In a laboratory set-up, Hans Hendriks discovered that in the immediate vicinity of the antibiotic-containing bone cement, the antibiotic concentrations are particularly high. However, this is predominantly during the first few days after the application of the cement and the long-term release of the antibiotic seems to be less effective.
Hendriks investigated the release of antibiotics under simulated real-life conditions. He first of all investigated the antibiotic concentration in the cavity between the surface of the bone and the bone cement. In the human body this cavity is about 0.2 mm wide.
The antibiotic concentrations in the cavity were found to be 1000 times higher than the lethal dose for most bacteria. Experiments with different bacterial species led Hendriks to conclude that virtually no bacteria could survive in this environment. Three weeks later, the concentration of antibiotics had decreased to the extent that increasingly fewer bacteria were inhibited by these.
Placing the bone cement under stress did not affect the release of antibiotics. Walking on a cemented prosthesis results in the bone cement being subjected to periodic stress. Small cracks can arise as a consequence of this. As the surface of such a crack has not previously been in direct contact with body fluids it could form a new surface for the release of the antibiotic. Using an experimental set-up, Hendriks demonstrated that no new release occurs even after 5 to 10 years of walking around on a prosthesis.
For the past 30 years, bone cement has contained antibiotics to prevent and cure infections around implants. However, opinions were divided with respect to the effectiveness of this treatment as well as the associated risks. Furthermore, the exact mechanism by which the cement released the antibiotics was unclear. However, it has been established that more than eighty percent of the antibiotics can still be found in the bone cement years later. Knowledge about the release of the antibiotics could contribute to the development of new antibiotic carriers to control infections in orthopaedic surgery.
For further information please contact Dr Hans Hendriks (Department of Biomaterials and Organ Technology, University of Groningen, now at South Leeuwarden Medical Centre Hospital), tel. 31-503-011-697 (home), e-mail: j.g.e.hendriks@med.rug.nl. The doctoral thesis was defended on 24 September 2003. Dr Hendriks' supervisors were Prof. J.R. van Horn, tel. 31-503-616-161, Prof. H.J. Busscher, email: h.j.busscher@med.rug.nl and Prof. H.C. van der Mei.
The research was funded by the Netherlands Organisation for Scientific Research.