Julien Clin

Preoperative Planning Simulator for Spinal Deformity Surgeries

Study Design. Proof of concept of a spine surgery simulator (S3) for the assessment of scoliosis instrumentation configuration strategies. Objective. To develop and assess a surgeon-friendly spine surgery simulator that predicts the correction of a scoliotic spine as a function of the patient characteristics and instrumentation variables. Summary of Background Data. There is currently no clinical tool sufficiently user-friendly, reliable and refined for the preoperative planning and prediction of correction using different instrumentation configurations. Methods. A kinetic model using flexible mechanisms has been developed to represent patient-specific spine geometry and flexibility, and to simulate individual substeps of correction with an instrumentation system. The surgeon-friendly simulator interface allows interactive specification of the instrumentation components, surgical correction maneuvers and display of simulation results. Results. The simulations of spinal instrumentation procedures of 10 scoliotic cases agreed well with postoperative results and the expected behavior of the instrumented spine (average Cobb angle differences of 3.5° to 4.6° in the frontal plane and of 3.6° to 4.7° in the sagittal plane). Forces generated at the implant-vertebra link were mostly below reported pull-out values, with more important values at the extremities of the instrumentation. Conclusion. The spine surgery simulator S3 has proven its technical feasibility and clinical relevance to assist in the preoperative planning of instrumentation strategies for the correction of scoliotic 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.

New brace design combining CAD/CAM and biomechanical simulation for the treatment of adolescent idiopathic scoliosis

BACKGROUND A numerical based brace design platform, including biomechanical simulation, Computer Aided Design and Computer Aided Manufacturing (CAD/CAM) was developed to rationalize braces for the treatment of adolescent idiopathic scoliosis. The objective of this study was to test the feasibility of the approach and assess the effectiveness of braces issued from this platform as compared to standard brace design. METHODS The biomechanical finite element model was built using the 3D reconstruction of the trunk skeleton from bi-planar radiographs and of the torso surface from surface topography. The finite element model is linked to a CAD/CAM software (Rodin4D), allowing the iterative design and simulation of the correction provided by the brace, as well as predicting pressures exerted on the torso. The resulting brace design was then fabricated using a numerical controlled carver. A brace designed using this platform (New Brace) as well as a standard thoraco-lumbo-sacral orthosis (Standard Brace) were built for six scoliotic patients. Both brace effectiveness was assessed using radiographs and compared to the simulations. FINDINGS The New Brace corrected on average the spine deformities within 5° of Cobb angle of the simulated correction and with a similar correction as compared to the Standard Brace (average correction of 16° vs. 11° (MT); P=0.1 and 13° vs. 16° (TL/L); P=0.5 for the Standard Brace and the New Brace respectively). The two braces had a similar 10° lordosing effect of the thoracic curve. The coronal balance was quite similar (7.3 vs. 6.8mm balance improvement respectively for New Brace vs. Standard Brace). INTERPRETATION These first clinical results showed the feasibility of building computer-assisted braces, equivalent to standard orthosis. An extended study on more cases is under way to fully assess this new design paradigm, which in the long term would allow improving brace design and rationalize the conservative treatments of scoliosis.

Biomechanical modeling of brace treatment of scoliosis: effects of gravitational loads

The biomechanics of bracing in adolescent idiopathic scoliosis is still not fully understood. Finite element models (FEM) have been used but the gravity forces were not included and the production of spinal stresses not evaluated. An improved FEM to simulate brace treatment was thus developed. The 3D geometry of the spine, rib cage, pelvis, and of the trunk external surface of five scoliotic patients was acquired using a multi-view X-ray technique and surface topography. A FEM of the patient’s trunk including gravity forces was created. Custom-fit braces were modeled and their installation simulated. Immediate geometrical corrections and pressures were computed and validated. The resulting compressive loads on the vertebral endplates were quantified. The influence of the strap tension, spine stiffness, and of the gravity forces was evaluated. Results showed that the brace biomechanical action was importantly to prevent the scoliotic spine from bending under the gravity forces. The immediate correction depended on the strap tension and spine stiffness. The distribution and amplitude of computed pressures were similar to those measured with the real braces. After the brace installation, the coronal asymmetrical compressive loading on the vertebral endplates was significantly reduced. In conclusion, the model developed presents improvements over previous models and could be used to better understand and optimize brace treatment.

Braces Optimized With Computer-Assisted Design and Simulations Are Lighter, More Comfortable, and More Efficient Than Plaster-Cast Braces for the Treatment of Adolescent Idiopathic Scoliosis

STUDY DESIGN Feasibility study to compare the effectiveness of 2 brace design and fabrication methods for treatment of adolescent idiopathic scoliosis: a standard plaster-cast method and a computational method combining computer-aided design and fabrication and finite element simulation. OBJECTIVES To improve brace design using a new brace design method. SUMMARY OF BACKGROUND DATA Initial in-brace correction and patients compliance to treatment are important factors for brace efficiency. Negative cosmetic appearance and functional discomfort resulting from pressure points, humidity, and restriction of movement can cause poor compliance with the prescribed wearing schedule. METHODS A total of 15 consecutive patients with brace prescription were recruited. Two braces were designed and fabricated for each patient: a standard thoracolumbo-sacral orthosis brace fabricated using plaster-cast method and an improved brace for comfort (NewBrace) fabricated using a computational method combining computer-aided design and fabrication software (Rodin4D) and a simulation platform. Three-dimensional reconstructions of the torso and the trunk skeleton were used to create a personalized finite element model, which was used for brace design and predict correction. Simulated pressures on the torso and distance between the brace and patients skin were used to remove ineffective brace material situated at more than 6 mm from the patients skin. Biplanar radiographs of the patient wearing each brace were taken to compare their effectiveness. Patients filled out a questionnaire to compare their comfort. RESULTS NewBraces were 61% thinner and had 32% less material than standard braces with equivalent correction. NewBraces were more comfortable (11 of 15 patients) or equivalent to (4 of 15 cases) standard braces. Simulated correction was simulated within 5° compared with in-brace results. CONCLUSIONS This study demonstrates the feasibility of designing lighter and more comfortable braces with correction equivalent to standard braces. This design platform has the potential to further improve brace correction efficiency and its compliance.

Biomechanical simulation and analysis of scoliosis correction using a fusionless intravertebral epiphyseal device.

Study Design. Computer simulations to analyze the biomechanics of a novel compression-based fusionless device (hemistaple) that does not cross the disc for the treatment of adolescent idiopathic scoliosis. Objective. To biomechanically model, simulate, and analyze the hemistaple action using a human finite element model (FEM). Summary of Background Data. A new fusionless growth sparing instrumentation device (hemistaple), which locally compresses the growth plate without spanning the disc, was previously developed and successively tested on different animal models. Methods. Patient-specific FEMs of the spine, rib cage, and pelvis were built using radiographs of 10 scoliotic adolescents (11.7 ± 0.9 yr; Cobb thoracic: 35° ± 7°, lumbar: 24° ± 6°). A validated algorithm allowed simulating the growth (0.8–1.1 mm/yr/vertebra) and growth modulation process (Hueter-Volkmann principle) during a period of 2 years. Four instrumentation configurations on the convex curves were individually simulated (Config 1: 5 thoracic vertebrae with hemistaples on superior endplates; Config 2: same as Config 1 with hemistaples on both endplates; Config 3: same as Config 1 + 4 lumbar vertebrae; Config 4: same as Config 2 + 4 lumbar vertebrae). Results. Without hemistaples, on average the thoracic and lumbar Cobb angles, respectively, progressed from 35° to 56° and 24° to 30°, whereas the vertebral wedging at curve apices progressed from 5° to 12°. With the hemistaple Config 1, the Cobb angles progressed but were limited to 42° and 26°, whereas the wedging ended at 8°. With Config 3, Cobb and wedging were kept nearly constant (38°, 21°, 7°). With hemistaples on both endplates (Config 2, Config 4), the Cobb and wedging were all reduced (thoracic Cobb for Config 2 and 4: 24° and 15°; lumbar Cobb: 21° and 11°; wedging: 2° and 1°). Conclusion. This study suggests that the hemistaple has the biomechanical potential to control the scoliosis progression and highlights the importance of the instrumentation configuration to correct the spinal deformities. It biomechanically supports the new fusionless device concept as an alternative for the early treatment of idiopathic scoliosis. Level of Evidence: 5

Biomechanical Assessment of Providence Nighttime Brace for the Treatment of Adolescent Idiopathic Scoliosis

STUDY DESIGN Biomechanical study of the Providence brace for the treatment of adolescent idiopathic scoliosis (AIS). OBJECTIVES To model and assess the effectiveness of Providence nighttime brace. SUMMARY OF BACKGROUND DATA Providence nighttime brace is an alternative to traditional daytime thoracolumbosacral orthosis for the treatment of moderate scoliotic deformities. It applies three-point pressure to reduce scoliotic curves. The biomechanics of the supine position and Providence brace is still poorly understood. METHODS Eighteen patients with AIS were recruited at our institution. For each patient, a personalized finite element model (FEM) of the trunk was created. The spine, rib cage, and pelvis geometry was acquired using simultaneous biplanar low-dose radiographs (EOS). The trunk surface was acquired using a three-dimensional surface topography scanner. The interior surface of each patients Providence brace was digitized and used to generate an FEM of the brace. Pressures at the brace/skin interface were measured using pressure sensors, and the average pressure distribution was computed. The standing to supine transition and brace installation were computationally simulated. RESULTS Simulated standing to supine position induced an average curve correction of 45% and 48% for thoracic and lumbar curves, while adding the brace resulted in an average correction of 62% and 64% (vs. real in-brace correction of 65% and 70%). Simulated pressures had the same distribution as measured ones. Bending moments on apical vertebrae were mostly annulled by the positioning in the supine position, and further overcorrected on average by 10% to 13%, but in the opposite direction. CONCLUSIONS The supine position is responsible for the major part of coronal curve correction, while the brace itself plays a complementary role. Bending moments induced by the brace generated a rebalancing of pressure on the growth plates, which could help reduce the asymmetric growth of the vertebrae. LEVEL OF EVIDENCE Level II.

Improved brace design combining CAD/CAM and finite element simulation for the conservative treatment of adolescent idiopathic scoliosis (AIS): preliminary results of a randomized control trial

Polytechnique Montreal, Montreal, Canada Full list of author information is available at the end of the article Figure 1 A) Acquisition of the internal geometry using the calibrated bi-planar radiographic 3D reconstruction technique; B) Acquisition of the external geometry using a surface topography system or a scan system; C) Internal 3D geometry; D) External 3D geometry E) Geometric registration F) Finite element model of the trunk Aubin et al. Scoliosis 2015, 10(Suppl 1):O59 http://www.scoliosisjournal.com/content/10/S1/O59

CAD/CAM and biomechanical simulations vs. standard technique for the design of braces in adolescent idiopathic scoliosis: first results

Methods So far, 4 AIS patients were recruited. Two braces were built for each patient: 1) a standard TLSO designed using the plaster-cast method (Std Brace), and 2) a brace designed and fabricated using a biomechanical 3D finite element model personalized to the patient’s geometry, and a CAD/CAM software (NewBrace). NewBrace was optimized using a computational brace simulator that allows virtual installation of the brace on the patient model, and prediction of its effect before fabrication. Several virtual braces were thus iteratively tested, and the one giving the best immediate correction was chosen for refinement by the orthotist, and fabricated using a computer-aided carver. Immediate brace effectiveness was assessed using radiographs in both braces. Results For the first 4 patients, the Std Brace corrected the thoracic and lumbar Cobb angles by 51% and 45% respectively, while NewBrace corrected these angles by 41% and 48%. There was little effect of the sagittal curves, and both braces maintained the coronal balance. The patients were more comfortable in the NewBrace. The predictions of the brace simulator were found to be reliable.

Biomechanical simulations of costo-vertebral and anterior vertebral body tethers for the fusionless treatment of pediatric scoliosis†

Compression‐based fusionless tethers are an alternative to conventional surgical treatments of pediatric scoliosis. Anterior approaches place an anterior (ANT) tether on the anterolateral convexity of the deformed spine to modify growth. Posterior, or costo‐vertebral (CV), approaches have not been assessed for biomechanical and corrective effectiveness. The objective was to biomechanically assess CV and ANT tethers using six patient‐specific, finite element models of adolescent scoliotic patients (11.9 ± 0.7 years, Cobb 34° ± 10°). A validated algorithm simulated the growth and Hueter–Volkmann growth modulation over a period of 2 years with the CV and ANT tethers at two initial tensions (100, 200 N). The models without tethering also simulated deformity progression with Cobb angle increasing from 34° to 56°, axial rotation 11° to 13°, and kyphosis 28° to 32° (mean values). With the CV tether, the Cobb angle was reduced to 27° and 20° for tensions of 100 and 200 N, respectively, kyphosis to 21° and 19°, and no change in axial rotation. With the ANT tether, Cobb was reduced to 32° and 9° for 100 and 200 N, respectively, kyphosis unchanged, and axial rotation to 3° and 0°. While the CV tether mildly corrected the coronal curve over a 2‐year growth period, it had sagittal lordosing effect, particularly with increasing initial axial rotation (>15°). The ANT tether achieved coronal correction, maintained kyphosis, and reduced the axial rotation, but over‐correction was simulated at higher initial tensions. This biomechanical study captured the differences between a CV and ANT tether and indicated the variability arising from the patient‐specific characteristics.