Bacterial Biofilms Are Associated With Tunnel Widening In Failed ACL Reconstructions

OBJECTIVES: Technical errors, traumatic re-injury, and biologic failure all play a potential role in failure after ACL reconstruction (ACLR). Recent work has demonstrated the frequent presence of biofilms on failed ACLR grafts. Tunnel widening is commonly observed upon presentation for revision ACLR but the relationship between biofilm presence and tunnel widening is unclear. The purpose of this study is to determine whether tunnel widening is associated with bacterial biofilms in failed ACL reconstructions. METHODS: 34 consecutive revision ACLR cases and 5 primary ACLR controls were included. Tissue biopsies were obtained from tibial, femoral, and intra-articular segments of revision cases and torn native ligament as well as excess hamstring graft after fixation from primary ACLR controls. Clinical cultures as well as PCR for bacterial DNA with a universal primer were obtained on all patients. Fluorescence microscopy was used to visually confirm presence of biofilm. No patients had clinical signs of infection. Tunnel diameters were measured on pre-operative 3-dimensional imaging. RESULTS: Bacterial DNA was present in 87% of cases and 20% of controls. Cultures were only positive (coagulase negative staphyloccous sp.) in one revision case, the widest measured tunnel diameters were in this same case (20.1 mm for the tibial tunnel and 16.9 mm for the femoral tunnel) Bacterial DNA was positively associated with wider femoral tunnels (median 10.6 mm with detectable bacterial DNA, median 7.6 mm without detectable bacterial DNA; p=0.04 Wilcoxon rank-sum). There was a trend toward higher rates of bacterial DNA in tibial tunnels with diameters greater than 12.5 mm (LR chi square p= 0.12). Fluorescence microscopy confirmed presence of staphylococcal biofilms adherent to the soft tissue graft surface (Figure 1) as well as inert fixation material including monofilament suture, braided suture, and PEEK and metal interference screws. CONCLUSION: Bacterial biofilms are commonly encountered on failed ACLR grafts. These biofilms do not cause clinically apparent infection symptoms but are associated with tunnel widening and may contribute to biologic failure.