Thesis

A study on stability of an all polyethylene pressfit acetabular cup

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Awarding institution
  • University of Strathclyde
Date of award
  • 2014
Thesis identifier
  • T13908
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Abstract
  • The primary stability of a pressfit acetabular cup is crucial for its proper performance due to the lack of screws or cement. The primary stability is only given by the pressfit, whereas the secondary fixating derives from osseointegration of the implant. While cemented cups are able to be fully loaded after surgery, uncemented pressfit cups need time for bone ongrowth and therefore micromotion has to be minimized. Mathys Orthopaedics Ltd released in 2002 the first titanium-coated pressfit polyethylene monobloc acetabular cup, which promises similar characteristics to bone, and therefore reduced micromotion and enhanced osseointegration, yet the initial stability is unknown. The "RM Pressfit vitamys" acetabular cup is available with various articulations for the same cup size and as a result with different wall thicknesses. Therefore two different articulations are tested for their stability. An in-vitro test was conducted with "RM Pressfit vitamys" acetabular cups from Mathys Orthopaedics Ltd. Therefore reamed polyethylene foam with the density of 0.5 g/cm³ was used to mimic human acetabulum bone. Two different cups sizes (28 and 32mm articulation) were placed into the bone substrate with 7kN and three different failures were induced 7 times in series by pulling out, twisting out and levering out the cup out of its cavity with a uniaxial testing machine. There was no statistically significant difference (p<0.05) between the 28mm and 32mm pressfit cup in the pull out and lever out test. The torsion test showed a difference of p=0.016 (28mm (57 ± 5.8) and 32mm (46.5 ± 8) in Nm and Mean ± SD). The results indicate that the overall stability of the cup matches the values from previous studies with full titanium alloy cups. Furthermore, the benefit of a greater femur head doesn't compromise the stability in terms of a thinner polyethylene wall.
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DOI
Date Created
  • 2014
Former identifier
  • 1042004

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