Abstract
Introduction
Wear debris induced osteolysis and loosening continue to be causes of clinical failure in total knee replacement (TKR). Laboratory simulation aims to predict the wear of TKR bearings under specific loading and motion conditions. However, the conditions applied may have significant influence on the study outcomes (1)
The aim of this study was to examine the influence of femoral setup and kinematic inputs on the wear of a conventional polyethylene fixed bearing TKR through experimental and computational models.
Methods
Six right Sigma CR fixed bearing TKRs (DePuy Synthes, Leeds, UK) with curved polyethylene inserts (GVF, GUR1020 UHMWPE) were tested in Prosim knee simulator (Simulator Solutions, UK). The femoral bearing was set up with the centre of rotation (CoR) on either on the distal radius of the implant (Distal CoR), as indicated by the device design, or according to the ISO specification (ISO CoR; ISO14243-3). The tests were conducted under ‘High Kinematics’ (2). It was necessary to reverse the direction of the anterior-posterior displacement for the tests conducted with the ISO centre of rotation to maintain the contact region within the insert surface (Reverse High Kinematics). Tests were conducted for three million cycles, lubricated with 25% bovine serum, with wear assessed gravimetrically.
The computational wear model for the TKR was based on the contact area and an independent experimentally determined non-dimensional wear coefficient, previously validated against the experimental data (3).
Results
Good agreement was found between our computational and experimental models (Figure 1). The effect of femoral setup (and adjusted input kinematics) was shown to be significant (ANOVA, p < 0.05), with lower wear under the ISO CoR conditions. The reduction in wear was approximately 49% compared with the Distal CoR. A comparison of the final wear scar area showed the scars to be smaller and located more anteriorly under the ISO CoR/Reverse High Kinematic conditions, compared with the distal CoR study (Figure 2).
Discussion
The femoral setup was shown to have a significant impact on the computational and experimental wear rates, with the ISO CoR condition having approximately half the wear of the Distal CoR. It appears that through changing the centre of rotation (and subsequently the anterior-posterior direction) the relative motion and contact mechanics at the articulating surface are altered (1). This study highlights the significant influence test setup conditions may have on the wear of a. It is proposed that there is a need to examine TKR bearings under a broad range of conditions, rather than one study condition to fully assess wear performance.
