The Role of Ashed Bone in Hard Tissue Implants
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THE ROLE OF ASHED BONE IN HARD TISSUE IMPLANTS ALEXIS S. NASH, LAURA DAHL AND MARK SHEPLER, Marquette University, Milwaukee, WI 53233; HAHN CHOO, SUN W. CHOI AND PHILIP NASH, Illinois Institute of Technology, Chicago, IL 60616 ABSTRACT A novel composite consisting of Ultra-High Molecular Weight Polyethylene, UHMWPE, and ashed bone has been evaluated for human implant applications. The structure and mechanical properties of this composite have been studied using x-ray diffractometry (XRD), scanning electron microscopy (SEM) and dynamic torsion tests. Dynamic properties of the composite and its role in the enhancement of bone ingrowth and damping of vibrations at bone-implant interface are discussed. The new composite offers a novel technique that can provide the desired biological and mechanical fixation in a total hip surgery. INTRODUCTION A review of the clinical literature on total hip replacement has shown up to a 40% incidence of stem loosenings within the acrylic sheath of the prostheses. Furthermore since gaps smaller than 100 microns are not detectable on clinical radiographs, it is feared that many cases of loosening are not diagnosed at its early stage (1). Additionally there has been much concern over the release of methyl methacrylate monomer, a toxic agent, twelve weeks post-operatively causing hypotension and thrombogenic damage to the lungs. Finally the long term concern in the application of acrylic cement is the development of microcracks leading to the stem loosening and failure of the prosthesis within five to ten years (2). The application of PMMA has been relatively more successful in elderly as compared to younger patients. Biological fixation of orthopaedic implants has been recognized as a superior fixation technique since the early seventies. However the success of this technique is dependent on the interfacial strength developed through bone ingrowth in the early days of total hip replacement and the damping of micromotions. PROCEDURE Bovine femoral compact bone was ashed in the range of 2001400C and characterized by XRD, SEM and infra-red spectroscopy. Collagen was decomposed in bone ashed above 600 C. Ashed bone at 800C for ten hours was ground using a mortar and pestle, milled in a plastic bottle with zirconia balls and sieved to -45 mesh. Ashed bone powder was mixed with UHMWPE powder (M.Wt.-3,000,000 and density-0.93g/cc). The powders were blended in rolling jars containing the nominal compositions of 0, 15, 25 and 35 wt.% ashed bone-UHMWPE. Powder blends were compacted in a steel mold at 170 C under 2210 psi for five minutes in a hot press and cooled to room temperature within ten minutes under slight pressure. Dynamic torsion properties were studied using: a. A free decay dynamic torsion system and b. a forced vibration Dynamic Mechanical Analysis, DMA, system; a Rheometric System 4. The dynamic torsion properties were obtained at room temperature for all samples. The free Mat. Res. Soc. Symp. Proc. Vol. 218. 01991 Materials Research Society
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decay samples were cylindrical, 50m
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