A surprising tribological validation: metal on metal total hip prosthesis with rolling friction

ABSTRACT The paper reports about the validation studies of the mode of functioning of a metal on metal (MoM) total hip prosthesis (THP) with rolling friction, obtained by introducing a number of balls between the femoral head and acetabular cup. After over 15 years of research upon the functional principle and constructive solution a final version that offered a coefficient of minimum friction in the hip joint came to light. This version was based on a constructive solution of motion with lower friction, “Omnitrack® movement solutions", which has been modified and rebuilt to be used as a joint of a total hip prosthesis-MOMJ. The prosthesis was built entirely in stainless steel, SS316L medical grade. Tests have been carried out on the experimental laboratory devices that showed very low values of the coefficient of friction (0.0225). For validation, the prosthesis had to be put through tests for 50000 cycles, in terms of physiological motion and dynamic loading, according to ISO 14242-3. Testing was conducted on a multiaxial dynamics machine, MTS Bionix, equipped with system for hip implant testing. The testing results of this total hip prosthesis with rolling friction have been successful in signing up for a friction moment of 0.525 (kN?mm) which means a coefficient of friction of μ = 0.0143, for a joint with femoral head diameter 28 mm. Keywords: Total hip prosthesis, rolling friction, balls, femoral head surface wear, Omnitrack® movement solutions, validation by laboratory testing.