Does the Addition of Low-Dose Antibiotics Compromise the Mechanical Properties of Polymethylmethacrylate (PMMA)?

Abstract

The increasing numbers of total joint replacements and related implant-associated infections demand solutions, which can provide a high-dose local delivery of antibiotics. Antibiotic-loaded bone cement (ALBC) is an accepted treatment method for infected joint arthroplasties. The mechanical properties of low-dose gentamicin-loaded bone cement (BC) in medium- and high-viscosity versions were compared to unloaded BC using a vacuum mixing system. As an additional control group, manual mixed unloaded BC was used. In a uniaxial compression test, ultimate compressive strength, compressive yield strength, and compression modulus of elasticity, as well as ultimate and yield strain, were determined according to ISO 5833-2022 guidelines. All groups exceeded the minimum compressive strength (70 MPa) specified in the ISO 5833 guidelines. Both ALBC groups showed a similar ultimate compressive and yield strength to the unloaded BC. The results showed that vacuum mixing increased the compression strength of BC. ALBC showed similar compressive strength to their non-antibiotic counterparts when vacuum mixing was performed. Added low-dose gentamicin acted as a plasticizer on bone cement. From a biomechanical point of view, the usage of gentamicin-based ALBC formulations is viable.

Keywords: antibiotic-loaded bone cement; compression testing; gentamicin; local delivery of antibiotics; mechanical properties; periprosthetic joint infection.

Figure 1

Distribution of the volume fraction in % across study groups.

Figure 2

Micro-CT imaging in the 50% cross-section across study groups with color mapping indicating density level. Graphs show the mean particle diameter distribution along the samples for the four different groups under investigation.

Figure 3

Example of stress–strain curves of the four different groups following uniaxial compression testing.

Figure 4

Box plots showing the mean ultimate compressive strength [MPa] as dots; the 25th, 50th, and 75th percentiles as boxes; and minimum/maximum as bars across study groups. ** indicates 0.002 > p > 0.001, *** indicates p < 0.001.

Figure 5

Box plots showing the mean yield strength [MPa] as dots; the 25th, 50th, and 75th percentiles as boxes; and minimum/maximum as bars across study groups. * indicates 0.05 > p > 0.002.

Figure 6

Box plots showing the mean ultimate compressive strain [%] as dots; the 25th, 50th, and 75th percentiles as boxes; and minimum/maximum as bars across study groups.

Figure 7

Box plots showing the mean yield strain [%] as dots; the 25th, 50th, and 75th percentiles as boxes; and minimum/maximum as bars across study groups. * indicates 0.05 > p > 0.002, *** indicates p < 0.001.

Figure 8

Box plots showing the mean compression modulus of elasticity [GPa] as dots; the 25th, 50th, and 75th percentiles as boxes; and minimum/maximum as bars across study groups. *** indicates p < 0.001.

Figure 9

Antibiotic elution profile of hand-mixed and vacuum-mixed Palacos R + G cements.