Metal-Metal Bearing Hips - Pete Thompson 26/4/2001
Metal on metal bearings 1
st
used in 1938 (Wilkes). Mckee-Farrar developed from Thompson's Hemi. But equatorial bearing + no clearance led to high frictional torque combined with neck impingement led to high early cup loosening. Aseptic loosening with UHMWPE led to development of 2
nd
generation of metal on metal implants in 1980's.
>60,000 Metasul implants used since 1988
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Author
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L. Dorr et al.
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Title
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THA with use of the Metasul metal on metal Articulation
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Reference
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JBJS 2000 Vol 82 A No.6 789-797
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Summary
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Prospective study of 56 pts with av. 5.2 yr follow-up. Assessed by Harris hip score, questionnaire + XR. 1 revision for cup loosening 2 for recurrent dislocation. 1 deep infection. No femoral loosening
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Critique
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Prospective. Deaths + recurrent dislocators excluded. Quoting 98% survival at 7yrs.
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2
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Author
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TP Schmalzried et al
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Title
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Long-duration metal-on-metal total hip arthroplasties with low wear of the articulating surfaces
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Reference
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The Journal of Arthroplasty 1996 Vol 11 No 3 322-331
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Summary
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Analysis of 6 long-term (>18 yrs) retrieved implants. Failed due to varus collapse. Only thin membrane with few acute inflam. Features. Surface roughness lowest at wt. bearing area. Wear rate of 4.2 µm/yr (25x less than UHMPE)
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Critique
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1
st
study looking at long term retrieved implants. Despite low nos. findings seem consistent with later studies.
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