Biomechanical analysis of additional vancomycin in articulating knee spacers: determining the threshold for...

Area of Science:

• Orthopedic surgery
• Biomaterials science
• Infectious disease management

Background:

• Periprosthetic joint infections (PJI) are a significant complication in arthroplasty.
• Two-stage revision with antibiotic-loaded polymethylmethacrylate (PMMA) spacers is standard for chronic PJI.
• The biomechanical effects of antibiotics in PMMA spacers require investigation.

Purpose of the Study:

• To evaluate the load-bearing capacity of PMMA knee spacers with varying vancomycin concentrations.
• To determine the structural failure thresholds of antibiotic-loaded PMMA spacers.
• To assess the impact of antibiotic concentration on spacer biomechanics.

Main Methods:

• Twenty PMMA knee spacers were tested, divided into low (5% vancomycin) and high (20% vancomycin) concentration groups.
• Spacers underwent uniaxial loading in standard weight-bearing and dislocated (10° angulation) positions.
• Breaking forces were measured, and statistical analyses (Mann-Whitney-U) were performed.

Main Results:

• Vancomycin concentration (5% vs. 20%) did not significantly affect breaking forces in either standard (38.7 vs. 35.5 kN) or dislocated (2.2 vs. 2.0 kN) positions.
• Dislocated configurations showed a 17-fold reduction in load capacity compared to standard positions.
• Spacer fractures occurred exclusively in the femoral components.

Conclusions:

• Vancomycin concentrations up to 20% do not compromise the structural integrity of PMMA knee spacers.
• Spacer positioning is a critical factor influencing biomechanical stability.
• Dislocation significantly reduces the load-bearing capacity of PMMA spacers.