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.

A patient-specific wear prediction framework for an artificial knee joint with coupled musculoskeletal multibody-dynamics and finite element analysis

“…Although the survivorship of knee implants may extend beyond two decades [2], wear debris of ultra-high molecular weight polyethylene (UHMWPE) in TKR induced aseptic loosening is still a major limitation to longevity [3][4][5][6].…”

Tibiofemoral wear in standard and non-standard squat: implication for total knee arthroplasty

“…Based on the new results of researchers and the technological advances of the manufacturers, more effective, affordable and reliable total knee replacements (TKRs) are provided to patients every year. It must be noted that the contemporary TKRs can last more than two decades 1 , however failures cannot be completely eliminated. Sharkey et al pointed out how quickly the trend of TKR failures changed in the past 10 years and moved to the direction of loosening, infection, instability, arthrofibrosis and periprosthetic fracture, while wear in the polyethylene parts became only the seventh most damaging factor in the line 2 .…”

Diffusion mechanism of byproducts resulting from the peroxide crosslinking of polyethylene

“…However, PE does not meet all of the requirements for industrial applications; thus, crosslinking is often performed to enhance certain properties, such as the structural integrity at high temperature and abrasion or chemical resistance. The crosslinking of PE allows it to be widely used in joint replacement applications, primary wire and cable insulation, tubes and pipes, and cable jackets …”