Scanning and motion capturing of vertebral kinematics
Date
2008-12
Authors
Christelis, Lorita
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
In the context of intervertebral disc replacement and customized implants, human simulation studies
are of great importance. Simulation models need input data. This study investigated different in vivo
motion capturing methods to capture spinal kinematics that will serve as input for simulation models.
Available scanning and motion capturing techniques for capturing cervical kinematics range from
simple clinical methods, to expensive specialized equipment and software. With a variety of
technologies comes a variety of applications. In this study the focus is on capturing the kinematics of
the cervical spine.
An important distinction was made between two types of motion capturing technologies: external
motion capturing and internal imaging technologies. The available external motion capturing
technologies pose many advantages in terms of cost, safety, simplicity, portability and producing
accurate three dimensional position and orientation. However, the ability for external motion capturing
technologies to give accurate information on the movements at each vertebral level is doubted by critics
reasoning that the true vertebral motion is concealed by the skin and soft tissue. Although it would be
ideal to use external motion capturing systems, one needs to be confident that these surface markers or
sensors truly reflect the vertebral motion at each vertebral level.
An empirical study was conducted to evaluate the relationship between motion captured on the skin
surface and motion of the vertebrae. Twenty-one subjects received low dosage X-rays, while radio
opaque markers were attached to the skin at each respective vertebral level. The motion of external
markers and that of the vertebrae could be seen simultaneously on one medium. In the empirical study,
two outputs were achieved. Firstly, intervertebral kinematic data, for use in further simulation studies
was obtained. Secondly, the relationship between surface markers and vertebrae in different motion
instances was investigated. Distance and angle parameters were constructed for vertebral prediction
from skin surface markers. The causes of variation in these parameters were identified by investigating
the correlations of these parameters with anthropometrical variables. Strong correlations of the
parameters were observed in flexion, but in extension, especially full extension, the correlations were
poor to insignificant. It was concluded that in neutral, half flexion and full flexion it is possible to
predict the vertebral position from surface markers by using the parameters and anthropometrical
variables. In half extension this prediction would be less accurate and in full extension alternative
methods should be investigated for external motion capturing.
Description
Thesis (MScEng (Industrial Engineering))--Stellenbosch University, 2008.
Keywords
Cervical spine, Kinematics, Motion capturing, X-rays, Dissertations -- Industrial engineering, Theses -- Industrial engineering