Arthrite septique après ligamentoplastie du pivot central sous arthroscopie : comparaison in vitro du comportement de deux types de vis d’interférence vis-à-vis de la fixation du Staphylococcus aureus

Abstract

L’arthrite septique de genou est une complication rare, mais problématique des ligamentoplasties arthroscopiques de reconstruction du pivot central. Les bactéries fixées sur les vis d’interférence et constituant un biofilm peuvent être à l’origine des échecs des traitements médicochirurgicaux. Nous avons testé le comportement de deux types différents de vis d’interférence face à la colonisation par Staphylococcus aureus (S. aureus). Six vis en titane et six vis biorésorbables ont été incubées 48 heures à 37° dans un bouillon nutritif contenant 10⁶ S. aureus par millilitre. La quantité de bactéries fixées sur les vis a été mesurée par le décompte des bactéries libérées après rinçage et trypsination. Même après quatre rinçages, il restait des bactéries adsorbées en phase aqueuse à la surface des deux types de vis. Les moyennes des bactéries fixées sur les vis en titane (17,695.10⁵ ± 3,88.10⁵) et sur les vis biorésorbables (45,86.10⁵ ± 3,61.10⁵) étaient statistiquement différentes par le test de Mann-Whitney (p = 0,0039). Ces résultats montrent que malgré plusieurs lavages et quelle que soit la nature du matériau utilisé, il existe une fixation microbienne persistante sur les deux types de vis. Les vis biorésorbables semblent plus propices à l’adhésion microbienne que les vis en titane.

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 9 mm × 25 mm, 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 (Δ) 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 0.0855.10⁵/ml for the titanium screw versus 0.223.10⁵/ml for the bioabsorbable screw. The mean count of germs fixed in the biofilm (mean △) was 17.695 ± 3.88.10⁵ for the titanium screw and 45.86 ± 3.61.10⁵ 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.