Dynamic Analysis of Intervertebral Efforts in Scoliosis

Details

Written by Gabriel Abedrabbo

Abstract

A biomechanical model, using the multibody dynamics approach, is developed to calculate the intervertebral efforts in spine. The latter are computed, via inverse dynamics, using kinematic information from gait. Optimization process is required in order to convert that information, expressed in absolute coordinates from the optometric sensors, into relative joint coordinates, in order to calculate joint forces and torques.

Motivation

The evaluation of internal forces and torques in the human body in motion could provide valuable information for the evaluation and follow-up of subjects with musculo-skeletal pathologies, such as scoliosis. But these data are still difficult to measure accurately. In this challenging context, the objective of this study is to check the hypothesis that there exist different dynamical behaviours and effects in the spine between a healthy subject and a scoliotic patient before and after spine fusion surgery.

Background

The SRS (Spine Research Society) definition of adolescent idiopathic scoliosis (AIS) is a structural lateral curvature of the spine that creates a thoracic and/or lumbar asymmetry on forward bending (a.k.a. the "Adams forward bend test") combined with a curve of at least 10 as measured by the Cobb technique on a standing radiograph of the spine with associated vertebral rotation along the vertebral direction (torsion). When scoliosis is defined as a Cobb angle of at least 10 degrees, epidemiologic studies estimate that 1% to 3% of children aged 10 to 16 years will have some degree of spinal curvature.

Methodology

Data acquisition

1. Optokinetic sensors and accelerometers.

2. Postero-anterior and lateral radiographs of the spine, enabling a static 3D reconstruction of the spine geometry.

    

  

Data acquisition Joint kinematic identification

The joint coordinates, velocities and accelerations are numerically determined via an optimization process that estimates the joint coordinates q of the multibody model that best fit the experimental kinematics.

Inverse dynamics

Using a recursive Newton-Euler formalism, a 3D multibody model provides the vector Q of the joint forces and torques during gait.

 Preliminary results.

Significant differences in kinematics and were observed between the subjects, leading to different internal effort behaviour in magnitude, maxima and minima when normalized to the subject mass. Considering for example the normalized anteroposterior torques (NAPT) between vertebrae:

1. the maximal absolute magnitude of the NAPT was higher for the scoliotic patient before surgery (2.5 Nm/kg) than after surgery (1.3 Nm/kg)

2. the NAPT maxima and minima were asymmetrical for the scoliotic subject

Collaborations

IMMC/CEREM Center for Research in Mechatronics, Université catholique de Louvain (UCL), Louvain-la-Neuve, Belgium

READ Unit at the Faculty of medicine (UCL) and Orthopaedic Research Laboratory, Cliniques universitaires St-Luc Clinics (UCL), Bruxelles, Belgium

CRME-CHU Sainte-Justine, École Polytechnique de Montréal, Montréal QC, Canada