An FE investigation simulating intra-operative corrective forces applied to correct scoliosis deformity

Abstract

BackgroundAdolescent idiopathic scoliosis (AIS) is a deformity of the spine, which may require surgical correction by attaching a rod to the patient’s spine using screws implanted in the vertebral bodies. Surgeons achieve an intra-operative reduction in the deformity by applying compressive forces across the intervertebral disc spaces while they secure the rod to the vertebra. We were interested to understand how the deformity correction is influenced by increasing magnitudes of surgical corrective forces and what tissue level stresses are predicted at the vertebral endplates due to the surgical correction.MethodsPatient-specific finite element models of the osseoligamentous spine and ribcage of eight AIS patients who underwent single rod anterior scoliosis surgery were created using pre-operative computed tomography (CT) scans. The surgically altered spine, including titanium rod and vertebral screws, was simulated. The models were analysed using data for intra-operatively measured compressive forces – three load profiles representing the mean and upper and lower standard deviation of this data were analysed. Data for the clinically observed deformity correction (Cobb angle) were compared with the model-predicted correction and the model results investigated to better understand the influence of increased compressive forces on the biomechanics of the instrumented joints.ResultsThe predicted corrected Cobb angle for seven of the eight FE models were within the 5° clinical Cobb measurement variability for at least one of the force profiles. The largest portion of overall correction was predicted at or near the apical intervertebral disc for all load profiles. Model predictions for four of the eight patients showed endplate-to-endplate contact was occurring on adjacent endplates of one or more intervertebral disc spaces in the instrumented curve following the surgical loading steps.ConclusionThis study demonstrated there is a direct relationship between intra-operative joint compressive forces and the degree of deformity correction achieved. The majority of the deformity correction will occur at or in adjacent spinal levels to the apex of the deformity. This study highlighted the importance of the intervertebral disc space anatomy in governing the coronal plane deformity correction and the limit of this correction will be when bone-to-bone contact of the opposing vertebral endplates occurs.

3D reconstruction of rib cage geometry from biplanar radiographs using a statistical parametric model approach

“…Rib cage global parameters, such as rib cage volume, spinal penetration index and rib hump angle (Dubousset et al 2003) and other morphological parameters complete the spine analysis, particularly for the deformed thorax which can raise clinically relevant issues for pulmonary restrictive disease (Sabourin et al 2010;Johnston et al 2011). Furthermore, 3D models are necessary for the development of realistic subject-specific finite element models (FEM) which are used to understand the mechanisms of initiation of structural deformation and predict treatment effects (Nie et al 2009;Clin et al 2010;Drevelle et al 2010;Little et al 2013) or used in crash simulation to investigate injury mechanisms.…”

Evaluation of Useful Biomechanical Parameters On Scoliosis Using Finite Element Method

“…In some studies, intervertebral discs are simulated and analyzed while they considered as one-piece. 25 In some other articles, the annulus section and nucleus part are simulated and analyzed separately. 32 To investigate this issue, all the results of this section compared between one-piece and two-piece intervertebral discs.…”

“…24 After precise finite element modeling of a patient with scoliosis in the thoracic-lumbar region and estimating the number of modification forces needed, Little and his colleagues found that in addition to the internal forces, the imposition of external forces to reform this condition was essential. 25 Also, in other research, 26 according to CT-scan images, they used the finite element method to model the thoracic-lumbar region of the vertebrae of a patient with scoliosis and investigated the modified vertebrae by orthopedic rods.…”

System reliability analysis of the scoliosis disorder

“…They found the correlation between the intensity of the force and the angle of correction by measuring the applied force. Little et al [19] tried to find out how deformation was affected by the severity of corrective forces to predict the severity of the tension required to treat spinal curvature in scoliosis abnormalities. Their research showed that there is a direct relationship between the compressive forces of the connections used and the degree of curvature change.…”