Strength of antimicrobial bone cement decreases with increased poragen fraction

Background: Adding soluble particulate poragens to antimicrobial-loaded bone cement increases the permeability of the bone cement and increases the antimicrobial release, but the mechanical effect of adding poragens is not well known. Questions/purposes: We therefore asked the following questions: (1) Does the poragen fraction in antimicrobial-loaded bone cement affect its antimicrobial release? (2) Does poragen fraction in antimicrobial-loaded bone cement affect its compressive strength; and (3) Does the effect on compressive strength change over time in elution? Methods: Antimicrobial-loaded bone cement made in the proportions of 40 g polymer powder, 20 mL monomer liquid, 1 g tobramycin powder and one of six different doses of poragen powder (0, 1, 2, 4, 8, or 16 g of particulate xylitol per batch) was formed into standardized test cylinders and eluted for 30 days. We determined the cumulative recovered tobramycin and the change in compressive strength over 30 days of elution. Results: Antimicrobial release progressively increased with increasing poragen fraction. Compressive strength progressively decreased with increasing poragen fraction and with increasing time in elution. Poragen fractions greater than 2 g per batch caused the compressive strength to decrease below 70 MPa over 30 days of elution. Clinical Relevance: The use of poragens can increase elution of antimicrobials from antimicrobial-loaded bone cement. However, for implant fixation, to avoid deleterious reduction of compressive strength, the amount of poragen that can be added in addition to 1 g of antimicrobial powder may be limited to 2 g per batch.