Differentiation of aseptic and septic nonunion using molecular biological, histopathological and laboratory criteria

Status:

completed 02/2024

Aims:

The treatment of aseptic and septic nonunion is based on different principles. Early, ideally preoperative determination of the genesis of nonunion is therefore an important step in optimizing treatment, also with regard to economic criteria. In addition, despite a typical clinical course of infection, microbiological diagnostics often fail to detect the presence of microorganisms, which delays the therapeutic procedure due to the need for further steps to confirm the diagnosis. The aim of this study was to develop further (pre-)operative diagnostic criteria to differentiate between aseptic and septic nonunion based on molecular, microbiological and histopathological findings to improve the differentiation of septic from aseptic nonunion.

Activities/Methods:

In a multicenter study, 45 patients with septic nonunion – including 23 patients with low-grade infection – and 62 patients with aseptic nonunion of the tibial or femoral shaft, as well as 34 patients with a regular healed tibial or femoral shaft fracture as a control group, were included. Preoperative blood counts, including routine inflammatory markers such as C-reactive protein, were obtained. Additionally, preoperative peripheral blood samples were collected for plasma biomarker analysis. During nonunion revision and implant removal, tissue samples were collected for long-term culture and histopathology. Osteosynthesis material was obtained for sonication and, additional tissue samples were collected for molecular biological analyses. Patients with nonunion were followed for twelve months.

Results:

Conventional intraoperative diagnostics demonstrated unsatisfactory diagnostic performance with a sensitivity of 69% and a specificity of 96% for long-term tissue culture, and a sensitivity and specificity of 14% and 87% for histopathology. The method of sonication with membrane filtration of the sonication fluid established in this study had a sensitivity of 52% and a specificity of 93%. In combination with long-term tissue culture, this method has the potential to increase the sensitivity of diagnosing septic nonunion from 55% to 62%. This method could become a routine clinical diagnostic tool. Additionally, interleukin-18 (IL-18) was identified as a potentially suitable preoperative biomarker in peripheral blood plasma. Hereby, in patients with an IL-18 level of less than 90.7 pg/ml infection as an underlying cause of nonunion can be excluded with a negative predictive value of 90%. Thus, IL-18 could potentially be used in clinical diagnostics after successful validation in another patient population. Analyses of systemic miRNA exosome profiles in a subset of the study population showed differences in the profiles of patients with septic versus aseptic nonunion. Therefore, the use of miRNA exosome profiles for diagnosing infection in nonunion is an innovative approach that should be explored in future studies based on these results.

Overall, the study results are highly relevant for accident insurance institutions as they represent a further step towards optimizing the diagnosis of nonunion, which is associated with a reduction in the number of revision surgeries and minimization of treatment costs. Additionally, the results may contribute to accelerating the reintegration of these patients back to work.

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