The contact mechanics and occurrence of edge loading in modular metal-on-polyethylene total hip replacement during daily activities

Abstract

Abstract:The occurrence of edge loading in hip joint replacement has been associated with 25 many factors such as prosthetic design, component malposition and activities of daily living. 26The present study aimed to quantify the occurrence of edge loading/contact at the articulating 27 surface and to evaluate the effect of cup angles and edge loading on the contact mechanics of 28 a modular metal-on-polyethylene (MoP) total hip replacement (THR) during different daily 29 activities. A three-dimensional finite element model was developed based on a modular MoP 30 bearing system. Different cup inclination and anteversion angles were modelled and six daily 31 activities were considered. The results showed that edge loading was predicted during normal 32 walking, ascending and descending stairs activities under steep cup inclination conditions 33 (≥ 55°) while no edge loading was observed during standing up, sitting down and knee 34 bending activities. The duration of edge loading increased with increased cup inclination 35 angles and was affected by the cup anteversion angles. Edge loading caused elevated contact 36 pressure at the articulating surface and substantially increased equivalent plastic strain of the 37 polyethylene liner. The present study suggested that correct positioning the component to 38 avoid edge loading that may occur during daily activities is important for MoP THR in 39 clinical practice. 40 41

Reducing stress concentration on the cup rim of hip implants under edge loading

“…In order to evaluate the effectiveness of different geometric features, four micro‐separations as the lateral displacement of the head with respect to the cup are considered, and they are 1, 1.5, 2, and 2.5 mm. The values are within the range of typical micro‐separations reported in previous experimental and computational studies . To simulate the micro‐separation, the head centre is moved to the lateral side by a certain distance so that the head touches the edge of the cup (ie, potential edge loading), as shown in Figure .…”

“…The values are within the range of typical micro-separations reported in previous experimental and computational studies. 11 To simulate the micro-separation, the head centre is moved to FIGURE 2 Illustration of contact between head and cup A, without and B, with micro-separation FIGURE 1 A, Illustration of a spline geometry B, Contact between head and cup at sharp corner, circular arc, and spline (new and proposed) geometry at the rim's corner the lateral side by a certain distance so that the head touches the edge of the cup (ie, potential edge loading), as shown in Figure 2. A 3D FE model of a hip implant consisting of the femoral head and the acetabular cup is developed.…”

“…For instance, an extended striped wear on either head or cup due to the concentrated contact pressure is a commonly reported indicator . As predicted via FE modelling of ceramic/metal‐on‐PE implants, edge loading induces severe stress and plastic strain leading to fatigue and fracture in soft polyethylene cup . The influence of the bearing component design, patient activities, and surgical factors on the likelihood of edge loading is investigated by many researchers, and the findings have clearly raised the underlying concerns for biomedical engineers to seek for potential solutions to its detrimental effects.…”

“…10 As predicted via FE modelling of ceramic/metal-on-PE implants, edge loading induces severe stress and plastic strain leading to fatigue and fracture in soft polyethylene cup. 11 The influence of the bearing component design, patient activities, and surgical factors on the likelihood of edge loading is investigated by many researchers, and the findings have clearly raised the underlying concerns for biomedical engineers to seek for potential solutions to its detrimental effects. Generally, as is widely accepted across the surgeon community, the golden standard of so-called "safe zone" considers cup inclination of 40 ± 10°and ante-version of 15 ± 10°.…”

Effect of an edge at cup rim on contact stress during micro-separation in ceramic-on-ceramic hip joints

“…Computational studies using finite element (FE) methods have been used to help understand wear mechanism of head-cup rim contact for total hip joint replacements [16], [25], [26], [27], [28]. Mak et al [16] predicted elevated contact stress as a result of micro-separation for CoC bearings but they were not able to carry out a convergence study pointing out the limitation in obtaining accurate stress values due to the sensitive nature of the model for edge contact.…”