In Vivo Lumbar Modeling

INTRODUCTION In 2008 413,171 spinal fusion surgeries were performed [1]. The various reasons for the surgery include spondylothesis, spinal stenosis, and herniated discs among others [2]. These conditions can cause the intervertebral discs, cartilaginous shock absorbers, to degenerate. Ultimately, this can cause the vertebral bodies to rub on each other, causing pain and discomfort. Spinal fusion surgery is the process of fusing two vertebrae that are impeding on each other together to prevent motion between the two. To do this a surgeon creates a bone graft between the two vertebrae [3]. While the surgery does help to alleviate spinal pain, the fusion can cause increased stress and degeneration at vertebrae above and below the site [3]. Current researchers have trouble studying dynamic movement in 3-D [4]. The standard is to capture two 2-D x-ray images, one at no amount of flexion and one at full flexion. This allows for the overall range of motion in the flexion-extension plane to be quantified [4]. Being able to view intervertebral movement in 3-D dynamically would allow for the quantification of range of motion (ROM) in every plane – sagittal, frontal, and axial, while also being able to view how the motion changes throughout the course of the dynamic movement. The current tool used to model 3-D dynamic intervertebral kinematics by the Orthopaedic Biodynamics Laboratory is a Dynamic Stereo X-Ray (DSX) system. The DSX system consists of two bi-plane x-ray systems emitting x-rays at a rate of 30 frames per second. At this frame rate more x-ray frames are able to be captured during a particular amount of time, and consequently a dynamic movement is able to be captured. The bi-plane x-ray system combined with a model based tracking software allows for the capturing of the 3-D in vivo dynamic process [4].