Biomedical subjects

Hubert Labelle

Publications and source records attributed to Hubert Labelle.

At least 19 recordsLinked to original sources

PubMed2006

Relation between the sagittal pelvic and lumbar spine geometries following surgical correction of adolescent idiopathic scoliosis.

Sagittal spinopelvic relations have been reported in adolescent idiopathic scoliosis (AIS), but there is little information on their effect following surgery. The objective of this study is to evaluate the relation between the pelvic and lumbar spine geometries following posterior spinal instrumentation and fusion (PSIF). Sixty patients with AIS undergoing PSIF were studied retrospectively. Thoracic kyphosis (TK), lumbar lordosis (LL), LL within and below fusion, pelvic incidence (PI), sacral slope (SS) and pelvic tilt (PT) were measured on preoperative and postoperative standing lateral radiographs. Significant postoperative correlations were found between PI and LL (r = 0.67), SS and LL (r = 0.90), PI and LL below fusion (r = 0.40), SS and LL below fusion (r = 0.48). Pelvic parameters did not influence LL within fusion. A strong correlation was found between LL below and within fusion (r = -0.76). The close interdependence between lumbar lordosis and pelvic geometry preoperatively is maintained postoperatively following PSIF. In the planning of surgery for AIS, it may be helpful to evaluate the sagittal pelvic morphology (PI) in addition to the spinal curves. Preoperative evaluation of the pelvic morphology could be used to optimize intraoperative positioning of the patient and to determine the optimal amount of LL that needs to be restored or preserved by the instrumentation, so that LL remains congruent with the pelvic morphology.

Adolescent↗

PubMed2006

Sagittal alignment of the spine and pelvis in the presence of L5-s1 isthmic lysis and low-grade spondylolisthesis.

STUDY DESIGN: A radiographic study of 82 patients with L5-S1 spondylolysis or spondylolisthesis of less than 50% displacement of L5 on S1. OBJECTIVE: To measure and describe the sagittal alignment of the spine and pelvis in patients with spondylolysis before the development of a large secondary deformity associated with progression of the spondylolisthesis. SUMMARY OF BACKGROUND DATA: Several publications have addressed the alignment of the spine and pelvis as an important factor in the occurrence, symptomatology, progression, and treatment of spondylolysis and spondylolisthesis. To our knowledge, this is the first report to systematically document the native sagittal alignment of affected patients and compare them to a large control population. MATERIALS AND METHODS: The sagittal alignment in this cohort of 82 patients was compared with a control population of 160 patients without symptoms of back pain or radiographic abnormalities of the spine and pelvis that was the subject of a previous study. RESULTS: Patients with spondylolysis and low-grade spondylolisthesis demonstrate increased pelvic incidence, increased lumbar lordosis, but less segmental extension between L5 and S1 than in a normal population. CONCLUSIONS: These data suggest that differences in the sagittal alignment of the spine and pelvis may influence the biomechanical environment that results in the development of spondylolysis and progressive spondylolisthesis.

Adolescent↗

PubMed2006

A proposal for a surgical classification of pediatric lumbosacral spondylolisthesis based on current literature.

The classification presented in this paper is the first specifically designed to guide surgical treatment of L5-S1 spondylolisthesis in children and adolescents. It also presents objective criteria to differentiate between low- and high-dysplastic spondylolisthesis and incorporates recent knowledge in the study of sagittal spinopelvic balance. The proposed classification is based on the following: (1) the degree of slip, (2) the degree of dysplasia, and (3) the sagittal spinopelvic balance. To classify a patient, the degree of slip is quantified first to determine if it is low-grade, high-grade, or a spondyloptosis. Then, the degree of dysplasia is evaluated based on seven criteria, in order to separate patients with low- and high-dysplastic spondylolisthesis. Finally, the sagittal spinopelvic balance is assessed from the measurement of the pelvic incidence (PI), sacral slope (SS), and pelvic tilt (PT). For low-grade spondylolisthesis, it is classified as low PI/low SS (nutcracker type) or high PI/high SS (shear type). For high-grade spondylolisthesis, it is classified as high SS/low PT (balanced pelvis) or low SS/high PT (retroverted pelvis). Such a comprehensive classification could allow to better evaluate and compare available surgical techniques, and to optimize the treatment of L5-S1 spondylolisthesis. Because the classification was designed so that groups are organized in an ascending order of severity, it becomes easier and more intuitive to develop an associated surgical algorithm because the complexity of the surgery should increase as the severity of the spondylolisthesis increases. A tentative treatment algorithm is proposed but it is not definitive because further studies are required to define the most appropriate treatment for each group.

Adolescent↗

PubMed2006

Three-dimensional classification of spinal deformities using fuzzy clustering.

STUDY DESIGN: A prospective study of a large set of three-dimensional (3D) reconstructions of spinal deformities in adolescent idiopathic scoliosis (AIS). OBJECTIVES: To determine the value of fuzzy clustering techniques to automatically detect clinically relevant 3D curve patterns within this set of 3D spine models. SUMMARY OF BACKGROUND DATA: Classification is important for the assessment of AIS and has been mainly used to guide surgical treatment. Current classification systems are based on visual curve pattern identification using two-dimensional radiologic measurements but remain controversial because of their low interobserver and intraobserver reliability. A clinically useful 3D classification remains to be found. METHODS: An unsupervised learning algorithm, fuzzy k-means clustering, was applied on 409 3D spine models. Analysis of data distribution using clinical parameters was performed by studying similar curve patterns, near each cluster center identified. RESULTS: The algorithm determined that the entire sample of models could be segmented in five easily differentiated curve patterns similar to those of the Lenke and King classifications. Furthermore, a system with 12 classes made possible the identification of subpatterns of spinal deformity with true 3D components. CONCLUSIONS: Automatic and clinically relevant 3D classification of AIS is possible using an unsupervised learning algorithm. This approach can now be used to build a relevant 3D classification of AIS using appropriate key features of 3D models selected by a panel of expert spinal deformity surgeons.

Adolescent↗

PubMed2006

Variability of spinal instrumentation configurations in adolescent idiopathic scoliosis.

Surgical instrumentation for the correction of adolescent idiopathic scoliosis (AIS) is a complex procedure involving many difficult decisions (i.e. spinal segment to instrument, type/location/number of hooks or screws, rod diameter/length/shape, implant attachment order, amount of rod rotation, etc.). Recent advances in instrumentation technology have brought a large increase in the number of options. Despite numerous clinical publications, there is still no consensus on the optimal surgical plan for each curve type. The objective of this study was to document and analyse instrumentation configuration and strategy variability. Five females (12-19 years) with AIS and an indication for posterior surgical instrumentation and fusion were selected. Curve patterns were as follows: two right thoracic (Cobb: 34 degrees, 52 degrees), two right thoracic and left lumbar (Cobb T/L: 57 degrees/45 degrees, 72 degrees/70 degrees) and 1 left thoraco-lumbar (Cobb: 64 degrees). The pre-operative standing postero-anterior and lateral radiographs, supine side bending radiographs, a three-dimensional (3D) reconstruction of the spine, pertinent 3D measurements as well as clinical information such as age and gender of each patient were submitted to six experienced independent spinal deformity surgeons, who were asked to provide their preferred surgical planning using a posterior spinal approach. The following data were recorded using the graphical user interface of a spine surgery simulator (6x5 cases): implant types, vertebral level, position and 3D orientation of implants, anterior release levels, rod diameter and shape, attachment sequence, rod rotation (angle, direction), adjustments (screw rotation, contraction/distraction), etc. Overall, the number of implants used ranged from 11 to 26 per patient (average 16; SD +/-4). Of these, 45% were mono-axial screws, 31% multi-axial screws and 24% hooks. At one extremity of the spectrum, one surgeon used only mono-axial screws, while at the other, another surgeon used 81% hooks. The selected superior- and inferior-instrumented vertebrae varied up to six and five levels, respectively (STD 1.2 and 1.5). A top-to-bottom attachment sequence was selected in 61% of the cases, a bottom-up in 29% and an alternate order in 11%. The rod rotation maneuver of the first rod varied from 0 degrees (no rotation) to 140 degrees, with a median at 90 degrees. In conclusion, a large variability of instrumentation strategy in AIS was documented within a small experienced group of spinal deformity surgeons. The exact cause of this large variability is unclear but warrants further investigation with multicenter outcome studies as well as experimental and computer simulation studies. We hypothesize that this variability may be attributed to different objectives for correction, to surgeon's personal preferences based on their previous experience, to the known inter-observer variability of current classification systems and to the current lack of clearly defined strategies or rational rules based on the validated biomechanical studies with modern multi-segmental instrumentation systems.

Adolescent↗

PubMed2006

Assessment of seated postural control in children: comparison of a force platform versus a pressure mapping system.

OBJECTIVE: To establish the validity and reliability of a pressure mapping system to measure seated postural control in children. DESIGN: A concurrent validity and reliability study. SETTING: Gait and posture laboratory of a rehabilitation center. PARTICIPANTS: Thirteen able-bodied children volunteers. INTERVENTION: Measurements were taken on a seating simulator in quiet sitting and while reaching. The localization of the center of pressure (COP) in the anteroposterior and mediolateral directions was measured simultaneously by means of a pressure mapping system and a force platform. MAIN OUTCOME MEASURES: Concurrent validity was first assessed by Pearson and Spearman correlation coefficients and then by Student paired t tests and Wilcoxon signed-rank test (P<.05) on the range and root mean square (RMS) amplitudes of COP. Reliability was evaluated using intraclass correlation coefficients and coefficients of variation. RESULTS: The COP signals were significantly correlated between both instruments for the RMS and range in both tasks and directions (mean r> or =.87) and for the time series while reaching (r> or =.99), as well as during quiet sitting (r> or =65). Both instruments showed generally fair to good reliability in quiet sitting and excellent reliability when reaching. CONCLUSIONS: The pressure mapping system can detect the COP displacement as effectively as the force platform. In a clinical context, it could help in the evaluation of seated stability and also help in evaluating the efficacy of seating components for wheelchair users.

Adolescent↗

PubMed2006

Computerized assessment of sagittal curvatures of the spine: comparison between Cobb and tangent circles techniques.

OBJECTIVE: The tangent circles technique has been proposed as an alternative to the Cobb angle technique to assess sagittal curves of the spine. However, it has never been compared directly to the Cobb technique. This study compares the reproducibility and clinical relevance of the maximum Cobb angle and tangent circles techniques. METHOD: Standing sagittal radiographs of the spine of 10 adolescents with idiopathic scoliosis, 10 adolescents with spondylolisthesis, and 10 healthy adolescents were used. Thoracic kyphosis (TK) and lumbar lordosis (LL) were measured by 3 observers using the maximum Cobb angle and the tangent circles techniques. Intra- and interobserver intraclass correlation coefficients (ICCs) were calculated. RESULT: Intra- and interobserver ICCs for TK were 0.88 and 0.85, respectively, for the maximum Cobb angle technique, and 0.94 and 0.83, respectively, for the tangent circles technique. Intra- and interobserver ICCs for LL were 0.97 and 0.77, respectively, for the maximum Cobb angle technique, and 0.88 and 0.94, respectively, for the tangent circles technique. The 2 techniques were highly correlated for the measurement of the TK (r=0.93) and LL (r=0.88). CONCLUSION: Both techniques provide excellent intra- and interobserver reproducibility. Tangent circles technique may be a good alternative to the Cobb angle technique because it allows the evaluation of the global geometry of sagittal spinal curves, especially when there is limited visibility of bony structures on radiographs.

Adolescent↗

PubMed2006

Classification of pediatric lumbosacral spondylolisthesis.

A surgical classification of pediatric lumbosacral spondylolisthesis has been proposed recently. In this classification involving 8 distinct types of spondylolisthesis, the patient is classified according to: 1) the slip grade (low- vs. high-grade), 2) the degree of dysplasia (low- vs. high-dysplastic), and 3) the sagittal spinopelvic balance. The objective of this preliminary study is to assess the reliability of the classification. Two observers classified on two separate occasions 40 subjects with lumbosacral spondylolisthesis, based on standing postero-anterior and lateral radiographs of the spine and pelvis. No direct measurements on the radiographs were performed. All 8 types of spondylolisthesis were identified by the observers. Intra-observer agreement for the first and second observers was respectively 92.5% and 87.5%, while inter-observer agreement was 75.0%. Thirty-nine of 40 subjects had agreement among both observers according to the slip grade. Within these 39 subjects, observers disagreed for 8 subjects with respect to the degree of dysplasia and for only one subject with respect to the spinopelvic balance. The proposed classification could be used to better evaluate and compare available surgical techniques, and to develop a treatment algorithm for spondylolisthesis. This new classification results in good intra- and inter-observer agreement. Further studies with observers not involved in the design of the classification are however needed in order to confirm the relevance of the classification.

Humans↗

PubMed2006

A novel framework for the 3D analysis of spine deformation modes.

Three-dimensional classification of scoliosis is important. However, analyzing large databases of 3D spine models is a difficult and time consuming task. To facilitate this task a method that automatically extracts the most important deformation modes from a set of 3D spine models is proposed. The 3D spine models are first converted into vertebrae relative positions and orientations. Then, a variability model composed of the Fréchet mean and of a generalized covariance is computed. A principal component analysis is applied to that variability model and the extracted components are converted into deformation modes. Those modes are visualized by animating a 3D spine model where the deformation strength varies (for a given mode). The proposed method was applied to a group of 307 scoliotic patients and meaningful deformation modes were successfully extracted. For example, patients' growth, double curves, simple thoracic curves and lumbar lordosis were extracted in the first four deformation modes. Moreover, the obtained deformation modes are not disconnected from conventional surgical classifications since a logistic regression confirmed that there is a statistically significant relation between King's classification and the first four principal deformation modes. The proposed method successfully extracted important deformation modes from a set of 3D spine models and can be used to refine arbitrary classes (King's or Lenke's classes, for instance), thus helping the design of new clinically relevant 3D classifications.

Databases, Factual↗

PubMed2006

Comparison of sacropelvic morphology between normal adolescents and subjects with adolescent idiopathic scoliosis.

Previous studies suggest that the pelvic morphology may be abnormal in adolescent idiopathic scoliosis. This study compares the sacropelvic morphology between normal adolescents and subjects with adolescent idiopathic scoliosis (AIS) in both sagittal and coronal planes. The sacropelvic morphology was assessed from the postero-anterior and lateral standing radiographs of 27 normal adolescents and 29 subjects with AIS presenting a major Cobb angle greater than 30 degrees . Sacropelvic morphology was characterized by 19 parameters in the sagittal plane and 26 parameters in the coronal plane. There was no difference in sacropelvic morphology between the two groups in the sagittal plane. In the coronal plane, significant differences were found for right pelvic length, right iliac height, left and right pubic length, left obturator foramen width, bicristal distance, bituberal distance, biacetabular distance, pubic symphysis width, pelvic inlet, and subpubic angle. There was no significant pelvic asymmetry in AIS subjects. This is the first study that specifically evaluates the sagittal and coronal sacropelvic morphology in AIS. The results suggest that the coronal sacropelvic morphology is distorted in AIS. A longitudinal study is required in order to evaluate the influence of sacropelvic morphology in the progression of AIS.

Adolescent↗

PubMed2006

Biomechanical modeling of brace design.

OBJECTIVE: To study the biomechanical effectiveness of brace design parameters in right thoracic idiopathic scoliosis. METHODS: A finite element model (FEM) of the spine, rib cage, pelvis and abdomen was adapted to the geometry of 8 patients with right-thoracic idiopathic scoliosis using a multi-view radiographic reconstruction technique. A detailed parametric FEM of a thoraco-lumbo-sacral orthosis and a Box, Hunter & Hunter experimental design method were used to analyze the contribution of brace design parameters (brace size, number of straps, strap tension, position of the thoracic pad, lordosis reduction design) and of patient's spine stiffness. RESULTS: The mean Cobb angle correction of the thoracic curve was 5.1 degrees (0 degrees to 16 degrees). The most influential parameters were, in descending order, the strap tension, lordosis reduction design and spine stiffness. Their effects are independent and remain weak (-3 degrees when strap tension increases from 20 N to 60 N). Changing the position of the thoracic pad (slightly above or below the apex) doesn't have a significant effect. No significant correction of the axial rotation and rib hump was obtained. DISCUSSION & CONCLUSION: Frontal curve correction varied significantly, which justifies the need for an adequate adjustment of the brace. A more efficient design for the correction of transverse deformities remains to be found. The "active" correction component by the muscles was not included, but one can anticipate that its action would be concurrent to the passive brace mechanisms, enabling supplementary correction. A new tool simulating brace treatment has been developed, which allows rational design of braces.

Biomechanical Phenomena↗

PubMed2006

Relation between the sagittal pelvic and lumbar spine geometries following surgical correction of adolescent idiopathic scoliosis: a preliminary study.

The influence of surgery on the relationship between the lumbar spine and the pelvis in adolescent idiopathic scoliosis (AIS) remains mostly unknown. The sagittal spinopelvic balance of 40 patients with AIS undergoing posterior spinal instrumentation and fusion was studied. After surgery, the total lumbar lordosis (LL) and the LL below fusion remained correlated to the sagittal pelvic geometry. LL within fusion, which is set by the instrumentation, was also related to the LL below fusion. This preliminary study shows that pelvic morphology probably has an important impact on the postoperative sagittal lumbar alignment. Evaluation of the sagittal pelvic geometry could therefore be useful in the preoperative planning of surgery for AIS. Further studies with more patients are still needed in order to confirm this hypothesis and to evaluate if the distal fusion level influences the spino-pelvic balance.

Adolescent↗

PubMed2006

Biomechanical assessment of variable instrumentation strategies in adolescent idiopathic scoliosis: preliminary analysis of 3 patients and 6 scenarios.

Since the introduction of modern multi-segmental instrumentation systems, disagreement exists about the appropriate instrumentation strategies for the "optimal" correction of scoliotic deformities, and the difference between alternative scenarios is difficult to predict a priori. The purpose of this study is to evaluate the effect of different instrumentation strategies using a computer assisted surgery simulator (S3). We obtained from 32 experienced Fellows of the Scoliosis Research Society and members of the Spinal Deformities Study Group the detailed preoperative planning for three AIS patients with Lenke curve types 1A, 3A and 5C. Their scenarios were individually simulated using a computer model implemented in a spine surgery simulator (S3). The resulting Cobb angles varied for the 3 cases (e.g.: main thoracic: 6-17 degrees; 16-29 degrees; 16-30 degrees). The variability of correction remained important when sub-classifying the results according to the instrumentation strategies: A- "Pedicle Screws Constructs"; B- "Hooks Constructs"; C- "Hybrid Constructs". But overall, the average correction was better in group A (71%) than in groups B (55%) and C (54%). For the first time the effect of various instrumentation strategies can be assessed preoperatively thanks to S3. A large variability of instrumentation strategies exist within experienced surgeons and these produce rather different results. This study also questions the criteria for optimal configuration and standards to objectively design the best surgical construct.

Adolescent↗

PubMed2006

Objectives for correction and related instrumentation strategies in scoliosis surgery for Lenke curve types 2, 3 and 5.

A recent study revealed a large variability among a group of 32 spine surgeons in the pre-operative instrumentation planning for the same 5 AIS patients. It is hypothesized that this variability may be attributed to different objectives for correction. In this new study we analyzed the objectives of correction and the related instrumentation strategies for three different Lenke curve types. Nine experienced surgeons from the Spinal Deformity Study Group were surveyed and asked to assess 11 different geometric parameters describing the spinal deformities for three different Lenke curve types (2, 3 and 5) according to their importance for an optimal 3D correction. These same 9 surgeons were asked to provide their preferred posterior instrumentation planning for three patients with the same curve types. Statistical analyses included: median, interquartile range IQR and Wilcoxon non parametric test. There was an overall agreement that sagittal and coronal balances were the most important parameters for an optimal correction. All other parameters were highly variable depending on the curve-type. Mobility was more important for the Lenke curve types 3 and 5 than for type 2 (p<0.032). A comparative analysis based on the coronal curves (Cobb) and the number of unfused vertebrae revealed a significant difference (p<0.025) between the correction objectives of the surgeons and their posterior instrumentation planning. In the three curves types analyzed, there is a large variability in scoliosis correction objectives, which is surgeon and curve-type dependent. There is a disagreement between the correction objectives and the instrumentation strategies. Optimal configuration of surgical instrumentation remains a controversial topic.

Adolescent↗

PubMed2006

Assessment of brace local action on vertebrae relative poses.

Bracing is a widely used treatment of scoliosis, but there is still no consensus about its actual effect. Previous studies were based on global descriptors of the spine shape (Cobb angle, plane of maximal deformity, etc.). We present a new method to analyze braces effects at a finer scale and to find which vertebral levels are significantly affected by this treatment. The proposed method compares a group of patients treated with a brace and a control group. The 3D spine geometry of the patients from the two groups was digitized on two separate occasions: with and without brace (first group) or two times without brace (control group). The modifications of the vertebrae relative poses (combination of relative translation and rotation between consecutive vertebrae) were then extracted from 3D reconstructions. Centrality and dispersion measures of the relative poses modifications were computed using a method that take into account the non-linearity of the rotation matrix. Then, finally, multivariate hypothesis tests were used to compare the centrality and dispersion of the two groups. The method was applied to 28 untreated scoliotic patients and 41 patients treated with a Boston brace. Significant differences (p<0.01) between the centrality and dispersion measures of the relative poses modifications were respectively found from T1 to T6 and from T8 to L1. Those significant differences concords with the back flattening effect and the spatially limited correction found in other studies; however the proposed method offers a more specific evaluation of the localization of those effects.

Braces↗

PubMed2006

Towards an automatic classification of spinal curves from x-ray images.

The objective of this research was to describe a multi-resolution technique for segmentation of the spinal curve on postero-anterior radiograph. Global features from the radiographs were first identified. From this approximate region, local regions of the spine curvature were iteratively filtered using diffusion and shock filters to enhance the boundaries of each vertebral body from radiographic noise. The spine curve going through the centroid of the vertebral bodies was successively identified for clinical classification of spinal deformities.

Adolescent↗

PubMed2006

A biomechanical study of L5-S1 low-grade isthmic spondylolisthesis using a personalized finite element model.

The pars interarticularis lesions in isthmic spondylolisthesis result generally from mechanical stresses in the neural arch due to repetitive overload during daily activities or to trunk imbalance resulting from spino-pelvic morphology. The L5-pelvis junction of a low-grade isthmic spondylolisthesis patient was modeled using a personalized finite element model to investigate the biomechanical behavior of the L5-S1 motion segment. Stress distribution and facet contact pressure in the altered segment were analyzed under 500 N simulating the gravitational load. High von Mises stresses were located in the pars interarticularis, in the pedicle, and in the outer region of the annulus. A high contact pressure was obtained at the facet surfaces. Influenced by the pelvic morphology, the inclination of L5-S1 junction affects the resulting shear forces and may play a crucial role in spondylolisthesis development.

Biomechanical Phenomena↗

PubMed2005

Sagittal spinopelvic balance in normal children and adolescents.

The sagittal spinopelvic balance is poorly documented in normal pediatric subjects. The purpose of this study is to characterize the sagittal spinopelvic balance in the pediatric population and to evaluate the correlations between spinopelvic parameters. Seven parameters were evaluated from the lateral standing radiographs of 341 normal subjects aged 3-18 years old: thoracic kyphosis (TK), thoracic tilt (TT), lumbar lordosis (LL), lumbar tilt (LT), sacral slope (SS), pelvic tilt (PT) and pelvic incidence (PI). The mean values for the pelvic parameters were 49.1+/-11.0, 7.7+/-8.0 and 41.4+/-8.2 degrees for PI, PT and SS, respectively. The mean values for the spinal parameters were 48.0+/-11.7, 44.0+/-10.9, -7.3+/-5.2 and -3.1+/-5.2 degrees for LL, TK, LT and TT, respectively. The spinopelvic parameters were different from those reported in normal adults, but the correlations between the parameters were similar. PI was significantly related to SS and PT. Significant correlations were found between the parameters of adjacent anatomical regions. Pelvic morphology (PI) regulates sagittal sacro-pelvic orientation (SS and PT). Sacral orientation (SS) is correlated with the shape (LL) and orientation (LT) of the lumbar spine. Adjacent anatomical regions of the spine and pelvis are interdependent, and their relationships result in a stable and compensated posture, presumably to minimize energy expenditure. Results from this study could be used as an aid for the planning of surgery in pediatric patients with spinal deformity in order to restore a relatively normal sagittal spinopelvic balance.

Adolescent↗