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Hope for people with severe spine fractures

Jan 7, 2004

Leeds University is at the forefront of research into implant technology and that research is just about to take a big leap forward in the spinal injuries sphere.


A new laboratory, the Frank Parkinson tissue engineering laboratory, has just opened at Leeds University.


It contains what is believed to be the world's first simulator capable of replicating the conditions of the human body to allow researchers to analyse how the spine might react to spine surgery techniques - the PROSIM spinal biomechanical fatigue simulator.


The simulator was developed by Simulation Solutions, a company with several years experience in the design and manufacture of knee, hip and friction simulators used in the testing of prosthetic implants.


John Fisher, professor in the School of Mechanical Engineering and pro vice chancellor for research at Leeds University explained: "In the past, surgeons were forced to rely on trial and error in the development of new techniques. Hip replacements were developed in the 1960s and the only way to improve them was following analysis after they had worn out or the patient had died. Naturally, this methodology involved a lengthy wait after each improvement and a frustratingly long design cycle."


"A few years ago, we commissioned special systems from Simulation Solutions, which reproduce years of wear on a joint in just a few months. Using pneumatics, these simulators put new artificial joints under both displacement and forced control millions of times in a controlled manner. To mimic the human body still further, the joints under test are worked in a bath of synovial fluid."


Spine surgery in the US has surged forward in recent years, but the analysis of its long-term efficacy has not kept pace with developments. New instrumentation has been developed which is attached to the spine during operations and disc replacement has begun.
In addition, when a spine is fractured, rods are used to fuse sections of the spine together and, most recently, there has been the development of vertebroplasty, a key hole surgery technique where liquid cement is injected into the vertebrae where it sets and fuses.
Ruth Wilcox, a research fellow in the bioengineering group at Leeds University commented: "No one is certain how the cement-augmented spine behaves over time, but our PROSIM spine simulator is the fastest way of finding out.


"It has six testing stations and these can operate round the clock to give us data, which should be of interest to spinal specialists around the world. I am also interested in testing a combination of current methods, such as using cement and rods together to treat more serious spinal fractures and even multiple fractures. Unlike implants in people, we can take ours out part way through to see how they are bearing up.We are working closely with surgeons at St James's Hospital. One element that should have a bearing on our data is the fact that we can study the implant in place on real bone rather than in isolation."

"The PROSIM spine simulator has two degrees of freedom, both axial and rotation, and will be able to measure accurately both the distances and loads we will be applying, but variations in bone density may have a significant bearing on the data we produce and efficacy of certain surgical techniques."


Simulation Solutions's use of pneumatics and servo-motors in all its simulators allows it to replicate the movements of the human body very closely. Empirical data have shown that patterns of wear from implants tested in the PROSIM knee and hip simulators are very similar to those taken from people after years of use.

Nick Heyes, technical manager with Simulation Solutions, said: "the use of a combination of servo-motors and pneumatics driven by closed loop, real-time feedback circuits, provides an effective way of accurately simulating the range of forces and motions joints are subjected to in everyday life. The system's control unit collects the data and creates a visual representation of the cycle. It is possible to monitor all six stations simultaneously and save the data collected for later analysis. Being able to subject six spine surgery techniques to close scrutiny over several months is what should enable researchers to determine the most successful solutions."

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