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A novel method to assess primary stability of press-fit acetabular cups
OAI: oai:purehost.bath.ac.uk:openaire_cris_publications/d60f934f-a6a9-4d04-8785-0fa1c4685a83 • DOI: https://doi.org/10.1177/0954411914557714
Abstract
Initial stability is an essential prerequisite to achieve osseointegration of press-fit acetabular cups in total hip replacements.
Most in vitro methods that assess cup stability do not reproduce physiological loading conditions and use simplified
acetabular models with a spherical cavity. The aim of this study was to investigate the effect of bone density and
acetabular geometry on cup stability using a novel method for measuring acetabular cup micromotion. A press-fit cup
was inserted into Sawbones foam blocks having different densities to simulate normal and osteoporotic bone variations
and different acetabular geometries. The stability of the cup was assessed in two ways: (a) measurement of micromotion
of the cup in 6 degrees of freedom under physiological loading and (b) uniaxial push-out tests. The results indicate that
changes in bone substrate density and acetabular geometry affect the stability of press-fit acetabular cups. They also suggest
that cups implanted into weaker, for example, osteoporotic, bone are subjected to higher levels of micromotion
and are therefore more prone to loosening. The decrease in stability of the cup in the physiological model suggests that
using simplified spherical cavities to model the acetabulum over-estimates the initial stability of press-fit cups. This novel
testing method should provide the basis for a more representative protocol for future pre-clinical evaluation of new
acetabular cup designs.
Most in vitro methods that assess cup stability do not reproduce physiological loading conditions and use simplified
acetabular models with a spherical cavity. The aim of this study was to investigate the effect of bone density and
acetabular geometry on cup stability using a novel method for measuring acetabular cup micromotion. A press-fit cup
was inserted into Sawbones foam blocks having different densities to simulate normal and osteoporotic bone variations
and different acetabular geometries. The stability of the cup was assessed in two ways: (a) measurement of micromotion
of the cup in 6 degrees of freedom under physiological loading and (b) uniaxial push-out tests. The results indicate that
changes in bone substrate density and acetabular geometry affect the stability of press-fit acetabular cups. They also suggest
that cups implanted into weaker, for example, osteoporotic, bone are subjected to higher levels of micromotion
and are therefore more prone to loosening. The decrease in stability of the cup in the physiological model suggests that
using simplified spherical cavities to model the acetabulum over-estimates the initial stability of press-fit cups. This novel
testing method should provide the basis for a more representative protocol for future pre-clinical evaluation of new
acetabular cup designs.