Abstract
Introduction: To develop a more physiologically relevant hip simulator test protocol and study the effect of microstructure on the wear performance of as-cast (AC) and double heat treated (DHT) devices under the new protocol.
Methods: Three pairs of AC and four pairs of DHT 50 mm CoCr metal-on-metal (MoM) devices were tested. The lubricant used was bovine serum. Stop-start motion was implemented between the two sets of kinetics and kinematics that alternated every 100 cycles throughout the test. Condition one: The flexion/extension was 30° and 15° respectively. The internal/external rotation was ±10°. The force was Paul type stance phase loading with a maximum load of 3 kN and a standard ISO swing phase load of 0.3 kN. Condition two: The flexion/extension was ±22°. The internal/external rotation was ±8°. The force was a maximum stance phase load of 2.2 kN and a swing phase load of 0.24 kN at 0.5 Hz frequency. Wear was assessed gravimetrically.
Result: The masking effect of 1 Hz speed and uninter-rupted motion, in providing exaggerated lubrication regime, was exposed under more physiologically relevant test conditions. The AC devices have significantly reduced wear when compared to the DHT devices. It can also be seen that from 0.5 to 2 Mc the divergence in wear has increased.
Conclusion: A more physiologically relevant hip simulator test protocol was successfully developed and implemented, in showing the effect of microstructure on wear as seen in vivo, where high wear of DHT devices has been observed. 295
Correspondence should be addressed to BHS c/o BOA, at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London, WC2A 3PE, England.
