REDUCTION OF UHMWPE WEAR IN TOTAL KNEE REPLACEMENTS THROUGH THE USE OF ROTATING PLATFORM MOBILE BEARINGS WITH TWO BEARING MATERIALS

Abstract

Reduction of ultra high molecular weight polyethylene (UHMWPE) surface wear in total knee replacements (TKR) may delay the onset of osteolysis and loosening of components. This study examined the wear of fixed bearing and rotating platform (RP) mobile bearing TKR with two different bearing materials.

Testing was completed on a Leeds ProSim six-station knee simulator under ‘high’ kinematics [1]. PFC Sigma fixed bearing and LCS RP mobile bearing knee designs were tested (DePuy). Non-crosslinked (non-irradiated (NI) or gas plasma (GP) sterilised) and moderately cross-linked (4.0 MRad gamma irradiation sterilisation under vacuum (GVF)) GUR1020 UHMWPE bearings were investigated for each TKR design. Components were tested in 25 % bovine serum solution for up to five million cycles (frequency = 1 Hz). Volumetric wear was determined from gravimetric measurements of the inserts.

The 1020 GVF fixed bearings exhibited a wear rate of 16.4 ± 4 mm3 per million cycles (MC). This was significantly greater (p < 0.05) than wear of the same bearing material in the rotating platform mobile bearing TKR (10.85 ± 2.39 mm3/MC). Similarly, when uncross-linked 1020 UHMWPE was introduced as the bearing material, a significant (p < 0.05) reduction in wear was observed between the fixed bearing (16 ± 7 mm3/MC) and the RP knee designs (5.85 ± 2.05 mm3/MC).

The RP design decouples the motions between the femoral-insert and tray-insert articulating surfaces. This translates complex knee motions into more unidirectional motions at two interfaces, thus reducing wear under high kinematics compared with fixed bearing TKR. This significant reduction in wear was observed with uncross-linked and moderately cross-linked bearing materials. Design of TKR is an important factor that influences UHMWPE surface wear and may affect long-term success of knee replacements in highly active patients.