Skip to main content
SpringerLink
Log in

Articular Cartilage: Functional Biomechanics

  • Chapter
  • First Online:
Cartilage Injury of the Knee

  • 2348 Accesses

Abstract

The complex architecture of the articular cartilage is due to interaction between the three main components of this tissue (collagen, proteoglycans, and water). This interaction is also responsible for providing the biomechanical properties of this tissue, permitting its main function which is the transmission of load with low frictional coefficient. If this interaction is lost because of the alteration of its composition, like in the osteoarthritis, or even an acute injury, the biomechanical properties of the cartilage are altered, and this important tissue loses the capacity to withstand stresses that affect the joint, beginning the process of degradation. The main components of the extracellular matrix of the cartilage are collagen (75% of the dry weight), proteoglycans (20–30% of the dry weight), and water, which constitutes from 65% to 80% of the total weight of the cartilage. The mechanical properties of cartilage are conferred by interaction of the cartilage components of the extracellular matrix. The cartilage can be described as a viscoelastic tissue since its load response exhibits both elastic and viscous behavior. As a result of a load applied in the cartilage, a combination of compressive, tensile, and shear stresses is generated and distributed across the tissue. Due to the structure and composition of the cartilage, its response to these stresses is different. Fluid flow is essential for resisting compressive stress and, on the other hand, the ECM is essential for resisting tensile and shear strains.

This is a preview of subscription content, log in via an institution to check access.

Access this chapter

Log in via an institution
eBook
USD 16.99
Price excludes VAT (USA)
  • Available as EPUB and PDF
  • Read on any device
  • Instant download
  • Own it forever
Softcover Book
USD 109.99
Price excludes VAT (USA)
  • Compact, lightweight edition
  • Dispatched in 3 to 5 business days
  • Free shipping worldwide - see info
Hardcover Book
USD 159.99
Price excludes VAT (USA)
  • Durable hardcover edition
  • Dispatched in 3 to 5 business days
  • Free shipping worldwide - see info

Tax calculation will be finalised at checkout

Purchases are for personal use only

Institutional subscriptions

Similar content being viewed by others

References

  1. Athanasiou K, Darling E, Hu J, et al. Articular cartilage. 2nd ed. Boca Raton, FL: CRC Press/Taylor & Francis Group; 2016.

    Google Scholar 

  2. Muir H. The chondrocyte, architect of cartilage. Biomechanics, structure, function and molecular biology of cartilage matrix macromolecules. BioEssays. 1995;17:1039–48. https://doi.org/10.1002/bies.950171208.

    Article  CAS  PubMed  Google Scholar 

  3. Andriacchi TP, Mündermann A, Smith RL, et al. A framework for the in vivo pathomechanics of osteoarthritis at the knee. Ann Biomed Eng. 2004;32:447–57. https://doi.org/10.1023/B:ABME.0000017541.82498.37.

    Article  PubMed  Google Scholar 

  4. Koo S, Andriacchi TP. A comparison of the influence of global functional loads vs. local contact anatomy on articular cartilage thickness at the knee. J Biomech. 2007;40:2961–6. https://doi.org/10.1016/j.jbiomech.2007.02.005.

    Article  PubMed  PubMed Central  Google Scholar 

  5. Liu F, Kozanek M, Hosseini A, et al. In vivo tibiofemoral cartilage deformation during the stance phase of gait. J Biomech. 2010;43:658–65. https://doi.org/10.1016/j.jbiomech.2009.10.028.

    Article  PubMed  Google Scholar 

  6. Bingham JT, Papannagari R, Van de Velde SK, et al. In vivo cartilage contact deformation in the healthy human tibiofemoral joint. Rheumatology. 2008;47:1622–7. https://doi.org/10.1093/rheumatology/ken345.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  7. Sutter EG, Widmyer MR, Utturkar GM, et al. In vivo measurement of localized tibiofemoral cartilage strains in response to dynamic activity. Am J Sports Med. 2015;43:370–6. https://doi.org/10.1177/0363546514559821.

    Article  PubMed  Google Scholar 

  8. Ramage L, Nuki G, Salter DM. Signalling cascades in mechanotransduction: cell-matrix interactions and mechanical loading. Scand J Med Sci Sport. 2009;19:457–69. https://doi.org/10.1111/j.1600-0838.2009.00912.x.

    Article  CAS  Google Scholar 

  9. Stockwell R. Biology of cartilage cells. Cambridge: Cambridge University Press; 1979.

    Google Scholar 

  10. Ulrich-Vinther M, Maloney MD, Schwarz EM, et al. Articular cartilage biology. J Am Acad Orthop Surg. 2003;11:421–30. https://doi.org/10.5435/00124635-200311000-00006.

    Article  PubMed  Google Scholar 

  11. Coleman JL, Widmyer MR, Leddy HA, et al. Diurnal variations in articular cartilage thickness and strain in the human knee. J Biomech. 2013;46:541–7. https://doi.org/10.1016/j.jbiomech.2012.09.013.

    Article  PubMed  Google Scholar 

  12. Lipshitz H, Etheridge R, Glimcher M. In vitro wear of articular cartilage. J Bone Jointt Surg. 1975;57A:527–37.

    Article  CAS  Google Scholar 

  13. McDevitt C, Muir H. Biochemical changes in the cartilage of the knee in experimental and natural osteoarthritis in the dog. J Bone Jointt Surg. 1976;58B:94–101.

    Article  CAS  Google Scholar 

  14. Mow VC, Guo XE. Mechano-electrochemical properties of articular cartilage: their inhomogeneities and anisotropies. Annu Rev Biomed Eng. 2002;4:175–209. https://doi.org/10.1146/annurev.bioeng.4.110701.120309.

    Article  CAS  PubMed  Google Scholar 

  15. Robin Poole A, Matsui Y, Hinek A, Lee ER. Cartilage macromolecules and the calcification of cartilage matrix. Anat Rec. 1989;224:167–79. https://doi.org/10.1002/ar.1092240207.

    Article  Google Scholar 

  16. Wilusz RE, Sanchez-Adams J, Guilak F. The structure and function of the pericellular matrix of articular cartilage. Matrix Biol. 2014;39:25–32. https://doi.org/10.1016/j.matbio.2014.08.009.

    Article  CAS  PubMed  Google Scholar 

  17. Deshmukh K, Nimni ME. Isolation and characterization of cyanogen bromide peptides from the collagen of bovine articular cartilage. Biochem J. 1973;133:615–22. https://doi.org/10.1042/bj1330615.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  18. Callaghan JJ. The adult knee. Philadelphia, PA: Lippincott Williams & Wilkins; 2003.

    Google Scholar 

  19. Luo Y, Sinkeviciute D, He Y, et al. The minor collagens in articular cartilage. Protein Cell. 2017;8:560–72. https://doi.org/10.1007/s13238-017-0377-7.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  20. Zelenski NA, Leddy HA, Sanchez-Adams J, et al. Type VI collagen regulates pericellular matrix properties, chondrocyte swelling, and mechanotransduction in mouse articular cartilage. Arthritis Rheumatol. 2015;67:1286–94. https://doi.org/10.1002/art.39034.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  21. Roughley P. The structure and function of cartilage proteoglycans. Eur Cells Mater. 2006;12:92–101. https://doi.org/10.22203/eCM.v012a11.

    Article  CAS  Google Scholar 

  22. Hardingham TE, Fosang AJ, Dudhia J. The structure, function and turnover of aggrecan, the large aggregating proteoglycan from cartilage. Eur J Clin Chem Clin Biochem. 1994;32:249–57.

    CAS  PubMed  Google Scholar 

  23. Mow VC, Lai WM. Recent developments in synovial joint biomechanics. SIAM Rev. 1980;22:275–317. https://doi.org/10.1137/1022056.

    Article  Google Scholar 

  24. Klika V, Gaffney EA, Chen YC, Brown CP. An overview of multiphase cartilage mechanical modelling and its role in understanding function and pathology. J Mech Behav Biomed Mater. 2016;62:139–57. https://doi.org/10.1016/j.jmbbm.2016.04.032.

    Article  PubMed  Google Scholar 

  25. Sophia Fox AJ, Bedi A, Rodeo SA. The basic science of articular cartilage: structure, composition, and function. Sports Health. 2009;1:461–8. https://doi.org/10.1177/1941738109350438.

    Article  PubMed  PubMed Central  Google Scholar 

  26. Carballo CB, Nakagawa Y, Sekiya I, Rodeo SA. Basic science of articular cartilage. Clin Sports Med. 2017;36:413–25. https://doi.org/10.1016/j.csm.2017.02.001.

    Article  PubMed  Google Scholar 

  27. Korhonen RK, Julkunen P, Wilson W, Herzog W. Importance of collagen orientation and depth-dependent fixed charge densities of cartilage on mechanical behavior of chondrocytes. J Biomech Eng. 2008;130 https://doi.org/10.1115/1.2898725.

  28. Gilbert SJ, Blain EJ. Cartilage mechanobiology: how chondrocytes respond to mechanical load. In: Mechanobiology in health and disease. London: Elsevier; 2018. p. 99–126.

    Google Scholar 

  29. Lv M, Zhou Y, Chen X, et al. Calcium signaling of in situ chondrocytes in articular cartilage under compressive loading: roles of calcium sources and cell membrane ion channels. J Orthop Res. 2018;36:730–8. https://doi.org/10.1002/jor.23768.

    Article  CAS  PubMed  Google Scholar 

  30. Vaca-González JJ, Guevara JM, Moncayo MA, et al. Biophysical stimuli: a review of electrical and mechanical stimulation in hyaline cartilage. Cartilage. 2019;10:157–72. https://doi.org/10.1177/1947603517730637.

    Article  PubMed  Google Scholar 

  31. Liu H-Y, Duan H-T, Zhang C-Q, Wang W. Study of the mechanical environment of chondrocytes in articular cartilage defects repaired area under cyclic compressive loading. J Healthc Eng. 2017;2017:1–10. https://doi.org/10.1155/2017/1308945.

    Article  Google Scholar 

  32. Lai WM, Hou JS, Mow VC. A triphasic theory for the swelling and deformation behaviors of articular cartilage. J Biomech Eng. 1991;113:245–58. https://doi.org/10.1115/1.2894880.

    Article  CAS  PubMed  Google Scholar 

  33. Mow VC, Ateshian GA, Spilker RL. Biomechanics of diarthrodial joints: a review of twenty years of progress. J Biomech Eng. 1993;115:460–7. https://doi.org/10.1115/1.2895525.

    Article  CAS  PubMed  Google Scholar 

  34. O’Hara BP, Urban JP, Maroudas A. Influence of cyclic loading on the nutrition of articular cartilage. Ann Rheum Dis. 1990;49:536–9. https://doi.org/10.1136/ard.49.7.536.

    Article  PubMed  PubMed Central  Google Scholar 

  35. Torzilli PA, Mow VC. On the fundamental fluid transport mechanisms through normal and pathological articular cartilage during function—II. The analysis, solution and conclusions. J Biomech. 1976;9:587–606. https://doi.org/10.1016/0021-9290(76)90100-7.

    Article  CAS  PubMed  Google Scholar 

  36. Teeple E, Fleming BC, Mechrefe AP, et al. Frictional properties of Hartley guinea pig knees with and without proteolytic disruption of the articular surfaces. Osteoarthr Cartil. 2007;15:309–15. https://doi.org/10.1016/j.joca.2006.08.011.

    Article  CAS  Google Scholar 

  37. Eckstein F, Tieschky M, Faber S, et al. Functional analysis of articular cartilage deformation, recovery, and fluid flow following dynamic exercise in vivo. Anat Embryol (Berl). 1999;200:419–24. https://doi.org/10.1007/s004290050291.

    Article  CAS  Google Scholar 

  38. Meng Q, An S, Damion RA, et al. The effect of collagen fibril orientation on the biphasic mechanics of articular cartilage. J Mech Behav Biomed Mater. 2017;65:439–53. https://doi.org/10.1016/j.jmbbm.2016.09.001.

    Article  CAS  PubMed  Google Scholar 

  39. MacConaill M. The movements of bones and joints; the mechanical structure of articulating cartilage. J Bone Joint Surg. 1951;33:251–7.

    Article  Google Scholar 

  40. Aspden R, Hukins D. The lamina splendens of articular cartilage is an artefact of phase contrast microscopy. Proc R Soc London Ser B Biol Sci. 1979;206:109–13. https://doi.org/10.1098/rspb.1979.0094.

    Article  CAS  Google Scholar 

  41. Fujioka R, Aoyama T, Takakuwa T. The layered structure of the articular surface. Osteoarthr Cartil. 2013;21:1092–8. https://doi.org/10.1016/j.joca.2013.04.021.

    Article  CAS  Google Scholar 

  42. Setton LA, Zhu W, Mow VC. The biphasic poroviscoelastic behavior of articular cartilage: role of the surface zone in governing the compressive behavior. J Biomech. 1993;26:581–92. https://doi.org/10.1016/0021-9290(93)90019-B.

    Article  CAS  PubMed  Google Scholar 

  43. Buckwalter J, Anderson D, Brown T, et al. The roles of mechanical stresses in the pathogenesis of osteoarthritis: implications for treatment of joint injuries. Cartilage. 2013;4(4):286–94.

    Article  Google Scholar 

  44. Wong M, Carter D. Articular cartilage functional histomorphology and mechanobiology: a research perspective. Bone. 2003;33:1–13. https://doi.org/10.1016/S8756-3282(03)00083-8.

    Article  CAS  PubMed  Google Scholar 

  45. Sakai N, Hashimoto C, Yarimitsu S, et al. A functional effect of the superficial mechanical properties of articular cartilage as a load bearing system in a sliding condition. Biosurface Biotribol. 2016;2:26–39. https://doi.org/10.1016/j.bsbt.2016.02.004.

    Article  Google Scholar 

  46. Nugent GE, Aneloski NM, Schmidt TA, et al. Dynamic shear stimulation of bovine cartilage biosynthesis of proteoglycan 4. Arthritis Rheum. 2006;54:1888–96. https://doi.org/10.1002/art.21831.

    Article  CAS  PubMed  Google Scholar 

  47. Lu XL, Mow VC. Biomechanics of articular cartilage and determination of material properties. Med Sci Sports Exerc. 2008;40:193–9. https://doi.org/10.1249/mss.0b013e31815cb1fc.

    Article  PubMed  Google Scholar 

  48. Muir H, Bullough P, Maroudas A. The distribution of collagen in human articular cartilage with some of its physiological implications. J Bone Joint Surg Br. 1970;52-B:554–63. https://doi.org/10.1302/0301-620X.52B3.554.

    Article  Google Scholar 

  49. Eyre D, Weis M, Wu J-J. Articular cartilage collagen: an irreplaceable framework? Eur Cells Mater. 2006;12:57–63. https://doi.org/10.22203/eCM.v012a07.

    Article  CAS  Google Scholar 

  50. Haapala J, Arokoski J, Hyttinen M, et al. Remobilization does not fully restore immobilization induced articular cartilage atrophy. Clin Orthop Relat Res. 1999;362:218–29.

    Article  Google Scholar 

  51. Brama PAJ, Tekoppele JMJ, Bank RA, et al. Functional adaptation of equine articular cartilage: the formation of regional biochemical characteristics up to age one year. Equine Vet J. 2010;32:217–21. https://doi.org/10.2746/042516400776563626.

    Article  Google Scholar 

  52. Shepherd DET, Seedhom BB. Thickness of human articular cartilage in joints of the lower limb. Ann Rheum Dis. 1999;58:27–34. https://doi.org/10.1136/ard.58.1.27.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  53. Froimson MI, Ratcliffe A, Gardner TR, Mow VC. Differences in patellofemoral joint cartilage material properties and their significance to the etiology of cartilage surface fibrillation. Osteoarthr Cartil. 1997;5:377–86. https://doi.org/10.1016/S1063-4584(97)80042-8.

    Article  CAS  Google Scholar 

  54. Whitesides TE. Orthopaedic basic science. Biology and biomechanics of the musculoskeletal system. 2nd ed. J Bone Jointt Surg Am. 2001;83:482. https://doi.org/10.2106/00004623-200103000-00040.

    Article  Google Scholar 

  55. Hall BK. Cartilage: structure, function, and biochemistry. New York: Academic Press, Inc.; 1983.

    Google Scholar 

  56. Kempson GE. The mechanical properties of articular cartilage. In: The joints and synovial fluid. New York: Elsevier; 1980. p. 177–238.

    Chapter  Google Scholar 

  57. Hayes WC, Mockros LF. Viscoelastic properties of human articular cartilage. J Appl Physiol. 1971;31:562–8. https://doi.org/10.1152/jappl.1971.31.4.562.

    Article  CAS  PubMed  Google Scholar 

  58. Mow VC, Kuei SC, Lai WM, Armstrong CG. Biphasic creep and stress relaxation of articular cartilage in compression: theory and experiments. J Biomech Eng. 1980;102:73–84. https://doi.org/10.1115/1.3138202.

    Article  CAS  PubMed  Google Scholar 

  59. Urban J, Hall A, Gehl K. Regulation of matrix synthesis rates by the ionic and osmotic environment of articular chondrocytes. J Cell Physiol. 1993;154:262–70.

    Article  CAS  Google Scholar 

  60. Hirsch C. The pathogenesis of chondromalacia of the patella. A physical, histologic and chemical study. Acta Chir Sand. 1944;83(1):1–06.

    Google Scholar 

  61. Salinas EY, Hu JC, Athanasiou K. A guide for using mechanical stimulation to enhance tissue-engineered articular cartilage properties. Tissue Eng Part B Rev. 2018;24:345–58. https://doi.org/10.1089/ten.teb.2018.0006.

    Article  PubMed  PubMed Central  Google Scholar 

  62. Soltz MA, Ateshian GA. Experimental verification and theoretical prediction of cartilage interstitial fluid pressurization at an impermeable contact interface in confined compression. J Biomech. 1998;31:927–34. https://doi.org/10.1016/S0021-9290(98)00105-5.

    Article  CAS  PubMed  Google Scholar 

  63. Kempson GE, Muir H, Pollard C, Tuke M. The tensile properties of the cartilage of human femoral condyles related to the content of collagen and glycosaminoglycans. BBA Gen Subj. 1973;297:456–72. https://doi.org/10.1016/0304-4165(73)90093-7.

    Article  CAS  Google Scholar 

  64. Akizuki S, Mow VC, Müller F, et al. Tensile properties of human knee joint cartilage: I. influence of ionic conditions, weight bearing, and fibrillation on the tensile modulus. J Orthop Res. 1986;4:379–92. https://doi.org/10.1002/jor.1100040401.

    Article  CAS  PubMed  Google Scholar 

  65. Huang C-Y, Soltz MA, Kopacz M, et al. Experimental verification of the roles of intrinsic matrix viscoelasticity and tension-compression nonlinearity in the biphasic response of cartilage. J Biomech Eng. 2003;125:84–93. https://doi.org/10.1115/1.1531656.

    Article  PubMed  Google Scholar 

  66. Woo SL-Y, Lubock P, Gomez MA, et al. Large deformation nonhomogeneous and directional properties of articular cartilage in uniaxial tension. J Biomech. 1979;12:437–46. https://doi.org/10.1016/0021-9290(79)90028-9.

    Article  CAS  PubMed  Google Scholar 

  67. Roth V, Mow VC. The intrinsic tensile behavior of the matrix of bovine articular cartilage and its variation with age. J Bone Joint Surg Am. 1980;62:1102–17.

    Article  CAS  Google Scholar 

  68. Kempson GE, Freeman MAR, Swanson SAV. Tensile properties of articular cartilage. Nature. 1968;220:1127–8. https://doi.org/10.1038/2201127b0.

    Article  CAS  PubMed  Google Scholar 

  69. Hayes WC, Bodine AJ. Flow-independent viscoelastic properties of articular cartilage matrix. J Biomech. 1978;11:407–19. https://doi.org/10.1016/0021-9290(78)90075-1.

    Article  CAS  PubMed  Google Scholar 

  70. Jaalouk DE, Lammerding J. Mechanotransduction gone awry. Nat Rev Mol Cell Biol. 2009;10:63–73. https://doi.org/10.1038/nrm2597.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  71. Choi JB, Youn I, Cao L, et al. Zonal changes in the three-dimensional morphology of the chondron under compression: the relationship among cellular, pericellular, and extracellular deformation in articular cartilage. J Biomech. 2007;40:2596–603. https://doi.org/10.1016/j.jbiomech.2007.01.009.

    Article  PubMed  PubMed Central  Google Scholar 

  72. Martinac B. Mechanosensitive ion channels: molecules of mechanotransduction. J Cell Sci. 2004;117:2449–60. https://doi.org/10.1242/jcs.01232.

    Article  CAS  PubMed  Google Scholar 

  73. Ingber D. Integrins as mechanochemical transducers. Curr Opin Cell Biol. 1991;3:841–8. https://doi.org/10.1016/0955-0674(91)90058-7.

    Article  CAS  PubMed  Google Scholar 

  74. Driscoll TP, Cosgrove BD, Heo S-J, et al. Cytoskeletal to nuclear strain transfer regulates YAP signaling in mesenchymal stem cells. Biophys J. 2015;108:2783–93. https://doi.org/10.1016/j.bpj.2015.05.010.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  75. Guilak F. Compression-induced changes in the shape and volume of the chondrocyte nucleus. J Biomech. 1995;28:1529–41. https://doi.org/10.1016/0021-9290(95)00100-X.

    Article  CAS  PubMed  Google Scholar 

  76. Buckwalter JA, Martin JA, Brown TD. Perspectives on chondrocyte mechanobiology and osteoarthritis. Biorheology. 2006;43:603–9.

    PubMed  Google Scholar 

  77. Buckwalter JA, Mankin HJ. Articular cartilage: degeneration and osteoarthritis, repair, regeneration, and transplantation. Instr Course Lect. 1998;47:487–504.

    CAS  PubMed  Google Scholar 

  78. Parkkinen JJ, Lammi MJ, Helminen HJ, Tammi M. Local stimulation of proteoglycan synthesis in articular cartilage explants by dynamic compression in vitro. J Orthop Res. 1992;10:610–20. https://doi.org/10.1002/jor.1100100503.

    Article  CAS  PubMed  Google Scholar 

Download references

Author information

Authors and Affiliations

  1. Hospital Israelita Albert Einstein, São Paulo, SP, Brazil

    Mário Ferretti, Lauro Augusto Veloso Costa & Noel Oizerovici Foni

Authors
  1. Mário Ferretti
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Lauro Augusto Veloso Costa
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Noel Oizerovici Foni
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Mário Ferretti .

Editor information

Editors and Affiliations

  1. Orthopaedic Surgery and Sports Medicine, Mayo Clinic, Rochester, MN, USA

    Aaron J. Krych

  2. University of Manchester, Manchester, UK

    Leela C. Biant

  3. Orthopedic Sugery, Hospital for Special Surgery, New York, USA

    Andreas H. Gomoll

  4. FIFA Medical Centre of Excellence, Clinica do Dragao, Espregueira-Mendes Sports Centre,, PORTO, Portugal

    João Espregueira-Mendes

  5. O.A.S.I. Bioresearch Foundation, Gobbi N.P.O., Milan, Italy

    Alberto Gobbi

  6. Institute for Medical Science in Sports, Osaka Health Science University, Osaka, Japan

    Norimasa Nakamura

Rights and permissions

Reprints and permissions

Copyright information

© 2021 ISAKOS

About this chapter

Check for updates. Verify currency and authenticity via CrossMark

Cite this chapter

Ferretti, M., Costa, L.A.V., Foni, N.O. (2021). Articular Cartilage: Functional Biomechanics. In: Krych, A.J., Biant, L.C., Gomoll, A.H., Espregueira-Mendes, J., Gobbi, A., Nakamura, N. (eds) Cartilage Injury of the Knee. Springer, Cham. https://doi.org/10.1007/978-3-030-78051-7_1

Download citation

  • DOI: https://doi.org/10.1007/978-3-030-78051-7_1

  • Published:

  • Publisher Name: Springer, Cham

  • Print ISBN: 978-3-030-78050-0

  • Online ISBN: 978-3-030-78051-7

  • eBook Packages: MedicineMedicine (R0)

Publish with us

Policies and ethics

Search

Navigation