• Hip and knee surgery

The hip joint is a ball-and-socket joint connecting the femur to the pelvis, allowing for a wide range of motion and supporting weight-bearing activities. It is covered with articular cartilage that cushions and facilitates smooth movement. However, osteoarthritis (OA) of the hip, a degenerative condition, can occur in the aging population. OA involves the gradual breakdown of cartilage, narrowing the joint space, and causing pain, stiffness, and reduced mobility. Various factors, including age, obesity, trauma, and genetics, contribute to the development of OA. While OA cannot be cured, it can be managed through painkillers, weight loss, physical therapy, and lifestyle modifications. When conservative treatments fail, total hip arthroplasty (THA) may be recommended. THA, also known as total hip replacement, involves replacing the damaged hip joint with an artificial prosthesis. The history of THA dates back to the late 19th century, with significant advancements occurring in the 1960s, thanks to Sir John Charnley's pioneering work. Today, THA is a common and successful orthopedic procedure performed worldwide, benefiting patients with conditions like OA, fractures, and hip diseases. However, it is not without risks, as complications can necessitate revision surgery. Revision surgery is performed to address complications, such as prosthetic joint infection (PJI), which can have serious implications for patients and lead to increased healthcare costs. Diagnosing PJI is challenging due to its variable clinical manifestations. Various tests, including cultures of intraoperative biopsies and synovial fluid analysis, have been used to diagnose PJI. Revision surgery due to PJI leads to prolonged hospital stays, increased re-admissions, and potential complications, including antibiotic-related side effects. Studies have shown varying outcomes regarding the risk of death after PJI revision, with further research needed for conclusive results. The incidence of PJI is on the rise, likely due to factors like an aging population and improved diagnostics. Identifying modifiable risk factors and taking preventive measures before planned THA is essential to reduce the risk of PJI. The impaction of general previous infection is important to investigate as some patients might be more prone to infections and preventive measures and strategies must be developed to reduce the risk of PJI. One potentially overlooked factor is the seasonality of PJI rates. Some studies have suggested a link between higher PJI rates during the summer, possibly due to climate-related factors. However, more research with larger sample sizes and comprehensive analyses is needed to fully understand this association. In conclusion, PJI is a serious complication following THA, with significant implications for patients and healthcare systems. Understanding and mitigating risk factors, including potential seasonality, is crucial to improving patient outcomes and reducing the burden of PJI on healthcare resources. This PhD study aims to contribute to this knowledge by analyzing extensive data from Danish health registers, offering valuable insights into PJI risk factors and their impact on patient outcomes following primary THA.

Study I:
“No association between previous general infection and prosthetic joint infection after total hip arthroplasty - A national register-based cohort study on 58,449 patients who have osteoarthritis“
This study investigated the association between any previous hospital-diagnosed or community treated infection up to 6 months before primary THA and the risk of revision due to PJI, any revision, and revision due to aseptic loosening. We included 58,449 patients who were operated with primary unilateral THA between 2010 and 2018. All patients had 1-year follow-up and found that previous hospital-diagnosed or community-treated infection 0 to 6 months before primary THA does not increase the risk of PJI revision. However, it may be associated with increased risk of any revision.

Study II:
“Total hip arthroplasty performed in summer is not associated with increased risk of revision due to prosthetic joint infection: A cohort study on 58,449 patients with osteoarthritis from the Danish Hip Arthroplasty Register”
This study investigated the association between season of primary THA and the risk of revision due to PJI, any revision, and revision due to aseptic loosening in a Northern European climate. The population was the same as study I, and thus we included the same 58,449 patients who were operated with primary unilateral THA between 2010 and 2018 with 1-year follow-up. We found no association between summer and the risk of PJI revision or any revision.

Study III:
“Risk of second revision and mortality following first-time revision due to prosthetic joint infection after primary total hip arthroplasty: Results on 1,669 patients from the Danish Hip Arthroplasty Register”
This study investigated the risk of any second revision, second revision due to PJI and mortality following first-time revision due to PJI after primary THA. We included 1,669 first-time revisions within 1 year following primary THA during 2010 and 2019 and followed the patients for up to 10 years. We found that the risk of any second revision and second revision due to PJI was significantly increased following first-time revision due to PJI compared to non-PJI. 1st revision due to PJI did not increase the mortality risk within 10 years after primary THA.