Comparative retrieval analysis of contemporary mobile and fixed unicompartmental knee bearing designs

There are two different concepts behind Unicompartmental Knee Replacement (UKR). Mobile bearings, as exemplified by the Oxford UKR, and fixed bearings, as exemplified by the Physica ZUK. These are the two most commonly implanted UKRs in the UK. For the first time, a comparison of the tribological features of 19 explanted Oxford and 19 explanted Physica ZUK UKRs was undertaken. Surface damage on the polyethylene (PE) inserts of the Oxford and Physica ZUK cohorts were assessed using an established semi-quantitative scoring method. The femoral components of both cohorts were assessed using a non-contact 3D profilometer to measure roughness values. It was found that the PE inserts of the Oxford cohort (22.54 ± 9.14) had statistically significant greater damage scores than the Physica ZUK cohort (16.50 ± 5.17) (p = 0.04). However, the femoral components of the Oxford cohort showed lower roughness values than the Physica ZUK cohort (p = 0.00). This is the first study that reports a comparative roughness analysis between retrieved Oxford and Physica ZUK UKR designs. •Explant analysis was undertaken of the most common types of unicompartmental knee replacements (UKRs) in the UK.•Nineteen Oxford mobile bearing UKRs were compared with 19 fixed bearing Physica ZUK UKRs.•The femoral components of the Oxford UKRs showed lower roughness values than the Physica ZUK UKRs.•However, the tibial inserts of the Oxford UKRs showed greater damage scores than the Physica ZUK UKRs.•This is the first comparative roughness analysis between explanted Oxford and Physica ZUK UKRs.