Ultrahigh molecular weight polyethylene as used in articular prostheses (a molecular weight distribution study)

Authors

  • Aldo M. Crugnola,

    1. Department of Plastics Technology, University of Lowell, Lowell, Massachusetts 01854
    Current affiliation:
    1. Harvard Medical School, Dep't. of Orthopaedic Surgery at The Children's Medical Center
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  • Eric L. Radin,

    1. Department of Plastics Technology, University of Lowell, Lowell, Massachusetts 01854
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  • Robert M. Rose,

    1. Department of Plastics Technology, University of Lowell, Lowell, Massachusetts 01854
    Current affiliation:
    1. Dep't. of Metallurgy and Material Sciences, Massachusetts Institute of Technology
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  • Igor L. Paul,

    1. Department of Plastics Technology, University of Lowell, Lowell, Massachusetts 01854
    Current affiliation:
    1. Dep't. of Mechanical Engineering, Massachusetts Institute of Technology
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  • Sheldon R. Simon,

    1. Department of Plastics Technology, University of Lowell, Lowell, Massachusetts 01854
    Current affiliation:
    1. Harvard Medical School, Dep't. of Orthopaedic Surgery at The Children's Medical Center
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  • Mark B. Berry

    1. Department of Plastics Technology, University of Lowell, Lowell, Massachusetts 01854
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Abstract

Currently there is widespread use of ultrahigh molecular weight polyethylene (UHMWPE) acetabular components in total joint replacement prostheses. What has been most surprising about the wear of UHMWPE under such circumstances is the occurrence of brittle fracture. Such fracture had not been observed in the usual engineering tests done in the laboratory on UHMWPE. It was only when prosthese which had been removed from patients were examined or run in hip joint simulators with serum or synovial fluid as the lubricant, that brittle fracture was encountered. The problem of environment-enhanced brittle fracture in plastics dates back to 1946. Interestingly, the phenomenon was first described in polyethylene. The prime variables involved are polymer molecular weight, sensitizing environment, stress filed, and temperature. Other things being equal, brittle behavior in polyethylene is extremely sensitive to the amount of low molecular weight polymer present. In the light of the foregoing we have studied the molecular weight distribution in six commercially available UHMWPE components. These were obtained from six different manufacturers. The specimens were characterized both on their bearing (wear) surfaces and in their interior bulk. The results obtained indicate that:

  • 1The UHMWPE components contain substantial amounts of low molecular weight polymer.
  • 2The UHMWPE components differ significantly in molecular weight distribution.
  • 3The UHMWPE components contain substantial amounts of crosslinked polymer.

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