Effect of slide track shape on the wear of ultra‐high molecular weight polyethylene in a pin‐on‐disk wear simulation of total hip prosthesis

Abstract

Prosthetic joints appear to show a strong relationship between the type of relative motion and wear, requiring careful consideration in the design of wear simulators. This relationship was studied with a 12-station pin-on-disk device, specifically adapted for the wear simulation of prosthetic hip joints. Each station had a unique motion, characterized by the so-called slide track, the track of the pin on the disk. The slide track shapes included 10 ellipses, their aspect ratio (AR) varying from 1.1 to 11.0, and a circle and a straight line as extreme cases. Hence for the first time in hip wear simulation, the motion was systematically varied over a wide range. Conventional UHMWPE pins were tested against polished CoCr disks in diluted calf serum three times for 3 million cycles. Below the AR value of 5.5, the polyethylene wear factor and wear mechanisms agreed with clinical observations. Above this value, the wear factor decreased to unrealistically low values, and the wear surface topography differed from that of retrieved acetabular cups. The wear particles, however, were similar to those isolated from periprosthetic tissues, irrespective of the AR value. In conclusion, it is recommended that the AR value be kept well below the critical point of 5.5.

The influence of wear paths produced by hip replacement patients during normal walking on wear rates

“…The relationships between sliding distance and activity levels and wear rates as predicted by tribology theory 26 were not reproduced. Similarly, the relationship between the degree of multidirectional wear paths and wear rates, as reported in vitro 5,10 did not appear in vivo. However, those patients with the lowest wear rates displayed a strong positive relationship between wear rate and multidirectional motion, activity level, and the sliding distance, relationships predicted from tribology theory and in vitro laboratory tests.…”

“…This correlation between the degree of multidirectional motion, patient activity level, and sliding distance and the wear rate reflects both tribology theory (Equation 1) and in vitro testing. 5,10 This group may represent those patients who experience kinematic, loading, and lubrication conditions at the joint that are similar to those that prevail in a well-controlled laboratory setting. These patients are most likely to possess smooth femoral heads and an articulation environment without third particle debris, as increased wear rates up to two orders of magnitude higher have been recorded for scratched compared to smooth femoral heads in vitro.…”

“…1,2 However, excessive wear of the ultrahigh molecular weight polyethylene (UHMWPE) acetabular component is one of the main causes of bone resorption, implant loosening, and ultimate failure of hip joint replacements. 3,4 Variation in the articulation patterns between the femoral head and the acetabular cup greatly influence wear rates in simulator tests [5][6][7][8] and computer models. 9 Unidirectional motion promotes orientation of the long polyethylene chains and subsequent hardening, 8 while multidirectional motion promotes an environment of continually changing shear.…”

“…7,8,11 Simulator wear rates approaching clinical values were recorded under conditions of multidirectional motion 12 while near zero wear rates were recorded for unidirectional motion. 5,7 Variation of wear paths between total hip arthroplasty patients has recently been proposed as a factor that may influence the wear properties of the UHMWPE cup. 9 In a previous study involving a small number of patients (n ¼ 19), the authors found a positive correlation between both measurements of multidirectional motion and sliding distance experienced at the patients' hip joints and the wear.…”

In vitro wear simulation on the RandomPOD wear testing system as a screening method for bearing materials intended for total knee arthroplasty

“…The wear factor of conventional UHMWPE is highly sensitive to the type of relative motion [Saikko et al, 2004;Saikko, 2014] and contact pressure [Saikko, 2006]. With decreasing multidirectionality and increasing contact pressure, the wear factor decreases significantly.…”