Archana Sangole

Three-dimensional Classification of Thoracic Scoliotic Curves

Study Design. Three-dimensional (3D) characterization of the thoracic scoliotic spine (cross-sectional study). Objectives. To investigate the presence of subgroups within Lenke type-1 curves by evaluating the thoracic segment indices extracted from 3D reconstructions of the spine, and to propose a new clinically relevant means (the daVinci representation) to report 3D spinal deformities. Summary of Background Data. Although scoliosis is recognized to be a 3D deformity of the spine its measurement and classification have predominantly been based on radiographs which are 2D projections in the coronal and sagittal planes. Methods. Thoracic segment indices derived from 3D reconstructions of coronal and sagittal standing radiographs of 172 patients with right thoracic adolescent idiopathic scoliosis, reviewed by the 3D Classification Committee of the Scoliosis Research Society, were analyzed using the ISOData unsupervised clustering algorithm. Four curve indices were analyzed: Cobb angle, axial rotation of the apical vertebrae, orientation of the plane of maximum curvature of the main thoracic curve, and kyphosis (T4–T12). No assumptions were made regarding grouping tendencies in the data nor were the number of clusters predefined. Results. Three primary groups were revealed wherein kyphosis and the orientation of the PMC of the main thoracic curve were the major discriminating factors with slight overlap between groups. A small group (G1) of 22 patients having smaller, nonsurgical (minor) curves was identified. Although the remaining patients had similar Cobb angles they were split into 2 groups (G2: 79 patients; G3: 71 patients) with different PMC (G2: 65°–81°; G3: 76°–104°) and kyphotic measures (G2: 23°–43°; G3: 7°–25°). Conclusion. Two distinct subgroups within the surgical cases (major curves) of Lenke type-1 curves were found thus suggesting that thoracic curves are not always hypokyphotic. The ISOData cluster analysis technique helped to capture inherent 3D structural curve complexities that were not evident in a 2D radiographic plane. The daVinci representation is a new clinically relevant means to report 3D spinal deformities.

Comparison of the biomechanical 3D efficiency of different brace designs for the treatment of scoliosis using a finite element model

The biomechanical influence of thoraco-lumbo-sacral bracing, a commonly employed treatment in scoliosis, is still not fully understood. The aim of this study was to compare the immediate corrections generated by different virtual braces using a patient-specific finite element model (FEM) and to analyze the most influential design factors. The 3D geometry of three patients presenting different types of curves was acquired with a multi-view X-ray technique and surface topography. A personalized FEM of the patients’ trunk and a parametric model of a virtual custom-fit brace were then created. The installation of the braces on the patients was simulated. The influence of 15 design factors on the 3D correction generated by the brace was evaluated following a design of experiments simulation protocol allowing computing the main and two-way interaction effects of the design factors. A total of 12,288 different braces were tested. Results showed a great variability of the braces effectiveness. Of the 15 design factors investigated, according to the 2 modalities chosen for each one, the 5 most influential design factors were the position of the brace opening (posterior vs. anterior), the strap tension, the trochanter extension side, the lordosis design and the rigid shell shape. The position of the brace opening modified the correction mechanism. The trochanter extension position influenced the efficiency of the thoracic and lumbar pads by modifying their lever arm. Increasing the strap tension improved corrections of coronal curves. The lordosis design had an influence in the sagittal plane but not in the coronal plane. This study could help to better understand the brace biomechanics and to rationalize and optimize their design.

Classification of Scoliosis Deformity Three-Dimensional Spinal Shape by Cluster Analysis

Study Design. Cluster analysis of existing database of spinal shape of patients attending a scoliosis clinic. Objective. To determine whether patients with scoliosis can be classified into distinct groups by 3-dimensional curve shape. Summary of Background Data. Subjective or semiquantitative methods can be used to classify curve types in scoliosis, with the goal of rationalizing surgical planning. There are very few reports of using objective methods such as cluster analysis to improve this process. Methods. One hundred ten patients who underwent radiography of the spine by a stereo technique, at a scoliosis clinic in the period between 1982 and 1990, were studied. Fifty-six were studied longitudinally (average 3.4 clinic visits each), providing 245 total observations. Selected patients had 2 scoliosis curves with apex between T4 and L3, and both Cobb angles >9° by an automated measurement. The 3-dimensional spinal shape was reconstructed from stereoradiographs. Each curve was quantified by its Cobb angle, apex level, apex vertebra rotation, and rotation of the plane of maximum curvature (PMC) (8 variables). Cluster analysis classified each patient at each visit by these variables. Results. When the analysis searched for 4 clusters, the largest cluster (148 of 245 observations) was the pattern having counterclockwise rotation of the PMC of both curves (typically, a right upper scoliosis curve with kyphosis and left lower scoliosis curve with lordosis). The other 3 clusters (48, 34, and 15 observations) were the other permutations of these variables. Substantial overlap of all the other variables between groups was observed. Of the 56 patients seen longitudinally, 25 were consistently grouped at all clinic visits. Conclusion. Spinal shape of patients in a clinic population with 2 scoliosis curves form distinct groups according to the 4 permutations of the signs of the rotations of the PMC in 2 curve regions. The pattern can change with repeated observation, often because a slight curvature in the sagittal plane can change because of postural variation and measurement errors. Overlap of the other curve-shape variables between groups suggests that these spinal deformity classifications alone should not determine treatment strategy.

Computer simulation for the optimization of instrumentation strategies in adolescent idiopathic scoliosis

Recent studies reveal a large variability of instrumentation strategies in adolescent idiopathic scoliosis (AIS). Determination of the optimal configuration remains controversial. This study aims to develop a method to define the optimal surgical instrumentation strategy using a computer model implemented in a spine surgery simulator (S3). A total of 702 different strategies were simulated on a scoliotic patient using S3. Each configuration was assessed using objective functions that represented different correction objectives. Twelve geometric parameters were used in the three anatomic planes and mobility, and their relative weights were defined by a spine surgeon according to his objectives for correction of scoliosis. Six instrumentation parameters were manipulated in a uniform experimental design framework. An interpolation technique was used to build an approximation model from the simulation results and to locate instrumentation parameters minimizing the objective function. Small or no differences in the correction between the simulated optimal strategy and the real postoperative results of the instrumented segments were observed in the three planes. But the same overall correction was obtained by using fewer implants (only screws) and less instrumented levels. This study demonstrates the potential and feasibility of using a spine surgery simulator to optimize the planning of surgical instrumentation in AIS.

The central hip vertical axis: a reference axis for the Scoliosis Research Society three-dimensional classification of idiopathic scoliosis.

Study Design. Reliability comparison of 2 radiographic axis systems by inter- and intraobserver variability. Objective. To determine whether the central hip vertical axis (CHVA) provides a more reliable reference axis for the evaluation of scoliosis. Summary of Background Data. Current practices in the evaluation of the scoliotic spine use the central sacral vertical line (CSVL), a true vertical drawn upward from the middle of S1, to assess the spinal deformity. However, the CVSL is defined only in the coronal radiographic view and has no corresponding definition in the sagittal view. Therefore, it represents a 2-dimensional positioning of the scoliotic segments relative to the pelvis. In view of this limitation, the Scoliosis Research Society 3-dimensional (3D) scoliosis committee proposed the CHVA, a true vertical bisecting the line segment joining the centers of the 2 femoral heads, as a reference line for the 3D evaluation of the spinal deformity. Unlike the CSVL, the CHVA can be identified in both radiographic views (coronal and sagittal) and has been shown to represent the physiologic center of balance of the spino-pelvic unit. Methods. A vertical axis was established on preoperative radiographs of 68 Lenke 1 main thoracic curves twice by 5 members of the Scoliosis Research Society 3D scoliosis committee assisted by dedicated software. The user digitized separately on the postero-anterior radiographs, the lateral borders of the S1 facets (for the CSVL), and 3 points on the 2 femoral heads (for the CHVA). The software then drew lines representing both axes. Then the observers determined the lumbar modifier (A, B, and C) using both axes. Results. There was no intra- and interobserver difference in the position of the CHVA (P > 0.1; SD: 0.4 mm), whereas intraobserver differences were found for the CSVL (P < 0.00007; SD: 0.9 mm). The CHVA was more reproducible and showed better intra- and interobserver agreement (kappa: 0.86/0.75; both excellent reliability), when compared with the CSVL (kappa 0.77/0.61; excellent and good reliability, respectively) for the identification of the lumbar modifier. The CSVL was on average 3.2 mm to the left, when compared with the CHVA generating a shift (A→B→C) in the assignment of the lumbar modifier. Conclusion. The CHVA is more reproducible and showed better intra- and interobserver agreement, when compared with the CSVL for the identification of the lumbar modifier. The CHVA can be easily computed in 3D and represents the physiologic center of balance of the spino-pelvic unit because it takes into account femoral head support. We recommend keeping the CSVL for 2-dimensional measurement to adapt the measures relative to the CSVL to the proposed CHVA axis and adopting CHVA as the reference axis for 3D evaluation of idiopathic scoliosis.

Characterizing pelvis dynamics in adolescent with idiopathic scoliosis.

Study Design. Pelvic dynamic analysis in adolescents with idiopathic scoliosis (AIS). Objective. To examine and characterize pelvis dynamics in AIS. Summary of Background Data. Although studies have examined spine and pelvis postural differences between female adolescents with and without scoliosis much is still unknown about the dynamics of pelvis in trunk-pelvic interaction and how the type of scoliosis compromises pelvic mobility consequently affecting the overall dynamics of the trunk-pelvis kinematic chain. Methods. A total of 25 female AIS (18 right thoracic: RT and 7 right thoracic-left lumbar: RTLL) and 12 controls were recruited. Reflective markers were placed on the trunk and pelvis and their trajectories were recorded using a 5-camera motion capture system. Three trials were carried out, one for each of the various trunk-pelvis movements (flexion/extension, lateral bend, and axial rotation on either side) performed by the subjects. Results. Pelvic alignment in the 3 planes were significantly different for all movement types (P < 0.001), with distinct differences in pelvic sagittal tilt and transverse plane rotation, particularly during lateral bending and axial rotation in patients with RT and LL curves (P = 0.035, P = 0.006, respectively). A majority of the patients from the 2 scoliotic groups had the pelvis rotated to the side of the major curve (right). Although RT subjects had similar dynamic pelvic responses as the controls, the RT-LL patients had relatively more pelvic sagittal tilt during lateral bending and axial rotation toward the major curve. Conclusion. In AIS, the initial three-dimensional alignment of the pelvis (sagittal and frontal tilt, transverse plane rotation) plays an essential role in dictating the biomechanics of the pelvis for any movement type. A spatial concurrency in pelvic alignment was noted wherein a change in 1 parameter will affect the remaining 2. Increased pelvic sagittal tilt in the RT-LL subjects was substituted by more pelvic rotation in the RT subjects during trunk flexion/extension. Differences in pelvic dynamics in AIS are not evident in discrete parameters, for example, total ranges-of-motion but more so in its biomechanics during the movement, which in turn is dictated by the initial alignment of the pelvis.

Three-dimensional spinopelvic relative alignment in adolescent idiopathic scoliosis.

Study Design. Three-dimensional (3D) analysis of the spinopelvic alignment in adolescent idiopathic scoliosis (AIS). Objective. To study the 3D pelvic alignment with respect to the spinal deformities in AIS subgroups. Summary of Background Data. Spinopelvic alignment is subject to change in scoliosis. Many sacropelvic parameters were developed to characterize spinopelvic alignment in the sagittal plane. However, not much is known about the 3D pelvic alignment with respect to the thoracic and lumbar spinal deformities in AIS. Methods. Eighty AIS subjects with right main thoracic (MT), 80 AIS with left thoracolumbar/lumbar (TL/L) curves, and 35 asymptomatic controls were included. Thoracic and lumbar Cobb angles, kyphosis, lordosis, pelvic incidence, pelvic tilt, and sacral slope were measured. Pelvic tilt and axial rotation in the coronal and transverse planes, respectively, were computed using the ipsilateral anterior superior iliac spine and posterior superior iliac spine positions. Leg length discrepancy was determined by the vertical difference in the position of the center of the femoral heads in the coronal plane. Results. In 59% of the MT subjects and 79% of the TL/L subjects in the erect position, the pelvis was tilted toward the convex side of the major curve in the coronal plane. The direction of the pelvic axial rotation in the transverse plane was in the same direction as the MT apical vertebra rotation in 84% of the MT subjects and 55% of the TL/L group. The pelvic incidence correlated to the lumbar lordosis in AIS (r = 0.41, P < 0.001). Pelvic coronal tilt correlated significantly to the leg length discrepancy in MT (r = 0.67) and TL/L (r = 0.61) subjects (P < 0.001). Conclusion. Novel pelvic parameters were introduced to characterize the spinopelvic relative alignment in scoliotic subgroups. The proposed method related the orientation of the pelvis in the coronal and transverse planes to both thoracic and lumbar spinal deformities. Level of Evidence: III

Fuzzy-logic-assisted surgical planning in adolescent idiopathic scoliosis.

Summary of Background Data Selection of appropriate curve fusion levels for surgery in adolescent idiopathic scoliosis (AIS) is a complex and difficult task and, despite numerous publications, still remains a highly controversial topic. Objective To evaluate a fuzzy-logic–based surgical planning tool by comparing the results suggested by the software with the average outcome recommended by a panel of 5 expert spinal deformity surgeons. It is hypothesized that, given the same information, the fuzzy-logic tool will perform as favorably as the surgeons. Study Design Proof-of-concept study evaluating the use of a fuzzy-logic–assisted surgical planning tool in AIS to select the appropriate spinal curve to be instrumented. Methods A cohort of 30 AIS surgical cases with a main thoracic curve was used. Each case included standard measurements recorded from preoperative standing postero-anterior and lateral, supine side bending, and 1-year postoperative standing radiographs. Five experienced spinal deformity surgeons evaluated each case independently and gave their preferred levels of instrumentation and fusion. The cases were then presented to the fuzzy-logic tool to determine whether the high thoracic and/or lumbar curves were to be instrumented. For each case, a percentage value was obtained indicating inclusion/exclusion of the respective curves in the surgical instrumentation procedure. Kappa statistics was used to compare the model output and the average decision of the surgeons. Results Kappa values of 0.71 and 0.64 were obtained, respectively, for the proximal thoracic and lumbar curves models, thus suggesting a good agreement of the fusion recommendations made by the fuzzy-logic tool and the surgeons. Conclusions Given the same information, the fuzzy-logic–assisted recommendation of the curve to be instrumented compared favorably with the collective decision of the surgeons. The findings thus suggest that a fuzzy-logic approach is helpful in assisting surgeons with the preoperative selection of curve instrumentation and fusion levels in AIS.

Preoperative assessment and evaluation of instrumentation strategies for the treatment of adolescent idiopathic scoliosis: computer simulation and optimization.

BackgroundA large variability in adolescent idiopathic scoliosis (AIS) correction objectives and instrumentation strategies was documented. The hypothesis was that different correction objectives will lead to different instrumentation strategies. The objective of this study was to develop a numerical model to optimize the instrumentation configurations under given correction objectives.MethodsEleven surgeons from the Spinal Deformity Study Group independently provided their respective correction objectives for the same patient. For each surgeon, 702 surgical configurations were simulated to search for the most favourable one for his particular objectives. The influence of correction objectives on the resulting surgical strategies was then evaluated.ResultsFusion levels (mean 11.2, SD 2.1), rod shapes, and implant patterns were significantly influenced by correction objectives (p < 0.05). Different surgeon-specified correction objectives produced different instrumentation strategies for the same patient.ConclusionsInstrumentation configurations can be optimized with respect to a given set of correction objectives.

Shape metamorphosis using deformable spherical maps

The transformation of a surface mesh from one form to another requires information about object geometry and node topology. Establishing a valid correspondence between the mesh nodes of the two bounding objects is critical for smooth shape deformation. The complexity of the task is increased if the meshes are originally created from separate sets of measured surface data. The shape transformation technique described in this paper utilizes a self-organizing feature map (SOFM), with a fixed number of nodes and known spherical topology, to fit a tessellated surface mesh around the reference data set. The nodal mesh is then allowed to gradually deform and assume the underlying geometry of the target data set. The mesh deformation is achieved through an unsupervised learning algorithm that iteratively modifies the location of nodes based on randomly selected coordinate points from the target surface. Furthermore, regional shape changes occur because the algorithm adjusts the location of nearest neighboring nodes in the evolving mesh. The correspondence between the neighboring nodes in the two bounding shapes is maintained during the intermediate stages of shape interpolation process. The algorithms performance is illustrated using scanned surface data from several freeform objects.