Biomechanical modelling of growth modulation following rib shortening or lengthening in adolescent idiopathic scoliosis

Abstract

A biomechanical model was developed to evaluate the long-term correction resulting from rib shortening or lengthening in adolescent idiopathic scoliosis (AIS). A finite element model of the trunk, personalised to the geometry of a scoliotic patient, was used to simulate rib surgery. Stress relaxation of ligaments following surgery was integrated into the model, as well as longitudinal growth of vertebral bodies and ribs and its modulation due to mechanical stresses. Simulations were performed in an iterative fashion over 24 months. A concave side rib shortening, inducing load patterns on the vertebral end-plates that could act against the scoliosis progression, was tested. A fractional factorial experimental design of 16 runs documented the effects of six modelling parameters. Wedging of the apical vertebra in the frontal plane decreased from 5.2 degrees initially to a mean value of 3.8 degrees after 24 months. The wedging decrease in the thoracic apical region was reflected by changes in the spine curvature, with a Cobb angle decrease from 46 degrees to 44 degrees immediately after the surgery and to a mean of 41 degrees after 24 months. However, both rib hump and vertebral axial rotation increased, on average, by 4 degrees at the curve apex. The most significant parameters were the growth sensitivity to stress in ribs and vertebrae and the rate of stress relaxation of intercostal ligaments. The results confirmed the potential of long-term correction of spinal curvature resulting from the rib shortening on the concavity. This modelling approach could be used for further design of less invasive surgery, taking into account residual growth, for scoliosis correction.

Computer simulation for the optimization of instrumentation strategies in adolescent idiopathic scoliosis

“…The method proposed in this study for the choice of weights in the objective function formulation (specified by the surgeon) was used to avoid the arbitrary choice proposed in other optimization studies [7,20,43] and to identify the best compromises available considering all aspects of the correction.…”

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

“…The representation of the wedge shape of the intervertebral discs following a biomechanical stimulus can still be achieved by modeling the disc in a similar fashion to the vertebral bodies (i.e. center element with beams distributed along the edge) [3] in order to enable the evaluation of internal stresses variation within the disc.…”

“…Finite element (FE) models of the spine integrating growth and growth modulation have been used to understand the process of curve progression [3,24,28] and to evaluate different hypotheses for the pathogenesis of AIS [29]. Pathogenesis studied by Villemure et al [29] consisted of shift or rotation at T8, which was assumed to be the apical vertebra of the future scoliosis.…”

Mechanobiological bone growth: comparative analysis of two biomechanical modeling approaches

“…In Stokes's model, the sensitive factor b l was assumed 1.2 MPa -1 , based on an experimentally determined range of 0.4-1.71 MPa -1 [4,31]. The longitudinal baseline growth for thoracic vertebrae was taken as Gm = 0.8 mm year -1 according to the published data on vertebral growth in adolescents [7].…”

“…The sensitivity factor b l is determined from experimental data and is considered independent of the external environment. This modeling approach was integrated in beam-type finite element models by simulating the resulting strain increments as thermal loadings or equivalent forces to carry out bone geometrical changes [4,27,36,37].…”