Biotribology of artificial hip joints

Figure 1 Total and resurfacing hip replacements.

Figure 2 Material couplings in hip implants.

Figure 3 Nominal vs real surfaces. A: Roundness; B: Roughness and waviness. Adapted from ASME B46.1-1995.

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Figure 4 Hertz problem of spheres in contact.

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Figure 5 Examples of finite element models of hip implants.

Figure 6 Maximum pressure (A) and contact radius (B) vs load for a MoP implant (head radius 14 mm, diametrical clearance 0. 2 mm, cup thickness 6 mm).

Figure 7 Microscopic detail of a rough contact.

Figure 8 Forces and equilibrium in sliding contact. N and T are the normal and frictional forces acting on the upper body at the interface. Note that T is opposite to the motion direction. W and P are external forces. At the equilibrium force magnitudes must satisfy W = N and T = P; moreover the line of action of N + T must be the same of W + P.

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Figure 9 Forces in a revolute/spherical joint: Frictionless (A) and frictional contact (B).

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Figure 10 Stribeck diagram: Coefficient of friction vs Sommerfeld number and identification of lubrication regimes.

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Figure 11 Hydrodynamic lubrication. A: Parallel plates; B, C: Fixed inclined slider bearing; D: k plot from equation (12).

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Figure 12 Squeeze film lubrication.

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Figure 13 Dry and lubricated contact: From Hertzian to elastohydrodynamic lubrication pressure profiles. EHL: Elastohydrodynamic lubrication.

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Figure 14 Adhesion and abrasion wear mechanisms.

Figure 15 Wear trends vs time for metallic surfaces.

Figure 16 Anisotropic wear in UHMWPE: Cross shear phenomenon.

Figure 17 Averages implant prices. MoP: Metal on plastic; CoC: Ceramic on ceramic; CoP: Ceramic on plastic; RHR: Resurfacing hip replacement.

Figure 18 Maximum pressure pm and contact half-width a, for different D_h (mm) and Cl (μm), in metal-on-metal (E = 230 GPa, ν = 0. 3) and metal on plastic (E = 1 GPa, ν = 0.4) implants under 2500 N load. MoP: Metal on plastic; MoM: Metal-on-metal.

Figure 19 Effect of the clearance Cl and the head diameter D_h of hip implants on the lubrication, in terms of minimum film thickness (A, B) and dimensionless film thickness λ (C, D)[46]. Test case: W = 2 kN, ω = 2 rad/s, μ = 2.5 mPas. MoM: Metal-on-metal; CoC: Ceramic on ceramic; MoM_RHR: Metal on metal resurfacing.

Figure 20 Edge loading phenomenon caused by steep cup inclination angles[52].

Figure 21 Trends in hip replacement implantation from 2003 to 2012. Data from[3]. MoM: Metal-on-metal; CoC: Ceramic on ceramic; MoM_RHR: Metal on metal resurfacing.

Figure 22 Trend of femoral head size from 2003 to 2012. Data from[3].

Figure 23 Revision risk (Cumulative hazard with 95%CI) for hip articulation. Data from[3]. MoM: Metal-on-metal; CoC: Ceramic on ceramic.