The dynamic volume changes of polymerising polymethyl methacrylate bone cement

Abstract

The Swedish hip register found an increased risk of early revision of vacuum-mixed cemented total hip replacements. The influence of cement mixing technique on the dynamic volume change in polymerising PMMA is not well understood and may be relevant to this observation. Applying Archimedes' principle, we have investigated the dynamic volume changes in polymerising cement and determined the influence of mixing technique. All specimens showed an overall volume reduction: hand-mixed 3.4% and vacuum-mixed 6.0%. Regression analysis of sectional porosity and volume reduction showed a highly significant relationship. Hand-mixed porous cement showed a transient volume increase before solidification. However, vacuum-mixed cement showed a progressive volume reduction throughout polymerisation. Transient expansion of porous cement occurs at the critical time of micro-interlock formation, possibly improving fixation. Conversely, progressive volume reduction of vacuum-mixed cement throughout the formation of interlock may damage fixation. Stable fixation of vacuum-mixed cement may depend on additional techniques to offset the altered volumetric behaviour of vacuum-mixed cement.

The mechanical behavior of PMMA/bone specimens extracted from augmented vertebrae: A numerical study of interface properties, PMMA shrinkage and trabecular bone damage

“…5, top left). Taken together, these effects reduced the initial stiffness of the PMMA/bone composite on average by 18%, at a low volumetric shrinkage of 2% (Muller et al, 2002). Accordingly, healing of the damaged trabecular bone will increase the stiffness.…”

“…This value was calculated from the back-calculated elastic modulus and a tissue yield strain of 1.1% (taken from Bayraktar et al, 2004). (4) A volumetric shrinkage of 2% (Muller et al, 2002;Kühn, 2000) was added to model 3 before the compression step to obtain model 4. A recently published shrinkage model (Briscoe and New, 2010) was used and thermal expansion was neglected.…”

“…Osteointegrative bone cements (Hench and Thompson, 2010) overcome this disadvantage by promoting attachment and ongrowth of bone such that a mechanically strong interface forms over time Goto et al, 2006;Mattila et al, 2009). The interface between PMMA based cements and bone is also affected by polymerization shrinkage, which ranges from 2.0% to 6.0% in volume (Muller et al, 2002), because gaps develop between bone and cement as a result of the volume change (Lewis, 2008). Shrinkage may also be an important factor for the mechanical properties of the composite's constituents.…”

“…Shrinkage may also be an important factor for the mechanical properties of the composite's constituents. First, the apparent volume change of the cement was highly correlated with its final porosity (Muller et al, 2002). Second, residual stresses will occur in the trabecular bone due to the interlocking with the shrinking cement and might result in bone damage.…”

CT volumetry of intravertebral cement after kyphoplasty. Comparison of polymethylmethacrylate and calcium phosphate in a 12-month follow-up

“…Thus we were able to measure absolute values of the cement volume. Baseline CT was not performed immediately after kyphoplasty because there are known dynamic volume changes of PMMA during the process of polymerization and temperature variations [30,31]. We considered a 48-h interval appropriate for PMMA and expected no dimensional changes from that time.…”