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Metal-carbon fiber composite femoral stems in hip replacements: a randomized controlled parallel-group study with mean ten-year follow-up.

The Journal of bone and joint surgery. American volume (2014-12-19)
D B Bennett, J C Hill, J Dennison, S O'Brien, J L Mantel, G H Isaac, D E Beverland
ABSTRACT

Attempts to improve proximal load transfer and minimize stress shielding have included reducing the stiffness of femoral stems and using alternative stem materials, including carbon fiber composites. An uncemented implant (SR71) composed of a carbon-fiber-composite distal section and a porous-coated titanium-alloy proximal section, designed to improve proximal load transfer and provide good fixation, was clinically evaluated in a prospective randomized study. Sixty patients were enrolled and randomized to receive either the SR71 stem or an all-metal stem (Stability). All patients received a cemented all-polyethylene acetabular component and a 28-mm metal femoral head. All uncemented stems were implanted by the same surgeon. Patients were followed for up to ten years with repeated assessments of bone mineral density, radiographs, Harris hip scores (HHS), and visual analog scale (VAS) pain scores. Ten years postoperatively, nineteen patients who had been treated with the SR71 stem and not lost to follow-up showed a significantly greater increase in proximal bone mineral density (Gruen zones 1 [p = 0.003] and 7 [p = 0.0007]) from baseline than did the twenty-two who had been treated with the Stability stem and not lost to follow-up. In contrast, the Stability group showed a significantly greater increase in distal bone mineral density (Gruen zones 2 [p = 0.0004], 3 [p = 0.0001], and 5 [p = 0.0035]) compared with the SR71 group. Radiographs demonstrated one case of progressive migration of an acetabular component used with an SR71 stem and one case of bone resorption in Gruen zones 7 and 14 in a patient treated with a Stability stem. There was no significant difference between the SR71 and Stability stems in terms of changes in the total HHS, HHS for pain, HHS for range of motion, or VAS pain scores ten years postoperatively relative to preoperative levels. There was one reported revision of an SR71 femoral stem at the ten-year review. The investigational SR71 implant provided increased proximal bone density and reduced distal bone density. The implant showed promising results at the time of early follow-up, and the clinical outcomes were similar to those of an all-metal stem at the time of a ten-year follow-up.

MATERIALS
Product Number
Brand
Product Description

Supelco
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Carbon, foil, 10x10mm, thickness 2.0mm, hOpg
Carbon, foil, 12mm disks, thickness 0.5mm, rigid graphite, fine grain size, 99.95%
Carbon, foil, 25x25mm, thickness 0.2mm, flexible graphite, 99.8%
Carbon, rod, 100mm, diameter 25mm, graphite, 99.95%
Carbon, foil, not light tested, 150x150mm, thickness 0.125mm, flexible graphite, 99.8%
Carbon, foil, 150x150mm, thickness 1.0mm, flexible graphite, 99.8%
Carbon, rod, 50mm, diameter 1.0mm, graphite, 99.95%
Carbon, microleaf, 25x70mm, thinness 0.025μm, specific density 5μg/cm2, temporary glass support, 99.997%
Carbon, foil, 12.5x12.5mm, thickness 0.125mm, rigid graphite, fine grain size, 99.95%
Carbon, foil, 50x50mm, thickness 0.35mm, flexible graphite, 99.8%
Carbon, microleaf, 25x70mm, thinness 1.25μm, specific density 250μg/cm2, 99.997%
Carbon, foil, 12mm disks, thickness 1.0mm, rigid graphite, fine grain size, 99.95%
Carbon, foil, 150x150mm, thickness 5.0mm, rigid graphite, medium grain size, 99.5%
Carbon, foil, 25x25mm, thickness 2.5mm, rigid graphite, fine grain size, 99.95%
Carbon, foil, 10mm disks, thickness 0.2mm, flexible graphite, 99.8%
Carbon, rod, 100mm, diameter 3.0mm, graphite, 100%
Carbon, foil, not light tested, 300x300mm, thickness 0.075mm, flexible graphite, 99.8%
Carbon, foil, 150x150mm, thickness 0.125mm, rigid graphite, fine grain size, 99.95%
Carbon, foil, not light tested, 150x150mm, thickness 0.075mm, flexible graphite, 99.8%
Carbon, microleaf, 25x70mm, thinness 2.5μm, specific density 500μg/cm2, 99.997%