title: 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.
authors.affiliation: Department of Trauma and Orthopaedics, The Medical School, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK. s.d.muller@net.ac.uk
authors.forename: Scott D
authors.initials: SD
authors.lastname: Muller
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Green
authors.forename: Andrew W
authors.initials: AW
authors.lastname: McCaskie
mesh_terms: D001843:Bone Cements / Q000009:adverse effects* / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D006622:Hip Prosthesis; D006801:Humans; D008422:Materials Testing; D008968:Molecular Conformation; D019904:Polymethyl Methacrylate / Q000009:adverse effects* / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D016062:Porosity; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013997:Time Factors; D014618:Vacuum
chemical_list: D001843:Bone Cements; D019904:Polymethyl Methacrylate