Wear versus Thickness and Other Features of 5-Mrad Crosslinked UHMWPE Acetabular Liners

Abstract

BackgroundThe low wear rates of crosslinked polyethylenes provide the potential to use larger diameters to resist dislocation. However, this requires the use of thinner liners in the acetabular component, with concern that higher contact stresses will increase wear, offsetting the benefits of the crosslinking.Questions/purposesWe asked the following questions: Is the wear of conventional and crosslinked polyethylene liners affected by ball diameter, rigidity of backing, and liner thickness? Are the stresses in the liner affected by thickness?MethodsWear rates were measured in a hip simulator and stresses were calculated using finite element modeling.ResultsWithout crosslinking, the wear rate was 4% to 10% greater with a 36-mm diameter than a 28-mm diameter. With crosslinking, wear was 9% lower with a 36-mm diameter without metal backing and 4% greater with metal backing. Reducing the thickness from 6 mm to 3 mm increased the contact stress by 46%, but the wear rate decreased by 19%.ConclusionsThe reduction in wear with 5 Mrad of crosslinking was not offset by increasing the diameter from 28 mm to 36 mm or by using a liner as thin as 3 mm.Clinical RelevanceThe results indicate, for a properly positioned 5-Mrad crosslinked acetabular component and within the range of dimensions evaluated, neither wear nor stresses in the polyethylene are limiting factors in the use of larger-diameter, thinner cups to resist dislocation.

Polyethylene Wear is Related to Patient-specific Contact Stress in THA

“…Conventional UHMWPE cups were implanted in all THAs included in this study. Modern crosslinked polyethylenes exhibit considerably lower wear related to contact stress [36] and other factors like thirdbody wear [5] might be more important for its wear in vivo. Sixth, current contact stress modeling is based on the assumption of elastic deformation of polyethylene.…”

“…Finally, cemented acetabular cups were included in the analysis. it is not likely to change the contact mechanics because no difference in wear between a cemented and an uncemented cup was found in a clinical study [33] and in hip simulator testing [36]. All implanted prostheses have the same femoral head diameter and polyethylene liners with a thickness of 6 mm or greater.…”

The Divergence of Wear Propagation and Stress at Steep Acetabular Cup Positions Using Ceramic Heads and Sequentially Cross-Linked Polyethylene Liners

“…However, in order to use larger femoral heads with a constant cup size, the liner thickness has to be reduced, which leads to higher stresses in the polyethylene [10]. The reduced mechanical properties of HX-PE [11,12] should be critically examined, especially with regard to low thickness of the liner.…”

Force-controlled dynamic wear testing of total ankle replacements

“…The linear restraint system is characterized and discussed afterwards (see Table 4 and discussion). [64][65][66][67] wear testing of established artificial joints like the hip or the knee. Therefore, a comparably relevant wear volume is also generated for TAR.…”