Biomet Cement and Cementing Systems

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Vacuum Mixing & Delivery

Influence of porosity on mechanical strength

Failure and loosening of a cemented implant is associated with poor biomechanical properties of the bone cement and can occur within the cement mantle itself. Large voids and flaws within the cement may lead to a cement mantle fracture caused by rapid crack propagation. Because macroporosity has been shown to be a cause of reduced fatigue strength and mechanical failure, reduction of cement porosity is a logical step.

Porosity at the cement–implant interface may result in biomechanical weakening and diminished longevity of a cemented hip arthroplasty. Several finite element model studies suggest that the cement–implant interface is the mechanical weak link of a cemented femoral prostheses. Improving the strength of this interface likely increases the longevity of the cemented implant.²³

Vacuum mixing techniques significantly influence cement porosity, strength and consequently, revision risk. Vacuum mixing itself has been shown to reduce cement interface porosity.^24,25

Fatigue properties
To ensure the survival and success of cement in vivo, it must be able to withstand the varying loads it endures. That is why a cement’s fatigue property is important in determining the long-term survival of the joint replacement it secures. Fatigue failure begins with a small crack that develops slowly under cyclical loading, leading eventually to sudden failure. The initial crack is likely to start in an area of weakness, e.g. a void in the material. Evidence of fatigue cracks indeed has been found in examining retrieved cement.^17,26

Reduction of porosity can postpone or prevent altogether the initiation of fatigue propagation.

Bone cement fatigue strength has been improved by modern mixing techniques. Vacuum mixing significantly reduces the number of air bubbles and increases fatigue strength.^7,16,26,27