Innovative procedure for hip-joint surgery preparation

Engineers, computer scientists and physicians are working on a virtual prosthesis

The virtual model shows the main stress lines after a hip operation.

12.11.2009, Press releases

Every year over one million people worldwide have a hip joint replaced. Yet the prognoses during the surgery preparation phase oftentimes remain inadequate. As a result, a high percentage of patients suffer from long-term consequences of this type of operation. Even the slightest deviation from the optimal form and position of the prosthesis can lead to strain on the bone, which in turn can result in inflammation or, in the long run, to bone atrophy. An interdisciplinary team of engineers, computer scientists and physicians at the International Graduate School of Science and Engineering at the Technische Universität München (TUM) has now developed a method to minimize these risks: a virtual prosthetic bone model.

In the future this procedure will make it possible to enter the exact spatial computer-tomography images (CT images) of every patient into a simulation program and then run tests at the computer screen: Which implant is the perfect match? How can the bone best support the body weight? And how should the prosthesis be fitted accordingly? “Using the new simulation method, we can distribute the weight on bones and prosthesis right on the screen and vary their position with respect to one another,” says project leader Dr. Martin Ruess, engineer at Professor Ernst Rank’s Chair for Computation in Engineering at the TUM.

In the past, when preparing this type of surgery, physicians have worked with X-ray images or, in special cases, with Styrofoam models of the bones, which they then mill on the basis of CT images. However, these models give no data on the real distribution of forces, nor can they be used to test the forces. The distribution of forces can, in fact, already be calculated on the computer at this stage, but only for research purposes, e.g. to develop a new type of artificial hip joint. Computerized prosthesis optimization for individual patients has not been feasible thus far because merely processing the computer tomography data for a single calculation can take many hours, making it nonviable for surgery preparation.

That is completely different in the computer models of the TUM researchers: They are developing models that can calculate the distribution of forces within a matter of seconds after the tomography. To ensure that the computer scientists’ virtual model corresponds to physical reality, the software is fed data from real bone-strain tests. The latter is provided by the team of Adj. Professor Rainer Burgkart, head of orthopedic research and teaching at the Klinikum Rechts der Isar. A team of researchers at the Chair for Computer Graphics and Visualization under Professor Rüdiger Westermann is is responsible for the interactive ‘virtual operation’ and the visualization of the simulation results. “The system should ultimately allow doctors to experiment with how a hip prosthesis can best be fitted on the patient before or even during the surgery itself,” says project leader Ruess.

Contact partner:

Dr. Martin Ruess
Chair for Computation in Engineering
Technische Universität München
Arcisstraße 21
80290 Munich

Telephone: 089.289.22425
E-mail: ruess@tum.de

Kontakt: presse@tum.de

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