Introduction: The current evidence on the efficacy of Antibiotic Loaded Bone Cement (ALBC) in reducing the risk of periprosthetic joint infections (PJI) after primary joint reconstruction is insufficient. In several European countries, the use of ALBC is routine practice unlike in the US where ALBC use is not approved in low-risk patients. It has been claimed that the antibiotic in ALBC increase the risk of aseptic loosening, risk of systemic toxicity, allergic reaction, and bacterial resistance. Therefore we designed a double-blinded (patients and data analysts) pragmatic multicenter register-based randomized controlled non-inferiority trial to investigate the effects of ALBC compared to plain bone cement in primary total knee arthroplasty (TKA).

Methods and analysis: A minimum of 9,172 patients undergoing full-cemented primary TKA will be recruited and equally randomized into the ALBC group and the plain bone cement group. This trial will be conducted in Norwegian hospitals that routinely perform cemented primary TKA. . The primary outcome will be risk of revision surgery due to PJI at 1-year of follow-up. Secondary outcomes will be:

• risk of revision due to any reason including aseptic loosening at 1-, 6-, 10-, and 20-years of follow-up;
• patient related outcome measures (PROMs) like function, pain, satisfaction, and health-related quality of life at 1-, 6-, and 10-years of follow-up;
• risk of changes in the microbial pattern and resistance profiles of organisms cultured in subsequent revisions at 1-, 6-, 10-, and 20-years of follow-up; and
• cost-effectiveness of routine ALBC vs plain bone cement use in primary TKA. We will use 1:1 randomization with random permuted blocks and stratify by participating hospitals to randomize patients to receive ALBC or plain bone cement. Inclusion, randomization, and follow-up will be through the Norwegian Arthroplasty Register.

Ethics and dissemination: The trial has been approved by the Western Norway Regional Committees on Medical and Health Research Ethics (REK-Vest) (reference number: 2019/751/REK vest) dated: 21.06.2019. The trial results will be reported following the Consolidated Standards of Reporting Trials Extension (CONSORT Extension) reporting guideline 2010 statement for non-inferiority trials. The trial results will be reported to the public through national and international scientific conferences, participating hospitals, patient organizations, and peer-reviewed journals.

Discussion: If we find that plain bone cement is non-inferior to the ALBC, it will challenge the routine use of ALBC in primary arthroplasty, due to ecological concerns and costs. However, if routine use of ALBC is associated with a reduced risk of PJI and with minor impact on bacterial resistance, PROMs, and costs, the well-established use of prophylactic ALBC in primary arthroplasty will be supported

Inclusion Criteria:

• all patients undergoing full-cemented primary TKA irrespective of the diagnosis leading to TKA

Exclusion Criteria:

• any history of infection in the knee, a need for fully stabilized or hinged TKA, a history of allergy to the antibiotics used in the cement, inability or not willing to consent for inclusion in NAR or the trial, and participation in other studies that might have pharmacological interaction with this trial.

This is a double blinded, non-inferiority register-based multicenter randomized controlled trial study. To ensure blinding of the patients, all patients are operated by the same surgical method and the type of cement is unknown to the patients. In this study, blinding of the surgeon is not possible because the surgeon recognizes the cement type and has to document the type of cement in the registration form. We believe the primary endpoint of this trial is not likely to be influenced by the surgeon knowledge of the cement used in the index surgery. The data analyst will be blinded for groups until the entire trial analysis has been completed to minimize the risk of bias that may be introduced during the statistical analysis because of the selective use and reporting of statistical tests.