Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Surgery

Supervisor

Vasarhelyi, Edward M.

2nd Supervisor

Lanting, Brent A.

Abstract

The role and clinical significance of microorganisms in presumed aseptic revision total hip (THA) and knee arthroplasty (TKA) is unclear. The primary aim of this thesis was to determine the prevalence and infection-free survival of presumed aseptic revisions with unexpected positive intraoperative cultures (UPC) by analyzing the largest cohorts of UPC in the literature. Secondarily, a prospective pilot study using modern molecular techniques with an emphasis on stringent control of contamination was designed to determine how frequently microorganisms are present on implants of presumed aseptic revisions, as well as their location and association with reason for revision.

The prevalence of UPC was approximately 10%, the infection-free survival is encouraging, and the infection-free survival from the same UPC microorganism is outstanding. Patients with ≥2 UPC or a single UPC treated with antibiotics were more likely to have recurrent infection caused by the UPC microorganism. Patients with a single UPC and no other signs of infection do not require antibiotic treatment

The rate of UPC in the prospective molecular pilot study was also approximately 10% and we hypothesize that microorganisms will frequently be found on implants of ‘aseptic’ failures and associated with location and reason for revision.

Summary for Lay Audience

Over 1-million total hip (THA) and knee replacements (TKA) are performed in North America every year. Unfortunately, about 12% of these fail by the 10-year mark and require revision surgery to treat. Infection is a common reason for failure, however, there is no perfect test to diagnose infection. This can lead to the problem of unexpected positive bacterial cultures (UPC) in revisions done for non-infected reasons (loosening, instability, others). This is a problem because the surgical treatment of infected versus non-infected failure differs greatly. How often UPC occurs in presumed non-infected revisions is unclear. The optimal treatment and outcomes for these patients is also unclear.

The first goal of this thesis was to study UPC in the largest group of presumed non-infected revision THA and TKA patients to date. We found that about 10% of presumed ‘non-infected’ revisions have UPC. Most patients with UPCs did well and only a small number required more surgery for infection-related failure. Patients with a higher number of UPCs and those that were deemed to require antibiotic treatment were more likely to have infection-related failure caused by the same UPC bacterial microorganism. Lastly, patients with only one UPC and no other signs of infection do not require antibiotic treatment.

Furthermore, it is now suspected that a large number of ‘non-infected’ loose or failed implants are actually undiagnosed infection because modern molecular methods have identified bacterial microorganisms on some failed implants and a proportion of known infections never grow a bacterial microorganism.

Therefore, the second goal of this thesis was to design a modern molecular gene sequencing study to identify how often and what type of bacterial microorganisms are on THA/TKA implants that required revision surgery for ‘non-infection' causes. We expect to show that implants are frequently contaminated with bacterial microorganisms, and that bacterial microorganisms are associated with certain locations of failed joint implants and the reason for failure. These results will provide an important steppingstone to develop future studies that can determine the role and significance of microorganisms in presumed ‘non-infected’ THA and TKA failure, which we think may be greatly underestimated.

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