Notch fatigue of ultrahigh molecular weight polyethylene (UHMWPE) used in total joint replacements.

Farzana Ansari, Bernd Gludovatz, Adam Kozak, Robert O Ritchie, Lisa A Pruitt

Journal: Journal of the mechanical behavior of biomedical materials 2017;60():267-279

PMID: 26919563

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Abstract

Ultrahigh molecular weight polyethylene (UHMWPE) has remained the primary polymer used in hip, knee and shoulder replacements for over 50 years. Recent case studies have demonstrated that catastrophic fatigue fracture of the polymer can severely limit device lifetime and are often associated with stress concentration (notches) integrated into the design. This study evaluates the influence of notch geometry on the fatigue of three formulations of UHMWPE that are in use today. A linear-elastic fracture mechanics approach is adopted to evaluate crack propagation as a function of notch root radius, heat treatment and Vitamin E additions. Specifically, a modified stress-intensity factor that accounts for notch geometry was utilized to model the crack driving force. The degree of notch plasticity for each material/notch combination was further evaluated using finite element methods. Experimental evaluation of crack speed as a function of stress intensity was conducted under cyclic tensile loading, taking crack length and notch plasticity into consideration. Results demonstrated that crack propagation in UHMWPE emanating from a notch was primarily affected by microstructural influences (cross-linking) rather than differences in notch geometry.

Address: Department of Mechanical Engineering, University of California, Berkeley, CA, USA. Electronic address: [email protected].; Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.; Cambridge Polymer Group, Boston, MA, USA.; Department of Mechanical Engineering, University of California, Berkeley, CA, USA; Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA; Department of Materials Science & Engineering, University of California, Berkeley, CA, USA.; Department of Mechanical Engineering, University of California, Berkeley, CA, USA.

DOI: 10.1016/j.jmbbm.2016.02.014

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MeSH Terms: Arthroplasty, Replacement, Materials Testing, Molecular Weight, Polyethylenes, Prostheses and Implants, Prosthesis Failure, Stress, Mechanical