Indicators of Bacterial Colonization in Failed Anterior Cruciate Ligament Reconstructions

OBJECTIVES: Anterior cruciate ligament (ACL) repair is one of the most common orthopedic procedures performed, with over 175,000 operations performed each year. While rare, graft failure can be a detrimental complication. A 2003 meta-analysis by Freedman et al. reported failure rates between 1.9% and 4.9%. There is a higher risk of ACL repair failure among younger patients and those that underwent allograft procedures (versus autograft). Despite extensive study of graft failure, the mechanism of graft failure remains poorly understood. However, traumatic loading, infection, and surgical error have all been suggested to play a roll. Colonization of ACL reconstruction graft with low virulence bacteria could cause graft tissue attenuation without overt clinical symptoms and predispose patients to ACL graft failure. Polymerase chain reaction (PCR) is a highly sensitive method for detecting bacteria present in very low concentrations and detecting species that cannot be reliably cultured clinically. We hypothesize that DNA form bacteria may be present in torn graft tissue at time of revision ACL reconstruction. METHODS: A total of 31 revision ACL cases (mean age 28; sd 5.1) and 5 primary ACL reconstruction controls (all hamstring autograft; mean age 27; sd 4.6) from one academic medical center were included. All revisions were first time revisions and had no clinical signs of infection. Among revision cases, autograft was used in 22/31 (71%) and allograft in 9/31 (29%) at the time of index operation. Mean time to failure was 15.8 months (range 6 months-7 years). A sample from the graft material was obtained using new sterile instruments from the tribal tunnel and directly transported ot the lab. DNA extraction techniques were used to isolate and purify DNA from each sample. PCR and DNA sequencing analysis were used to determine the presence and quantity of DNA in each sample. RESULTS: Bacterial DNA was detectable in graft tissue in the majority of revision ACL cases 27/31 (87.0%) and less commonly 1/5 (20%) in primary ACL autograft controls (p=0.002, Chi-square test). Median bacterial DNA concentration in torn grafts at time of revision ACL was low at 17.5 ng/ml (range 0-101) with no difference found between revision patients with allograft (median 18.6 ng/ml range 0-45) vs. autograft (median 17.1 ng/ml range 0-105) used at time of primary ACL reconstruction (p=0.56, Wilcoxon rank sum). CONCLUSION: Bacterial DNA was detectable in graft tissue in the majority of revision ACL cases 27/31 (87.0%) and less commonly 1/5 (20%) in primary ACL autograft controls (p=0.002, Chi-square test). Median bacterial DNA concentration in torn grafts at time of revision ACL was low at 17.5 ng/ml (range 0-101) with no difference found between revision patients with allograft (median 18.6 ng/ml range 0-45) vs. autograft (median 17.1 ng/ml range 0-105) used at time of primary ACL reconstruction (p=0.56, Wilcoxon rank sum).