BIPLANE FLUOROSCOPY PROJECT

Fluoroscopy is a technique that uses x-ray radiation to create a movie of moving bones as opposed to the still, snapshot that a regular x-ray system produces. This research project at the Steadman-Hawkins Research Foundation aims to build a state-of-the-art, highly accurate stereoscopic fluoroscopy system.  With this system, the research possibilities will be limitless, ranging from comparing ACL reconstruction techniques to understanding the effect of post-surgical scarring/adhesions on the development of osteoarthritis in the knee; from validating clinical examinations to understanding joint instability in the hip; from recording joint motion in unstable shoulders to comparing rotator cuff repair techniques and joint prostheses function in the shoulder; from showing the effects of spinal manipulations and herniated disk surgery on spine mobility to understanding the intricate interplay of the multitude of bones in the foot and hand. The system may even measure cartilage indentation in the knee during walking, running and landing from a jump.  We have already begun an ambitious research project in which we are applying this technology to better understand how knee adhesions (scarring) can cause and/or accelerate the degeneration of the cartilage in the knee and how certain surgical procedures can spare the knee from this type of degeneration.  Without this new technology this type of study would not be scientifically possible.

Currently there is only one such high-performance system in the world (Henry Ford Hospital, Detroit, MI). An additional 5 groups in the world use single or lower performance fluoroscopy systems to actively study joints and/or joint replacements. Thus, the acquisition of this system will put the Steadman-Hawkins Research Foundation immediately at the forefront of this exciting, new and developing field.

There are several reasons why this system will significantly contribute to the field of orthopedics and biomechanics. First, accurate measurement of bone and joint motion (kinematics) is important to these fields as it provides critical information for the understanding of normal and diseased joint function, as well as for the understanding and improvement of surgical treatments. Traditionally, joint motion has been measured using video systems that record the location of reflective markers attached to the skin while the subjects perform activities such as walking, running, bending or even throwing a ball.  However, the motion of the skin and adipose tissues does not always reflect the motion of the bones and joints moving beneath them.  For this reason, these systems do not provide the accuracy needed to measure small but clinically essential changes in joint motion.  Even attaching the reflective markers to pins surgically inserted into the bones yields errors of 2-4mm, far higher than the sub-millimeter accuracy necessary to measure crucial changes in joint motion.  For instance, the difference between two ACL reconstruction techniques may be less than 1mm of translation during walking; yet this small difference may result in the development of osteoarthritis after one surgical technique and not the other.  Concurrently, cadaveric and animal experiments used to investigate joint and ligament function as well as surgical treatments have taught us a great deal.  However, these experiments do not necessarily give an accurate portrayal of how living tissues behave in real human life (in vivo).  Therefore, a novel and highly accurate motion analysis system is needed that measures bone and joint motion directly in vivo with high resolution

Methods using fluoroscopy to accurately measure 3D in vivo skeletal motion during dynamic activities have been developed only in the last few years. These methods evolved from 3D techniques first developed in the mid to late 1990s to track joint implants in vivo. Using computer graphics techniques, the tracking algorithms work by calculating a synthetic fluoroscopy image based on detailed computer models of the fluoroscopy system itself and the objects being imaged such as a bones, implants, or small implanted beads. The location and orientation of the objects are then systematically adjusted until the synthetic fluoroscopy image best matches the recorded fluoroscopy image. The locations of the bones, implants or implanted beads have been shown to be measured with an accuracy of better than 1.0 mm in general, with accuracies of 0.14mm or better in specific instances. Highest accuracy is obtained when two fluoroscopy systems with crossing x-ray beams are used simultaneously (biplane fluoroscopy system).

The building of our biplane fluoroscopy system will require the purchase of two standard OR fluoroscopy units (c-arms) which will then be significantly modified. First, the existing c-arms are too restrictive to our subjects to perform their activities. Therefore, the c-arm structures will be removed and completely new frames will be built to allow for maximum freedom of movement of the subjects as well as the imaging of any joint of the body from head to toe. Second, we are primarily interested in motions which challenge joints. These motions are typically fast and require fast acquisition of the radiographic images. The imaging systems of commercial fluoroscopy units are rather slow (30 images per second maximum). We will replace the existing image capture systems with high-speed cameras (up to 1000 images per second).

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