New Technology Recognises Faults in Joint Prostheses
 

Scientists of Leibniz Universität Hannover Have Developed a Test Procedure to Prevent Patients from Being Given Faulty Artificial Joints

A new technology could in future prevent the implantation of damaged artificial hip or knee joints. Prostheses with slight surface faults often loosen prematurely and make it necessary to re-operate early in order to exchange the artificial joints. Scientists from the Institute of Production Engineering and Machine Tools (IFW) at the Production Technology Centre (PZH) of Leibniz Universität Hannover have developed a new technique - the so-called extended dark field method - in order to discover scratches on artificial joints reliably with the aid of light reflection. The faulty prostheses are then reworked or discarded.

The current state of the technology is that artificial joints are examined manually by a tester. The result is highly dependent on the qualification of the tester and on his form on the day. An automatic test procedure can guarantee the objectivity and reproducibility of the quality control and protect the manufacturer from faulty products. Industry has already signalled its great interest in the new technology. Discussions are currently being held with well-known producers of prostheses, initially so that field studies can be started on a larger number of artificial joints.

The development of the dark field method is part of the OptiGIP project in the IFW, in which work is being carried out under the direction of Prof. Berend Denkena on different methods for the quality testing of surfaces of prostheses. The researchers have already further developed the existing simple dark field method. In the simple dark field method the surface of the metal prosthesis, which is similar to a curved mirror, is illuminated in such a way that the light falls past the observer. A surface fault, such as a scratch can be observed as a bright line in the camera image when the angle is correct. Dipl.-Ing. Wolfram Acker from the IFW compares the principle with a well-known everyday method: “If one holds a reflecting surface against the light it sometimes flashes when scratches are present.” Since, however, in the simple dark field method the illumination is provided by only one source of light from only one angle, the surface faults are discovered only when the light falls on the surface from the right angle. Therefore the researchers have developed the extended dark field method further. Here the angle of the beam of light is varied, and the surface is illuminated consecutively from many directions. The approximately 140 individual images are then superimposed. Thus surface faults can be discovered very reliably, and even very small scratches shine up brightly. For the OptiGIP project Leibniz Universität Hannover is working together with the Hannover Medical School (MHH), the Society for Optical Measurement Technology (GOM) from Braunschweig as well as the Argomedical company from Gifhorn and the 4D company from Groß-Gerau.

If prostheses with slight surface faults are implanted there is a danger that larger particles will be shaved off in the region of a scratch. The immune system recognises these particles as foreign bodies and encloses them, with the result that they are enlarged even further. The particles move freely in the joint capsule and also move between the bone and the prosthesis, where they can cause loosening. “We want to provide an automatic procedure for the quality control of prostheses”, says Wolfram Acker. “They are many patients with large problems, and there is a clear need for this.”

Meldung vom 12.04.2007