The goal of this clinical trial is to learn if intraosseous antibiotic (cefazolin) administration can improve antibiotic levels in adults undergoing primary total hip replacement. The main question it aims to answer is:

• Does intraosseous cefazolin increase antibiotic concentrations in blood and tissue compared with standard intravenous cefazolin alone? Researchers will compare patients receiving intraosseous cefazolin plus standard intravenous cefazolin to those receiving placebo injection plus standard intravenous cefazolin to see if local antibiotic delivery improves outcomes.

Participants will:

• Receive standard intravenous cefazolin before surgery and either intraosseous cefazolin or placebo
• Provide blood samples before and after antibiotic administration
• Have small tissue samples collected during surgery
• Complete routine postoperative follow-up and outcome assessment for 90 days

Inclusion Criteria:

• Age ≥ 18 years
• Scheduled to undergo primary total hip arthroplasty
• Receiving standard institutional antibiotic prophylaxis with IV bolus cefazolin prior to surgery

Exclusion Criteria:

• Reduced renal function (GFR < 30)
• Reduced liver function (AST/ALT > 3× upper limit of normal)
• Weight > 120 kg
• Undergoing bilateral total hip arthroplasty
• Documented cefazolin anaphylaxis
• Active joint infection
• History of diabetes
• Inflammatory arthropathies
• Inability to understand written and/or spoken English
• Undergoing revision total hip arthroplasty