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Carl-Eric Aubin

Publications and source records attributed to Carl-Eric Aubin.

At least 19 recordsLinked to original sources
PubMed2007

Biomechanical study of anterior spinal instrumentation configurations.

The biomechanical impact of the surgical instrumentation configuration for spine surgery is hard to evaluate by the surgeons in pre-operative situation. This study was performed to evaluate different configurations of the anterior instrumentation of the spine, with simulated post-operative conditions, to recommend configurations to the surgeons. Four biomechanical parameters of the anterior instrumentation with simulated post-operative conditions have been studied. They were the screw diameter (5.5-7.5 mm) and its angle (0 degrees - 22.5 degrees), the bone grip of the screw (mono-bi cortical) and the amount of instrumented levels (5-8). Eight configurations were tested using an experimental plan with instrumented synthetic spinal models. A follower load was applied and the models were loaded in flexion, torsion and lateral bending. At 5 Nm, average final stiffness was greater in flexion (0.92 Nm/degrees) than in lateral bending (0.56 Nm/degrees) and than in torsion (0.26 Nm/degrees). The screw angle was the parameter influencing the most the final stiffness and the coupling behaviors. It has a significant effect (p < or = 0.05) on increasing the final stiffness for a 22.5 degrees screw angle in flexion and for a coronal screw angle (0 degrees) in lateral bending. The bi-cortical bone grip of the screw significantly increased the initial stiffness in flexion and lateral bending. Mathematical models representing the behavior of an instrumented spinal model have been used to identify optimal instrumentation configurations. A variation of the angle of the screw from 22.5 degrees to 0 degrees gave a global final stiffness diminution of 13% and a global coupling diminution of 40%. The screw angle was the most important parameter affecting the stiffness and the coupling of the instrumented spine with simulated post-operative conditions. Information about the effect of four different biomechanical parameters will be helpful in preoperative situations to guide surgeons in their clinical choices.

Biomechanical Phenomena↗
PubMed2006

Pedicle growth asymmetry as a cause of adolescent idiopathic scoliosis: a biomechanical study.

Over the last century the neurocentral junction (NCJ) has been identified as a potential cause of adolescent idiopathic scoliosis (AIS). Disparate growth at this site has been thought to lead to pedicle asymmetry, which then causes vertebral rotation and ultimately, the development of scoliotic curves. The objectives of this study are (1) to incorporate pedicle growth and growth modulation into an existing finite element model of the thoracic and lumbar spine already integrating vertebral body growth and growth modulation; (2) to use the model to investigate whether pedicle asymmetry, either alone or combined with other deformations, could be involved in scoliosis pathomechanisms. The model was personalized to the geometry of a nonpathological subject and used as the reference spinal configuration. Asymmetry of pedicle geometry (i.e. initial length) and asymmetry of the pedicle growth rate alone or in combination with other AIS potential pathogenesis (anterior, lateral, or rotational displacement of apical vertebra) were simulated over a period of 24 months. The Cobb angle and local scoliotic descriptors (wedging angle, axial rotation) were assessed at each monthly growth cycle. Simulations with asymmetrical pedicle geometry did not produce significant scoliosis, vertebral rotation, or wedging. Simulations with asymmetry of pedicle growth rate did not cause scoliosis independently and did not amplify the scoliotic deformity caused by other deformations tested in the previous model. The results of this model do not support the hypothesis that asymmetrical NCJ growth is a cause of AIS. This concurs with recent animal experiments in which NCJ growth was unilaterally restricted and no scoliosis, vertebral wedging, or rotation was noted.

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

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

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

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

Biomechanical simulations of scoliotic spine correction due to prone position and anaesthesia prior to surgical instrumentation.

BACKGROUND: The positioning of patients during scoliosis surgery has been shown to affect the scoliosis curve, yet positioning has not been exploited to help improve surgical outcome from a biomechanics point of view. Biomechanical models have been used to study other aspects of scoliosis. The goal of this study is to simulate the specific influence of the prone operative position and anaesthesia using a finite element model with patient personalized material properties. METHODS: A finite element model of the spine, ribcage and pelvis was created from the 3D standing geometry of two patients. To this model various positions were simulated. Initially the left and right supine pre-operative bending were simulated. Using a Box-Benkin experimental design the material properties of the intervertebral disks were personalized so that the bending simulations best matched the bending X-rays. The prone position was then simulated by applying the appropriate boundary conditions and gravity loads and the 3D geometry was compared to the X-rays taken intra-operatively. Finally an anaesthesia factor was added to the model to relax all the soft tissues. FINDINGS: The behaviour of the model improved for all three positions once the material properties were personalized. By incorporating an anaesthesia factor the results of the prone intra-operative simulation better matched the prone intra-operative X-ray. However, the anaesthesia factor was different for both patients. For the prone position simulation with anaesthesia patient 1 corrected from 62 degrees to 47 degrees and 43 degrees to 31 degrees. Patient 2 corrected from 70 degrees to 55 degrees and 40 degrees to 32 degrees for the thoracic and lumbar curves respectively. INTERPRETATION: Positioning of the patient, as well as anaesthesia, provide significant correction of the spinal deformity even before surgical instrumentation is fixed to the vertebra. The biomechanical effect of positioning should be taken into consideration by surgeons and possibly modify the support cushions accordingly to maximise 3D curve correction. The positioning is an important step that should not be overlooked by when simulating surgical correction and biomechanical models could be used to help determine optimal cushion placement.

Adolescent↗
PubMed2004

Biomechanical evaluation of the Boston brace system for the treatment of adolescent idiopathic scoliosis: relationship between strap tension and brace interface forces.

STUDY DESIGN: Prospective study to evaluate the association between strap tension and brace interface forces in the treatment of adolescent idiopathic scoliosis using the Boston brace system. OBJECTIVES: To determine the strap tension associated with optimal brace interface forces. SUMMARY OF BACKGROUND DATA: Trim lines, pad placement, and areas of relief for the brace are guided by radiographic studies. However, optimal adjustment of strap tension is unclear and remains mostly empirical. METHODS: Brace interface forces in all regions of the trunk were measured for 41 patients with adolescent idiopathic scoliosis at three standardized strap tensions (20 N, 40 N, and 60 N). The brace interface forces were assessed using a mat made of force-sensing transducers. Equivalent interface pressure for each trunk region was also calculated to estimate the distribution of the interface forces. RESULTS: The brace interface forces and the corresponding effective areas increased along with the strap tension for all patients. For patients with a single right thoracic curve, the interface pressure tended to increase with increasing strap tension. This increase was significant in the left axillary, right thoracic, right pelvic, and sternal regions. For double right thoracic-left lumbar curves, the increase in interface pressure was significant in the left axillary, right pelvic, and sternal regions. However, most of this increase occurred between 20 N and 40 N of strap tension, with only slight increase or even a decrease in interface pressures between 40 N and 60 N. CONCLUSIONS: The strap tension should be set as high as possible (up to 60 N) for right thoracic curves. For right thoracic-left lumbar curves, the optimal strap tension was approximately 40 N. However, clinicians should ensure that the prescribed strap tension does not cause excessive skin pressure or affect the compliance with the brace. A side opening in the right lumbar area may improve the effectiveness of the brace for double right thoracic-left lumbar curves, but care must be taken to avoid skin problems at the opening.

Adolescent↗
PubMed2004

Spinal shape changes resulting from scoliotic spine surgical instrumentation expressed as intervertebral rotations and centers of rotation.

This paper reports the changes in spinal shape resulting from scoliotic spine surgical instrumentation expressed as intervertebral rotations and centers of rotation. The objective is to test the hypothesis that the type of spinal instrumentation system (Cotrel-Dubousset versus Colorado) does not influence these motion parameters. Intervertebral rotations and centers of rotation of the scoliotic spines were computed from the pre- and post-operative radiographs of 82 patients undergoing spinal correction. The three-dimensional (3D) reconstruction of six anatomical landmarks was achieved for each of the thoracic and lumbar vertebrae. A least-squares approach based on singular value decomposition was used to calculate the rigid body transformation parameters. Average centers of rotation for all intervertebral levels are located in the neural canal at the mid-sagittal plane and approximately at the superior endplate level of the inferior vertebra. Intervertebral rotations have components in all planes: 6.7 degrees (frontal), 5.5 degrees (sagittal) and 4.5 degrees (transverse) RMS for all intervertebral levels. Nearly all intervertebral rotations and centers of rotation are not significantly different for the two instrumentation systems. Various intervertebral rotations and 3D reconstruction errors were simulated on a theoretical model of a lumbar functional unit to assess the proposed method. Intervertebral rotation errors were 1.7 degrees when simulating 3D errors of 3mm on the position of the landmarks. Maximum errors for the position of centers of rotation were below 1cm in the case of intervertebral rotations larger than 2.5 degrees (most cases), but were larger (38 mm) for small intervertebral rotations (<1 degrees ). The type of instrumentation system did not influence intervertebral rotations and centers of rotation. These results provide valuable data for the development and validation of simulation models for surgical instrumentation of idiopathic scoliosis.

Adult↗
PubMed2003

Boston brace correction in idiopathic scoliosis: a biomechanical study.

STUDY DESIGN: To analyze Boston brace biomechanics, pressure measurements and finite element simulations were done on 12 adolescent idiopathic scoliosis patients. OBJECTIVES: The aim was to analyze the Boston brace effectiveness using a finite element model and experimental measurements. SUMMARY OF BACKGROUND DATA: There are not very many biomechanical studies of Boston brace effectiveness, and its biomechanical action is not completely understood. METHODS: This study was performed on 12 girls with scoliosis treated with the Boston brace system. The experimental protocol was composed of the acquisition of two sets of multiplanar radiographs with and without brace followed by the pressure acquisition at the brace-torso interface. A personalized finite element modeling of the trunk was generated from the 3D reconstruction of the patient's geometry. The brace treatment was simulated by the application of equivalent forces calculated from the pressure measurements. RESULTS: Two Boston brace force patterns were defined from the pressure measurements. The first one consisted of high right thoracic forces of 31-113 N, lumbar forces less than 47 N, and included a left thoracic extension working as a counter pad. The second one consisted of low thoracic forces less than 20 N, lumbar forces up to 70 N, without left thoracic extension. The simulations showed that the passive forces only produced a coronal Cobb angle correction up to 9 degrees, whereas real correction was up to 16 degrees. CONCLUSION: High thoracic pads reduced more effectively both thoracic and lumbar scoliotic curves than lumbar pads only. The study suggests that mechanisms other than brace pads produce correction and contribute to the force equilibrium within the brace.

Adolescent↗
PubMed2003

Evaluation of a transpedicular drill guide for pedicle screw placement in the thoracic spine.

Insertion of pedicle screws in the thoracic spine is technically difficult and may lead to major complications. Although many computer-assisted systems have been developed to optimize pedicle screw insertion, these systems are expensive, not user-friendly and involve significant radiation from pre-operative computed tomographic (CT) scan imaging. This study describes and evaluates a transpedicular drill guide (TDG) designed to assist in the proper placement of pedicle screws in the thoracic spine. Pilot holes were made manually using the TDG in the thoracic spine (T1-T11) of three human cadavers before inserting 4.5-mm-diameter screws. CT scans followed by visual inspection of the spines were performed to evaluate the position of the screws. Five of 66 screws (7.6%) violated the pedicle wall: two (3.0%) medially and three (4.5%) laterally. The medial and lateral perforations were within 1 mm and 2 mm of the pedicle wall, respectively. The medial perforations were not at risk of causing neurological complications. No screw penetrated the superior or inferior pedicle wall. The TDG is easy to use and can decrease the incidence of misplaced thoracic pedicle screws. The TDG could be used as a complement to fluoroscopy in certain applications, especially for training surgeons.

Aged↗
PubMed2002

The effect of the Relton-Hall operative frame on trunk deformity in adolescent idiopathic scoliosis.

The prone operative position affects the geometry of the scoliotic spine. However, the literature provides little information concerning the effect of operative position on the scoliotic trunk geometry. This study compared the trunk deformity of 31 adolescent idiopathic scoliosis patients in two standardized positions: standing and prone on a Relton-Hall frame. The geometry of the trunk was assessed using 11 magnetic sensors placed on anatomical landmarks. Eight geometric indices of the trunk were compared using paired Student t-tests (alpha=0.01). The transverse rotation of shoulders, the coronal rotation of shoulders, the lateral shift of C7 with respect to S1, and the thoracic and lumbar angles of trunk rotation assessed in the operative position did not show any significant change compared to the standing position. Therefore, operative positioning using the Relton-Hall frame did not lead to an overall reduction in the scoliotic trunk deformity. Modifications to the Relton-Hall frame are required for optimal presurgical correction of the scoliotic trunk deformity.

Adolescent↗
PubMed2002

Is Cobb angle progression a good indicator in adolescent idiopathic scoliosis?

STUDY DESIGN: A retrospective follow-up study of spine geometry after posterior instrumentation and fusion for adolescent idiopathic scoliosis (AIS). OBJECTIVES: To evaluate 1) if Cobb angle progression is a reliable indicator of the crankshaft phenomenon; 2) if significant growth of the spine can occur after surgery without the development of a crankshaft phenomenon? SUMMARY OF BACKGROUND DATA: Anterior fusion of the spine is often recommended for skeletally immature scoliotic patients to avoid the risk of a crankshaft phenomenon, a long-term loss of curve correction caused by residual growth of the spine combined with the constraints of a posterior fusion. The crankshaft phenomenon is usually assessed indirectly by documenting progression of the Cobb angle on frontal radiographs. Thus far, no study has directly measured the three-dimensional growth of the spine after surgery in AIS. METHODS: Cobb angle, spine length and spine height were obtained from three-dimensional radiographic reconstructions of the spine in 48 adolescent scoliotic patients undergoing posterior instrumentation and fusion. Measurements were done before surgery, after surgery and at skeletal maturity. A significant growth of the spine was defined as a > or = 10 mm increase in spine length, while a significant curve progression was defined as a > or = 10 degrees increase in Cobb angle at skeletal maturity. RESULTS: In the majority of patients (56%), there was no significant change in spinal length or in Cobb angle measurements at an average 2.4 years post surgery. A crankshaft phenomenon was detected in 6 patients (12%) for which significant increases both in spinal length and Cobb angle measurement were found. Significant curve progression without any change in spine length was noted in 9 patients (19%) while an increase in spine length with no evidence of curve progression was present in 6 patients at last follow-up. CONCLUSION: Spinal growth as indicated by an increase in spinal length can be measured in a significant proportion of adolescents with idiopathic scoliosis after posterior instrumentation and fusion. Some of these study participants will develop a crankshaft phenomenon but Cobb angle progression is not a reliable indicator of this complication, since it may occur without any detectable growth of the spine.

Adolescent↗
PubMed2002

Three-dimensional imaging for the surgical treatment of idiopathic scoliosis in adolescents.

Scoliosis is not simply a lateral deviation of the spine but is a complex deformity of the entire trunk. Recent advances in 3-dimensional (3-D) imaging have improved our understanding of the 3-D nature of adolescent idiopathic scoliosis (AIS) and have resulted in the development of a new generation of spinal instrumentation. Stereophotogrammetry, computed tomography, magnetic resonance imaging and surface topography all have their specific 3-D applications and relevance in the clinical management of AIS. In the near future, novel 3-D imaging applications will provide tools to guide the surgeon in the planning, performance and evaluation of increasingly sophisticated and less invasive surgical procedures, thus improving the outcome of surgical treatment for AIS.

Adolescent↗
PubMed2002

Relationships between strap tension, interface pressures and spine correction in brace treatment of scoliosis.

The Boston brace has been shown to efficiently prevent scoliosis curve progression. However, it rarely achieves complete 3-D correction; its adjustment being often empirical and its biomechanical modes of action still remaining poorly understood. This study investigates the in-brace spinal shape (correction) in relationship with the patient's out-of-brace deformation, and the adjustment parameters of the brace, namely the strap tensions and the equivalent forces calculated at the patient-brace interface. Many of the observed relationships illustrate the fact that the in-brace spinal shape is strongly related to the characteristics of the patient's out-of-brace deformation. The pattern of pressure distribution as described by the equivalent forces computed in the thoracic, lumbar, pelvic and sternal regions has important effect on the in-brace Cobb angles, lumbar lordosis, frontal and sagittal imbalances and the apical axial rotations. The complex role of the strap tension on the correction has not been explained and needs further investigation. This project has the potential to give insight into the biomechanical effects of brace treatment by providing a statistical model leading to more rational and personalized brace adjustments.

Adolescent↗
PubMed2002

Intraoperative tracking of the trunk during posterior instrumentation of the scoliotic spine: a feasibility study.

Scoliosis involves spine and trunk deformities. However, during posterior instrumentation of the scoliotic spine, only the exposed spine is currently seen or tracked using navigation systems. A technique for intraoperative tracking of the trunk was developed in order to optimize the surgical correction of the scoliotic trunk deformity. The feasibility of this technique was assessed by comparing the trunk geometry between 19 normal and 21 scoliotic subjects, using an experimental set-up simulating the position adopted during posterior scoliosis surgery. Eleven magnetic sensors placed on anatomical landmarks of the trunk were used to compute nine geometric indices. The geometric indices were closer to zero for normal subjects. Therefore, indices approaching zero during the surgical manoeuvres would indicate a reduction of the trunk asymmetry. Only three of the nine indices were significantly different between normal and scoliotic subjects. This result indicates that the positioning of the subjects on the Relton-Hall frame tends to "normalize" the trunk geometry since the standing position gives more significant differences between normal and scoliotic subjects. The real-time quantification of the trunk geometry during surgical correction of scoliosis may allow the surgeon to improve the correction of both spinal and trunk deformities or to optimize the positioning of the patients on the operating table.

Adolescent↗