devices (maximal difference of 1.3 degrees between the simulated and experimental curves for the intermediate joint stiffness sets). The smallest rotations of the highly contoured backrest (6.3 degrees versus 8.9 degrees for TLT and 3.9 degrees versus 6.7 degrees for TTR) suggest that the contouring of the mid torso is more efficient than the lower torso to provide stability to the wheelchair user. This model is an adequate tool to test and improve the design of seating aids.

Development of a vertebral endplate 3-D reconstruction technique.

The increase of low back problems has stimulated the development of different analysis and evaluation techniques. Among these methods, the direct linear transformation (DLT) technique is commonly used to reconstruct the spine in three dimensions by means of its known image coordinates on radiographs. Despite its efficiency and precision, general reconstruction of some standard anatomical landmarks (7-11) does not give all the necessary data for a detailed analysis of the intrinsic geometrical characteristics of lumbar vertebrae. Thus, in order to obtain such geometrical information a three-dimensional (3-D) reconstruction vertebral endplate contour technique has been developed. This technique involves 1) iterative optimization and reconstruction processes of the vertebral endplate centroid and 2) 3-D reconstruction of vertebral endplate contour. Validation based on mathematical simulations demonstrated that two or three iterations are necessary to correct (within 2 mm) the endplate centroid position for simulated error higher than 10 mm. Other validations based on 3-D reconstructions of a chamfered tube and a dry vertebra contours of known dimensions have given mean errors of 2 mm. Application on a healthy subject demonstrated the potential of this 3-D reconstruction technique. Finally, 3-D data obtained on vertebral endplates would allow the development of new clinical measurements that could be used to evaluate the lumbar spine geometrical behavior and orthoses biomechanical effects.

Optimized vertical stereo base radiographic setup for the clinical three-dimensional reconstruction of the human spine.

This paper presents a method to determine the stereoradiographic planes and anatomical vertebral landmarks giving the most reliable three-dimensional reconstructions of the thoracic and lumbar spine for clinical studies. The present investigation was limited to stereoradiographic setups with a normal vertical stereo base. Possible X-ray tube positions are thus corresponding to angles ranging from 0 (conventional posteroanterior radiograph) up to 30 degrees (dimension of the X-ray room). An X-ray phantom was used as a specimen from which three-dimensional reconstructions with the direct linear transformation (DLT) algorithm were obtained. Visibility of landmarks located on pedicles, end-plates, transverse and spinous processes was evaluated for the whole thoracic and lumbar spine (T1 to L5). Process landmarks were discarded because their poor visibility on radiographs produced inaccurate three-dimensional reconstructions. Considering the size, shape and orientation of vertebrae, an angle of 20 degrees between the posteroanterior horizontal position and the angled position of the X-ray tube gave optimal results. Landmarks located on pedicles and end-plates produced the most reliable three-dimensional reconstructions of the spine. Pedicles were found to be more reliable landmarks than end-plates. Validation of the technique with reconstructed steel beads reveals three-dimensional errors under 1.0 mm. Since vertebral landmarks were more difficult to identify on radiographs than steel beads, reconstruction results were compared with those obtained with a biplanar orthogonal setup. This shows that three-dimensional errors of 8.0 mm may be expected on actual reconstructions of the spine and errors as large as 15.0 mm may be present on poorly visible landmarks.

Measurements of the three-dimensional shape of the rib cage.

A stereoradiographic method was developed to measure the three-dimensional shape of the rib cage in vivo in order to provide descriptive data and to study symmetry in the normal population. The method is also intended for use in description of rib asymmetry in scoliosis. Rib midlines were reconstructed from digitized points on lines drawn through the middle of each rib image in stereo-radiographs of the rib cage. The method relied on pairing points in one image with a corresponding point found in the second image. The error term obtained from a Direct Linear Transformation (DLT) reconstruction program was used for optimizing this correspondence. The method was used on test objects of known shape where the standard deviation of measurement errors was found to be 0.72 mm. Studies in which different sets of points on the rib midlines were selected for digitizing showed that the precision of the method was 1.04 mm (S.D.). Rib shape was described by intrinsic measurements (arc and chord length, maximum curvature and enclosed area) and rib orientation by extrinsic measurements (frontal and lateral angulations and posterior rib cage rotation). No statistically significant rib shape asymmetry was found among ten subjects without spinal or thoracic abnormalities, although a trend of inequality of rib angulation at all anatomical levels was observed.

Scoliosis assessment in Friedreich's ataxia by means of intrinsic parameters.

Spinal deformities have been evaluated in a five year retrospective study where 28 boys and 25 girls all having Friedreich's ataxia were on the average assessed once a year in a multidisciplinary clinic. Scoliosis seems somewhat more progressive in girls than in boys and more severe in non-ambulatory than ambulatory patients. Some of those scolioses are very progressive reaching 60 degrees to 100 degrees Cobb angle values requiring spinal surgery while other progress less rapidly and do well on their own. In addition it was shown that the intrinsic geometric spine curve parameters namely that of curvature and torsion are a powerful diagnostic tool in the assessment of evolutive scoliosis.

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.

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.

Three-dimensional effect of the Boston brace on the thoracic spine and rib cage.

STUDY DESIGN: Three-dimensional reconstructions of the spine and rib cage were done and compared just before and 1 month after initiation of treatment with a Boston brace in a group of adolescents with idiopathic scoliosis. OBJECTIVES: To document the immediate changes in shape of the thoracic spine and rib cage induced by the original Boston brace design. SUMMARY OF BACKGROUND DATA: The effect of the Boston brace has been well documented in the frontal plane but is poorly understood in the other planes of deformity. METHODS: Three-dimensional reconstructions were obtained with and without the brace using a stereoradiographic technique in a group of 40 adolescents with idiopathic scoliosis. Several geometric indices of the spine and rib cage were compared using Student t tests. RESULTS: The brace produced significant curve correction of the spinal deformity in the frontal plane at the expense of a significant reduction of thoracic kyphosis in the sagittal plane, as well as in the plane of minimum deformity. No significant effect on rotation of the thoracic apical vertebra, on the rib hump, or on frontal balance could be documented, but changes were noted in the sagittal orientation of the rib cage and in the sagittal balance of the spine. CONCLUSIONS: The original Boston brace does not completely correct the three-dimensional deformities associated with thoracic idiopathic scoliosis, although it reduces Cobb angles in the frontal plane.

Rib cage-spine coupling patterns involved in brace treatment of adolescent idiopathic scoliosis.

STUDY DESIGN: The three-dimensional (3-D) interrelations in the correction of the spine and rib cage produced by the Boston brace were analyzed in a group of adolescents with idiopathic scoliosis. OBJECTIVES: To investigate the coupling movements between the spine and rib cage initiated by brace wear (i.e., the displacements of the spine that take place in other directions than the ones generated by brace pressures on the thorax). SUMMARY OF BACKGROUND DATA: The effects of thoraco-lumbo-sacral orthosis in the frontal plane have been well documented, but they have never been studied in terms of 3-D coupled movements between the spine and rib cage. METHODS: The spine and rib cage of 36 adolescents with idiopathic scoliosis with and without their Boston brace were reconstructed in 3-D using a stereo-radiographic technique. Several geometric indices were evaluated on the trunk, and the relative motions of the spine and rib cage resulting from brace wearing were compared by means of Student t tests, Pearson correlation matrices, and linear regressions. RESULTS: Rib cage transverse plane translations resulting from brace pressures are related to those of the spine. Coupled movements between the spine and rib cage were found to alter substantially the expected 3-D correction of the trunk. Significant anterior displacements of the thorax were observed and were statistically associated with lateral displacements of the spine and with an increase of spinal thoracic curvatures in the frontal and sagittal planes. CONCLUSION: Brace loads are not applied in an optimal way to correct the 3-D deformities associated with thoracic idiopathic scoliosis. Loads applied on the posterior rib hump should be reequilibrated to reduce anterior displacement of the trunk.

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.