PI-78: (ISO 14242-4) Implants for surgery - wear of total hip-joint prostheses - Part 4: Testing total hip joint prostheses under variations in surgical positioning
Hard-on-hard bearings in Total Hip Replacements (THR) have shown very low wear rates when tested according to ISO 14242-1 under standard gait conditions. ISO 14242-4 specifies a more severe loading scenario, simulating edge loading due to steep acetabular cup inclination and dynamic separation (micro-separation).
Clinically micro-separation is assumed to occur during the swing phase when the load is minimal and is associated with joint laxity, medialized cups or femoral head offset deficiency. For in-vitro testing, micro-separation is generated by a spring, which produces a medial-superior translation of the cup relative to the femoral head resulting in localized contact between the head and the superior rim of the cup. The distraction of the head from the cup is measured using latest high-accuracy digital contact sensors.