Biomedical subjects

H Labelle

Publications and source records attributed to H Labelle.

At least 19 recordsLinked to original sources

PubMed1999

Intraoperative comparison of two instrumentation techniques for the correction of adolescent idiopathic scoliosis. Rod rotation and translation.

STUDY DESIGN: A prospective and controlled comparative study of two instrumentation techniques used for the correction of adolescent idiopathic scoliosis. OBJECTIVE: To measure the three-dimensional intraoperative correction obtained with a rotation maneuver as compared with that obtained with a translation maneuver of the first instrumentation rod inserted to determine the difference, if any, in the two techniques for achieving three-dimensional correction. SUMMARY OF BACKGROUND DATA: Adequate three-dimensional correction of scoliotic deformities has been reported with the Cotrel-Dubousset instrumentation using the rod-rotation maneuver. More recently, however, authors of studies with newer instrumentation systems have claimed that better correction can be obtained using a translation technique. So far, no report has clearly demonstrated the three-dimensional changes obtained with this more recent instrumentation technique. METHODS: The changes in position of thoracic and lumbar vertebrae exposed during surgery were documented using a three-dimensional magnetic digitizer in 70 adolescents with idiopathic scoliosis undergoing correction by a posterior approach. Vertebral positions were measured intraoperatively before and after the surgical maneuver in 39 patients with the Cotrel-Dubousset instrumentation (rod rotation) and in 31 patients with the Colorado instrumentation (translation). RESULTS: In both groups, adequate three-dimensional correction of the scoliotic deformities was documented, with significant changes in the frontal and sagittal planes and in the orientation of the plane of maximum deformity for thoracic and lumbar curves. On the other hand, no significant differences were documented between the two procedures except in the frontal plane where a tendency for greater correction was observed for thoracic curves with the translation technique. CONCLUSIONS: The two instrumentation techniques are equally able to achieve a comparable and effective three-dimensional correction of the scoliotic deformities. The use of either a rotation maneuver or a translation technique during surgery does not result in any significant measurable difference in three-dimensional correction.

Adolescent↗

PubMed1999

Variability of strap tension in brace treatment for adolescent idiopathic scoliosis.

STUDY DESIGN: A mechanical evaluation of brace strap tensions to document their variability in different patient positions and to assess their biomechanical effectiveness. OBJECTIVES: To measure the strap tensions at which adolescents with scoliosis are wearing their braces and to determine the variations in strap tension in different patient positions. SUMMARY OF BACKGROUND DATA: The biomechanical action of thoracolumbosacral orthoses in still not well understood, and there is no standardized strap tension at which the brace should be fastened to obtain optimal results. METHODS: This study was conducted in 34 adolescents with idiopathic scoliosis wearing thoracolumbosacral orthoses. Brace straps were instrumented with load cells and tightened at four tensions (the ones prescribed by their treating physician and three standardized values: 20, 40, and 60 N). In each case, the tension was recorded while the patients assumed nine positions corresponding to normal daily tasks. The variability of strap tension was evaluated by comparing the changes from the original standing position. RESULTS: The prescribed tensions measured in thoracic and pelvic straps were markedly variable. The greatest changes in tension occurred when the patients were lying down. Relaxation of strap tension was found when the patients returned to the standing position after having completed the tasks. CONCLUSIONS: If strap tension affects the biomechanical actions of the brace, these results indicate that regular brace strap tension adjustments are needed and raise questions about the efficacy of nighttime bracing to correct spinal deformities.

Adolescent↗

PubMed1999

Long-term three-dimensional changes of the spine after posterior spinal instrumentation and fusion in adolescent idiopathic scoliosis.

This is a prospective study comparing the short- and long-term three-dimensional (3D) changes in shape, length and balance of the spine after spinal instrumentation and fusion in a group of adolescents with idiopathic scoliosis. The objective of the study was to evaluate the stability over time of the postoperative changes of the spine after instrumentation with multi rod, hook and screw instrumentation systems. Thirty adolescents (average age: 14.5+/-1.6 years) undergoing surgery by a posterior approach had computerized 3D reconstructions of the spine done at an average of 3 days preoperatively (stage I), and 2 months (stage II) and 2,5 years (stage III) after surgery, using a digital multi-planar radiographic technique. Stages I, II and III were compared using various geometrical parameters of spinal length, curve severity, and orientation. Significant improvement of curve magnitude between stages I and II was documented in the frontal plane for thoracic and lumbar curves, as well as in the orientation of the plane of maximum deformity, which was significantly shifted towards the sagittal plane in thoracic curves. However, there was a significant loss of this correction between stages II and III. Slight changes were noted in apical vertebral rotation, in thoracic kyphosis and in lumbar lordosis. Spinal length and height were significantly increased at stage II, but at long-term follow-up spinal length continued to increase while spinal height remained similar. These results indicate that although a significant 3D correction can be obtained after posterior instrumentation and fusion, a significant loss of correction and an increase in spinal length occur in the years following surgery, suggesting that a crankshaft phenomenon may be an important factor altering the long-term 3D correction after posterior instrumentation of the spine for idiopathic scoliosis.

Adolescent↗

PubMed1999

[Simulation of lateral bending tests using a musculoskeletal model of the trunk].

INTRODUCTION: The lateral bending test is used for the preoperative evaluation of scoliotic patients in order to determine the type of spinal curvatures as well as to assess spine flexibility and possible corrections. However, very few biomechanical studies have been dedicated to the analysis of lateral bending. In this article, a biomechanical model of the human trunk has been used in order to evaluate the possibility of simulating lateral bending tests. METHODS: This model includes elements representing the osseo-ligamentous structures of the spine, rib cage and pelvis, as well as 160 muscle fascicles represented by bilinear cable elements. For 4 scoliotic patients (right thoracic and left lumbar curvatures), 3D upright standing and bending reconstructions were generated from calibrated x-rays and used to calculate the displacements of the vertebrae T1 and L5. These displacements were applied to the model in standing position in order to simulate lateral bending. The resulting geometry of the deformed model was compared to the reconstructed geometry in lateral bending for the other vertebral levels (T2 to L4). RESULTS: The model allows the reproduction of the thoracic Cobb angle modifications with an accuracy superior to 2 degrees, as well as the vertebral rotations in the frontal plane (agreement greater than 85%). The positions of the vertebral body centroids following the simulations showed an agreement of over 77% with reconstructed positions. The direction of the axial angulation for the thoracic and lumbar apical vertebrae is correctly reproduced by the model. The axial rotation for these vertebrae does not result in a common pattern for the 4 patients, which is consistent with the diversity of published data concerning the direction of this coupling. CONCLUSIONS: This study shows the feasibility of simulating lateral bending tests using a 3D biomechanical model integrating muscles. The effect of muscle forces on trunk stiffness and intersegmental mobility can also be assessed using this approach. Future developments should enable the evaluation of the biomechanical properties of scoliotic deformities, thus providing a useful tool for preoperative surgical planning.

Biomechanical Phenomena↗

PubMed1999

[Comparison between clinical Cobb angles and measurements performed on vertebral bodies, pedicle centroids and spinous processes].

GOAL: Evaluate the relations between the clinical Cobb angle measured on radiographic images and the computerized Cobb angles measured on curves passing through: 1) the vertebral body centroids, 2) the pedicle centroids and 3) the spinous process tips, in the frontal plane, the sagittal plane and the plane of maximum curvature. MATERIAL AND METHODS: A bi-planar radiographic technique was used to reconstruct in 3D the spine geometry for 39 adolescent girls having double-curved idiopathic scoliosis. The Cobb angles were measured clinically on the radiographs and were computed on the 3 curves. RESULTS: Every relation was found significant and their determination coefficient (R2) was between 0.38 and 0.98. Linear relations were established between clinical and computerized angles. Angles measured on the curve passing through the pedicle centroid correlated best with clinical indices. CONCLUSIONS: The computerized measurements of Cobb angles from 3D models can be used with confidence and are interchangeable, provided the appropriate conversion factor is used.

Adolescent↗

PubMed1999

[Correlation study between spinal curvatures and vertebral and disk deformities in idiopathic scoliosis].

Idiopathic scoliosis involves complex tridimensional (3D) deformations of the spine associated with intrinsic alterations (wedging) of vertebral bodies (VB) and intervertebral disks (ID). This study intends to evaluate analytically in vivo 2D and 3D scoliotic descriptors, based on clinical data from 40 thoracic curves of scoliotic adolescents, and to establish relationships between the regional curve deformations and the local VB and ID deformities. A multiplanar radiographic technique provided 3D positioning of vertebral landmarks. Cobb angle in the postero-anterior (PA) view, in the plane of maximum deformity (CobbP.Max) and the angular orientation of the plane of maximum deformity were used as regional descriptors. Vertebral body endplates were modeled as 3D oriented ellipses. Axial rotation, global PA and local frontal wedgings (inclinations of projected ellipses in the global and vertebral frontal planes), 3D maximum wedging (real inclination of adjacent ellipses) as well as the angular orientation of 3D wedging were calculated to characterize local deformations at the thoracic apex. Mean values for CobbPA, CobbP.Max and the angular orientation of the maximum deformity (with respect to the sagittal plane) reached 44 degrees, 48 degrees and 67 degrees respectively. On average, vertebral axial rotation, global PA, local frontal and 3D wedging angles were respectively 15 degrees, 8.3 degrees, 8.2 degrees and 9.7 degrees. Analyses indicated statistical correlation between: a) Cobb angles and vertebral wedging; b) the orientations of the maximum deformity and of 3D vertebral wedging; c) the axial rotation and CobbPA; d) the axial rotation and the angular orientation of 3D vertebral wedging. At the thoracic level, statistical analyses indicated that vertebral wedging and axial rotation increase with curve progression. Scoliosis severity, as measured by Cobb angles, evolves simultaneously to a coronalization of the plane of maximum deformity, revealing an hypokyphotic phenomenon, and to a real vertebral wedging shifting towards the frontal plane of the vertebra. These 3D in vivo analyses allowed interpretation of spatial relationships between regional and local scoliotic deformities. Compared to 2D in vivo or 3D in vitro analyses alone, this 3D in vivo study provides a more complete assessment of spinal curve progression to fully interpret the real 3D curvature and intrinsic deformations as well as their evolution processes.

Adolescent↗

PubMed1999

[Perioperative radiographic reconstruction of the scoliotic vertebral column].

We have developed a new per-operative three dimensional (3D) reconstruction technique to evaluate the 3D correction of a scoliotic spine induced by surgery using Cotrel-Dubousset instrumentation. A small object with 15 embedded markers was used to calibrate the radiographic system. During surgery, the calibration object was sterilized and fixed to the patient just before the acquisition of two pairs of posterior-anterior and sagittal radiographs; one pair before the rotation maneuver of the rod and one pair after the maneuver. The markers were digitized on each radiograph and their relative 3D positions were measured to establish the relation between the 3D positions of the anatomical structures and their 2D positions on the radiographs. This relation was used to calculate the 3D position of six anatomical landmarks per vertebra (the centers of the superior and inferior vertebral body endplates and the proximal and distal bodies of both pedicles) from the identification of these landmarks on each radiograph. We made a 3D representation of the thoracic and lumbar spine of three patients with idiopathic scoliosis undergoing corrective surgery by the posterior approach. Clinical indices (Cobb angle, axial rotation and the plane of maximum curvature) computed from the 3D reconstruction of the spine obtained before and after the rotation maneuver of the rod were compared to evaluate the 3D correction performed during the surgery. The new proposed approach allows the surgeon to evaluate the per-operative shape of the spine. This approach is simpler, faster and less risky for the patient than the previous method which employed an electromagnetic digitizer to measure the 3D coordinates of anatomical landmarks located on the posterior part of the spine. Furthermore, the 3D representation of the spine visualized from different points of view gives the surgeon an accurate evaluation of the 3D correction during the surgical procedure.

Adolescent↗

PubMed1998

Morphologic discrimination among healthy subjects and patients with progressive and nonprogressive adolescent idiopathic scoliosis.

STUDY DESIGN: A prospective and controlled comparative study. OBJECTIVES: To identify variables that would allow discrimination among patients with progressive adolescent idiopathic scoliosis, patients with nonprogressive adolescent idiopathic scoliosis, and control subjects. SUMMARY OF BACKGROUND DATA: In a previous study, the correlation was demonstrated between morphologic somatotypes and adolescent idiopathic scoliosis. METHODS: One hundred forty-six subjects were evaluated anthropometrically and were classified according to their morphologic somatotype. Of these subjects, 52 were adolescent girls with progressive idiopathic scoliosis, whereas 32 girls had nonprogressive idiopathic scoliosis. The control group was composed of 62 healthy adolescent girls. Somatotype values for ectomorphism, mesomorphism, and endomorphism were obtained according to a technique based on Sheldon's method, and 77 anthropometric measurements of segments of the thorax, head, and limbs were taken. RESULTS: The discriminant analysis realized on a subset of 18 variables allowed the correct identification of each subject's group in 84% of the cases. CONCLUSIONS: It is possible to differentiate healthy adolescent subjects, patients with nonprogressive adolescent idiopathic scoliosis, and patients with progressive idiopathic scoliosis by using anthropometric measurements and morphologic classification. These findings may be useful in the early detection of children at risk for progression of scoliosis and may allow earlier application of treatment methods without waiting for a significant increase in the curve.

Adolescent↗

PubMed1998

Estimation of 3D location and orientation of human vertebral facet joints from standing digital radiographs.

This study provides a biplanar radiographic reconstruction method of volumes of interest to evaluate the location, dimensions and orientation of human facet joints. Visibility of facet anatomical landmarks and areas of interest was evaluated on digital radiographs of 20 idiopathic scoliotic adolescents. Areas of interest have provided the most reliable evaluation of facet joints on postero-anterior and lateral digital radiographs. Volumes of interest of a thoracic and lumbar spinal segment (T1 to L3) were computed using the proposed biplanar 3D reconstruction method and compared with serial tomographic reconstructed models. Differences of 1.5 +/- 0.7 mm in 3D location and 1.8 +/- 1.2 degrees in sagittal orientation of volumes of interest were observed between both representations. This in vivo geometric information on human vertebral facet joints will help us to understand their role in spinal disorders and will provide important data for personalised biomechanical simulations.

Adolescent↗

PubMed1998

Three-dimensional measurement of wedged scoliotic vertebrae and intervertebral disks.

Idiopathic scoliosis involves complex spinal intrinsic deformations such as the wedging of vertebral bodies (VB) and intervertebral disks (ID), and it is obvious that the clinical evaluation obtained by the spinal projections on the two-dimensional (2D) radiographic planes do not give a full and accurate interpretation of scoliotic deformities. This paper presents a method that allows reconstruction in 3D of the vertebral body endplates and measurement of the 3D wedging angles. This approach was also used to verify whether 2D radiographic measurements could lead to a biased evaluation of scoliotic spine wedging. The 3D reconstruction of VB contours was done using calibrated biplanar X-rays and an iterative projection computer procedure that fits 3D oriented ellipses of adequate diameters onto the 3D endplate contours. "3D wedging angles" of the VB and ID (representing the maximum angle between adjacent vertebrae) as well as their angular locations with respect to the vertebral frontal planes were computed by finding the positions of the shortest and longest distances between consecutive endplates along their contour. This method was extensively validated using several approaches: (1) by comparing the 3D reconstructed endplates of a cadaveric functional unit (T8-T9) with precise 3D measurements obtained using a coordinate measuring machine for 11 different combinations of vertebral angular positions; (2) by a sensitivity study on 400 different vertebral segments mathematically generated, with errors randomly introduced on the digitized points (standard deviations of 0.5, 1, 2, and 3 mm); (3) by comparing the clinical wedging measurements (on postero-anterior and lateral radiographs) at the thoracic apical level of 34 scoliotic patients (15 degrees < Cobb < 45 degrees) to the computed values. Mean errors for the 11 vertebral positions were 0.5 +/- 0.4 mm for VB thickness, less than 2.2 degrees for endplate orientation, and about 11 degrees (3 mm) for the location of the maximum 3D wedging angle along the endplate contour. The errors below 2 mm (introduced on the digitized points) slightly affected the 3D wedging angle (< 2 degrees) and its location (< 4 degrees) for the ID. As for the clinical evaluation, average angular errors were less than 0.4 degrees in the radiographic frontal and lateral planes. The mean 3D wedged angles were about 4.9 degrees +/- 1.9 degrees for the VB and 6.0 degrees +/- 1.7 degrees for the ID. Linear relations were found between the 2D and the 3D angles, but the 3D angles were located on diagonal planes statistically different than the radiographic ones (between 100 degrees and 221 degrees). There was no statistical relation between the 2D radiographic angles and the locations of the 3D intervertebral wedging angles. These results clearly indicate that VB and ID endplates are wedged in 3D, and that measurements on plain radiographs allow incomplete evaluation of spinal wedging. Clinicians should be aware of these limitations while using wedging measurements from plain radiographs for diagnosis and/or research on scoliotic deformities.

Algorithms↗

PubMed1998

[Customized 3D radiographic reconstruction of the human pelvis].

The pelvis is an essential element in the study of scoliosis since it constitutes the base of the spine and its orientation may affects postural balance. In order to study the role of the pelvis in the evolution and treatment of this disease, a new technique for the 3D personalised reconstruction of the pelvis was developed. It consists in identifying and digitizing 19 pelvic anatomical landmarks on postero-anterior and lateral x-rays and to reconstruct them in 3D with two techniques: the DLT algorithm developed by Marzan (1976) and, for 6 of the 19 landmarks, an adaptation of it called DLT with confidence coefficients. The latter takes into account the confidence given to the identification of the landmarks on each x-rays. Two methods were used to validate the reconstruction of the pelvis. The first one, used for 11 scoliotic patients and 2 dry pelvis specimens, consists in applying the reconstruction algorithm in an inverse way on the 3D coordinates of the reconstructed landmarks to obtain their 2D retroprojection on the x-ray planes, and thus comparing the retroprojected coordinates with the 2D digitized coordinates. The second method consists in measuring a dry pelvis specimen and comparing the 3D measured landmarks with the ones reconstructed with the x-rays of this specimen. For the first validation, results have shown that the lowest retroprojection errors (less than 2.5 +/- 2.6 mm) for the scoliotic patient group are located on the superior base of the sacrum, on the sacral curve and on the acetabula, while the highest (6.4 +/- 7.2 mm) were on the iliac crests. For the dry specimens, the retroprojection errors were below the millimeter. The second validation method showed 3D differences of 2.4 +/- 1.2 mm between measured and reconstructed landmarks of a dry specimen, which is of the same order of magnitude as what is reported in the literature for vertebrae. The reconstruction of the pelvis is thus considered adequate and its graphical wireframe representation allows to visualise and measure clinical indices concerning its orientation in space. Moreover, the reconstructed landmarks will be used to develop a personalised geometrical and mechanical model of the pelvis which, when integrated with the one for the spine and rib cage, will allow to simulate in a more realistic manner the biomechanical behaviour of the scoliotic trunk, particularly for the study of orthopaedic treatments with braces leaning on it.

Acetabulum↗

PubMed1998

[Biomechanical modeling of instrumentation for the scoliotic spine using flexible elements: a feasibility study].

Surgical instrumentation of the scoliotic spine is a complex procedure with many parameters, such as the spinal segment to operate on, the number and position of the hooks and screws, etc. Biomechanical modeling is a tool which can be used to determine the influence of these parameters. However, technical difficulties due to the large stiffness range of involved components and the large deformations associated with surgical maneuvers are encountered when using the finite elements method. Thus, the objective of this study is to adapt a modeling approach using analysis of flexible mechanisms and evaluate its feasibility. The model combines rigid bodies for the vertebrae and flexible elements representing intervertebral structures. The mechanical properties were calculated from published data and the geometry was personalized with intraoperative measurements. Following the installation of the hooks and screws on the modeled spine, two steps were used to simulate the surgical maneuvers: 1) translation and attachment of the hooks/screws on the first rod; 2) rod rotation. The feasibility of this modeling approach was evaluated by simulating the surgical maneuvers on 2 cases: 1) a physical model; 2) a clinical case. The agreement between intraoperative measurements and simulation results (frontal curvatures are reproduced with over 80% accuracy) shows the feasibility of the modeling approach. This approach also reduces computational convergence problems because of its limited sensitivity to stiffness differences between elements, which demonstrates the advantage of flexible mechanism modeling relative to finite element modeling. Long term goals of subsequent refinements are the development of a tool for surgical correction predictions and for the design of more efficient instrumentation.

Adolescent↗

PubMed1998

[Morphometric characteristics of the scoliotic spine].

GOAL: Results from a morphometric investigation performed on a rare complete scoliotic specimen are presented. The aim of the study is to describe the vertebral body wedging. MATERIALS: The specimen used in the study presented a thoracic curve of 150 degrees Cobb angle with the apex at T8. The measures were made using 3D-computer graphics models. The wedging in the frontal and sagittal planes as well as the 3D wedging were measured. The height variation of the vertebral bodies was also measured. RESULTS: The wedging measures show that it increases progressively with the vertebral level to reach a maximum of 27 degrees at the apex. Perdriolle has found a linear relation between the vertebral body wedging and the Cobb angle. The relation predicts a wedging of 24 degrees for 150 degrees of Cobb angle. An inflection point was identified on the vertebral end plate on the convex side. These inflection points were described by Perdriolle as being on the concave side of the vertebra. CONCLUSION: Our measures follow the relation between the Cobb angle and the wedging of the vertebral body, even for very large Cobb angles. Furthermore, inflection points on the vertebral body were identified on the convex side as opposed to the concave side in the literature. This leads us to believe that the vertebral body wedging progressively affects the vertebral endplates.

Adult↗

PubMed1998

[A biomechanical study of new orthotic treatment approaches for the 3D correction of scoliosis].

Scoliosis is a complex deformity of the spine and rib cage often treated by the Boston brace. The goal of this research is to study the simulation of two new treatment approaches and to compare their results to the Boston brace. A personalized biomechanical model has been used to simulate the treatment on 20 scoliotic teenagers with double curvature. On the first treatment, different forces were applied at the thoracic apex level and the posterior displacement of the rib hump was locked. For the second treatment, an oblique force oriented 45 degrees with respect to the frontal plane was added at the lumbar apex. Following each simulation, geometrical and clinical measurements were calculated and compared to the initial geometry and the Boston brace treatment. Overall, the two new treatment modalities correct the thoracic Cobb angle in the frontal plane while maintaining the normal physiological curvatures in the sagittal plane, move the thoracic plane of maximum deformity towards the sagittal plane and reduce axial rotation and rib hump. In comparison, the Boston brace reduces the Cobb angles in the frontal as well as in the sagittal planes, moves the planes of maximum deformities towards the coronal plane and has no effect on axial rotation and rib hump. This biomechanical study shows force patterns that correct scoliosis more efficiently than the Boston brace. These new treatment approaches must be personalized for each patient and still require clinical evaluation.

Adolescent↗

PubMed1997

Relation between adolescent idiopathic scoliosis and morphologic somatotypes.

STUDY DESIGN: A prospective and controlled comparative study. OBJECTIVES: To verify the difference in morphologic appearance between a group of adolescents with progressive adolescent idiopathic scoliosis and a control group of normal adolescents. SUMMARY OF BACKGROUND DATA: In a previous retrospective study, the possibility of a relation between progressive adolescent idiopathic scoliosis and specific morphotypes was demonstrated. METHODS: Fifty-two adolescent girls with progressive adolescent idiopathic scoliosis were compared with an age-matched control group of 62 unaffected girls using a classification technique based on morphologic somatotypes. Morphotypes were evaluated with standardized pre-established criteria based on Sheldon's technique. RESULTS: Patients with progressive adolescent idiopathic scoliosis showed significantly less mesomorphism (mean value of 0.88 +/- 0.51) than control girls (mean value of 1.72 +/- 0.52). CONCLUSION: Adolescent girls with progressive adolescent idiopathic scoliosis have a morphologic somatotype that is different from the normal adolescent population. Subjects with progressive adolescent idiopathic scoliosis are significantly less mesomorphic than control girls. This observation may be of value as a predictive factor for early identification of subjects with adolescent idiopathic scoliosis at greater risk of progression.

Adolescent↗

PubMed1997

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.

Biomechanical Phenomena↗

PubMed1997

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 (PA0 degree) and postero-anterior with 20 degrees angled down incidence (PA20 degrees). The following accuracies are found for these reconstructions obtained from different radiographic setups: 2.1 +/- 1.5 mm for the combination with PA0 degree-LAT views, and 5.6 +/- 4.5 mm for the PA0 degree-PA20 degrees stereopair. Higher errors are found in the postero-anterior direction, especially for the PA0 degree-PA20 degrees 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 modeling of the spine.

Evaluation Studies as Topic↗

PubMed1997

[Intra-observer variability of measurement of posture with three-dimensional digitization].

A new system based on 3D digitization with magnetic fields has been developed by our research team. The focus of this study was to evaluate the intratester reproducibility of this technique of measurement. Twenty key morphological parameters were used twice to digitize the fourty five female subjects aged 7 to 23 years. The results of variance analysis (ANOVA) for repeated measures showed no statistically significant difference between the two series of measurements for the twenty angles studied. In 56% of the measurements, the difference of the means was less than 1 degree, the greatest being 1.82 degrees. These results confirm the reliability of this new technique of postural evaluation when the measurements are taken by the same tester. Therefore, 3D digitization with magnetic fields could be an interesting alternative to X-Rays for the evaluation of scoliosis.

Adolescent↗