Proper and rapid diagnosis of orthopedic device-related infection is important for successful treatment. Sonication has been shown to improve the diagnostic performance. We hypothesized that the combination of sonication with a novel method called microcalorimetry will further improve and accelerate the diagnosis of implant infection. We prospectively included 39 consecutive patients (mean age 59 years, 62% males) at our institution from whom 29 orthopedic prostheses and 10 osteosynthesis material were explanted. The explanted device was sonicated. The resulting sonication fluid was analyzed using microcalorimetry. Using standardized criteria to define orthopedic device-related infection, 12 cases (31%) were defined as infected. In all, positive periprosthetic tissue cultures were found. The sensitivity and specificity of microcalorimetry of sonication fluid were 100% and 97%, respectively. Mean time to detection, defined as time to reach a rising heat flow signal of 20 mW measured after equilibiration needed to get accurate measurement, was 10.9 h. In summary, microcalorimetry of sonication fluid is a reliable and a fast method in detecting the presence of microorganisms in orthopedic device-related infection. Keywords: microcalorimetry; sonication; implanted orthopedic device; infection Orthopedic implants such as joint prosthesis and fracture fixation devices are increasingly used to restore the functionality of the affected joint and the fractured bone.1,2 Unfortunately, it is estimated that 1-2% of these implants become infected.3 Orthopedic device-related infections are associated with significant morbidity and substantial health expenditures. 4 It is essential to differentiate implant-related infections from aseptic loosening because of the difference in clinical consequences. 4 However, it is difficult to make the diagnosis of implant-related infections because of variable and often subtle clinical presentation. Moreover, there are no uniform criteria for the diagnosis. 4 The diagnosis of implant related infection relies frequently on combination of clinical, imaging and histological findings, together with isolation of microorganisms from joint fluid or tissue.5 Next of being accurate, a diagnostic method for implant-related infection should be rapid in order to prompt appropriate treatment and shorten the duration of patient's morbidity.More recently, microbial cultures of samples obtained by sonication of prostheses have been shown to improve the diagnosis of prosthesic joint infection. 6 Yet, it can take up to five days before the definitive results can be released. More rapid diagnosis of implant-related infection is arguably needed in order to provide appropriate treatment.4 Isothermal microcalorimetry is a newly introduced technique in orthopedics. It can be used to detect the presence of microorganisms rapidly by measuring microbial heat production produced by microbial growth and metabolism. [7][8][9] This technique has been applied in medicine where rapid detection of microorganisms i...