Scoliotic Trunk Research Articles

Determination of Three-Dimensional Corrective Force in Adolescent Idiopathic Scoliosis and Biomechanical Finite Element Analysis.

AimsIn this study we have considered the three dimensional corrective forces for correction of scoliosis by using a patient specific finite element model.Materials and MethodsAn objective function of corrective forces in three-dimensional space was defined. Computed tomography images were used to reconstruct three dimensional model of scoliotic trunk. Computer aided engineering software Abaqus was used to establish finite element model of deformed spine and its biomechanical characteristics were analyzed. By adjusting magnitude and position of corrective forces, objective function was minimized to achieve best orthopedic effect. The proposed corrective conditions were divided into three groups: (1) thoracic deformity; (2) lumbar deformity; (3) both thoracic and lumbar deformities were considered.ResultsIn all three cases, the objective function was reduced by 58, 52, and 63%, respectively. The best correction forces point was located on convex side of maximum displacement of vertebral body.ConclusionUsing minimum objective function method, spinal deformity in three-dimensional space can be sufficiently reduced. This study provides scientific basis for design of a new corrective brace for treatment of scoliosis.

Analysis of Center of Mass and Gravity-Induced Vertebral Axial Torque on the Scoliotic Spine by Barycentremetry

Study DesignRetrospective observational study. ObjectivesTo determine the mass distribution along the scoliotic trunk using barycentremetry and its relationship with vertebral axial rotation and torque. Summary of the Background DataDeformity progression in adolescent idiopathic scoliosis (AIS) is not yet fully understood, but gravity load on the spine could play a role. Barycentremetry allows to characterize body mass distribution in standing position, which could provide a better understanding the mechanisms of progression. Methods81 subjects (27 healthy adolescents and 53 AIS patients) underwent biplanar radiography and 3D reconstruction of the spine and body envelope. Position of the gravity line was estimated, as well as trunk segmental centers of mass COMs at each vertebral level and resulting axial torques to each vertebra. ResultsThe COM of all trunk segments was less than 1 cm from the gravity line in the frontal plane for healthy subjects, and less than 1.5 cm for AIS patients. Vertebral axial torque was 0.7 ± 0.5 Nm in healthy subjects, 2.9 ± 2.1 Nm at the junctional vertebrae of AIS patients and 0.5 ± 0.5 at the apex. A strong association was found between high torque and high intervertebral rotation at junctions, with low torque and low intervertebral axial rotation at the apex. ConclusionResults suggest that AIS patients can maintain the COM of each body segment close to their gravity line, irrespective of the severity and asymmetry of their deformity. Moreover, torque analysis shed some light on the importance of junctional vertebrae in the spinal deformity and, potentially, in the vicious cycle determining scoliosis progression. Level of EvidenceLevel III.

Kyphosis – A risk factor for positioning brachial plexopathy during spinal surgeries

ObjectiveThe aim of this study was to evaluate the differences in transcranial electric motor-evoked potentials – TceMEP on upper limbs and the incidences of postoperative brachial plexopathy between patients with kyphotic and scoliotic trunk shapes. MethodsIn the period of January 2011–January 2017, 61 consecutive patients (mean age: 18.4 years ± 4.4 years (range: 10–32)) with pediatric spinal deformity underwent surgery in our Department. Eight of them had a kyphotic trunk deformity (Scheuermann kyphosis, neurofibromatosis, posterior thoracic hemivertebra), and the rest of the 53 patients had a scoliotic trunk deformity (mostly adolescent idiopathic scoliosis – AIS, lateral hemivertebra). The TceMEP recordings in all four limbs were analyzed every 30 min, or upon the surgeon's command. Upper limb TceMEP recordings were used as a control of systemic and anesthetic related changes, and as the indicator of positioning brachial plexopathy. ResultsFour out of 8 patients (50.0%) from the kyphotic group experienced noteworthy decreases in TceMEP amplitude (≥65%) in one or both arms, and only 2 out of 53 patients (3.8%) from the scoliotic group, confirming significant statistical difference (Chi-square 16.75, p < 0.05). Two out of 8 patients with decreases in TceMEP amplitude suffered from transitory postoperative brachial plexopathy, and both of them were from the kyphotic group. ConclusionIt seems that kyphotic trunks have a higher risk for positioning-related brachial plexopathy, probably due to distribution of trunk's weight onto only four points (two iliac bones and two shoulders), compared to the scoliotic trunks that have wider weight-bearing areas. We emphasize the importance of proper patient positioning and close intraoperative neuro-monitoring of all four limbs in more than one channel per limb. Level of EvidenceLevel IV Therapeutic Study.

3D reconstruction of adolescent scoliotic trunk shape from biplanar X-rays: a feasibility study

ABSTRACTAdolescent idiopathic scoliosis (AIS) is a 3D deformity of the spine detectable by trunk asymmetry. As a decision-aid tool, body scanners can assess non-invasively the external shape of the trunk. If AIS is diagnosed, additional 3D reconstructions of the spine, rib cage and pelvis are useful to plan a treatment such as bracing. Body scanners cannot currently guarantee reliable bones reconstruction but low-dose biplanar X-rays (BXR) is a relevant alternative. Recently, 3D body shape reconstruction of asymptomatic subjects from BXR was also proved to be accurate. To prevent AIS patients from multiple examinations, we investigated the feasibility of trunk shape reconstruction from BXR. The proposed method relied on the 3D reconstructions of the spine, rib cage and pelvis on which a statistical shape model was fitted. Additional 10 radio-opaque markers could also be considered yielding automatic deformations of the model. Finally, few manual adjustments were performed. This method was evaluated on 15 scoliotic subjects (13.7 ± 1.3 years, Cobb = 23.3° ± 8.5°). Using a larger set of markers, signed marker-to-surface differences were computed and appeared unbiased. Reproducibility on mesh nodes distribution was lower than 7mm. This study is a first step toward computer-aided brace design with a single examination.

Spectral Shape Analysis of Human Torsos: Application to the Evaluation of Scoliosis Surgery Outcome.

This paper aims at evaluating the effect of spinal surgery on the torso shape appearance of adolescent patients. Current methods that assess the surgical outcome on the trunk shape are limited to its global asymmetry or rely on unreliable manual measurements. We introduce a novel framework to evaluate pre- to postoperative local asymmetry changes using a spectral representation of the torso shape, more specifically, the Laplacian spectrum (eigenvalues and eigenvectors) of a graph. We conduct a statistical analysis on the eigenvalues to efficiently select the spectral space and determine the significant components between preop and postop groups. On the selected eigenvectors, we propose a local analysis based on the concept of Euler characteristic to detect their local maxima and minima, which are then used to compute local left-right (L-R) asymmetries of torso shape. On 49 patients with a thoracic spinal deformity, the method captures significant pre- to postoperative changes of asymmetry at the waist, shoulder blades, shoulders, and breasts. We have evaluated average correction rates for L-R asymmetry of the waist height (67%), shoulder-blade height (64%) and depth (67%), lateral offset between shoulder and neck (61%), and breast height (52%). Spectral torso shape analysis provides a novel approach to quantify the surgical correction of the scoliotic trunk from local shape asymmetry. The proposed method could help the surgeon to understand the impact of different spinal surgery strategies on the postoperative appearance and choose the one that should provide better patient's satisfaction.

Segmental torso masses in adolescent idiopathic scoliosis

BackgroundAdolescent idiopathic scoliosis is the most common type of spinal deformity whose aetiology remains unclear. Studies suggest that gravitational forces in the standing position play an important role in scoliosis progression, therefore anthropometric data is required to develop biomechanical models of the deformity. Few studies have analysed the trunk by vertebral level and none have performed investigations of the scoliotic trunk. The aim of this study was to determine the centroid, thickness, volume and estimated mass, for sections of the scoliotic trunk. MethodsExisting low-dose CT scans were used to estimate vertebral level-by-level torso masses for 20 female adolescent idiopathic scoliosis patients. ImageJ processing software was used to analyse the CT images and enable estimation of the segmental torso mass corresponding to each vertebral level. FindingsThe patients' mean age was 15.0 (SD 2.7) years with mean major Cobb angle of 52 (SD 5.9)° and mean patient weight of 58.2 (SD 11.6) kg. The magnitude of torso segment mass corresponding to each vertebral level increased by 150% from 0.6kg at T1 to 1.5kg at L5. Similarly, segmental thickness from T1–L5 increased inferiorly from a mean 18.5 (SD 2.2) mm at T1 to 32.8 (SD 3.4) mm at L5. The mean total trunk mass, as a percentage of total body mass, was 27.8 (SD 0.5) % which was close to values reported in previous literature. InterpretationThis study provides new anthropometric reference data on segmental (vertebral level-by-level) torso mass in adolescent idiopathic scoliosis patients, useful for biomechanical models of scoliosis progression and treatment.

Head and trunk mass and center of mass position estimations in able-bodied and scoliotic girls

Anthropometric tables are not applicable to calculate the scoliotic trunk mass and center of mass (COM). The purposes of this study were: (1) to estimate the head and trunk mass and COM in able-bodied and scoliotic girls using a force plate method, (2) to estimate head and trunk COM offset compared to those of the body, and (3) the use of mean ratios to estimate the head and trunk COM calculated in this study and that calculated according to a conventional three-dimensional (3D) method compared to the measured values. Twenty-one scoliotic and twenty able-bodied girls participated. The subjects stood upright with arms beside the trunk on a force plate that collected data at 60Hz for a period of 5s. The anteroposterior and mediolateral positions of the body COM were obtained from the mean center of pressure values. The height of the body COM was estimated by the reaction board method. Afterwards a body segment was displaced and changes in force plate readings were recorded and applied to estimate the head and trunk mass and COM. Trunk offset was defined as the difference between the COM of the body and head and trunk. The measured head and trunk COM was compared to values obtained by the mean ratios calculated from this study and given by the conventional 3D method. The relative head and trunk mass and the anteroposterior trunk offset were larger in scoliotic girls. The force plate method gave similar results to measured COM values for both groups underlying its capability to provide a more accurate estimation of COM related values. Thus, the use of mean ratios of 0.5538 and 0.6438 obtained in this study to estimate the head and trunk mass and COM position in scoliotic girls can overcome the main drawbacks of current anthropometric methods, if direct measurements cannot be taken.

Scoliosis Follow-Up Using Noninvasive Trunk Surface Acquisition

Adolescent idiopathic scoliosis (AIS) is a musculoskeletal pathology. It is a complex spinal curvature in a 3-D space that also affects the appearance of the trunk. The clinical follow-up of AIS is decisive for its management. Currently, the Cobb angle, which is measured from full spine radiography, is the most common indicator of the scoliosis progression. However, cumulative exposure to X-rays radiation increases the risk for certain cancers. Thus, a noninvasive method for the identification of the scoliosis progression from trunk shape analysis would be helpful. In this study, a statistical model is built from a set of healthy subjects using independent component analysis and genetic algorithm. Based on this model, a representation of each scoliotic trunk from a set of AIS patients is computed and the difference between two successive acquisitions is used to determine if the scoliosis has progressed or not. This study was conducted on 58 subjects comprising 28 healthy subjects and 30 AIS patients who had trunk surface acquisitions in upright standing posture. The model detects 93% of the progressive cases and 80% of the nonprogressive cases. Thus, the rate of false negatives, representing the proportion of undetected progressions, is very low, only 7%. This study shows that it is possible to perform a scoliotic patient's follow-up using 3-D trunk image analysis, which is based on a noninvasive acquisition technique.

A new method to include the gravitational forces in a finite element model of the scoliotic spine

The distribution of stresses in the scoliotic spine is still not well known despite its biomechanical importance in the pathomechanisms and treatment of scoliosis. Gravitational forces are one of the sources of these stresses. Existing finite element models (FEMs), when considering gravity, applied these forces on a geometry acquired from radiographs while the patient was already subjected to gravity, which resulted in a deformed spine different from the actual one. A new method to include gravitational forces on a scoliotic trunk FEM and compute the stresses in the spine was consequently developed. The 3D geometry of three scoliotic patients was acquired using a multi-view X-ray 3D reconstruction technique and surface topography. The FEM of the patients' trunk was created using this geometry. A simulation process was developed to apply the gravitational forces at the centers of gravity of each vertebra level. First the "zero-gravity" geometry was determined by applying adequate upwards forces on the initial geometry. The stresses were reset to zero and then the gravity forces were applied to compute the geometry of the spine subjected to gravity. An optimization process was necessary to find the appropriate zero-gravity and gravity geometries. The design variables were the forces applied on the model to find the zero-gravity geometry. After optimization the difference between the vertebral positions acquired from radiographs and the vertebral positions simulated with the model was inferior to 3 mm. The forces and compressive stresses in the scoliotic spine were then computed. There was an asymmetrical load in the coronal plane, particularly, at the apices of the scoliotic curves. Difference of mean compressive stresses between concavity and convexity of the scoliotic curves ranged between 0.1 and 0.2 MPa. In conclusion, a realistic way of integrating gravity in a scoliotic trunk FEM was developed and stresses due to gravity were explicitly computed. This is a valuable improvement for further biomechanical modeling studies of scoliosis.

Real time noninvasive assessment of external trunk geometry during surgical correction of adolescent idiopathic scoliosis

BackgroundThe correction of trunk deformity is crucial in scoliosis surgery, especially for the patient's self-image. However, direct visualization of external scoliotic trunk deformity during surgical correction is difficult due to the covering draping sheets.MethodsAn optoelectronic camera system with 10 passive markers is used to track the trunk geometry of 5 scoliotic patients during corrective surgery. The position of 10 anatomical landmarks and 5 trunk indices computed from the position of the passive markers are compared during and after instrumentation of the spine.ResultsInternal validation of the accuracy of tracking was evaluated at 0.41 +/- 0.05 mm RMS. Intra operative tracking during surgical maneuvers shows improvement of the shoulder balance during and after correction of the spine. Improvement of the overall patient balance is observed. At last, a minor increase of the spinal length can be noticed.ConclusionTracking of the external geometry of the trunk during surgical correction is useful to monitor changes occurring under the sterile draping sheets. Moreover, this technique can used be used to reach the optimal configuration on the operating frame before proceeding to surgery. The current tracking technique was able to detect significant changes in trunk geometry caused by posterior instrumentation of the spine despite significant correction of the spinal curvature. It could therefore become relevant for computer-assisted guidance of surgical maneuvers when performing posterior instrumentation of the scoliotic spine, provide important insights during positioning of patients.

Improving excellence in scoliosis rehabilitation: A controlled study of matched pairs

Physiotherapy programmes so far mainly address the lateral deformity of scoliosis, a few aim at the correction of rotation and only very few address the sagittal profile. Meanwhile, there is evidence that correction forces applied in the sagittal plane are also able to correct the scoliotic deformity in the coronal and frontal planes. So it should be possible to improve excellence in scoliosis rehabilitation by the implementation of exercises to correct the sagittal deformity in scoliosis patients. An exercise programme (physio-logic exercises) aiming at a physiologic sagittal profile was developed to add to the programme applied at the centre or to replace certain exercises or exercising positions. To test the hypothesis that physio-logic exercises improve the outcome of Scoliosis Intensive Rehabilitation (SIR), the following study design was chosen: Prospective controlled trial of pairs of patients with idiopathic scoliosis matched by sex, age, Cobb angle and curve pattern. There were 18 patients in the treatment group (SIR + physio-logic exercises) and 18 patients in the control group (SIR only), all in matched pairs. Average Cobb angle in the treatment group was 34.5 degrees (SD 7.8) Cobb angle in the control group was 31.6 degrees (SD 5.8). Age in the treatment group was at average 15.3 years (SD 1.1) and in the control group 14.7 years (SD 1.3). Thirteen of the 18 patients in either group had a brace. Outcome parameter: average lateral deviation (mm), average surface rotation ( degrees ) and maximum Kyphosis angle ( degrees ) as evaluated with the help of surface topography (Formetric-system). Lateral deviation (mm) decreased significantly after the performance of the physio-logic programme and highly significantly in the physio-logic ADL posture; however, it was not significant after completion of the whole rehabilitation programme (2.3 vs 0.3 mm in the controls). Surface rotation improved at average 1.2 degrees in the treatment group and 0.8 degrees in the controls while Kyphosis angle did not improve in both groups. The physio-logic programme has to be regarded as a useful 'add on' to Scoliosis Rehabilitation with regards to the lateral deviation of the scoliotic trunk. A longitudinal controlled study is necessary to evaluate the long-term effect of the the physio-logic programme also with the help of X-rays.

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.