Wear simulation of ultra-high molecular weight polyethylene hip implants by incorporating the effects of cross-shear and contact pressure

Abstract

The effect of multi-directional cross-shear (CS) motion and contact pressure on ultra-high molecular weight polyethylene (UHMWPE) wear was investigated in this study, based on an integrated experimental and computational approach. The wear factor as a function of CS was determined experimentally from a multi-directional pin-on-plate wear tester under a nominal contact pressure of 1 MPa. A computational wear model was developed which included the effects of CS as well as the load and sliding distance imposed on the hip joint employing a UHMWPE cup against a metallic femoral head under both gait and Leeds ProSim hip joint simulator conditions. The CS ratios were quantified over the articular surface of the UHMWPE cup and the CS-dependent wear factors derived from multi-directional pin-on-plate studies were applied in the computational wear model. Outputs from the computational wear model were validated independently against an experimental hip simulator study. Comparisons of linear and volumetric wear were made between the computational wear model and the hip simulator testing for a nominal conventional (0 MRad) UHMWPE cup of 28mm diameter and a highly cross-linked (10 MRad) UHMWPE cup. The difference between the computed and experimental volumetric wear was approximately 30 per cent for the 0 MRad UHMWPE, although the worn areas between the prediction and the measurement were similar. For the 10 MRad UHMWPE, the discrepancy was reduced to 16 per cent. In both cases, the computational model predicted a lower wear rate than the experimental simulator testing. The effect of using alternative wear factors under a different nominal contact pressure of 3MPa was also considered. The input wear factor to the computational model, derived from a constant loaded pin-on-plate test configuration, may underestimate the dynamic effect due to the variation in the load in the hip joint simulator.

The effect of anterior–posterior shear load on the wear of ProDisc-L TDR

“…However, an increasing wear rate was seen in the 5DOF tests, which may be due to an increasing contact area, which was supported by the wear scar measurements. In opposition to classical wear theory (Archard's wear law) [29], increased contact area has been shown to increase polyethylene wear rates [30], provided that the contact stress is still below the yield stress, which would otherwise lead to fatigue failure. Archard's law holds true for cases where the asperity contacts deform plastically, such as in metallic contacts.…”

High Cup Angle and Microseparation Increase the Wear of Hip Surface Replacements

“…Flexion/extension (15°-30°) and internal/external rotation (± 10°) were applied to the components, the combination of which resulted in the production of both open elliptical and figure of eight wear paths on the surface as described previously [1,10] Microseparation was produced on the Leeds Mk II hip simulator by applying a small lateral load to the cup causing approximately 0.5 mm medial and superior translation of the cup relative to the head during swing phase, as described previously [16] with the cup positioned at an inclination angle of 55°. Wear was determined gravimetrically after 1 million and 2 million cycles for the high cup and microseparation studies and at 1 million, 2 million, and 5 million cycles for the standard conditions study using methods reported previously [13].…”

Enhanced computational prediction of polyethylene wear in hip joints by incorporating cross-shear and contact pressure in additional to load and sliding distance: Effect of head diameter

“…In other words, use of these variables as inputs to the computational wear model, along with load and sliding distance, and the predicted wear can be independently validated against separate hip simulator conditions. To date, the effect of cross-shear on the computational wear modelling has only been considered for the hip (Kang et al, 2008a) and knee joint (Hamilton et al, 2005;Knight et al, 2005). The effect of both cross-shear and contact pressure-dependent wear factor has not been considered previously in computational wear modelling of polyethylene hip implants.…”