Burroughs, Brian R, et al. “In Vitro Comparison of Frictional Torque and Torsional Resistance of Aged Conventional Gamma-in-Nitrogen Sterilized Polyethylene Versus Aged Highly Crosslinked Polyethylene Articulating Against Head Sizes Larger Than 32 Mm”. Acta Orthopaedica, vol. 77, no. 5, Jan. 2006, pp. 710-8, doi:10.1080/17453670610012881.