A prospective, non-blinded, randomized controlled trial with the purpose of investigating, whether preoperative electrical clipping of body hair affects the risk of intraoperative contamination.

The primary investigators hypothesis is this: Preoperative electrical clipping of body hair in the operative field lowers the risk of intraoperative contamination.

200 male participants, 18 years or older, with a planned primary knee replacement surgery, will be enrolled.

During surgery, four microbiological samples will be taken from each participant.

The primary outcome is whether there is intraoperative contamination of the surgical site or not, determined by identification of any grown bacteria from the samples.

If this study finds, that the contamination rate is lowered by preoperative electrical clipping of body hair, it will provide a cost-effective method of reducing the risk of intraoperative contamination and consequent postoperative infection, a solid argument for a change of current guidelines for preoperative hair removal, and provide additional information pointing towards body hair as a possible explanation for the increased infection rate in men.

A late ph.d.-study conducted at Herlev and Gentofte Hospital has shown a 15 percentage difference in contamination rates when comparing participants who had their body hair removed preoperatively, and those who did not.

Based on the finds in the aforementioned study, the hypothesis for this study is that preoperative electrical clipping of body hair in the operative field lowers the risk of intraoperative contamination.

The purpose of this study is to investigate, whether preoperative electrical clipping of body hair affects the risk of intraoperative contamination.

A prospective, non-blinded, randomized controlled trial will be performed. The study population consists of 200 male patients, 18 years or older, with a planned primary knee replacement surgery. The study population consists of only male patients, since males generally have denser body hair and a higher contamination rate than females. Exclusion criteria include known skin disease, use of antibiotics 4 weeks prior to surgery, if patients due to mental reasons, a language barrier or other reasons are unable to participate in the study, as well as no body hair in the surgical field.

Participants will be randomized to either the intervention group (preoperative electrical clipping) or the control group (leaving the body hair intact) using a 1:1 randomization ratio. The randomization is performed electronically by a medical student or the operating surgeon and the pre-assessment consultation.

Clipping is performed by hospital staff on the day of surgery. The degree of body hair on both knees is photo-documented for all participants, for the intervention group after the clipping of body hair on the relevant knee has been performed.

During the surgery, biological material from every participant is collected as four microbiological samples, taken using Copan ESwabs. The first swab is taken before the skin is surgically prepared, the second immediately after incision of the skin, the third swab is taken just prior to the change of gloves performed before cementation of the prothesis, and the last swab is taken after closure of the joint capsule before closure of the skin. Samples will be collected at Orthopedic Departments of Gentofte Hospital. All samples will be sent to Department of Clinical Microbiology, Herlev Hospital, for culturing.The bacteria will be identified following Danish guidelines.

The material consists of culture results from all samples. The primary outcome is whether there is intraoperative contamination of the surgical site or not. This is determined by identification of any grown bacteria.The material will be statistically analyzed using the program R Studio. Since data is categorial, a chi-squared test will be performed to evaluate the significance of the possible difference of contamination rate in the two participant groups.

All possibilities for conducting the study are known to exist, as the method described above has previously been used in the PhD study conducted at the department: "Intraoperative microbial contamination, its prevention and its consequences for outcomes following knee replacement surgery- The ICON study".

Personal data is processed as part of the project. All handling and processing of personal data follows the Data Protection Regulation and the Data Protection Act.

Data collected during the pre-assessment consultation will be entered directly into a database. Only data in this database will be available to the investigators conducting the study, for further analysis. Information about the microbiological samples and cultures will be entered into the database as well. All information in the database will be anonymized 2 years after collection of data is complete.

By consenting to participating in this study, participants also consent to the investigators conducting the study, Herlev-Gentofte Hospital and their representatives to be given direct access to the collected data. Consenting to participate also involves consenting that the Regional Committee on Health Research Ethics are allowed direct access to all data collected, to facilitate their control with the project.

If this study finds, that the contamination rate is lowered by preoperative electrical clipping of body hair, it will not only provide a cost-effective method to reduce the risk of intraoperative contamination and consequent postoperative infection, but may also lead to a change of current guidelines to preoperative electrical clipping of body hair becoming a permanent practice. In addition, the study will confirm existing finds pointing towards body hair as a possible explanation for the increased infection rate in men.

A decrease in the incidence of infections will save patients from unpleasant and often prolonged consequences of infection, including pain, revisions, antibiotic treatments and, at worst, loss of mobility. In addition, fewer infections will lead to savings in the health care system, with the release of funds and beds, to the benefit of patients in general and the social economy.

Inclusion Criteria:

• Planned primary knee replacement surgery

Exclusion Criteria:

• Known skin disease
• Use of antibiotics 4 weeks prior to surgery
• If patients due to mental reasons, a language barrier or other reasons are unable to participate in the study
• No body hair in the surgical field

The study population consists of only males, since males generally have denser body hair and a higher contamination rate than females.

There is no plan to share individual partcipant data, but anonymized data can be made available upon request after publication of the study.