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Research Papers: Biotribology

Lubrication of the Human Ankle Joint in Walking

[+] Author and Article Information
Miroslav Hlaváček

Institute of Theoretical and Applied Mechanics, Academy of Sciences of the Czech Republic, Prosecká 76, 19000 Prague 9, Czech Republichlavacek@itam.cas.cz

J. Tribol 132(1), 011201 (Nov 11, 2009) (8 pages) doi:10.1115/1.4000278 History: Received April 10, 2009; Revised August 31, 2009; Published November 11, 2009; Online November 11, 2009

Human ankle joint lubrication in walking is analyzed. A biphasic mixture model is considered for articular cartilage (ideal interstitial fluid and elastic porous matrix that is transversely isotropic and inhomogeneous throughout its thickness). Synovial fluid is considered Newtonian. Its viscosity is due to the macromolecules of hyaluronic acid that are too large to enter the matrix pores. Due to the fluid pressure gradient water and small solutes pass through the matrix pores and across the articular surface in both directions. The effect of the time varying concentration of hyaluronic acid or of the synovial fluid viscosity on the synovial film thickness distribution is small and neglected in the model. Periodic sliding motion of the articular surfaces and periodic loading of the joint as encountered in walking are included in the analysis. Synovial fluid serves as a fluid lubricant. The model shows that soon after the onset of walking the normal human ankle joint works in a mixed lubrication mode (a combination of boundary and fluid-film lubrications). A protective gel layer formed in the gap due to the synovial fluid filtration by cartilage may serve as a boundary lubricant. The synovial gel layer is not guaranteed in the osteoarthritic case, and the rough sliding surfaces may get repeatedly into an intimate contact and wear off due to the reciprocating sliding motion.

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Figures

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Figure 1

Cross section of the synovial film for the human ankle joint

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Figure 2

Variation of dry contact SF pressure pd(x) and quasisteady SF pressure pq(x) for W(t) and U(t) at t=0.25T in the human ankle joint for unbounded articular surfaces

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Figure 3

Variation of n(t)=J(t)/P=LW(t)/P, the joint force J(t) normalized to the bodyweight P, for the human ankle joint in walking with the step period T=1 s(22)

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Figure 4

Variation of angular displacement γ(t) and entraining velocity U(t) for the human ankle joint in walking (23)

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Figure 5

Fluid flow qU(x,tc) during the tenth step (for tc=9.1:0.1:10.0T)

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Figure 6

Fluid flow qL(x,tc) during the tenth step (for tc=9.1:0.1:10.0T)

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Figure 7

Synovial film profile h(x,tc) during the tenth step (for tc=9.1:0.1:10.0T)

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