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Updated: Aug 23, 2025
An Improved Mechanical Testing Method to Assess Bone-implant Anchorage
Published on: February 10, 2014
Mechanical strength of antibiotic-loaded PMMA spacers in two-stage revision surgery
Andre Lunz1, Kevin Knappe2, Georg W Omlor2
1Clinic for Orthopedics, Center for Orthopedics, Trauma Surgery and Spinal Cord Injury, Heidelberg University Hospital, Schlierbacher Landstrasse 200a, 69118, Heidelberg, Germany. andre.lunz@med.uni-heidelberg.de.
Background:
Antibiotic-loaded polymethylmethacrylate (PMMA) bone cement spacers provide high local antibiotic concentrations and patient mobility during the interim period of two-stage revision for periprosthetic joint infection (PJI). This study compares mechanical characteristics of six dual antibiotic-loaded bone cement (dALBC) preparations made from three different PMMA bone cements. The study`s main objective was to determine the effect of time and antibiotic concentration on mechanical strength of dALBCs frequently used for spacer fabrication in the setting of two-stage revision for PJI.
Methods:
A total of 84 dual antibiotic-loaded bone cement specimens made of either Copal spacem, Copal G + V or Palacos R + G were fabricated. Each specimen contained 0.5 g of gentamicin and either 2 g (low concentration) or 4 g (high concentration) of vancomycin powder per 40 g bone cement. The bending strength was determined at two different timepoints, 24 h and six weeks after spacer fabrication, using the four-point bending test.
Results:
Preparations made from Copal G + V showed the highest bending strength after incubation for 24 h with a mean of 57.6 ± 1.2 MPa (low concentration) and 50.4 ± 4.4 MPa (high concentration). After incubation for six weeks the bending strength had decreased in all six preparations and Palacos R + G showed the highest bending strength in the high concentration group (39.4 ± 1.6 MPa). All low concentration preparations showed superior mechanical strength compared to their high concentration (4 g of vancomycin) counterpart. This difference was statistically significant for Copal spacem and Copal G + V (both p < 0.001), but not for Palacos R + G (p = 0.09).
Conclusions:
This study suggests that mechanical strength of antibiotic-loaded PMMA bone cement critically decreases even over the short time period of six weeks, which is the recommended interim period in the setting of two-stage revision. This potentially results in an increased risk for PMMA spacer fracture at the end of the interim period and especially in patients with prolonged interim periods. Finally, we conclude that intraoperative addition of 4 g of vancomycin powder per 40 g of gentamicin-premixed Palacos R + G (Group D) is mechanically the preparation of choice if a dual antibiotic-loaded bone cement spacer with high antibiotic concentrations and good stability is warranted. In any case the written and signed informed consent including the off-label use of custom-made antibiotic-loaded PMMA bone cement spacers must be obtained before surgery.
Insights
Antibiotic-loaded PMMA bone cement spacers lose significant mechanical strength within six weeks. Palacos R+G with 4g vancomycin is recommended for dual antibiotic-loaded bone cement spacers needing stability.
Area of Science:
- Biomaterials Science
- Orthopedic Surgery
- Infectious Disease
Background:
- Antibiotic-loaded polymethylmethacrylate (PMMA) bone cement spacers are crucial for managing periprosthetic joint infection (PJI).
- These spacers provide high local antibiotic delivery and maintain patient mobility during two-stage revision surgery.
- Understanding the mechanical properties of dual antibiotic-loaded bone cement (dALBC) is vital for spacer integrity.
Purpose of the Study:
- To compare the mechanical characteristics of six different dual antibiotic-loaded bone cement preparations.
- To evaluate the impact of time (24 hours vs. six weeks) and vancomycin concentration (2g vs. 4g) on the bending strength of dALBC.
- To determine the optimal dALBC formulation for stability in two-stage PJI revision.
Main Methods:
- Eighty-four dALBC specimens were fabricated using three PMMA bone cements: Copal spacem, Copal G+V, and Palacos R+G.
- Each specimen contained 0.5g gentamicin and either 2g (low) or 4g (high) vancomycin per 40g bone cement.
- Bending strength was assessed using a four-point bending test at 24 hours and six weeks post-fabrication.
Main Results:
- Copal G+V exhibited the highest bending strength at 24 hours for both low (57.6 MPa) and high (50.4 MPa) vancomycin concentrations.
- After six weeks, all preparations showed decreased bending strength.
- Palacos R+G with high vancomycin concentration (39.4 MPa) demonstrated superior strength at six weeks compared to other high-concentration groups. Low-concentration preparations were consistently stronger than high-concentration ones.
Conclusions:
- Mechanical strength of antibiotic-loaded PMMA bone cement significantly declines within six weeks, increasing the risk of spacer fracture.
- Palacos R+G with 4g vancomycin is the preferred preparation for dALBC spacers requiring high antibiotic concentration and mechanical stability.
- Informed consent for off-label use of custom antibiotic-loaded PMMA spacers is mandatory before surgery.
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