Polyurethane: An Old Material for a New Generation of Antibiotic Spacer Implants

Background

Polyurethane tibial and acetabular inserts that release high concentrations of antibiotics were used with debridement and implant retention to treat prosthetic joint infections. The hypothesis was that a low-friction, antibiotic-releasing bearing could provide a simpler, safer, and more patient-accepted treatment for infection using antibiotic cement and intravenous antibiotics.

Methods

Patients (n = 106) with culture-positive infections received antibiotic inserts. Vancomycin and tobramycin were mixed into the polyurethane polymer at 7% by weight. Contraindications to debridement antibiotics and implant retention were a sinus tract, loose prostheses, and/or the wound could not be closed. Measurable outcomes were success in controlling infection, complications, patient acceptable symptomatic state, and need for revision surgery. Antibiotic levels were measured in joint fluid and blood; laboratory mechanical wear tests were performed; and results were compared to bone cement and polyethylene containing antibiotics.

Results

Antibiotic-infused spacers sustained joint fluid antibiotic levels 8-12 times the therapeutic level and produced low serum levels with no toxicities. Mechanical testing showed low wear and retained mechanical integrity. All patients achieved complication-free remission of infection at a follow-up of 5-26 years. All patients had Harris hip and Knee Society scores above 85, and 68% achieved patient acceptable symptomatic state.

Conclusions

All patients achieved remission of infection, fewer complications compared to revision using antibiotic bone cement, no antibiotic toxicity or adverse drug reactions, and 68% achieved patient acceptance. The antibiotic polyurethane inserts provided antibacterial efficacy comparable with currently used bone cement spacers, and their wear rate was approximately 20 times lower than bone cement as an articulation.