Metal‐on‐metal bearing wear with different swing phase loads

Abstract

There is currently much discussion about the most clinically relevant testing methods for evaluating total hip replacements. This study examined the effect of different swing phase loads, including microseparation, on the wear, friction, and wear particles of metal-on-metal (MOM) hip replacements. MOM hip replacements were tested for 5 million cycles with the use of a hip simulator; prostheses were tested with a low (100-N) and ISO (280-N) swing phase load, and under microseparation conditions. Increasing the swing phase load from 100 to 280 N in the same hip simulator increased the wear of the MOM hip replacements by over tenfold. Introducing microseparation into the gait cycle increased wear further, and stripe wear was observed on the femoral heads, accompanied by corresponding rim damage on the acetabular cups. No significant difference in wear particle size was observed between wear particles produced by low load and microseparation hip simulator conditions. Introducing microseparation into the hip simulator gait cycle increased the wear of MOM prostheses. Joint laxity and separation may lead to increased wear rates of MOM prostheses in vivo. Additionally elevated positive swing phase loads may also increase wear. Variable swing phase load conditions in vivo may contribute to variations in clinical wear rates.

(iv) The science of metal-on-metal articulation

“…The difference between low in vitro wear in simulators and in vivo wear has been investigated through studies with elevated loads, stop/start motion, 5,6 and different kinematics. 7,8 These studies have shown that changes in tribological conditions resulted in an increase in wear rates. These factors together with the effect that head diameter and diametral clearance have on the wear of MOM hip prostheses will be discussed in more detail below.…”

“…The effects of kinematics and load have been studied by Firkins et al 9 and Williams et al 7 , respectively. Firkins et al 9 compared the wear of MOM hip prostheses in two different hip simulators with different kinematic inputs.…”

“…The study by Firkins et al 9 applied different swing phase loads in two different simulators, and hence the differences in wear rates may have been due to the application of different loads rather than differences in kinematics alone. Williams et al 7 investigated the effect that swing phase load exerted on the wear of MOM hip prostheses. These authors investigated a number of different load conditions, including a low swing phase load (100 N), a swing phase load as recommended by ISO14242-1 (280 N), and a small (100 N) negative load applied during the swing phase, which caused separation of the head and insert.…”

Effect of bearing size on the long‐term wear, wear debris, and ion levels of large diameter metal‐on‐metal hip replacements—An in vitro study

“…17,18 The size 39 components had a nominal diameter of 38.5 mm and a mean diametrical clearance of 126 lm, the size 55 components had a nominal diameter of 54.5 mm and a mean diametrical clearance of 111 lm (Table I). The wear rates of individual couples were compared with the individual couples clearances.…”

New Insights into Wear and Biological Effects of Metal-on-Metal Bearings

“…1 surface replacement; DePuy, Warsaw, Indiana) and a 28-mm Ultima head (DePuy) in Figure 1, A and B, respectively, these tribolayers seem to be absent and/or worn off under high-stress conditions. For example, Pourzal et al 24 demonstrated that the tribolayer is absent in the stripe wear region of metal-on-metal joints (the stripe wear region is the area that interacts with the acetabular rim because of microseparation) 26 . It is also speculated that the implantation of the acetabular component in excessive anteversion and/or abduction may destabilize the layer and lead to excessive wear.…”