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MODELLING SCOLIOSIS CORRECTION
Presentation 1243 − Topic 40. Spine biomechanics
S603
MODELLING SCOLIOSIS CORRECTION Gerdine Meijer (1,2), Jasper Homminga (1), Bert van Rietbergen (2), Chris Arts (3), Keita Ito (2), Bart Verkerke (1,4)
1. University of Twente, The Netherlands; 2. Eindhoven University of Technology, The Netherlands; 3. Maastricht University Medical Centre, The Netherlands; 4. University Medical Center Groningen, The Netherlands.
Introduction Scoliosis is a three-dimensional deformity of the human spine and trunk. To support the development of new surgical non-fusion techniques that correct the three-dimensional deformity, we have developed a numerical model of a scoliotic spine and trunk.
Methods The model is derived from a validated Finite Element model of a healthy adolescent trunk [Meijer 2010 & Meijer 2011] by subsequently changing it into a scoliotic adolescent model (figure 1). The simulated scoliotic deformation is characterised by a Cobb angle of 32 ° (T6-T10) and an axial rotation of 24 ° of the apex (T8).
resulting in a correction of both the Cobb angle (lateral curvature) and axial rotation. Long-term correction is simulated by multiple iteration steps. Adaptation of the soft tissues is modeled by resetting the strain to zero after each step. In each following step, the correctional moment is changed; as the trunk is corrected the loads applied by the implant decrease.
Results The applied torsional correction moment resulted in a correction of the axial and Cobb angle, which both increased over the subsequent steps (Table 1). Step 1 2 3
Correction moment 1.5 Nm 1.4 Nm 1.3 Nm
Correction in Cobb angle 1.6 ° 2.3 ° 2.8 °
Correction in axial rotation 1.8 ° 3.0 ° 4.0 °
Table 1: Applied moments and the resulting correction (cumulative over all previous steps).
Discussion
Figure 1: Posterior view of models of a healthy (left) and scoliotic (right) adolescent trunk. This model contains all relevant mechanical structures of the trunk: vertebrae and ribs are modelled as rigid bodies, intervertebral discs are modelled with incompressible nucleus and annuluses including linear fibres, ligaments are modelled with non-linear tension-only bars, facet and costovertebral joints are modelled as contact with non-linear force-penetration properties, intercostal and abdominal muscles are given a stiffness in correspondence with low activation levels, and the interabdominal pressure is modelled by an incompressible volume with an overpressure. Scoliosis correction is simulated by a torsional correction moment applied to the scoliotic model,
This study demonstrates the feasibility of modeling both the instantaneous and the long-term scoliosis correction by assuming total adaptation of the soft tissues. Major limitations of these long-term simulations are the unknown time scale for the adaptation of the soft tissues and the assumed decrease of the correction moment for each iteration step. By implementation of mechanical models of the new implants, the latter limitation can be solved. By implementing mechanical models of visco-elastic behavior and growth, a more realistic prediction of the long term behavior will be possible in the future.
Acknowledgement This research forms part of the Project P2.05 Spineguide of the research program of the BioMedical Materials institute, co-funded by the Dutch Ministry of Economic Affairs, Agriculture and Innovation.
References Meijer et al, J Biomech, 43:1590-97, 2010. Meijer et al, Spine, 36:E929-E935, 2011.
ESB2012: 18th Congress of the European Society of Biomechanics
Journal of Biomechanics 45(S1)
S603
MODELLING SCOLIOSIS CORRECTION Gerdine Meijer (1,2), Jasper Homminga (1), Bert van Rietbergen (2), Chris Arts (3), Keita Ito (2), Bart Verkerke (1,4)
1. University of Twente, The Netherlands; 2. Eindhoven University of Technology, The Netherlands; 3. Maastricht University Medical Centre, The Netherlands; 4. University Medical Center Groningen, The Netherlands.
Introduction Scoliosis is a three-dimensional deformity of the human spine and trunk. To support the development of new surgical non-fusion techniques that correct the three-dimensional deformity, we have developed a numerical model of a scoliotic spine and trunk.
Methods The model is derived from a validated Finite Element model of a healthy adolescent trunk [Meijer 2010 & Meijer 2011] by subsequently changing it into a scoliotic adolescent model (figure 1). The simulated scoliotic deformation is characterised by a Cobb angle of 32 ° (T6-T10) and an axial rotation of 24 ° of the apex (T8).
resulting in a correction of both the Cobb angle (lateral curvature) and axial rotation. Long-term correction is simulated by multiple iteration steps. Adaptation of the soft tissues is modeled by resetting the strain to zero after each step. In each following step, the correctional moment is changed; as the trunk is corrected the loads applied by the implant decrease.
Results The applied torsional correction moment resulted in a correction of the axial and Cobb angle, which both increased over the subsequent steps (Table 1). Step 1 2 3
Correction moment 1.5 Nm 1.4 Nm 1.3 Nm
Correction in Cobb angle 1.6 ° 2.3 ° 2.8 °
Correction in axial rotation 1.8 ° 3.0 ° 4.0 °
Table 1: Applied moments and the resulting correction (cumulative over all previous steps).
Discussion
Figure 1: Posterior view of models of a healthy (left) and scoliotic (right) adolescent trunk. This model contains all relevant mechanical structures of the trunk: vertebrae and ribs are modelled as rigid bodies, intervertebral discs are modelled with incompressible nucleus and annuluses including linear fibres, ligaments are modelled with non-linear tension-only bars, facet and costovertebral joints are modelled as contact with non-linear force-penetration properties, intercostal and abdominal muscles are given a stiffness in correspondence with low activation levels, and the interabdominal pressure is modelled by an incompressible volume with an overpressure. Scoliosis correction is simulated by a torsional correction moment applied to the scoliotic model,
This study demonstrates the feasibility of modeling both the instantaneous and the long-term scoliosis correction by assuming total adaptation of the soft tissues. Major limitations of these long-term simulations are the unknown time scale for the adaptation of the soft tissues and the assumed decrease of the correction moment for each iteration step. By implementation of mechanical models of the new implants, the latter limitation can be solved. By implementing mechanical models of visco-elastic behavior and growth, a more realistic prediction of the long term behavior will be possible in the future.
Acknowledgement This research forms part of the Project P2.05 Spineguide of the research program of the BioMedical Materials institute, co-funded by the Dutch Ministry of Economic Affairs, Agriculture and Innovation.
References Meijer et al, J Biomech, 43:1590-97, 2010. Meijer et al, Spine, 36:E929-E935, 2011.
ESB2012: 18th Congress of the European Society of Biomechanics
Journal of Biomechanics 45(S1)