J. Dansereau

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 subjects 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 /spl plusmn/ 3.8 mm, making it an adequate tool for clinical studies and mechanical analysis purposes.

Morphometric evaluations of personalised 3D reconstructions and geometric models of the human spine

In the past, several techniques have been developed to study and analyse the 3D characteristics of the human spine: multi-view radiographic or biplanar 3D reconstructions, CT-scan 3D reconstructions and geometric models. Extensive evaluations of three of these techniques that are routinely used at Sainte-Justine Hospital (Montréal, Canada) are presented. The accuracy of these methods is assessed by comparing them with precise measurements made with a coordinate measuring machine on 17 thoracic and lumbar vertebrae (T1-L5) extracted from a normal cadaveric spine specimen. Multi-view radiographic 3D reconstructions are evaluated for different combinations of X-ray views: lateral (LAT), postero-anterior with normal incidence (PAOo) and postero-anterior with 20o angled down incidence (PA20o). The following accuracies are found for these reconstructions obtained from different radiographic setups: 2.1±1.5 mm for the combination with PAOo-LAT views, and 5.6±4.5 mm for the PAOo-PA20o stereopair. Higher errors are found in the postero-anterior direction, especially for the PAOo-PA20o view combination. Pedicles are found to be the most precise landmarks. Accuracy for CT-scan 3D reconstructions is about 1.1±0.8 mm. As for a geometric model built using a multiview radiographic reconstruction based on six landmarks per vertebra, accuracies of about 2.6±2.4 mm for landmarks and 2.3±2.0 mm for morphometric parameters are found. The geometric model and 3D reconstruction techniques give accurate information, at low X-ray dose. The accuracy assessment of the techniques used to study the 3D characteristics of the human spine is important, because it allows better and more efficient quantitative evaluations of spinal dysfunctions and their treatments, as well as biomechanical modelling of the spine.

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.

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.

Variability of geometric measurements from three-dimensional reconstructions of scoliotic spines and rib cages.

SummaryThree-dimensional (3-D) reconstructions of the spine are being used with increasing frequency to describe scoliotic deformities, but the reproducibility of most of these techniques and the implication for the reliability of measurements made on the reconstructions has not been reported. How reliable are these reconstructions, and can a clinician interpret with confidence the results of studies based on such mathematical models? A reproducibility study of various computerised measurements obtained from 3-D reconstructions of the spine and rib cage for five subjects with adolescent idiopathic scoliosis was done to evaluate the errors associated with repeated measurements and compare them with inter-and intraobserver errors reported for similar commonly used clinical measurements. The mean variation for the Cobb angle differed according to the plane of computation from 0.6° in the frontal plane to 6.7° in the sagittal plane; vertebral axial rotation varied from 2.3° to 5.9° according to the vertebral level, and rib hump measurements displayed an average variation of 1.4°. All these variations are below or within the error levels reported for equivalent 2-D measurements used by clinicians, which suggests that this 3-D model of idiopathic scoliosis may be used with confidence for clinical evaluations.

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 apexes. The torsional phenomenon can be unidirectional or bidirectional in both single and double major curves.

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.

Peroperative three-dimensional correction of idiopathic scoliosis with the Cotrel-Dubousset procedure

STUDY DESIGN An experiment was conducted to investigate the effect of wearing a weight lifting belt on the endurance and fatigue characteristics of the extensor muscles of the spine. OBJECTIVE To evaluate the effectiveness of back belts in preserving the endurance characteristics of the spinal musculature. SUMMARY OF BACKGROUND DATA Previous studies have investigated the use of back belts in increasing intra-abdominal pressure and thus increasing the stabilization of the spine. Other studies have looked at the association of low back disability and wearing back belts. No study has examined the relationship between wearing back belts and measures of spinal muscle fatigue and endurance. METHODS Thirteen male industrial workers performed a lifting and lowering task from the floor to a 76.2 cm height at 4.3 min-1 2 days a week for 4 weeks. The load was psychophysically determined and averaged 28.1 kg for a total of 28.9 metric tons moved in 4 hours. Subjects lifted for 1, 2, 3, and 4 hours, respectively, for the first 4 days of the experiment. These were considered training days. During the last 4 days, subjects lifted for 4 hours per day; 2 days with a back belt, and 2 days without a back belt. Maximum isokinetic endurance of the extensors was measured for 50 repetitions (5 sets of 10 repetitions) at the end of 4 hours of lifting. Median frequencies of the electromyographic signal from six locations over the back extensors were measured for 30 seconds at 80% of maximum isometric voluntary contraction after 4 hours of lifting. RESULTS There were no significant differences in maximum isokinetic endurance, or in the slope of median frequency, between lifting with a back belt and lifting without a back belt. Similarly, a modified Borg scale and a postexperiment survey question were unable to distinguish between wearing a back belt and not wearing a back belt. CONCLUSION There were no significant differences in maximum isokinetic endurance and electromyographic spectral parameters of the back extensor muscles as a result of wearing a back belt during heavy lifting and lowering tasks.Study Design. A peroperative measurement technique based on magnetic fields was used to document the thoracic and lumbar vertebral changes induced by derotation of the concave rod during corrective surgery of idiopathic scoliotic deformities with Cotrel‐Dubousset instrumentation. Objectives. Objective was to accurately document the immediate changes induced by the derotation maneuver to gain a better understanding of its effect on curve correction during a surgical procedure. Summary of Background Data. Accurate peroperative documentation of these three‐dimensional changes was very limited, and the exact contribution of the derotation maneuver in the entire process of correction of a scoliotic deformity was still poorly understood. Methods. A digitizer using magnetic fields was used to record the three‐dimensional orientation and x, y, and z coordinates of the tip of every spinous process exposed at surgery before and after derotation of the concave rod in a group of 22 female patients with idiopathic scoliosis. Results. A significant improvement of the scoliotic deformity was noted in the frontal plane, and improvement of thoracic hypokyphosis and lumbar hypolordosis in the sagittal plane was seen. Vertebral axial rotation remained unchanged. Conclusions. The derotation maneuver is effective in achieving three‐dimensional correction of idiopathic scoliosis, but vertebral axial derotation is not an important component of this correction.

Optimization method for 3D bracing correction of scoliosis using a finite element model

Abstract Scoliosis is a complex three-dimensional deformity of the spine and rib cage frequently treated by brace. Although bracing produces significant correction in the frontal plane, it generally reduces the normal sagittal plane curvatures and has limited effect in the transverse plane. The goal of this study is to develop a new optimization approach using a finite element model of the spine and rib cage in order to find optimal correction patterns. The objective function to be minimized took account of coronal and sagittal offsets from a normal spine at the thoracic and lumbar apices as well as the rib hump. Two different optimization studies were performed using the finite element model, which was personalized to the geometry of 20 different scoliotic patients. The first study took into account only the thoracic deformity, while the second considered both the thoracic and lumbar deformities. The optimization produced an average of 56% and 51% reduction of the objective function respectively in the two studies. Optimal forces were mostly located on the convex side of the curve. This study demonstrates the feasibility of using an optimization approach with a finite element model of the trunk to analyze the biomechanics of bracing, and may be useful in the design of new and more effective braces.

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/spl deg/ to 45/spl deg/ posterior tilt, while the seat to back angle varied from 90/spl deg/ to 120/spl deg/. A maximum of 40.2% of weight shift was found when combining a system tilt angle of 45/spl deg/ to a seat to back angle of 120/spl deg/. 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/spl deg/ in a posterior direction. We can put forward here that a small tilt /spl les/15/spl deg/ 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 /spl plusmn/30% from the neutral posture for the able-bodied subjects and is fairly constant at 15/spl deg/ 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.