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Maintenance of Proximal Cortical Bone with Use of a Less Stiff Femoral Component in Hemiarthroplasty of the Hip without Cement. An Investigation in a Canine Model at Six Months and Two Years*
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Investigation performed at Rush Institute of Arthritis and Orthopedics, Department of Orthopedic Surgery, Rush-Presbyterian-St. Luke's Medical Center, Chicago
J Bone Joint Surg Am, 1997 Sep 01;79(9):1381-90
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A canine model of hemiarthroplasty of the hip was used to determine if the use of a less stiff femoral stem can reduce the amount of bone loss induced by stress-shielding. Two types of stem were used: the stiffer stems were made of a titanium alloy, and the less stiff stems were composed of a cobalt-chromium-alloy core with an outer polymer layer. The stems were identical in shape, and both types were circumferentially coated along their entire length (except for the distal five millimeters) with commercially pure titanium fiber metal. Ten dogs with each type of stem were followed for six months, and twelve dogs with each type of stem were followed for two years. Loss of cortical bone from the proximal part of the femur was associated with both types of stem, but typically 50 per cent less bone was lost with the less stiff implants. Most of the cortical loss occurred at the subperiosteal surface. The amount of medullary bone adjacent to the proximal and distal aspects of both types of stem increased; the less stiff stems were associated with a greater increase in the proximal region, and the stiffer stems were associated with a greater increase in the distal region. Similarly, there were peaks in the amount of bone growth into the proximal and distal portions of both types of stem, with a greater peak in proximal bone growth into the less stiff stems and a greater peak in distal bone growth into the stiffer stems.CLINICAL RELEVANCE: The data indicate that an effective means of promoting proximal transfer of load from the implant to the host femur is to reduce the stiffness of the stem. This is a design-related mechanism to decrease stress-shielding, thereby suppressing the loss of bone in the proximal part of the femur following hemiarthroplasty of the hip performed without cement. Such bone loss can eventually lead to loosening of the component and make subsequent reconstruction difficult.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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