DNA-analysis of bacteria in prosthesis and implant infections after hip surgery.

For people undergoing prosthetic surgery, prosthetic joint infection (PJI) is one the most fearsome complications.1 PJI involves interactions between microorganisms and the implant and host immune system.2 The incidence of prosthetic joint infections is 1-2% in the existing literature, however this rate is higher with non-elective hip surgery (4-5%).

With an increasing number of joint replacement procedures worldwide, it is expected that the number of PJIs will increase as well.3 PJIs are associated with prolonged hospital stay, (multiple) revision surgeries, recurring infections, prolonged use of antibiotics, late aseptic loosening of prosthesis and poor functional outcome.4 PJI treatment is expensive, time-consuming and resource-intensive. Hospital costs per episode are approximately 89,000 and 116,000 dollars for hip and knee PJIs respectively.2 

Several risk factors for PJIs have been identified, a distinction can be made between surgical and patient related factors. The surgery-related risk factors include the location of arthroplasty, whether primary or revision surgery is performed, potential for soft tissue healing or soft tissue related complications, and the potential for presence of subclinical infection at the time of surgery. Postoperative complications such as wound dehiscence and hematoma are additional complications. Patient related factors are for example presence of comorbidities, such as diabetes mellitus, obesity and malignancy.5

A lot of preventative measures are taken in prosthetic surgery. Infection prevention strategies can be divided in strategies that target exogenous sources and endogenous sources. In orthopaedics the focus lies on targeting the exogenous factors such as limiting operating room traffic, laminar flow systems and sterility.6

Despite all these measures, the incidence of elective PJIs is still 1-2% (not accounting for (semi) acute surgery). The origin of the infection in clean skin incisions remains a matter of debate. There are various theories about the origin of the microorganism causing the infection. In the Deventer Hospital, the infection rate of the last few years was 4-5%, including non-elective surgery. Prior microbiological studies suggest that surgical site infections may arise from endogenous reservoirs of colonizing microbiota carried by the patient.7

Previous microbiological studies show that decolonizing of nasal carriers of S. aureus reduces the rate of surgical-site infections acquired in the hospital suggesting that surgical-site infections may arise from endogenous reservoirs.7-9 However, most guidelines continue to focus on environment related factors. Long et al presents a generalized model of surgical-site infection in patients undergoing spinal surgery using whole genome sequencing. They conclude that most surgical-site infections are caused by endogenous routes of infection, rather than microbes from the environment.7 No large study has been set up to study the origin of prosthetic joint infections. As the origin of infection remains a matter of debate and only little research is done in this field, this study might lead to new insights. 

As Staphylococcus aureus is the main pathogen in PJIs,10 this study will mostly include mono-infections with S. aureus. However, all infection pathogens will be analyzed. Most PJIs in Deventer Hospital are seen in hip surgery. Prosthetic hip surgery presents a useful model to study the origin of PJIs as this is a clean skin incision procedure. All prosthetic or trauma hip surgeries will be included in this study, total hip arthroplasty (THA), partial hip replacement/hemiarthroplasty, dynamic hip screws (DHS), and Trochanteric Fixation Nail Advanced (TFNA). The population undergoing hip surgery is varied, with a similar number of men and women. 

Using whole genome sequencing we will investigate whether the strain of bacteria causing the prosthetic joint infection is present in the patient’s microbiome preoperatively.

Whole genome comparison between microorganisms cultured from PJI and those cultured from preoperative swabs of the patients’ microbiome, to determine the origin of the infection. 

This study is a prospective, single-center, cohort, feasibility and proof-of-concept study that will be performed in the Deventer Hospital.

Acute or elective hip surgery with the implantation of fixative or prosthetic material.

The risks of participation in this study are neglectable for patients. Swabs will be taken nasally, orally, from the skin and around the anus. Taking swabs is a routine handling and will be performed with care by the operating personnel. Worst case scenario a minor wounding can occur. 

There are no clear benefits for the participating patients, but hopefully, with the outcomes of this study, the risk of postoperative infections can be reduced in the future.

Risks of the surgery will not change due to participation in this study.