Three-dimensional shape analysis of the scoliotic spine using invariant shape parameters

The Validity of Rasterstereography: A Systematic Review

To investigate and monitor the progression of scoliosis and other spinal deformities in patients following idiopathic scoliosis (IS), non-invasive and radiation-free techniques are recommended because of the need for repeated radiographs. In a clinical setting, spine parameters can be quickly, cheaply and easily assessed using rasterstereography (RS). To assess the validity of the radiation-free technique RS based on surface topography compared with radiographs. MEDLINE, the Cochrane Library and EMBASE were systematically searched for studies which investigate the validity of rasterstereography compared with x-ray measurements. Studies published between January 1, 1990 and July 31, 2013 in English, German and French were included. Studies dealing with magnetic resonance imaging were excluded. Twelve studies with 570 patients were included; these articles were published between 1990 and 2013. The majority of studies investigated patients with IS, but other spinal pathologies included were thoracic hyperkyphosis and Scheuermann’s disease. With regard to the quality assessment criteria for the included studies, three out of twelve studies were evaluated using a twelve point scale and two used a scale with eleven points. We conclude that RS facilitates clinical practice by analysing the spinal column. It is completely radiation-free and could help to monitor scoliosis progression.

A versatile 3D reconstruction system of the spine and pelvis for clinical assessment of spinal deformities

This paper presents a three-dimensional (3D) reconstruction system of the human spine for the routine evaluation of musculoskeletal pathologies like idiopathic scoliosis. The main objective of this 3D reconstruction system is to offer a versatile and robust tool for the 3D analysis of spines in any healthcare centre with standard clinical setup using standard uncalibrated radiographic images. The novel system uses a self-calibration algorithm and a weak-perspective method to reconstruct the 3D coordinates of anatomical landmarks from bi-planar radiographic images of a patient's trunk. Additionally, a small planar object of known dimensions is proposed to warrant an accurately scaled model of the spine. In order to assess the validity of the 3D reconstructions yielded by the proposed system, a clinical study using 60 pairs of digitized X-rays of adolescents was conducted. The subject cohort in the study group was composed of 51 scoliotic and 9 non-scoliotic patients, with an average Cobb angle on the frontal plane of 25 degrees. For each case, a 3D reconstruction of the spine and pelvis was obtained with the previous system used at our hospital (which requires a positioning apparatus and a calibration jacket), and with the proposed method. Results show that 3D reconstructions obtained with the new system using uncalibrated X-ray images yield geometrically accurate models with insignificant differences for 2D and 3D clinical indexes commonly used in the evaluation of spinal deformities. This demonstrates the system to be a viable and accurate tool for clinical studies and biomechanical analysis purposes, with the added advantage of versatility to any clinical setup for routine follow-ups and surgical planning.

Identification of spinal deformity classification with total curvature analysis and artificial neural network

In this study, a multilayer feedforward, back-propagation Artificial Neural Network is implemented to identify the classification patterns of the scoliotic spinal deformity. At first step the simplified three-dimensional spine model is constructed from coronal and sagittal x-ray images. The features of the central axis curve of the spinal deformity patterns in 3D space are extracted by the Total Curvature analysis. The discrete form of the Total Curvature, including the curvature and the torsion of the central axis of the simplified 3D spine model is derived from the Difference Quotients. The values of Total Curvature of 17 vertebrae from first thoracic to the fifth lumbar spine formed a Euclidean space of 17 dimensions. Either the curvature or the torsion of the three-dimensional curve of the central axis of the spine model could provide the input of the artificial neural network. The King Classification model is tested on the neural network. Five sets of King spinal deformity patterns are randomly selected by the definition of King classification. The output layer of the artificial neural network has five neurons representing the five King classification types. The network validation was conducted by the Hold-Out method, one of Cross-Validation variant. The performance of the neural network is compared between two network topologies, one with one hidden layer and another with two hidden layers. The results are shown in a table with each of five datasets leave-out and all five datasets participating the training, with either one hidden layer or two hidden layer network.

The correlation comparison of vertebral axial rotation relative to curvature and torsion in scoliosis by simplified 3D spine model

This paper reports a study on correlation comparison of the vertebral axial rotation relative to curvature and torsion of scoliotic spine. The goal of this study is to understand whether the vertebral axial rotation is more correlated to the curvature or to the torsion of the scoliosis spinal deformity. For this purpose, the simplified 3D spine models are constructed on the randomly chosen images of scoliosis patients. The 3D spine model is based on two orthogonal spinal radiographic images taken from coronal and sagittal planes. Superimposed on these two images, the 3D Bezier curves are fitted interactively onto the center of the spine on both coronal and sagittal images. Upon the 3D Bezier Curve fitting, a series of simplified 3D vertebrae are implemented onto the 3D Bezier Curve proportional in size to its axis. The curvature and torsion then are obtained by difference quotients algorithm. In determining the vertebral axial rotation, the measurements are conducted directly on the coronal spine images. The lateral margins and centers of pedicles are used as landmarks for the rotation calculation. The correlation coefficients are calculated from both vertebral axial rotation relative to the curvature and to the torsion found on each vertebra. The strength of correlations from both cases is compared in the table.

Geometric torsion in idiopathic scoliosis: three-dimensional analysis and proposal for a new classification

STUDY DESIGN

Three-dimensionally reconstructed spines of 62 subjects with idiopathic scoliosis were reviewed for three-dimensional pattern classification based on the measurement of geometric torsion.

OBJECTIVES

To evaluate the relevance of geometric torsion as a three-dimensional index of scoliosis, and to develop a three-dimensional classification of deformity for idiopathic scoliosis as opposed to the current classifications based on two-dimensional frontal views.

SUMMARY OF BACKGROUND DATA

Attempts have been made to measure the geometric torsional shape of scoliotic curves represented curvilinearly. However, the geometric torsion phenomenon has never been properly analyzed and thus has never been precisely defined.

METHODS

Standardized stereoradiographs of 62 patients with idiopathic scoliosis were obtained and used to generate three-dimensional reconstructions. A continuous parametric form of the curved line that passes through the vertebrae was created by least square fitting of Fourier series functions. Frenet's formulas then were used to calculate the geometric torsion.

RESULTS

Analysis of geometric torsion associated with 94 major scoliotic curves allowed three basic categories of torsion curve patterns to be identified. Scoliotic spines with multiple major curves are described by a combination of basic torsion patterns, one for each curve.

CONCLUSIONS

A three-dimensional analysis of the spine in terms of geometric torsion has defined three distinct patterns of torsion in a group of scoliotic curves. Geometric torsion had extreme values at the levels of upper and lower vertebrae, but zero or nearly zero values at the levels of the apices. The torsional phenomenon can be unidirectional or bidirectional in both single and double major curves.

A mathematical expression of three-dimensional configuration of the scoliotic spine

Three-dimensional configuration of the scoliotic spine was mathematically expressed by a spatial curve passing through each vertebral centroid ("vertebral body line"). Three-dimensional location of the vertebral centroid was determined from digitization on the frontal and sagittal roentgenograms. Cobb angle, which is clinically used for measuring scoliosis curvature, was calculated in space to evaluate scoliosis deformity three-dimensionally. In forty-five scoliotic spines, regardless of curvature and curve patterns, the spinal configurations were excellently approximated by vertebral body lines. Vertebral body lines swerved from the sagittal plane at the end vertebrae, but aligned on a certain plane within the scoliosis region. Three-dimensional Cobb angle, which was larger than that in the frontal plane, can be utilized to evaluate the scoliosis deformity.

The relationship between surface and radiological deformity in adolescent idiopathic scoliosis: effect of change in body position

Three-dimensional (3D) surface deformity of the trunk in adolescent idiopathic scoliosis (AIS) is affected by changes in patient position. Initial quantification of the curve and its associated deformity, as well as subsequent monitoring, relies on both radiological and surface measurements. However, there is often a discrepancy between radiological and apparent surface deformity. The present investigation studied the dynamics of the 3D deformity associated with changes in patient position on 27 patients with AIS. The trunk deformity was quantified in three positions by measuring the angle of thoracic inclination at each vertebral level using a scoliometer. The patients all had full spine radiography in the antero-posterior erect position. Vertebral rotation and lateral spinal curvature were measured from the radiographs. Body position altered the magnitude of the surface deformity over the whole trunk, with the prone position offering the optimum relationship between 3D trunk shape and radiological deformity. This could be attributed to the ease and standardisation of positioning for prone measurements, together with increased patient comfort. It is suggested that adoption of standardised positioning and measurement of surface and radiological deformity will permit consistency of clinical judgement based on these parameters.

Biomechanical analyses of surgical correction techniques in idiopathic scoliosis: significance of bi-planar characteristics of scoliotic spines

Biomechanical analyses of Harrington distraction, Harrington distraction-compression, Cotrel and Luque correction techniques simulated mechanically on a three-dimensional mathematical model of scoliotic spines are developed and relationships between mechanical forces and achievable corrections are derived in terms of Cobb angle, vertebral inclination from the frontal plane, and bi-plane bending stiffness of motion segments. For all four systems, nomograms between Cobb angles and corrective forces with correction factors as parameters are prepared in terms of given bi-plane characteristics of scoliotic spines. Parametric studies to show the influence of the torsion plane bending stiffness of motion segments and vertebral inclinations from the frontal plane on the mechanical effectiveness of the surgical correction techniques are presented. The mechanical effectiveness of each of the four surgical correction techniques determined with the use of this model compares reasonably well with the clinical findings.

Improvements in measuring vertebral rotation from the projections of the pedicles

In radiological assessment of scoliosis, some prognostic value is given to vertebral rotation. An improved method for measuring vertebral rotation is introduced. It differs from the known methods by a specific selection of vertebral model parameters describing location of pedicles relative to the vertebral body. Vertebral model parameters have been determined from 150 axial X-rays of vertebral specimens. Application of measured parameters yields accuracy of about +/- 5 degrees in assessing vertebral rotation. Good agreement is found with parameters of six scoliotic vertebrae, investigated by CT-scans. A method for clinical presentation of measurement results is proposed.