| Summary: | Viscoelastic properties of bone cement are crucial to determining the integrity of the fixation interface in cemented arthroplasty. The curing process of polymethylmethacrylate (PMMA) bone cement is highly dependant upon particular environmental conditions and therefore it is extremely difficult to accurately predict key stages for delivery based upon time alone. Current surgical procedures rely on subjective and time-based measurements to indicate the delivery of bone cement and insertion of joint prostheses. Therefore, a need was identified for a more reliable method of measuring the properties of curing bone cement in a peri-operative environment. A prototype rheometer for bone cement was developed based on previously validated self- sensing actuator technology. The device was designed for laboratory use and was shown to repeatably characterise the complete curing behaviour of a wide range of orthopaedic PMMA bone cements in terms of their viscoelastic properties. Operation of the device was made possible via a computer interface that provided real time rheological data used to indicate specific points in cure for the in vitro investigation of cemented total hip arthroplasty procedures. Methods were established to identify a range of key viscoelastic properties of commercial bone cements and simultaneously investigate typical variability in subjective measurement techniques. Identified clinical viscoelastic properties were used .to investigate experimentally the effect of bone cement viscosity on the level of interdigitation in a standardised bone model and resulting cement-bone constructs were examined using three-dimensional image analysis. The effect of identified viscoelastic properties on stem insertion and fixation was also explored using a standardised stem insertion model. The results demonstrated that subjective handling techniques for identifying bone cement properties are unreliable, particularly for late stages in cure. Variations in the viscoelastic properties of bone cement at delivery were shown to produce a significant difference in the level of interdigitation, however cement formulation was also shown to be a critical factor for the flow of cement through trabecular bone. Viscosity at the point of stem insertion was shown to affect insertion force and the strength of the cement-stem interface and results indicated that late stem insertion may be recommended for improved fixation at the cement- bone interface.
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