Antibiotic calcium sulphate beads lower the bacterial burden and prevent infection in a mouse model of periprosthetic joint infection.

Abstract

Delayed postoperative inoculation of orthopaedic implants with persistent wound drainage or bacterial seeding of a haematoma can result in periprosthetic joint infection (PJI). The aim of this in vivo study was to compare the efficacy of vancomycin powder with vancomycin-eluting calcium sulphate beads in preventing PJI due to delayed inoculation. A mouse model of PJI of the knee was used. Mice were randomized into groups with intervention at the time of surgery (postoperative day (POD) 0): a sterile control (SC; n = 6); infected control (IC; n = 15); systemic vancomycin (SV; n = 9); vancomycin powder (VP; n = 21); and vancomycin bead (VB; n = 19) groups. Delayed inoculation was introduced during an arthrotomy on POD 7 with 1 × 10⁵ colony-forming units (CFUs) of a bioluminescent strain of <i>Staphylococcus aureus</i>. The bacterial burden was monitored using bioluminescence in vivo. All mice were killed on POD 21. Implants and soft-tissue were harvested and sonicated for analysis of the CFUs. The mean in vivo bioluminescence in the VB group was significantly lower on POD 8 and POD 10 compared with the other groups. There was a significant 1.3-log₁₀ (95%) and 1.5-log₁₀ (97%) reduction in mean soft-tissue CFUs in the VB group compared with the VP and IC groups (3.6 × 10³ vs 7.0 × 10⁴; p = 0.022; 3.6 × 10³ vs 1.0 × 10⁵; p = 0.007, respectively) at POD 21. There was a significant 1.6-log₁₀ (98%) reduction in mean implant CFUs in the VB group compared with the IC group (1.3 × 10⁰ vs 4.7 × 10¹, respectively; p = 0.038). Combined soft-tissue and implant infection was prevented in 10 of 19 mice (53%) in the VB group as opposed to 5 of 21 (24%) in the VP group, 3 of 15 (20%) in the IC group, and 0% in the SV group. In our in vivo mouse model, antibiotic-releasing calcium sulphate beads appeared to outperform vancomycin powder alone in lowering the bacterial burden and preventing soft-tissue and implant infections.