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PEDICLE GROWTH ASYMMETRY AS A CAUSE OF ADOLESCENT IDIOPATHIC SCOLIOSIS: A BIOMECHANICAL SIMULATION STUDY

¹ Ecole Polytechnique & ² Sainte-Justine University Hospital Centre; Montreal, Canada ³ University of Alberta, Edmonton, Canada.

Background: The neurocentral junction often has been identified as a potential cause of adolescent idiopathic scoliosis (AIS). Disparate growth at this site has been thought to lead to pedicle asymmetry, which then causes vertebral rotation in the transverse plane and ultimately, the development of scoliotic curves.

Objectives:

1. To develop a model that incorporates pedicle growth and growth modulation into an existing finite element model of the thoracic and lumbar spine already integrating vertebral growth and growth modulation
   
2. Using the model to investigate whether pedicle asymmetry, either alone or combined with other deformations, could be involved in scoliosis pathomechanisms.
   

Methods: The model was personalised to the geometry of a non-pathological subject and used as the reference spinal configuration. Left/right asymmetry of pedicle geometry (i.e. initial length) and left/right asymmetry of the pedicle growth rate alone or in combination with other AIS potential pathogenesis (anterior, lateral, or rotational displacement of apical vertebra) were simulated over a period of 24 months. The Cobb angle and local scoliotic descriptors (wedging angle, axial rotation) were assessed at each monthly growth cycle.

Results: Simulations with asymmetrical pedicle geometry did not produce significant scoliosis, vertebral rotation or wedging. Simulations with asymmetry of pedicle growth rate did not cause scoliosis independently and did not amplify the scoliotic deformity caused by other initial deformations tested by Villemure (2004).

Discussion and Conclusion: The results of this biomechanical model do not support the hypothesis that asymmetrical neurocentral junction growth is a cause of AIS. This concurs with recent animal experiments in which neurocentral junction growth was unilaterally restricted and no scoliosis, vertebral wedging or rotation was noted. With regards to addressing the aetiology of scoliotic curve development, biomechanical modelling represents a powerful tool to investigate cause and affect relationships since AIS patients typically present to the scoliosis clinic well after curves have manifested.

Contact person and Presenter: Carl-Éric Aubin, Ph.D., Canada Research Chair "CAD Innovations in Orthopedic Engineering", Department of Mechanical Engineering, Ecole Polytechnique, Montreal, Canada, Tel: (514) 340-4711, ext. 4437; Fax: (514) 340-5867; E-mail: carl-eric.aubin{at}polymtl.ca

Correspondence should be addressed to Jeremy C T Fairbank at The Nuffield Orthopaedic Centre, Windmill Road, Headington, Oxford OX7 7LD, UK