Coloured bone cements have been introduced to make the removal of cement debris easier at the time of primary and revision joint replacement. We evaluated the physical, mechanical and pharmacological effects of adding methylene blue to bone cement with or without antibiotics (gentamicin, vancomycin or both). The addition of methylene blue to plain cement significantly decreased its mean setting time (570 seconds (sd 4) vs 775 seconds (sd 11), p = 0.01), mean compression strength (95.4 MPa (sd 3) vs 100.1 MPa (sd 6), p = 0.03), and mean bending strength (65.2 MPa (sd 5) vs 76.6 MPa (sd 4), p < 0.001) as well as its mean elastic modulus (2744 MPa (sd 97) vs 3281 MPa (sd 110), p < 0.001). The supplementation of the coloured cement with vancomycin and gentamicin decreased its mean bending resistance (55.7 MPa (sd 4) vs 65.2 MPa (sd 5), p < 0.001).The methylene blue significantly decreased the mean release of gentamicin alone (228.2 µg (sd 24) vs 385.5 µg (sd 26), p < 0.001) or in combination with vancomycin (498.5 µg (sd 70) vs 613 µg (sd 25), p = 0.018) from the bone cement. This study demonstrates several theoretical disadvantages of the antibiotic-loaded bone cement coloured with methylene blue.

Introduction: A novel device for two-stage septic revision of TKA was checked to evaluate for mechanical and pharmacological properties. Methods: The articulated knee spacer is a temporary device made entirely of gentamicin bone cement industrially preformed and available in 3 sizes. It maintains joint space and motion, allowing partial weight-bearing. It provides an in situ release of antibiotic. Static and dynamic mechanical testing was performed according to ISO/DIN 14243-1. Surface rugosity was assessed according to DIN 4768. Pharmacological behaviour was evaluated according to the European Pharmacopoeia. Results: Static mechanical testing: the device resists a load > 10000N (physiological load peak = 2500N). Dynamic mechanical testing: no breakage after 500.000 cycles at 1300N (half load for physiological knee joint). Wear produced by the PMMA-PMMA coupling is not much higher than wear produced by PE-metal coupling. Surface rugosity (polishing effect) decreases of an order of magnitude after 8 weeks of implantation, and no difference is found between 8 weeks and 5 months of implantation. The in vitro gentamicin release in 7 days is around 2% of the initial amount of antibiotic and ranges from 15 mg (small) and 35 mg (large). Conclusions: The articulated knee spacer has excellent mechanical properties comparable to standard prostheses, which guarantee safety of use for the time of implantation foreseen (up to 6 months). As an ancillary property it delivers locally a high concentration of gentamicin.