Vancomycin elution from gamma-irradiated cancellous bone allograft: an in vitro study linking soaking concentration to clinically relevant antimicrobial thresholds.

Antibiotic-impregnated bone grafts can deliver high local antimicrobial concentrations while restoring structural defects, but wider adoption is held back by inconsistent preparation methods and elution data that are difficult to translate into intraoperative decisions. Gamma-irradiated cancellous femoral head allografts were morselised and soaked for 30 min in vancomycin solutions ranging from 0 to 100 mg/mL, using a standardised graft-to-solution ratio. Elution was assessed qualitatively by agar diffusion against Staphylococcus aureus and quantitatively by high-performance liquid chromatography (HPLC). Daily eluates were collected for up to 30 days and compared with the minimal inhibitory concentration (MIC) for S. aureus and with experimentally derived anti-biofilm reference values. A 1:1 (g:mL) graft-to-solution ratio gave mass-independent loading. Release followed a burst-then-decay profile across all concentrations. A 10 mg/mL soak sustained eluate concentrations above the S. aureus MIC for 14 days, consistent with a prophylactic use case. Soaks at 60-100 mg/mL produced Day 1 eluate concentrations of 1043-1920 mg/L, exceeding the experimental anti-biofilm reference range; these high levels were not sustained beyond the burst phase. Vancomycin elution from gamma-irradiated cancellous allograft is concentration-dependent. Pairing standardised soaking conditions with clinically relevant antimicrobial thresholds offers a practical basis for selecting graft preparation strategies-lower concentrations for prophylaxis and higher concentrations for adjunctive use after debridement. In vivo and biofilm-model validation is needed before clinical translation.