[Septic arthritis after arthroscopic cruciate ligament reconstruction: in vitro comparison of the behavior of two types of interference screws towards the Staphylococcus aureus adherence].

PURPOSE OF THE STUDY: We report the results of an experimental study designed to investigate the behaviour of two types of interference screws (bioabsorbable versus titanium) in a context of Staphylococcus aureus infection. The main objective was to study one of the possible sources of failure for the treatment of acute arthritis of the knee after arthroscopic reconstruction of the cruciate ligament.

MATERIAL AND

METHODS

We used six interference screws made of titanium and six bioabsorbable screws (PLLA-PDLLA). All screws measured 9mmx25mm, were cannulized and sterilized. These screws were submitted to a protocol elaborated in cooperation with the bacteriologists. After contamination with a strain of S. aureus, the screws were washed four times in saline solution to eliminate germs adsorbed in the aqueous phase. The last step was trypsination to detach germs remaining fixed onto the screws and contained in the biofilms of glycocalix. A germ count was made after each step. For each screw, we determined the difference (Delta) corresponding to the number of germs really adherent to the screw. Mann-Whitney analysis was performed.

RESULTS

On average, the germ count in the aqueous phase was 0.0855.10(5)/ml for the titanium screw versus 0.223.10(5)/ml for the bioabsorbable screw. The mean count of germs fixed in the biofilm (mean Delta) was 17.695+/-3.88.10(5) for the titanium screw and 45.86+/-3.61.10(5) for the bioabsorbable screw. The difference was statistically significant (p=0.0039).

DISCUSSION: Our experimental results support the efficacy of abundant arthroscopic lavage in a context of infection, confirming the results of very recent studies. However, irrespective of the type of material used, bioabsorbable screws are more prone to persistent microbial adherence than titanium screws. It is hypothesized that the hydrophilic, more porous microstructure of bioabsorbable screws favors bacterial adherence. In practice, this implies that arthroscopic washout must be as abundant and as complete as possible, yet may not be sufficient to clean the entire surface of potentially contaminated screw positioned deep in a bony tunnel.