Time-dependent microbial colonisation of temporary external fixations: a prospective descriptive study

The temporary use of external fixators is an established method for stabilising fractures, particularly for injuries that do not initially allow definitive treatment. Despite its frequent use, it remains unclear whether the interval between fixator application and subsequent definitive fracture treatment affects microbial colonisation of the fixation screws prior to internal fixation.

This prospective, single-centre study included patients aged 18 years or older between April 2023 and April 2024 who received a temporary fixator during initial fracture management. During definitive osteosynthesis, two bone-anchored Schanz screws were removed under sterile conditions and processed by sonication; the study was approved by the local ethics committee with written informed consent obtained from all participants. The primary endpoint was the incidence of positive sonication. In cases with microbial detection, the microbial spectrum was assessed, and the influence of fixation time and patient-related factors on colonisation and microbial distribution was analysed. Statistical analyses included chi-square testing, univariate analyses, and multivariable logistic regression with fixation duration modelled both dichotomously and as a continuous variable.

A total of 271 patients (n = 542 samples; two screw tips per patient processed together) were included. The median fixation time until definitive osteosynthesis was 8 days. Positive microbial colonisation was observed in 88 patients (32.5%). Patients with an external fixation time > 8 days (n = 120) showed a significantly higher colonisation rate of 43.3% (odds ratio 2.44, 95% CI 1.46-4.09; p = 0.001) compared with patients with ≤ 8 days (n = 151; colonisation rate 23.8%; p < 0.001). Frequently detected organisms included Staphylococcus epidermidis, Staphylococcus capitis and Staphylococcus aureus. Pre-existing conditions such as type 2 diabetes mellitus, nicotine abuse and BMI showed no significant impact on colonisation. An ASA score ≥ 3 was associated with a higher colonisation rate in multivariate analysis (OR 1.59; 95% CI 1.01-2.49; p = 0.043).

Fixation duration showed a significant time-dependent association with microbiologically detected colonisation of Schanz screw tips. When modelled continuously, each additional day of fixation was associated with increased odds of colonisation. An ASA score ≥ 3 was independently associated with colonisation probability.