An articulated antibiotic spacer used for infected total knee arthroplasty: A comparative in vitro elution study of Simplex® and Palacos® bone cements

Abstract

For the staged management of infected total knee arthroplasty (TKA), antibiotic laden polymethylmethacrylate (PMMA) spacers have been recommended. Antibiotic-impregnated PMMA spacers target drug delivery, achieving high local levels while limiting the potential for host toxicity associated with parenteral antimicrobial therapy. This study examined the elution characteristics of an articulating PMMA TKA spacer that has been useful clinically. Tobramycin and vancomycin are both active against many organisms leading to joint infections. We used various combined antibiotic concentrations (maintaining a relative ratio of 55% tobramycin to 45% vancomycin w/w), and then assayed the elution profile of the TKA spacer in vitro. Additionally, the elution qualities of two brands of bone cement, Simplexm and Palaces@, were compared. Briefly, three groups of PMMA spacers, impregnated with different antibiotic loads, were fashioned from a mold replicating a femoral TKA component. The entire spacer surface area was immersed in sterile phosphate buffered saline (PBS) in a 1.6 ratio of grams of cement to milliliters of PBS and incubated at 37 "C for 24 h. After 24 h, aliquot eluates were taken, the PBS discarded, and replaced with fresh, sterile PBS. PBS was changed daily and an aliquot was taken at least weekly for nine weeks. Eluate samples were stored at -70 "C until assayed. Each spacer eluate sample's antibiotic concentration was determined by disc diffusion bioassay against Bacillus subtilis. Mean zone inhibition diameters were extrapolated from the standard curve to yield micrograms per milliliter of antibiotic in PBS. In all groups the Palaces@ spacers demonstrated higher elution levels, above the MIC for the organism used, for a longer period of time than those made with Simplexa. Based on the observed elution profiles, antibiotic-impregnated Palaces@ bone cement may offer a more effective vehicle for local drug delivery during staged treatment of infected TKA.

Sufficient Release of Antibiotic by a Spacer 6 Weeks after Implantation in Two-stage Revision of Infected Hip Prostheses

“…Our data showing a local tissue concentration of antibiotics in excess of the MIC, even after 6 weeks of implantation, are consistent with data from the few studies analyzing antibiotic levels around the spacer in vitro or aspirates after several weeks [4,21,32]. Moreover the low rate of recurrence of infection with a two-stage approach supports the conclusion that the spacer releases sufficient, high amounts of antibiotics after that interval to treat infection and is not just fulfilling a physical, jointmaintaining function [9,10,25].…”

Comparing PMMA and calcium sulfate as carriers for the local delivery of antibiotics to infected surgical sites

“…Lastly, this work would be furthered by testing other types of PMMA monomer, which have been reported to have different elution characteristics and pore size. 19 In addition, various concentrations and combination of antibiotics in different cements should also be tested.…”

High concentration and bioactivity of vancomycin and aztreonam eluted from Simplex™ cement spacers in two‐stage revision of infected hip implants: A study of 46 patients at an average follow‐up of 107 days

“…In vivo and in vitro studies have demonstrated that many commonly used antibiotics are released from PMMA bone cement with a very high initial rate of drug delivery followed a rapid decline over a few days. [12][13][14][15] The articulating antibiotic PMMA spacers, however, are essentially different from the beads. The spacers have a cement-on-cement bearing surface, and obviously have a much smaller surface area to volume ratio.…”