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.