title: The femoral stem pump in cemented hip arthroplasty: an in vitro model.
abstract: The presence of an intra-articular pump has been proposed as a central mechanism in the process of osteolysis and aseptic loosening of hip arthroplasty. It is not known if this pump exists and its mechanism remains uncharacterised. This study describes a new in vitro model of a cemented femoral stem in which cement/stem interface fluid pressures can be reliably measured under dynamic loads simulating stair climbing. A stem pump mechanism was found that generates both positive and negative clinically significant pressures (mean pressure ranges 5000-17,000 Pa). The timing of pressure peaks on the anterior and posterior aspects of the stem were in anti-phase, giving rise to oscillatory pressure gradients and potentially generating oscillatory fluid flows during the simulated physiological load cycle. The pump mechanism was shown to occur at the interface of a newly implanted polished double-tapered stem and emphasizes the importance of a complete mantle to protect the femoral bone from the raised fluid pressures.
authors.affiliation: OOEC/Nuffield Department of Orthopaedic Surgery, University of Oxford, Nuffield Orthopaedic Centre, Oxford, UK.
authors.forename: G E
authors.initials: GE
authors.lastname: Bartlett
authors.forename: D J
authors.initials: DJ
authors.lastname: Beard
authors.forename: D W
authors.initials: DW
authors.lastname: Murray
authors.forename: H S
authors.initials: HS
authors.lastname: Gill
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation* / Q000379:methods*; D002484:Cementation; D005269:Femur / Q000502:physiology*; D006801:Humans; D008954:Models, Biological; D011312:Pressure