The purpose of this study is to determine whether or not giving a lower dose of antibiotics (Vancomycin) in the area where it is needed (the knee joint) is more effective at obtaining adequate tissue levels of the antibiotic than the current standard dose which is given intravenously (IV) through a wrist vein. The use of intraosseous regional administration (IORA) of vancomycin requires the use of a tourniquet for the duration of the procedure. Many surgeons prefer to perform the surgery with tourniquet use minimised or without a tourniquet at all. The aim of this study is to evaluate whether IORA vancomycin can achieve effective tissue concentrations with tourniquet use minimised.

Patients are assigned to one of two groups by chance (like a coin toss):

GROUP A - Will receive 15mg/kg based on actual body weight (maximum of 2g) of vancomycin via the systemic route at a rate of 15mg/kg as per hospital guidelines. Systemic IV vancomycin is given via a forearm vein, given over an infusion timed to finish immediately prior to surgery.

GROUP B - Will have the limb exsanguinated and an above knee tourniquet inflated to 300 mmHg. Immediately following tourniquet inflation, Group B will receive 500mg of vancomycin, via an EZ-IO intraosseous cannula. The vancomycin would be administered in 150ml of saline solution. The intraosseous cannula would be placed into the epiphysis of the proximal tibia. The tourniquet will be left inflated for 10 minutes following completion of the IORA injection then deflated.

Both Groups will receive weight-based dose of systemic cefazolin ( or alternative antibiotic if allergic to cefazolin 15 minutes prior to inflation of tourniquet. This ensures all patients in the study receive effective antibiotic prophylaxis regardless of randomization. Both groups of patients would then undergo routine prep and draping For both groups, Total knee replacement would then be carried out as normal and the tourniquet will be inflated for cementation of the implants.

TISSUE SAMPLES Ten (10) tissue samples will be taken from each patient, 6 'fat' samples and 4 'bone' samples. Each sample is very small, around the size of a pinhead. Bone samples will be taken from the femur only to ensure no direct contamination from the site of injection (tibia) In addition, drain samples will be taken from the intra-articular drain site to measure vancomycin concentration the morning following surgery.

Three blood samples will be taken in both groups, intraoperatively, in recovery, and the following morning.

These samples are frozen and sent to a lab for analysis.

Inclusion Criteria

Primary Total Knee Arthroplasty for osteoarthritis Informed consent given

Exclusion Criteria

Current or treatment with IV Vancomycin within preceding 7 days Previous hypersensitivity to vancomycin Significant cardiac or respiratory abnormality Patient has contraindications to IO vascular access using the EZ-IO

Adverse events were collected from approximately 90 minutes prior to surgery to the morning after surgery for each subject, over the duration of approximately four months.