High prevalence of bacteria in clinically aseptic non-unions of the tibia and the femur in tissue biopsies

Purpose There are several hints that bacterial colonization might be an often overseen cause of non-union. Modern procedures like PCR have been reported to diagnose bacterial colonization with a high degree of accuracy. While PCR is not ubiquitously available, we hypothesize that biopsies from the non-union site are comparable to PCR results reported in the literature. Methods Retrospective analysis of microbiological results of biopsies from non-unions (femoral or tibial, history of revision surgery, and/or open fracture) with stable osteosynthesis, no clinical signs of local infection were analysed. CRP and leucocyte count were taken on admission. Multiple tissue samples (soft tissue and bone) were from the non-union (1–4 cm incision). Samples were cultivated for 2 weeks and tested following EUCAST protocols using VITEK ® 2. Results 11 tibia- and 7 femur non-union (44 ± 23.9 years), 11 open fractures (1 I°, 6 II°, 4 III° Gustillo Anderson), 0–5 revisions, and 4.1 (± 1.8) tissue samples were taken 8.5 (± 1.7) months after trauma. Cultures were positive in 8/18 (44,4%) (3/18 Propionibacterium acnes , 1/18 S. capitis , and 4/18 S. epidermidis ). There was neither a correlation between number of biopsies taken and positive culture results (Pearson R : − 0.0503, R 2 0.0025), nor between positive culture results and leucocytes counts (Pearson R : − 0.0245, R 2 0.0006) or CRP concentration (Pearson R : 0.2823, R 2 0.0797). Conclusion The results confirm that the presence of bacteria in cases with no clinical signs of infection is a relevant issue. The prevalence of bacteria reported here is comparable that reported from cohorts tested with PCR or sonication. In most cases, there was only one positive biopsy, raising the question whether a contamination has been detected. Thus, to better understand the problem, it is necessary to gather more knowledge regarding the sensitivities and specificities of the different diagnostic procedures.