The hip joint is a spherical joint between the femoral head and the acetabulum in the pelvis (Fig. 1); it is a diarthrosis or synovial joint, since it is wrapped in a capsule that contains the synovial fluid (SF), a biological lubricant that acts also like a shock-absorber [1] .he tribological performance of artificial hip joints is a critical issue for their success, because adverse tissue reaction to wear debris causes loosening and failure. Many studies on wear and lubrication of hip prostheses have been published in the last 10 years, mostly on experimental tests.