Rotational Axis Design
Fixed Axis Mixing Mechanism Design
Research suggests that the quality of the cement mix is critical in achieving long term joint survival
Summit Medical Ltd recognises the importance of prolonged patient well-being
Bone cement must be able to withstand the high and complex loading that it is subjected to throughout the lifetime of the implant.
During walking, the hip joint force exceeds 4 times body weight and this is applied cyclically .
Mixer design has been found to significantly influence the quality of cement . Figure 1&2
This paper shows significantly better mix quality from a rotational axis device compared to that created by hand mixing or a fixed axis bowl.
Patients with hip/knee replacements take on average 5000 steps per day  and these conditions can lead to fatigue failure of the cement mantle  and .Therefore fatigue resistance of the cement should be optimised to prevent fatigue failure. Figure 3
This test data reinforces the work by Kurdy and shows significantly higher fatigue life from cement mixed with the HiVac™ Bowl (rotational axis mechanism) compared to that produced by hand or from a fixed axis device.
To further enhance fatigue life, cement needs to be mixed under optimal vacuum levels. If the vacuum level is too low then the cement will contain high levels of porosity, but if too high, excessive thermal shrinkage can create cracking in the cement mantle. The HiVac™ range operates at 550mmHg, which has been shown to give improved mechanical properties. Figure 4
Exposure to methylmethacrylate (MMA) fumes is a concern of many people who work in the vicinity of bone cement mixing. Health and Safety Executive (HSE) guidelines recommend a maximum exposure for these fumes of 100ppm during a 15 minute period . The HiVac™ range uses charcoal filters that reduce fumes down to levels that are only a small fraction of these guideline limits. Figure 5
1. Paul, 1976. Approaches to design; Force actions transmitted by joints in the human body. Proc R Soc Lond B, 192, 163-172
2. Kurdy NMG, Hodgkinson JP, and Haynes R, 1996. Acrylic bone-cement; influence of mixer design and unmixed powder. J Arthroplasty, 11(7), 813-819
3. Schmalzried TP, Szuszczewicz ES, Northfield MS, Akizuki KH, Belcher G and Amstutz HC, 1998. Quantitive assessment of walking activity after total hip or knee replacement. J Bone Surgery, 80A (1), 54-59
4. Jasty M, Maloney WJ, and Bragdon CR, 1991.The initiation of failure in cemented femoral components of hip arthoplasties. J Bone Joint Surgery, 73B, 551-558.
5. Topoleski LDT, Ducheyne P and Cuckler JM, 1990. A fractographic analysis of in vivo polymethylmethacrylate bone cement failure mechanisms. J Biomed Materials Res, 24, 145-154
6. Cary R, Morris L, Cocker J, Groves J and Ogunbiyi A, 1995. Methylmethacrylate: Criteria Document for an occupational exposure limit. Health and Safety Executive
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