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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.

Original publication




Journal article


Med eng phys

Publication Date





1042 - 1048


Arthroplasty, Replacement, Hip, Cementation, Femur, Humans, Models, Biological, Pressure