Elution and Biomechanical Properties of Meropenem-Loaded Bone Cement

Concomitant Cement Spacer and Peri-spacer Fractures Seven Years After First-stage Revision Knee Arthroplasty: A Case Report

Introduction

Prosthetic joint infections (PJIs) remain an undesirable complication after total knee arthroplasties. Two-stage revision arthroplasty is the current standard of care for treating PJIs. However, the incidence of spacer retention for prolonged periods is increasing, with little known about its potential complications.

Case Report

We present a case of a 64-year-old female of Southeast Asian descent who had a cement spacer maintained in-situ for 7 years due to poor patient compliance with subsequent follow-up.

Conclusion

While patients have satisfactory functional outcomes with the cement spacer, it is not meant for permanent weight bearing. Two-stage revision arthroplasties are only as effective as patients' compliance with subsequent follow-up and surgery. Clinicians must discourage patients from forgoing subsequent follow-up visits and surgery despite satisfactory function and quality of life with the cement spacer in situ to prevent complications related to prolonged retention of cement spacers.

Effects of vancomycin and tobramycin on compressive and tensile strengths of antibiotic bone cement: A biomechanical study

Purpose

This study aims to compare the compressive and tensile strengths of bone cement mixed with various concentrations of vancomycin, tobramycin, and combinations of the two.

Methods

12 mm × 6 mm antibiotic bone cement samples were created by vacuum mixing 0-4 g of vancomycin, tobramycin, and combinations of the two in 0.5 g increments per one pouch (40 g) of Palacos LV cement. An Instron 3369 Universal Testing System was used to determine the compressive and tensile strengths.

Results

Compressive and tensile strengths of the bone cement without antibiotics were 118 ± 4 MPa and 30.3 ± 12 MPa, respectively. 4 g of vancomycin alone decreased the compressive strength to 108 ± 4 MPa (p-value 0.001) and decreased the tensile strength beginning at 2 g which yielded a strength of 28.1 ± 12 MPa (p-value 0.016). Tobramycin alone decreased the tensile strength beginning at 1.5 g yielding a strength of 27.7 ± 7 MPa (p-value 0.003). Although it decreased compressive strength at 1 g to 117 ± 7 MPa (p-value 0.002), it demonstrated variable effects with increasing concentrations. A combination of vancomycin and tobramycin decreased both the compressive (111 ± 5 MPa, p-value 0.014) and tensile (27.9 ± 8 MPa, p-value 0.007) strengths beginning at 1 g each.

Conclusions

Various combinations of vancomycin and tobramycin affect the compressive and tensile strengths of bone cement. Clinicians should be diligent when mixing these antibiotics in bone cement to prevent possible failure of the constructs.

Mechanically stable rifampin antibiotic cement inhibits Pseudomonas aeruginosa biofilm surface growth

Rifampin has been proven to be effective in the treatment of prosthetic infections due to its ability to intercalate into biofilms. The use of rifampin in antibiotic spacers is not well described, which would be especially important in the local periprosthetic environment where parenteral doses have poor penetration. The null hypothesis tests if rifampin use in polymethyl methacrylate (PMMA) cement will show no clinically significant impact on mechanical strength at antibiotic concentrations that remain bactericidal. Test antibiotic cement samples supplemented with 0, 30, 50, 100, 150, or 200 mg of rifampin into a standard 40 g bag were tested for compression to failure using published ASTM standards. The samples were then inoculated with Pseudomonas aeruginosa and either evaluated for lipopolysaccharide (LPS) presence as a marker of biofilm or tested by elution as the Kirby Bauer assay. Rifampin concentrations of 30 and 50 mg, showed no statistically different mechanical characteristics from control PMMA (p > 0.05). The 100-mg sample fell within the acceptable range of compressive strength and had significantly less LPS and bacterial presence compared to the control at 12 and 24 h. The ability of PMMA with 100 mg of rifampin to maintain its structural integrity and have significant bacterial inhibition at 12 and 24 h makes it a great candidate as an antibiotic bone cement additive. PMMA loaded with up to 100 mg of rifampin shows promise in the treatment and prevention of periprosthetic joint infection for total knee and total hip arthroplasty.