Intraoperative tissue sampling for histology in chronic osteomyelitis shows high neutrophil infiltration centrally and low remains in debrided presumed infection-free regions

Introduction: Histology of debrided bone tissue is a confirmatory diagnostic criterion for fracture related infection (FRI) and prosthetic joint infection (PJI). The aim of the present study was to describe the histopathology of the first and last debrided bone tissue in chronic osteomyelitis (CO) according to the international diagnostic guidelines for FRI and PJI.Methods: 15 patients with CO were allocated to surgical treatment using a one-stage protocol including extensive debridement. Suspected infected bone tissue eradicated early in the debridement procedure was collected as a clearly infected sample (S1). Likewise, the last eradicated bone tissue was collected as a suspected non-infected sample (S2). The samples were processed for histology. HE-stained sections were patho-morphologically examinated. Immunohistochemistry with MAC-387 antibodies towards calprotectin was used for estimation of neutrophil granulocyte (NP) score (0, 1, 2 or 3).Results: S1 samples showed a mean NP score of 2.6 (3 is confirmatory for infection). Following debridement, the NP score was significantly (p = 0.005) reduced to a mean NP score of 1.6. The S1 samples showed a mix of fibrovascular tissue, dense fibrosis, viable bone, bone necrosis and bone debris. S2 samples contained mostly viable bone tissue, however, often small fragments of necrotic bone or bone debris were present.Conclusion: The inflammatory response of CO still exists after debridement, although the response fades from the center. Therefore, sampling of debrided bone tissue for histology must be performed initially during surgery, otherwise there is a risk for underestimation of NP infiltration. The present results might also be highly relevant for FRI and PJI.