Biomedical subjects

C-E Aubin

Publications and source records attributed to C-E Aubin.

10 recordsLinked to original sources

PubMed2006

Finite-element analysis of geometrical factors in micro-indentation of pollen tubes.

Micro-indentation is a new experimental approach to assess physical cellular properties. Here we attempt to quantify the contribution of geometrical parameters to a cylindrical plant cell's resistance to lateral deformation. This information is important to correctly interpret data obtained from experiments using the device, such as the local cellular stiffness in pollen tubes. We built a simple finite-element model of the micro-indentation interacting partners - micro-indenter, cell (pollen tube), and underlying substratum, that allowed us to manipulate geometric variables, such as geometry of the cell, cell radius, thickness of the cell wall and radius of the indenting stylus. Performing indentation experiments on this theoretical model demonstrates that all four parameters influence stiffness measurement and can therefore not be neglected in the interpretation of micro-indentation data.

Elasticity↗

PubMed2006

Biomechanical modeling of anterior spine instrumentation in AIS.

This study is part of a larger project regarding the development of a Spine Surgery Simulator (S3), which has shown good results for posterior instrumentation surgeries. The aim was to develop a biomechanical model for the anterior instrumentation of the scoliotic spine. A biomechanical model using flexible mechanism was developed and surgical manoeuvres (instrumentation, rod installation and compression) were reproduced. Validation of the model was done by comparing the results for the instrumented part of the spine to the post-operative data (analytical Cobb angles in the frontal and sagittal planes, plane of maximum deformity, etc.). To date, surgeries of four patients operated by thoracotomy were reproduced. Preliminary results show that anterior instrumentation of the scoliotic spine can be adequately modelled using pre-operative geometric data and using mechanical properties from literature. Once validated with a larger sample of cases, the anterior instrumentation model could be implemented into S3 and used by orthopaedic surgeons to test various instrumentation strategies in virtual reality before performing the actual surgery.

Adolescent↗

PubMed2004

Thoracic pedicle screw insertion using a transpedicular drill guide: a preliminary study.

Insertion of thoracic pedicle screws can lead to major complications. This study reports the use of a transpedicular drill guide (TDG) for safe pedicle screw insertion in the thoracic spine. The conventional anatomic technique and the TDG were both used to drill pilot holes into the pedicles of four anatomic models of the thoracic spine. Ninety-nine percent of the 96 pilot holes drilled with the TDG were within 2 mm from the pedicle wall compared with 79% for the anatomic technique (P < 0.001). The TDG reduced the proportion and the extent of medial perforations. The TDG was easy to use and was superior to the conventional anatomic technique. It could be combined with fluoroscopy and pedicle palpation in certain clinical applications, especially for training surgeons, but only after confirming its accuracy in a cadaveric study.

Bone Screws↗

PubMed2003

Biomechanical modeling of posterior instrumentation of the scoliotic spine.

Scoliosis is a three-dimensional deformation of the spine that can be treated by vertebral fusion using surgical instrumentation. However, the optimal configuration of instrumentation remains controversial. Simulating the surgical maneuvers with personalized biomechanical models may provide an analytical tool to determine instrumentation configuration during the pre-operative planning. Finite element models used in surgical simulations display convergence difficulties as a result of discontinuities and stiffness differences between elements. A kinetic model using flexible mechanisms has been developed to address this problem, and this study presents its use in the simulation of Cotrel-Dubousset Horizon surgical maneuvers. The model of the spine is composed of rigid bodies corresponding to the thoracic and lumbar vertebrae, and flexible elements representing the intervertebral structures. The model was personalized to the geometry of three scoliotic patients (with a thoracic Cobb angle of 45 degrees, 49 degrees and 39 degrees ). Binary joints and kinematic constraints were used to represent the rod-implant-vertebra joints. The correction procedure was simulated using three steps: (1) Translation of hooks and screws on the first rod; (2) 90 degrees rod rotation; (3) Hooks and screws look-up on the rod. After the simulation, slight differences of 0-6 degrees were found for the thoracic spine scoliosis and the kyphosis, and of 1-8 degrees for the axial rotation of the apical vertebra and for the orientation of the plane of maximum deformity, compared to the real post-operative shape of the patient. Reaction loads at the vertebra-implant link were mostly below 1000 N, while reaction loads at the boundary conditions (representing the overall action of the surgeon) were in the range 7-470 N and maximum torque applied to the rod was 1.8 Nm. This kinetic modeling approach using flexible mechanisms provided a realistic representation of the surgical maneuvers. It may offer a tool to predict spinal geometry correction and assist in the pre-operative planning of surgical instrumentation of the scoliotic spine.

Adolescent↗

PubMed2002

Biomechanical simulation of Colorado instrumentation of the scoliotic spine: a preliminary study.

Few biomechanical models of the scoliotic spine were developed to simulate the Cotrel-Dubousset instrumentation, although none was dedicated to the Colorado system. The objective of this study is to adapt and assess an existing biomechanical model to simulate the effect of the Colorado instrumentation of the scoliotic spine as a function of pre-operative geometry and surgical planning. Fifteen scoliotic patients operated with a Colorado system were analysed using a knowledge extraction technique to simplify surgical procedure and to establish the biomechanical model (boundary conditions, simulation procedures,...). Preliminary results on one patient show that the Colorado surgical technique can be adequately modelled using the preoperative geometric data and limited simulation strategy parameters.

Biomechanical Phenomena↗

PubMed2002

Feasibility study of patient-specific surgical templates for the fixation of pedicle screws.

Surgery for scoliosis, as well as other posterior spinal surgeries, frequently uses pedicle screws to fix an instrumentation on the spine. Misplacement of a screw can lead to intra- and post-operative complications. The objective of this study is to design patient-specific surgical templates to guide the drilling operation. From the CT-scan of a vertebra, the optimal drilling direction and limit angles are computed from an inverse projection of the pedicle limits. The first template design uses a surface-to-surface registration method and was constructed in a CAD system by subtracting the vertebra from a rectangular prism and a cylinder with the optimal orientation. This template and the vertebra were built using rapid prototyping. The second design uses a point-to-surface registration method and has 6 adjustable screws to adjust the orientation and length of the drilling support device. A mechanism was designed to hold it in place on the spinal process. A virtual prototype was build with CATIA software. During the operation, the surgeon places either template on patient's vertebra until a perfect match is obtained before drilling. The second design seems better than the first one because it can be reused on different vertebra and is less sensible to registration errors. The next step is to build the second design and make experimental and simulations tests to evaluate the benefits of this template during a scoliosis operation.

Bone Screws↗

PubMed2002

Evolution of 3D deformities in adolescents with progressive idiopathic scoliosis.

The objective of this study was to conduct an intrasubject longitudinal study quantifying the evolution of two- and three-dimensional geometrical scoliotic descriptors. The evolution of regional and local scoliotic descriptors was analyzed between two scoliotic visits on a cohort of 28 adolescents with progressive idiopathic scoliosis. Mean age at the first visit was 12.7 +/- 1.7 years old and averaged time interval between two assessments reached 22.8 +/- 10.8 months. Scoliotic descriptors were obtained from three-dimensionally reconstructed spines. The initial thoracic Cobb angle was on average 35.3 degrees +/- 8.4 degrees (range, 14 degrees-54 degrees). The evolution of spinal curvatures and vertebral deformities was assessed statistically in terms of descriptor absolute variations, and of descriptor variations normalized with respect to time and to the increase in Cobb angle. At the thoracic level, vertebral wedging increased with curve severity in a relatively consistent pattern for most scoliotic patients and axial rotation mainly increased towards curve convexity with scoliosis severity. No consistent evolution was associated with the angular orientation of the maximum wedging. Thoracic kyphosis changes (increase and decrease) were observed in important proportions. Results of this study challenge the existence of a typical scoliotic evolution pattern and suggest that the scoliotic evolution is quite variable and patient-specific.

Adolescent↗

PubMed2002

Spinal mobility and EMG activity in idiopathic scoliosis through dynamic lateral bending tests.

Lateral bending test is a common evaluation of AIS patients prior to their surgical correction. Traditionally this evaluation is made by the assessment of the curve's flexibility from side-bending radiographs. As a complement to this static test, dynamic bending was experimented while simultaneously quantifying muscular and kinematic behavior of the spine. The biggest contribution to total EMG output was 36% from lumbar muscles in healthy and 35% from abdominal muscles in scoliotic subjects. Continuous measuring of kinematics and muscle activation patterns throughout lateral bending could be an evaluation tool for distinguishing pathological from normal behavior.

Abdominal Muscles↗

PubMed2002

Study of patient positioning on a dynamic frame for scoliosis surgery.

The goal of this clinical trial was to measure patient geometry on a dynamic positioning frame in various prone positions. Fourteen subjects (2 males and 12 females) were recruited from the scoliosis clinic at Ste-Justine Hospital on a volunteer basis. The subjects were AIS patients who were potential candidates for surgery. The Cobb angle, averaged 50 degrees (32 degrees-64 degrees). The mean age was 14.1 years (11-17). A Polaris system (Northern Digital inc, Canada) with 10 passive reflective markers was used to measure various indices of the patient's trunk geometry. Acquisitions were made while the unanaesthetized patient was in five different prone positions: I similar to the standard positioning on a Relton-Hall frame; II addition of a force applied to the ribcage at the apex of the curve; III application of a force at the apex of the curve in the lumbar region; IV, the shoulder pads were elevated to increase the patient's kyphosis; V adjustment of each pad and the application of thoracic and lumbar forces to obtain an optimal correction. The measurements of trunk geometry at each position were compared using position I as a base. A paired student t-test determined a significant difference between positions. When comparing position I to position II there was a significant difference and correction of the rib hump. There was also a significant change in shoulder angle that resulted in over correction. Position III had a significantly negative change in the rib hump. During position IV, there was a measurable increase in kyphosis. During the optimal correction, position V, a significant increase in spine length was observed as well as a significant correction in rib hump and shoulder angle. Patient trunk geometry can be improved by the application of different forces on a dynamic positioning frame. Caution is necessary as over correction and unintended negative effects were observed. The optimal patient position has not yet been found and future studies are directed at determining this.

Adolescent↗

PubMed2002

Spinal surgery procedure discretization.

In the last decades, scientists developed analytic models of spinal surgery to assess surgical choices and instrumentation parameters. They noted the difficulty to represent the boundary conditions on their deterministic models and recognize the lack of knowledge in surgical procedures. This paper presents a formalization technique applied to spinal surgery to improve the formulation of biomechanical models. This technique consisted into two steps: knowledge extraction and knowledge representation. The protocol was established with an expert surgeon using Colorado2 instrumentation. Surgeon's knowledge acquisition has permitted to define eleven detailed independent data cards for the different steps of surgery like hook or screw insertion, rod installation, etc... The behaviour of the concerned elements on its neighbouring entity were specified using three matrices. The link between surgery and modelling becomes easier and permits to better define the boundary conditions on each entity during the simulation.

Artificial Intelligence↗