Abstract
Aim
Unexpected positive infections are distinct entity in prosthetic revision surgery. The prevalence and characteristics of unexpected positive cultures in internal fixation are however less established. The aim of this study was to describe the prevalence and characteristics of unexpected diagnosis of infection in a prospective cohort of revision surgeries following internal fixation.
Method
We reviewed the microbiological results following 356 surgeries that included partial or complete removal of internal fixation, performed in 328 patients (54% male, mean age 53 ± 17 years), in which infection was not initially suspected. This prospective study was performed in a large single center for musculoskeletal surgery from 2013–2017. The implants most commonly removed were plate and/or screws (281 cases, 78,9%), followed by intramedullary nails (64 cases, 18,0%). The main indications for surgery were nonunion (89 cases, 25%) and symptomatic hardware (70 cases, 19,7%). All removed implants were sonicated, and tissue cultures were obtained depending on the surgeon's criteria. Diagnosis of infection was established by the presence of 2 or more positive tissue cultures (1 with a highly virulent microorganism), or ≥ 50 colony-forming units found in the sonication fluid.
Results
Infection was confirmed in 47 cases (13,2%); diagnosis was obtained with tissue cultures in 5 cases (1,4%), sonication in 14 cases (3,9%) and a combination of both sonication and tissue samples in 28 cases (7,9%). In another 24 cases (6,7%), ≥ 50 CFU of low-virulence microorganisms were isolated in the sonication fluid, but no tissue samples were available to confirm the diagnosis. Low-virulent microorganisms such as Propionibacterium acnes (22 cases / 46,8%) or coagulase-negative Staphycoccci (13 cases, 27,7%) were most commonly isolated. Sonication was key for the diagnosis of 61,7% of unexpected-positive surgeries. Nearly half of the patients received a new implant (internal fixation in 40,4%; arthroplasty in 6,4%), but only 34% of the patients were treated with antibiotics on discharge.
Conclusions
Unexpected diagnosis of infection occurs in approximately 13,2% of revision surgeries following internal fixation, most commonly due to low-virulent microorganisms. Sonication was key for the diagnosis of the majority of these infections. The clinical relevance of these infections remains unclear, though the insertion of new implants raises concern. We recommend sonication of all internal fixation devices removed, especially if new implants are inserted in the revision surgery.
