Abstract
Introduction: Contemporary surgical interventions for adolescent idiopathic scoliosis (AIS) include both anterior and posterior rod systems, in which a single or double rod construct provides curve correction and stability. This paper presents a methodology for development of patient-specific finite element methods to predict the biomechanical outcomes of scoliosis surgery pre-operatively, with the aim of optimising the performance of instrumentation constructs for anterior single rod AIS surgery.
Methods: Geometry for each patient-specific finite element model is obtained from pre-operative thoracolumbar CT scans taken in the supine position using a low dose multi-slice imaging protocol. The finite element model incorporates vertebrae, intervertebral discs, and posterior processes with associated ligaments and zygapophysial joints. A custom pre-processor generates the entire model according to user-specified meshing parameters, providing rapid model generation once the geometric parameters have been extracted from each CT dataset. Material properties are currently based on published values. Simulated movements about axes corresponding to flexion/extension, left/right lateral bending, and trunk rotation are solved using the ABAQUS/Standard software, allowing assessment of predicted loads and stresses before and after addition of instrumentation.
Results: The total time per patient required for model generation is currently about six hours, with manual measurement of spine geometry from the CT stack accounting for most of this time. Actual solution time for each finite element model is expected to be around four hours, making patient-specific pre-operative planning for endoscopic scoliosis surgery a feasible option at least in terms of processing time per patient.
Discussion: A finite element methodology has been developed for patient-specific simulation of endoscopic scoliosis surgery. Issues to be addressed in future include prescription of patient-specific material properties, analysis of errors associated with geometry measurement from CT scans, and validation of the methodology by comparison of predicted and actual outcomes for scoliosis patients. Patient-specific simulation of scoliosis surgery has the potential to optimize surgical outcomes and reduce biomechanical complications associated with the use of endoscopic scoliosis instrumentation systems.
The abstracts were prepared by I. B. McPhee. Correspondence should be addressed to the Spine Society of Australia Secretariat, The Adelaide Centre for Spinal Research, Institute of Medical and Veterinary Science, PO Box 14, Rundle Mall, Adelaide SA 5000, Australia.
