Biomedical subjects
Publications and source records attributed to R Eveleigh.
This is the first in a series of four consecutive articles on bone cement mixing. It aims to bring to the perioperative practitioners' attention, all of the factors that will influence the quality and reproducibility of the bone cement they produce. The series will demonstrate how perioperative practitioners can have a direct influence on the successful long-term result of a hip or knee replacement.
The hip joint is subjected to large, repetitive loads. It is therefore clear that the bone cement, which allows the transfer of load across the new joint, must be able to withstand the everyday loads that it will be subjected to. Improving the mechanical properties of the cement to withstand high stresses, fatigue and creep loading will reduce the chances of failure, ultimately increasing the longevity of the joint replacement. To date, work in this area has concentrated on improving the mechanical properties of bone cement through improved bone cement mixing techniques. In the next issue we will be covering the effect that the design of the mixer and vacuum mixing has on improving the mechanical properties, such as the strength, fatigue and creep resistance, of the bone cement.
The aim of a good cement mix is to produce bone cement that has the best mechanical properties possible in order that it can carry out its load transfer role successfully over the lifetime of the implant. The data presented shows that vacuum mixing reduces the cement porosity, which results in improved strength, and resistance to creep deformation and fatigue failure in the bone cement. It seems, however, that eliminating a high degree or all of the cement porosity may be detrimental because it leads to greater shrinkage and cracking in the material. A moderate vacuum level will improve the mechanical properties, but reduce the risk of thermal shrinkage and cracking which is seen at higher vacuum levels. In addition, the mixer design has a significant influence on the quality of the cement produced, affecting porosity, unmixed powder and subsequently the mechanical properties of the material. In the next issue we will be concluding this series of articles by covering the importance of temperature and its effects on the phases of the cement polymerisation process. Bone cement training courses are being run within hospitals by Summit Medical as part of our commitment to enhancing the skills of the perioperative practitioner and to ensuring the best long-term outcome for the patient.
Bone cement mixing is often seen as a simple procedure, but the skill of the perioperative practitioner in mixing the cement may ultimately be the difference between the success and failure of a hip or knee joint replacement. Klaus-Dieter Kühn (2000) states: 'The nurses (together with the surgeon) have enormous influence on the quality of the cement dough produced; in the end, this will considerably influence the clinical long-term result of a cemented hip, acetabulum or cemented knee.' (Bone Cements). This process doesn't happen by default. It is the result of good education, supported by sound evidence and backed up by practical experience. This series of articles has explained every aspect of cement management, covering technique, temperature, timing, mixing equipment, the importance of reproducible cement quality and health and safety issues.
Syringe mixing systems have been introduced, but few data exist regarding the mechanical performance of cement they produce. We compared the properties of polymethyl methacrylate cement produced by these systems with that produced by a multiaxial bowl. Mixtures of cement were prepared using the Optivac, Cemvac, and Summit syringes and the Summit bowl. The mixtures were cured in molds to create casts that were radiographed and analyzed for void content, then cut into strips, weighed, measured, and tested to failure in 4-point bending. Syringe-mixed cement was of greater density, bending modulus, and bending strength than bowl-mixed cement (Mann-Whitney, P < .01) and contained fewer microvoids and macrovoids (Mann-Whitney, P < .01). No significant differences between the syringes were found for these variables (Kruskall-Wallis, P > .05).