Mechanical strength of antibiotic-loaded PMMA spacers in two-stage revision surgery

Abstract

Background Antibiotic-loaded polymethylmethacrylate (PMMA) bone cement spacers provide high local antibiotic concentrations and patient mobility during the interim period of two-stage revision for periprosthetic joint infection (PJI). This study compares mechanical characteristics of six dual antibiotic-loaded bone cement (dALBC) preparations made from three different PMMA bone cements. The study`s main objective was to determine the effect of time and antibiotic concentration on mechanical strength of dALBCs frequently used for spacer fabrication in the setting of two-stage revision for PJI. Methods A total of 84 dual antibiotic-loaded bone cement specimens made of either Copal spacem, Copal G + V or Palacos R + G were fabricated. Each specimen contained 0.5 g of gentamicin and either 2 g (low concentration) or 4 g (high concentration) of vancomycin powder per 40 g bone cement. The bending strength was determined at two different timepoints, 24 h and six weeks after spacer fabrication, using the four-point bending test. Results Preparations made from Copal G + V showed the highest bending strength after incubation for 24 h with a mean of 57.6 ± 1.2 MPa (low concentration) and 50.4 ± 4.4 MPa (high concentration). After incubation for six weeks the bending strength had decreased in all six preparations and Palacos R + G showed the highest bending strength in the high concentration group (39.4 ± 1.6 MPa). All low concentration preparations showed superior mechanical strength compared to their high concentration (4 g of vancomycin) counterpart. This difference was statistically significant for Copal spacem and Copal G + V (both p < 0.001), but not for Palacos R + G (p = 0.09). Conclusions This study suggests that mechanical strength of antibiotic-loaded PMMA bone cement critically decreases even over the short time period of six weeks, which is the recommended interim period in the setting of two-stage revision. This potentially results in an increased risk for PMMA spacer fracture at the end of the interim period and especially in patients with prolonged interim periods. Finally, we conclude that intraoperative addition of 4 g of vancomycin powder per 40 g of gentamicin-premixed Palacos R + G (Group D) is mechanically the preparation of choice if a dual antibiotic-loaded bone cement spacer with high antibiotic concentrations and good stability is warranted. In any case the written and signed informed consent including the off-label use of custom-made antibiotic-loaded PMMA bone cement spacers must be obtained before surgery.

Daptomycin-Impregnated PMMA Cement against Vancomycin-Resistant Germs: Dosage, Handling, Elution, Mechanical Stability, and Effectiveness

“…Despite Lunz et al [29] pointing out that an antibiotic concentration exceeding 10% of the powder volume significantly reduces the mechanical strength of PMMA spacers, they recommend manually admixing 4 g of vancomycin with 40 g of PALACOS ® R+G instead of using the commercially available COPAL ® G+V. These spacers do not comply with the ISO requirements, as the bending strength for PALACOS ® R+G + 4 g of vancomycin is below the minimum threshold of 50 MPa and comes with the potential risk of bone cement or spacer fracture [15,19,21,29]. Therefore, we assessed the mechanical stability of a daptomycin-containing bone cement.…”

“…To best treat MRSE, MRSA, or enterococci, the PIF Pocket Guide [16] recommends increasing the vancomycin concentration in commercially available COPAL ® G+V (40 g) by another 2 g. But an increase in the addition of antibiotic powder beyond a total concentration of 10% results in a spacer cement that no longer fulfills the mechanical ISO requirements for bone cement [15,19,28]. Despite Lunz et al [29] pointing out that an antibiotic concentration exceeding 10% of the powder volume significantly reduces the mechanical strength of PMMA spacers, they recommend manually admixing 4 g of vancomycin with 40 g of PALACOS ® R+G instead of using the commercially available COPAL ® G+V. These spacers do not comply with the ISO requirements, as the bending strength for PALACOS ® R+G + 4 g of vancomycin is below the minimum threshold of 50 MPa and comes with the potential risk of bone cement or spacer fracture [15,19,21,29].…”

Systematic Review on the Current Situation and Development of Local Antimicrobial Agents in Revision Arthroplasty for Periprosthetic Joint Infection (PJI)

“…The local delivery reduces the systemic side effects that are related with prolonged oral or intravenous antibiotic therapy. Cement spacers play also a role in providing mechanical stability which allows for the preservation of joints as well as mobility during treatment, this especially makes them feasible for example in cases where the infected prosthetic may need to be temporarily removed (Lunz et al, 2022).…”

Surgical Management of Periprosthetic Joint Infections in Hip and Knee Megaprostheses

“…In our own practice, antibiotic-loaded polymethylmethacrylate (PMMA) spacers are inevitable in staged revisions with large bone defects, but obviously require secondary removal, and antibiotic elution from the PMMA is limited [41,42]. In the past, antibiotic collagen sponges with the addition of gentamicin were used, but there is little evidence to support their use in megaprosthetic reconstructions and relevant amounts of antibiotics might only be present for a few days [43].…”