Scanning and motion capturing of vertebral kinematics

[摘要] In the context of intervertebral disc replacement and customized implants, human simulation studiesare of great importance. Simulation models need input data. This study investigated different in vivomotion 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 fromsimple clinical methods, to expensive specialized equipment and software. With a variety oftechnologies comes a variety of applications. In this study the focus is on capturing the kinematics ofthe cervical spine.An important distinction was made between two types of motion capturing technologies: externalmotion capturing and internal imaging technologies. The available external motion capturingtechnologies pose many advantages in terms of cost, safety, simplicity, portability and producingaccurate three dimensional position and orientation. However, the ability for external motion capturingtechnologies to give accurate information on the movements at each vertebral level is doubted by criticsreasoning that the true vertebral motion is concealed by the skin and soft tissue. Although it would beideal to use external motion capturing systems, one needs to be confident that these surface markers orsensors truly reflect the vertebral motion at each vertebral level.An empirical study was conducted to evaluate the relationship between motion captured on the skinsurface and motion of the vertebrae. Twenty-one subjects received low dosage X-rays, while radioopaque markers were attached to the skin at each respective vertebral level. The motion of externalmarkers 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 studieswas obtained. Secondly, the relationship between surface markers and vertebrae in different motioninstances was investigated. Distance and angle parameters were constructed for vertebral predictionfrom skin surface markers. The causes of variation in these parameters were identified by investigatingthe correlations of these parameters with anthropometrical variables. Strong correlations of theparameters were observed in flexion, but in extension, especially full extension, the correlations werepoor to insignificant. It was concluded that in neutral, half flexion and full flexion it is possible topredict the vertebral position from surface markers by using the parameters and anthropometricalvariables. In half extension this prediction would be less accurate and in full extension alternativemethods should be investigated for external motion capturing.

[发布机构] Stellenbosch University