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 [1].
Mixer design has been found to significantly influence the quality of cement [2]. 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 [3] and these conditions can lead to fatigue failure of the cement mantle [4] and [5].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 [6]. The HiVac™ range uses charcoal filters that reduce fumes down to levels that are only a small fraction of these guideline limits. Figure 5 |
