title: Effect of femoral head size on the wear of metal on metal bearings in total hip replacements under adverse edge-loading conditions.
abstract: Metal-on-metal (MoM) bearings have shown low-wear rates under standard hip simulator conditions; however, retrieval studies have shown large variations in wear rates and mechanisms. High-wear in vivo has caused catastrophic complications and has been associated with steep cup-inclination angle (rotational malpositioning). However, increasing the cup-inclination angle in vitro has not replicated the increases in wear to the same extent as those observed in retrievals. Clinically relevant wear rates, patterns, and particles were observed in vitro for ceramic-on-ceramic bearings when microseparation (translational malpositioning) conditions were introduced into the gait cycle. In the present study, 28 and 36-mm MoM bearings were investigated under adverse conditions. Increasing the cup angle from 45° to 65° resulted in a significant increase in the wear rate of the 28 mm bearings. However, for the 36 mm bearings, head-rim contact did not occur under the steep cup-angle condition, and the wear rate did not increase. The introduction of microseparation to the gait cycle significantly increased the wear rate of the MoM bearings. Cup angle and head size did not influence the wear rate under microseparation conditions. This study indicated that high-in vivo wear rates were associated with edge loading due to rotational malpositioning such as high-cup-inclination angle and translational malpositioning that could occur due to several surgical factors. Translational malpositioning had a more dominant effect on the wear rate. Preclinical simulation testing should be undertaken with translational and rotational malpositioning conditions as well as standard walking cycle conditions defined by the ISO standard.
authors.affiliation: Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Leeds, United Kingdom.
authors.forename: Mazen
authors.initials: M
authors.lastname: Al-Hajjar
authors.forename: John
authors.initials: J
authors.lastname: Fisher
authors.forename: Sophie
authors.initials: S
authors.lastname: Williams
authors.forename: Joanne L
authors.initials: JL
authors.lastname: Tipper
authors.forename: Louise M
authors.initials: LM
authors.lastname: Jennings
mesh_terms: D001696:Biomechanical Phenomena; D019544:Equipment Failure Analysis; D005270:Femur Head / Q000473:pathology* / Q000601:surgery*; D005684:Gait / Q000502:physiology; D006622:Hip Prosthesis / Q000009:adverse effects; D006801:Humans; D008422:Materials Testing; D008670:Metals; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013499:Surface Properties; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D008670:Metals