Increased Wear in Low and High Crosslinked Polyethylene Due to Microseparation of Total Hip Arthroplasty Components

Introduction:

Microseparation has resulted in more than ten-fold increase in ceramic-on-ceramic and metal-on-metal bearing wear, and even fracture in a zirconia head [1–4]. However, despite the greater microseparation reported clinically for metal-on-polyethylene wear, less is known about its potential detrimental effects for this bearing couple. This study was therefore designed to simulate the effects of micromotion using finite element analysis and to validate computational predictions with experimental wear testing.

Methods:

Experimental wear rates for low and highly crosslinked polyethylene hip liners were obtained from a previously reported conventional hip wear simulator study [5]. A finite element model of the wear simulation for this design was constructed to replicate experimental conditions and to compute the wear coefficients that matched the experimental wear rates. We have previous described out this method of validation for knee wear simulation studies [6,7]. This wear coefficient was used to predict wear in a Dual-Mobility hip component (Fig 1).

Dual mobility total hip arthroplasty components, Restoration ADM (Fig 1), with highly crosslinked acetabular liners were experimentally tested: the control group was subjected to wear testing using the ISO 14242-1 waveform on a hip wear simulator. The microseparation group was subjected to a nominal 0.8 mm lateral microseparation during the swing phase by engaging lateral force springs and reducing the swing phase vertical force.

Results:

The wear coefficients that matched experimental wear rates for the low and highly crosslinked polyethylene liners were 4.57×10⁻¹⁰ and 5.89×10⁻¹¹ mm³N⁻¹mm⁻¹, respectively. Introducing microseparation in the conventional hip increased the wear rate by 15.59 mm³/million cycles in the low crosslinked liner and by 1.12 mm³/million cycles in the highly crosslinked liner (Fig 2).

Discussion:

Microseparation did increase predicted wear rates for the low crosslinked polyethylene liner and supports the hypothesis that microseparation can adversely affect the wear of hip arthroplasty. However, the predicted and experimental increase for the dual mobility highly crosslinked liners due to microseparation was low (3.3 mm³ and 2.9 mm³/million cycles, respectively) and below the threshold for clinical relevance. The small increase in wear rate in our study supports the high wear tolerance to wear of a dual-mobility sequentially crosslinked polyethylene liner.