Bhumbra, Rej Paul; (1998) Sealing the bone-implant interface around total hip replacements using guided bone regeneration. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The aim of this project was to prevent wear debris from reaching the interface of the acetabular cup and femoral component by the use of a partially occlusive e-PTFE membrane. This membrane would initially act as a physical seal, which would become incorporated by bone and soft tissue, forming a secondary biological seal. The hypothesis was that these physical and biological seals, would prevent the debris from accessing the interfacial tissues where they cause bone loss and implant loosening. The biocompatibility of the membrane, and the glue used to attach the membrane was initially assessed by in vitro testing. Osteosarcoma cell proliferation over e-PTFE used with butyl-cyanoacrylate for 24 hours occurred at 20% the rate of controls. In a rabbit study, the membrane protected a femoral defect into which bone would grow more rapidly than an unprotected site. The second component of the rabbit study demonstrated that e-PTFE significantly (P0.02) enhanced the osseo-integration of a trans-femoral titanium screw. A wear test characterised a surface roughness and morphology that wore at a known accelerated rate, producing particles of the same number, size and shape to those seen around human hip replacements after ten years. An animal model was developed to test the hypothesis. The model would replicate the mechanisms of loosening where the effects of wear debris could be studied. Using femoral heads with the appropriate roughness, as determined by the wear test, a goat model produced the radiological and histological presentation of loosening as observed in human total hip replacements. Loosening was assessed by measurement of the radiolucent line, and attributable to wear debris by histological investigation. The e-PTFE membrane prevented acetabular implant loosening, to a statistical significance of 0.02 in a blinded assessment, when compared to the control groups. Loosening of the first 5mm of the proximomedial aspect of the femur was also prevented. To summarise, we prevented wear particle induced osteolysis in the acetabular component of a loosening goat model by using an e-PTFE membrane to seal the bone-cement interface.

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