JOINT LUBRICATION - DNB Orthopaedics MS Orthopedics MRCS Exam GUIDE -

DNB Orthopaedics  MS Orthopedics  MRCS Exam GUIDE -

Orthopaedic Guidance for DNB Orthopaedics,MS Orthopaedics and Mrcs exams.Cme courses for orthopaedic surgeons.Davangere notes,solved question papers.DNB Ortho,MS Ortho MRCS,Exam Guide videos and notes 9087747888


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Tuesday 10 April 2018



  • difference of human joints from bearings in engineering
    • operate in low sliding speed
    • expected to last a life time
  • types lubrication
    joint lubrication

  • Tribology : science of rubbing surfaces
  • as on surface slides over another the movement is restricted by frictional force – lubrication decreases the frictional force and produce smooth movement – reduces wear and tear of bearing surfaces by interposing a substance that keeps them apart
Types of lubrication
  • Boundary lubrication
  • Fluid film lubrication
Boundary lubrication
  • depends on chemical property of lubricant
  • synovial fluid – special type of protein – lubrin – adsorbed to each articular surface – prevent direct surface to surface contact
Fluid film lubrication
  • depends on viscosity of fluid – fluid film completely separates the surfaces
  • two types of mechanisms occur when joint is loaded
    • hydrodynamic
    • squeeze film
  • hydrodynamic
    • occurs when two non parallel surfaces move tangentially on each other
    • fluid forms into converging wedge of fluid – lifts the bearing surfaces apart
    • motion of surfaces drags the fluid into the gap between surfaces
  • squeeze film
    • occurs when surfaces move perpendicular to each other
    • tendency to squeeze liquid film out – resisted by viscosity of fluid
    • very high fluid pressure generated – supports the heavy load transiently – but eventually the film becomes thin – contact between surface occurs
  • Enhancements of fluid film lubrication
    • elasto-hydro-dynamic
    • boosted
  • elasto – hydro-dynamic
    • occur in both hydro-dynamic and squeeze film mechanisms
    • occurs when surfaces are not rigid – surfaces get deformed under load
    • deformation increases the surface contact area – also prevent the escape of lubricating fluid
  • boosted
    • occurs in squeeze film mechanism and sliding loads
    • depends on ability of the solvent of synovial fluid to pass into articular cartilage in perpendicular motion
    • decrease in solvent component increases the hyaluronic acid protein complex concentration – increases viscosity – boosts the lubrication
    • as load increases – fluid gets trapped between the asperities on surface – progressively becomes more viscous by boosting mechanism
Normal joint motion
  • swing phase ( slight loading)
    • fluid drawn between the surfaces
  • stance phase ( and in case of severe loads)
    • boundary lubrication
    • fluid film maintained by squeeze film
  • motion starts
    • combination of boundary and fluid film lubrication
    • as the speed increases film enhanced by elastohydrodynamic mechanism
    • as slows down – squeeze film mechanism operates
  • cycle
    • boundary lubrication – squeeze film – elasto hydro-dynamic – squeeze film – boundary lubrication
  • exudation of fluid from cartilage surface when gets deformed – Weeping lubrication
  • trapping of fluid in the undulations of cartilage to enhance lubrication – Trapped pool lubrication
  • increasing the concentration of fluid – boosted lubrication
Replaced joints

  • ineffective squeeze film mechanism
    • hard material of surfaces
    • limited surface area
  • boundary lubrication seen more – after total replacement synovial fluid quantity would be small

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