This study aims to improve how doctors diagnose infections in patients with broken bones around joint replacements. Currently, there are no clear guidelines to help determine when an infection is present, making treatment decisions difficult. By studying how often infections are found through lab tests and identifying factors that predict infection, the investigators hope to create better ways to diagnose and care for these patients.

All steps in the protocol will be completed under the standard of care for our hospital's orthopedic joints and trauma surgeons. All patients identified under the inclusion criteria will undergo preoperative imaging. In accordance with current standards of care, patients with periprosthetic fractures (PPFs) around the hip will receive three views of X-rays of the hip and femur as well as the anterior-posterior view of the pelvis. Likewise, patients with PPFs around the knee will undergo X-rays that include the knee and femur. No advanced imaging (Computed Tomography, Magnetic Resonance Imaging, etc.) will be obtained for the purpose of this study.

Preoperative laboratory analysis will include C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) as inflammatory markers. Intraoperative synovial fluid analysis will be performed using synovial white blood cell (WBC) count and polymorphonuclear (PMN) percentage. Three cultures will be obtained from the involved joint fluid and tissue, and incubated for 14 days for analysis of aerobic, anaerobic bacterial cultures, fungal and acid-fast bacilli (AFB) analysis. The cultures will be collected from synovial fluid, peri-implant femoral synovium/periosteum, peri-implant tibial or acetabular synovium/periosteum. These laboratory tests and cultures are part of the standard protocol our surgeons have determined for their patient care.

Based on the Musculoskeletal Infection Society (MSIS) criteria for positive histology intraoperative histology will be performed utilizing frozen section analysis. These slides will be isolated from synovium, peri-implant femoral synovium/periosteum, and peri-implant tibial or acetabular synovium/periosteum. Additional cultures may be sent at discretion of surgeon but would not be included in analysis.

Per institutional protocol, preoperative cefazolin and vancomycin will be administered intravenously and continued for 24 hours perioperatively. Patients who are allergic to vancomycin will receive daptomycin, and those who are allergic to beta-lactam drugs including cephalosporins will be given gentamicin. No intra-articular antibiotics will be routinely administered.

All cultures will be followed until final. If cultures become positive, our institutional infectious disease (ID) department will be consulted for further recommendations and consideration for treatment.

Inclusion Criteria:

• Adult patients (>18 years old) with periprosthetic fractures around primary or revision hip or knee arthroplasty
• Patients requiring operative management for these fractures (fixation or revision arthroplasty)
• Patients presenting to the University of Chicago Medical Center during two (2) year period (October 2025 to October 2027)

Exclusion Criteria:

• Patients undergoing non-operative management for periprosthetic fractures
• Any documented or reported history of past prosthetic joint infection of the involved joint
• Sinus tract at the time of presentation at the involved joint

This population would include all consenting patients older than 18 years who present to the University of Chicago Medical Center with periprosthetic hip or knee fractures and will require operative management of the fracture or infection.