Title:
Biotribology of a mobile bearing posterior stabilised knee design--effect of motion restraint on wear, tibio-femoral kinematics and particles.

Abstract:
The objective of our study was to evaluate the impact of a biphaseal anterior-posterior (AP) and internal-external (IE) motion restraint system on the wear behaviour, tibio-femoral kinematics and particle release of a mobile bearing posterior stabilised knee design in comparison to the widely used linear restraint. in vitro wear simulation was performed using a posterior stabilised total knee replacement with a mobile rotating platform gliding surface design to compare the standard ISO 14243-1:2002 (E) protocol with a linear AP and IE motion restraint and the new ISO 14243-1:2009 (E) protocol with a biphaseal AP and IE motion restraint. For the mobile gliding surfaces, an increase in wear rate by more than a magnitude was measured applying the biphaseal protocol (8.5±1.6 mg/million cycles) in a direct comparison to the linear protocol (0.33±0.07 mg/million cycles), with statistically significant difference. The amplitudes of AP displacement were 3.22±0.47 mm for the biphaseal test, compared to 1.97±0.22 mm in the linear test and the amplitudes of the IE rotation angle had mean values of 7.32°±0.91° under the biphaseal setup, compared to 1.97°±0.14° under linear motion restraint test conditions. From our observations, we conclude that the changes in AP translation and IE rotation motion restraints from ISO linear to ISO biphaseal test conditions highly impact the knee joint kinematics and wear behaviour of a mobile bearing posterior stabilised knee design.