A recent submission to ASTM, WK28778 entitled “Standard test method for determination of friction torque and friction factor for hip implants using an anatomical motion hip simulator”, describes a proposal for determining the friction factor of hip implant devices. Determination of a friction factor in an implant bearing couple using a full kinematic walking cycle as described in ISO14242-1 may offer designers and engineers valuable input to improve wear characteristics, minimize torque and improve long term performance of hip implants. The aim of this study was to investigate differences in friction factors between two commercially available polyethylene materials using the procedure proposed. Two polyethylene acetabular liner material test groups were chosen for this study: commercially available Marathon® (A) and AltrX® (B). All liners were machined to current production specifications with an inner diameter of 36mm and an outer diameter of 56mm. Surface roughness (Ra) of the liner inner diameters were measured using contact profilometry in the head-liner contact area, before and after 3Mcyc of wear testing. Liners were soaked in bovine serum for 48 hours prior to testing. Friction factor measurements were taken per ASTM WK28778 prior to, and after wear testing using an external six degrees of freedom load cell (ATI Industrial Automation) and a reduced maximum vertical load of 1900N. Friction factor and wear testing was conducted in bovine serum (18mg/mL total protein concentration) supplemented with 0.056% sodium azide (preservative) and 5.56mM EDTA (calcium stabilizer) on a 12-station AMTI (Watertown, MA) ADL hip simulator with load soak controls per ISO 14242-1:2014(E). The liners were removed from the machine, cleaned and gravimetric wear determined per ISO 14242-2:2000(E) every 0.5 million cycles (MCyc) through a total of 3Mcyc to evaluate wear.Introduction and Aims
Methods
