Pedicle growth asymmetry as a cause of adolescent idiopathic scoliosis: a biomechanical study

Huynh, Anne-Marie; Aubin, Carl‐Éric; Rajwani, T.; Bagnall, K. M.; Villemure, Isabelle

doi:10.1007/s00586-006-0235-4

Cited by 50 publications

(26 citation statements)

References 25 publications

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“…Further, the relative motion between vertebrae was monitored to ensure segmental motion remained within physiologic range. Moreover, it was previously demonstrated that irregular pedicle growth did not produce scoliotic curves in a FEM [12]. Nevertheless, the authors recognize that if a contact between posterior elements occurred it may influence local relative displacements between adjacent segments.…”

Section: Discussionmentioning

confidence: 84%

Biomechanical comparison of fusionless growth modulation corrective techniques in pediatric scoliosis

Driscoll

Aubin

Moreau

et al. 2011

Med Biol Eng Comput

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Fusionless growth-sparing implants for the treatment of adolescent idiopathic scoliosis (AIS) attempt to manipulate vertebral growth to restore spinal alignment. This study critically explores different implants utilizing a human spine scoliotic finite element model (FEM). Stainless steel (SS) and shape memory alloy (SMA) staples and flexible tethers were modeled and alternatively integrated around the apex of the convexity of the scoliotic model. Stress profiles over vertebral growth plates were obtained. Two years of growth was simulated with non-instrumented and instrumented models, as curvature changes were quantified. Apical asymmetrical stresses in non-instrumented and instrumented scoliotic models with SS staple, flexible tether, and SMA staple were 0.48, 0.48, 0.23, and 0.33 MPa, respectively. Patient data and non-instrumented model progressed from 28° to 62° of thoracic Cobb angle over 2 years. Simulated projected long-term thoracic Cobb angles of instrumented models are 31° with SS staple, 31° with flexible tether, and 34° with SMA staple. Initial implant compression achieved during instrumentation provided a significant influence on initial and long-term spinal profiles. The developed FEM provides an effective platform with which to explore, critique, and enhance fusionless growth-sparing techniques.

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Section: Discussionmentioning

confidence: 84%

Biomechanical comparison of fusionless growth modulation corrective techniques in pediatric scoliosis

Driscoll

Aubin

Moreau

et al. 2011

Med Biol Eng Comput

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“…In the coronal plane, the centers of gravity were hypothetically assumed to be positioned along the scoliotic spine curve [2,10,29]. The influence of this simplifying hypothesis was not evaluated.…”

Section: Introductionmentioning

confidence: 99%

“…Computer models have been used to analyze the biomechanics of asymptomatic [1,15,18,24,25,31] and scoliotic spines [2,6,10,26,27,29]. To compute the stresses in the scoliotic spine, the gravitational forces were generally included in the models and sometimes an assumption about the muscles contribution was made.…”

Section: Introductionmentioning

confidence: 99%

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

Clin

Aubin

Lalonde

et al. 2011

Med Biol Eng Comput

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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.

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“…It is considered important for vertebral growth in the transverse plane [3,4,6,14,20]. NCS growth asymmetry can produce an axial deformity, which may result in three-dimensional deformity of the spine (scoliosis) [1,5,10,12,13]. We previously demonstrated a unilateral pedicle screw fixation, which traverses the NCS in an immature pig model, produced NCS epiphysiodesis on the operative side resulting in scoliosis with the convexity on the side of the screw fixation resulting from continued growth of the unaffected side [18].…”

Section: Introductionmentioning

confidence: 99%

Neurocentral Synchondrosis Screws to Create and Correct Experimental Deformity: A Pilot Study

Zhao

Sucato

2011

Clinical Orthopaedics &Amp; Related Research

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Background Unilateral pedicle screw epiphysiodesis of the neurocentral synchondrosis (NCS) can produce asymmetric growth of the synchondrosis to create scoliosis in an immature animal model. Questions/purposes We asked whether a preexisting experimentally created scoliosis could be limited and corrected by modulating the growth of the faster-growing NCS by a similar method. Methods Nine 1-month-old pigs were assigned to each of three groups: (1) a sham group in which three animals received a sham operation but without a pedicle screw fixation; (2) an experimental group with double right pedicle screws placed across the NCS from T7 to T14 (scoliosis-untreated); and (3) an experimental group treated in the same way except a second set of double pedicle screws was placed in the left pedicles 6 weeks after the screws were placed on the right (scoliosis-treated). All animals were euthanized at 17 weeks, and radiographs and axial CT images of the spine were obtained. Results A scoliotic curve was not seen in any of the animals in the sham group, in three of three in the scoliosisuntreated group with an average of 34°, and in three of three in the scoliosis-treated group with an average of 20°. In comparison to the scoliosis-untreated group, the second set of pedicle screws produced a 41% correction of the scoliosis. Conclusions We found the pedicle screw inhibited the overgrowth of the NCS to prevent further curve progression and obtained some correction of the deformity. The NCS screw epiphysiodesis can create and reverse scoliosis in an immature pig model.

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Pedicle growth asymmetry as a cause of adolescent idiopathic scoliosis: a biomechanical study

Cited by 50 publications

References 25 publications

Biomechanical comparison of fusionless growth modulation corrective techniques in pediatric scoliosis

Biomechanical comparison of fusionless growth modulation corrective techniques in pediatric scoliosis

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

Neurocentral Synchondrosis Screws to Create and Correct Experimental Deformity: A Pilot Study

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