The dynamic volume changes of polymerising polymethyl methacrylate bone cement

Area of Science:

• Biomaterials Science
• Orthopedic Surgery
• Materials Engineering

Background:

• An increased risk of early revision for vacuum-mixed cemented total hip replacements has been observed.
• The impact of cement mixing techniques on the dynamic volume changes of polymerizing polymethyl methacrylate (PMMA) is not fully understood.
• These volumetric changes may be linked to the observed clinical outcomes.

Purpose of the Study:

• To investigate the dynamic volume changes in polymerizing bone cement.
• To determine the influence of different mixing techniques (hand-mixed vs. vacuum-mixed) on these volume changes.
• To correlate volume changes with cement porosity and potential effects on implant fixation.

Main Methods:

• Application of Archimedes' principle to measure dynamic volume changes during cement polymerization.
• Preparation of both hand-mixed and vacuum-mixed cement specimens.
• Regression analysis to assess the relationship between sectional porosity and volume reduction.

Main Results:

• All cement specimens exhibited overall volume reduction: 3.4% for hand-mixed and 6.0% for vacuum-mixed.
• A highly significant relationship was found between sectional porosity and volume reduction.
• Hand-mixed cement showed a transient volume increase before solidification, while vacuum-mixed cement demonstrated progressive volume reduction throughout polymerization.

Conclusions:

• The transient expansion in hand-mixed cement may enhance fixation by improving micro-interlock formation.
• Progressive volume reduction in vacuum-mixed cement during interlock formation could potentially compromise fixation.
• Stable fixation with vacuum-mixed cement might necessitate additional techniques to counteract its altered volumetric behavior.