Chapter 10

Applications of Medical Image Processing

in the Diagnosis and Treatment

of Spinal Deformity

Clayton Adam and Geoff Dougherty

10.1 Introduction

Spinal deformities are a group of disorders characterized by abnormal curvature of the spine. In the healthy spine, natural curves occur in the sagittal plane, with a lordosis (concave curvature) in the lower back (lumbar) region and kyphosis (convex curvature) in the upper back (thoracic) region. In some spinal deformities, these natural curves can be either suppressed or amplified, as in the case of hypokyphosis (flatback) or hyperkyphosis (exaggerated thoracic curvature or ‘hunchback’). However, the most common type of deformity is scoliosis, which is defined as abnormal lateral (side to side) curvature of the spine accompanied by axial rotation. Because of the combined sagittal curvature, abnormal lateral curvature, and axial rotation, scoliosis is a complex three-dimensional deformity which cannot be visualised in any single viewing plane (Fig. 10.1).

This chapter describes the application of image processing to the assessment and treatment of spinal deformity, with a focus on the most common deformity, adolescent idiopathic scoliosis (AIS). We will briefly describe the natural history of spinal deformity and current approaches to surgical and non-surgical treatment to give some background to the problem, and present an overview of current clinically used imaging modalities. We will introduce the key metric currently used to assess the severity and progression of spinal deformities from medical images, the Cobb angle, and discuss the uncertainties involved in manual Cobb angle measurements. An alternative metric, the Ferguson angle, will also be discussed. This provides the context for an examination of semi-automated image processing approaches for improved measurement of spinal curve shape and severity, including the development of discrete and continuum representations of the thoracolumbar

C. Adam ( )

Queensland University of Technology, Brisbane, Australia e-mail: [e-mail]

G. Dougherty (ed.), Medical Image Processing: Techniques and Applications, Biological

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and Medical Physics, Biomedical Engineering, DOI 10.1007/978-1-4419-9779-1 10, © Springer Science+Business Media, LLC 2011

228	C. Adam and G. Dougherty

Fig. 10.1 Three dimensional CT reconstructions of a scoliotic spine showing overall spine and ribcage shape (left), sagittal, and coronal close-up views of the vertebral column (right)

spine and tortuosity measures. The newly defined metrics are applied to a dataset of idiopathic scoliosis patients and assessed by comparison with clinical Cobb angle measurements for the same patient group. Finally, areas for future image processing research applied to spinal deformity assessment and treatment are discussed.

10.1.1 Adolescent Idiopathic Scoliosis

While scoliosis can occur as a secondary consequence of a primary pathology (such as a leg length inequality or congenital malformation), most (70–80%) scoliosis cases occur during the adolescent growth spurt without known cause. These deformities are classified as AIS, and affect 2–4% of the population.

People with scoliosis often have no symptoms beyond a slight increase in pain and reduced lung capacity. However, progressive scoliosis leads to an increasingly severe cosmetic deformity and can compromise the function of internal organs in severe cases. For these reasons, both conservative (non-surgical) and surgical treatments for spinal deformities have been developed. Bracing is a common