title: Using a surrogate contact pair to evaluate polyethylene wear in prosthetic knee joints.
abstract: With recent improvements to the properties of ultra-high molecular weight polyethylene (UHMWPE) used in joint replacements, prosthetic knee and hip longevity may extend beyond two decades. However, it is difficult and costly to replicate such a long in vivo lifetime using clinically relevant in vitro wear testing approaches such as walking gait joint simulators. We advance a wear test intermediate in complexity between pin-on-disk and knee joint simulator tests. The test uses a surrogate contact pair, consisting of a surrogate femoral and tibial specimen that replicate the contact mechanics of any full-scale knee condyle contact pair. The method is implemented in a standard multi-directional pin-on-disk wear test machine, and we demonstrate its application via a two-million-cycle wear test of three different UHMWPE formulations. Further, we demonstrate the use of digital photography and image processing to accurately quantify fatigue damage based on the reduced transmission of light through a damage area in a UHMWPE specimen. The surrogate contact pairs replicate the knee condyle contact areas within -3% to +12%. The gravimetric wear test results reflect the dose of crosslinking radiation applied to the UHMWPE: 35 kGy yielded a wear rate of 7.4 mg/Mcycles, 55 kGy yielded 1.0 mg/Mcycles, and 75 kGy (applied to a 0.1% vitamin E stabilized UHMWPE) yielded 1.5 mg/Mcycles. A precursor to spalling fatigue is observed and precisely measured in the radiation-sterilized (35 kGy) and aged UHMWPE specimen. The presented techniques can be used to evaluate the high-cycle fatigue performance of arbitrary knee condyle contact pairs under design-specific contact stresses, using existing wear test machines. This makes the techniques more economical and well-suited to standardized comparative testing.
authors: Ortho Development Corp., 12187 Business Park Dr., Draper, Utah, 84020.|Department of Mechanical Engineering, University of Utah, 50 S. Central Campus Dr., MEB 2122, Salt Lake City, Utah, 84112.
authors: Anthony P
authors: AP
authors: Sanders
authors: Department of Mechanical Engineering, University of Utah, 50 S. Central Campus Dr., MEB 2122, Salt Lake City, Utah, 84112.
authors: Carly A
authors: CA
authors: Lockard
authors: Department of Orthopaedic Surgery and Rehabilitation, University of Nebraska Medical Center, 985360 Nebraska Medical Center, Omaha, Nebraska, 68198-5360.
authors: Joel N
authors: JN
authors: Weisenburger
authors: Department of Orthopaedic Surgery and Rehabilitation, University of Nebraska Medical Center, 985360 Nebraska Medical Center, Omaha, Nebraska, 68198-5360.
authors: Hani
authors: H
authors: Haider
authors: Department of Mechanical Engineering, University of Utah, 50 S. Central Campus Dr., MEB 2122, Salt Lake City, Utah, 84112.
authors: Bart
authors: B
authors: Raeymaekers
mesh_terms: D006801:Humans; D007719:Knee Joint; D007720:Knee Prosthesis; D011095:Polyethylenes
chemical_list: D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene
keywords: UHMWPE; fatigue; knee replacement; pin-on-disk; standards; testing; wear