Measuring spinal and trunk shape using an electromagnetic sensor.

Abstract

A critical component in the clinical assessment of spinal and trunk disorders is the analysis of posture. Currently the gold-standard is restricted by repeated radiation exposure and whilst alternative surface methods are available, these are limited to detection of spinal shape only. To date, no surface method has been extended to also quantify trunk shape. In order to address this, the aims of this research were 1) develop a method for measuring spinal and trunk shape using an electromagnetic system; 2) determine the validity and reliability of this method and 3) explore the optimal data processing for this method. Using a repeated measures design, data were collected on phantom models of different shapes using an electromagnetic system. This provided the three- dimensional co-ordinates from which spine and trunk angles were derived. The 6th order polynomial fit was deemed optimal for spinal shape measurements with an electromagnetic system. These measurements were highly reliable (ICC = >0.999), highly repeatable (MDC = <0.018º, SEM = <0.007º) and shown to be valid compared to a flexicurve method. The Lowess function was recommended for trunk shape measurements as it yielded good-to-excellent repeatability (ICC = 0.809-0.999), high absolute reliability (MDC = 0.18-4.0º, SEM = 0.06-0.07º) and angles derived were valid compared to a flexicurve method. This study addressed a clinical need by developing a novel method for measuring trunk shape in addition to spinal shape using a surface method which was shown to be valid and reliable. Exploration of the method’s optimal data processing techniques found the 6th order polynomial fit and Lowess function to be best for spinal shape and trunk shape measurements respectively. Additionally, whilst it is recommended that tangent lengths should not be used interchangeably, the tangent length chosen should not significantly affect measurements if used consistently. Meanwhile, the method’s non-invasive, non-ionising and low-cost features make it clinically attractive. Therefore, this research holds future prospects for the examination and monitoring of disease and treatment outcomes as well as, the understanding of many disorders, such as scoliosis. Although further research is warranted, this method has the potential for use in routine clinical practice.