Comparison of Soft Tissue Culture and Bone Tissue Culture in Diabetic Foot Infections with Osteomyelitis

INTRODUCTION: This study aimed to compare soft tissue and bone tissue cultures obtained from patients with diabetic foot infections accompanied by osteomyelitis.
METHODS: The study included 36 patients aged 18 years and older who underwent bone debridement or amputation due to diabetic foot infection with osteomyelitis between April 1, 2017, and April 1, 2018. The data of 36 patients were analyzed prospectively. Bone tissue cultures were compared with soft tissue cultures taken during debridement or amputation. Statistical analyses were performed using IBM SPSS Statistics 22. The concordance between soft tissue and bone tissue cultures was assessed using the McNemar test and the kappa coefficient.
RESULTS: A total of 36 patients participated in this study, 80.5% (29/36) of whom were male, with a mean age of 64.2±11.6 years (range 43-86). According to the Wagner classification, 14 patients (38.9%) had stage 3, 17 patients (47.2%) had stage 4, and 5 patients (13.9%) had stage 5 diabetic foot wounds. The most common wound localization was the plantar area. Osteomyelitis was diagnosed in 28 patients (68.7%) through clinical evaluation and direct radiographs, in 6 patients (16.6%) by MRI, in 1 patient (2.8%) by CT, and in 1 patient (2.8%) by histopathology. The most frequently isolated microorganisms from bone and soft tissue cultures were Pseudomonas aeruginosa (16.6%), coagulase-negative Staphylococcus (CNS) (15.1%), and Escherichia coli (13.6%). The same microorganism was detected in both bone and soft tissue cultures in 20 (55.5%) of the 36 patients. In five patients (13.9%) with culture-positive soft tissue specimens, bone culture specimens remained sterile. In one patient (2.8%) with a culture-positive bone specimen, the soft tissue specimen remained sterile. One patient (2.8%) had different microorganisms in bone and soft tissue specimens. In nine patients (25%), no bacterial growth was observed in either bone or soft tissue cultures. A total of 29 patients (80.5%) were found to have concordant bone and soft tissue cultures. In the statistical analysis, the kappa coefficient was 0.574, which was considered moderate agreement (p>0.05, kappa coefficient=0.574).
DISCUSSION AND CONCLUSION: According to the results of our study, soft tissue cultures may be used instead of bone tissue cultures to predict microorganisms in diabetic foot osteomyelitis. However, our findings need to be validated by studies with larger sample sizes.