Experimental and finite studies of acetabular cement pressurisation and socket fixation in total hip replacement

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Effect of hip stem taper on cement stresses

The aim of this study was to use finite element models to investigate the effect of the design of the taper of polished, collarless, total hip replacement femoral components on stresses in the cement mantle surrounding the component. A single-taper prosthesis, double-taper prosthesis, and triple-taper prosthesis were compared. Peak stresses and stress distributions in the cement mantle were found to be a function of taper design, although the differences between designs were minor. Using a probability of failure technique based on the initial cement stress distribution, a triple-taper prosthesis was predicted to cause less cement mantle damage (0.15% of the volume of the cement mantle failing after 20 million loading cycles) than a double-taper prosthesis (0.74%) or a single-taper prosthesis (1.50%). Further research is required to confirm this finding

An ultrasound technique for monitoring polymerisation of acrylic bone cement

This paper describes a technique for monitoring polymerisation of acrylic bone cements by measuring changes in the characteristics of the transmission of ultrasound through the cement brought about by the polymerisation reaction. To the authors’ knowledge, this is the first time that a technique for the continuous monitoring of the mechanical properties of polymerising bone cement has been presented. The cement exhibits the expected behaviour of low modulus until approximately 300-450s from the time of mixing, after which a period of rapid polymerization occurs. In future work, we aim to extend the technique to allow simultaneous measurements of compressive and shear properties using a combined compression/shear wave transducer

Bone remodelling inside a cemented resurfaced femoral head

Background. Although the short-term performance of modern resurfacing hip arthroplasty is impressive, the long-term performanceis still unknown. It is hypothesised that bone remodelling and the resulting changes in stress/strain distribution within the resurfaced femur influence the risk of fixation failure.Method. Three-dimensional finite element models and adaptive bone remodelling algorithms have been used to predict long-term changes in bone density following cemented femoral head resurfacing. Applied loading conditions include normal walking and stair climbing. The remodelling simulation was validated by comparing the results of an analysis of a proximal femur implanted with a Charnley femoral component with known clinical data in terms of bone density adaptations.Findings. Resurfacing caused a reduction of strain of 20–70% in the bone underlying the implant as compared to the intact femur, immediately post operative. Elevated strains, ranging between 0.50 and 0.80% strain, were generated post-operatively around the proximal femoral neck regions, indicating a potential risk of neck fracture. However, this strain concentration was considerably reduced after bone remodelling. After remodelling, bone resorption of 60–90% was observed in the bone underlying the implant. Reduction in bone density of 5–47% occurred in the lateral femoral head. Bone apposition was observed in the proximal–medial cortex, around the inferior edge of the implant. Hardly any changes in bone density occurred in the distal neck or the femoral diaphysis.Interpretation. Although resurfacing has produced encouraging clinical results, bone remodelling within the femoral head might be a concern for long-term fixation. Regions of strain concentration at the head–neck junction, which may increase the initial risk of femoral neck fracture, are reduced with bone remodelling. In order to reduce this risk of femoral neck fracture, patients should avoid activities which induce high loading of the hip during the early rehabilitation period after surgery