Effects of test sample shape and surface production method on the fatigue behaviour of PMMA bone cement

Abstract

There is no consensus over the optimal criterion to define the fatigue life of bone cement in vitro. Fatigue testing samples have been made into various shapes using different surface preparation techniques with little attention being paid to the importance of these variations on the fatigue results. The present study focuses on the effect of test sample shape and surface production method on the fatigue results. The samples were manufactured with two cross sectional shapes: rectangular according to ISO 527 and circular according to ASTM F2118. Each shape was produced using two methods: direct moulding of the cement dough and machining from oversized rods. Testing was performed using two different bone cements: SmartSet GHV and DePuy CMW1. At least 10 samples of each category were tested, under fully reversed tension-compression fatigue stress at ±20MPa, to allow for Weibull analysis to compare results. The growth of fatigue cracks was observed by means of the changes in the absorbed energy and apparent modulus. It was found that fatigue crack growth can be altered by the sample shape and production method; however it is also dependent on the chemical composition of the cement. The results revealed that moulded samples, particularly those based on the ASTM F2118 standard, can lead to up to 5.5 times greater fatigue lives compared to the machined samples of the same cement. It is thus essential, when comparing the fatigue results of bone cement, to consider the effect of production method along with the shape of the test sample.

Influence of test specimen fabrication method and cross-section configuration on tension–tension fatigue life of PMMA bone cement

“…Table 3 Comparison of the changes in the fatigue performance index (I) due to the change in loading type for different sample types of SmartSet GHV and CMW1 bone cements Table 3 Comparison of the changes in the fatigue performance index (I) due to the change in loading type for different sample types of SmartSet GHV and CMW1 bone cements, showing tension-tension (T.T) vs. tensioncompression (T.C). The tension-compression data taken from Sheafi and Tanner (2014).…”

“…Pore size was checked visually. All the other testing conditions and data acquisition procedures were as in our previous study (Sheafi and Tanner, 2014). The cycles to failure, N f , and cyclic stress-strain data were recorded.…”

“…For the third method, the instantaneous absorbed energy (area inside the hysteresis cyclic stress-versus strain plot) and the secant modulus (slope of the cyclic stressstrain plot) for certain load cycles were each plotted against N f (Sheafi and Tanner, 2014;Slane et al, 2014).…”

“…As yet, there seem to be no studies considering the effect of loading type on stress-controlled fatigue behaviour of bone cement or of using various specimen types while maintaining the same general testing conditions. Using identical testing procedures to our previous study on the effects of sample type on the fully reversed fatigue behaviour of bone cement (Sheafi and Tanner, 2014), this study examines the fatigue behaviour of bone cement when applying tension only fatigue on various sample types and compares the findings to those for fully reversed tension-compression at the same stress amplitude.…”

Biomechanics of Natural Fiber Green Composites as Internal Bone Plate rafted

“…The probability of failure, Pi, the probability of failure of sample i of the n samples in the group, was calculated using Bernard's correction [12]:…”