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Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
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Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
Joint biomechanics
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Joint biomechanics

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  • Synovial joint lubrication: in spite of the massive loads generated in them, synovial joints are efficient bearings with very low friction. The coefficient of friction of a synovial joint is around 0.02. This compares to 0.03 for ice sliding on ice. A coefficient of friction of 0.01 means that a load of 100 lb could be made to slide by applying a force of 1lb. Joint lubrication is the key to reduced friction. So, it is helpful to understand them in order to better understand and treat joint wear. It is still unclear how lubrication works, but there are many theories, based on man-made ball-bearings. What is clear is that no single mechanism is responsible and different modes of lubrication work at different stages of joint function. The joint is lined by wear resistant hyaline cartilage and is bathed by synovial fluid. Unlike a typical newtonian fluid synovial fluid has a viscosity that decreases with increasing shear rate. The function of a lubricant is to provide an intermediate layer with low shear resistance in between the two sliding surfaces to reduce friction. A thixotropic fluid would fit the bill perfectly.\nBasic lubrication is of two types: fluid-film, boundary and mixed.\nFluid film : a thin fluid film separates the bearing surfaces. Of two types: hydrodynamic and squeeze film. Hydrodynamic lubrication is unlikely to be feasible in vivo as the sliding velocity of joints are too low to generate a substantial fluid film. Squeeze film lubrication takes place by the production of a fluid film under pressure as the two bearing surfaces move perpendicularly towards each other. Fluid film and resultant load bearing capacity depends on fluid viscosity. It could explain lubrication under sudden loading but is not suitable for prolong loading conditions.\nBoundary: the bearing surfaces come to contact with each other, but "lubricin" from synovial fluid is attached to the cartilage surface and offers an interposed layer which when rubbed provides less resistance to shear.\nMixed: weeping lubrication: on load application synovial fluid is released or "wept" from articular cartilage. It separates the two bearing surfaces and reduces friction due to the hydrostatic pressure. On unloading the fluid is squeezed back in. This mechanism is not dependent on sliding speed .\n
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  • Transcript

    • 1. Joint mechanics Lennard Funk
    • 2. Joint mechanicsHundreds of articulations in the human bodyMany injuries occur to these joint structuresNo two joints are structurally identical
    • 3. Joint LubricationSynovial fluid – Reduction of friction – Distribution of force – Nutrition for tissuesInjury implication: joint wear
    • 4. Joint
    • 5. Joint LubricationSynovial fluid produced by SynoviocytesArthritis => damaged synoviocytes
    • 6. Articular CartilageType II collagenDifferent fibres orientation – Shear forces – tensile resistance to swellingCreep – constant load – compression loadCyclic loading – Benefits vs. damage
    • 7. Articular Cartilage lubricationSynovial joints – Low coefficients of friction . 01-.04 moleculesTheories of lubrication – Boundary • "lubricin" from synovial fluid – Fluid film • hydrodynamic (non deformable) Fluid • Squeeze Film – right angle movement – short duration – Mixed
    • 8. Articular Cartilage: AdaptationActive loading & unloadingDegenerative changes (OA)Aging – ↓ water content – ↓ PG – ↓ collagen content
    • 9. Joint Mobility andMobility sometimes has very distinct endpoints – Elbow or knee hyperextensionIn other cases variable soft tissue properties and other factors limit ROMSome see stability as the joint’s ability to resist dislocation. Stability
    • 10. Joint Mobility andMobility sometimes has very distinct endpoints – Elbow or knee hyperextensionIn other cases variable soft tissue properties and other factors limit ROMSome see stability as the joint’s ability to resist dislocation. Stability hi p! pt the e Exc
    • 11. Lever SystemsMost motion at the major joints results from the body’s structures acting as a system of levers – Multiple “classes” of lever systemsFunctions: – Increase the effect of an applied force • Moment arms – Increase the effective velocity of movement • v=rω
    • 12. Levers
    • 13. Levers• Levers are used to alter the resulting direction of the applied force
    • 14. Levers• Levers are used to alter the resulting direction of the applied force• A lever is a rigid bar (bone) that turns about an axis of rotation or fulcrum (joint)
    • 15. Levers• Levers are used to alter the resulting direction of the applied force• A lever is a rigid bar (bone) that turns about an axis of rotation or fulcrum (joint)• The lever rotates about the axis as a result of a force (from muscle contraction)
    • 16. Levers• Levers are used to alter the resulting direction of the applied force• A lever is a rigid bar (bone) that turns about an axis of rotation or fulcrum (joint)• The lever rotates about the axis as a result of a force (from muscle contraction)• The force acts against a resistance (weight, gravity, opponent, etc.)
    • 17. Levers
    • 18. LeversThe relationship of the points determines the type of lever
    • 19. LeversThe relationship of the points determines the type of leverThe axis (joint), force (muscle insertion point), and the resistance (weight, etc.)
    • 20. First ClassF R A F A R
    • 21. First Class
    • 22. First Class A R F
    • 23. Neck extensionFirst Class A R F
    • 24. Neck extensionFirst Class Erector spinae and Splenius A R F
    • 25. First Class
    • 26. First ClassF A R
    • 27. First Class Elbow extensionF A R
    • 28. First Class Elbow extension TricepsF A R
    • 29. First ClassF R A A
    • 30. First ClassDesigned for speed and range of motion when the axis is closer to the forceF R A A
    • 31. First ClassDesigned for speed and range of motion when the axis is closer to the forceDesigned for strength when the axis is closer to the resistanceF R A A
    • 32. Second Class R FA A R F
    • 33. Second Class
    • 34. Second ClassR F A
    • 35. Second Class Plantar flexionR F A
    • 36. Second Class Plantar flexion Gastrocnemius and SoleusR F A
    • 37. Second Class
    • 38. Second ClassDesigned more for force
    • 39. Third Class F RA A F R
    • 40. Third Class
    • 41. Third Class F A R
    • 42. Elbow flexionThird Class F A R
    • 43. Elbow flexionThird Class Biceps brachii and Brachialis F A R
    • 44. Third Class
    • 45. FUNCTIONAL RELATIONSHIP PRACTICAL HUMANCLASS ARRANGEMENT ARM MOVEMENT DESIGN TO AXIS EXAMPLE EXAMPLE1ST F-A-R Resistance arm Balanced Axis near Seesaw Erector and force arm movements middle spinae neck in opposite extension direction Speed and Axis near Scissors Triceps range of force motion Force Axis near Crow bar (Strength) resistance2ND A-R-F Resistance arm Force Axis near Wheel Gatroc and and force arm (Strength) resistance barrow, soleus in same nutcracker direction3RD A-F-R Resistance arm Speed and Axis near Shoveling Biceps and force arm range of force dirt, catapult brachii in same motion direction
    • 46. Factors In Use ofAnatomical Levers F
    • 47. Factors In Use of Anatomical LeversA lever system can be balanced if the F and FA equal the R and RA F
    • 48. Factors In Use of Anatomical LeversA lever system can be balanced if the F and FA equal the R and RA F
    • 49. Factors In Use of Anatomical LeversA lever system can be balanced if the F and FA equal the R and RA F(A = Arm - distance from A)
    • 50. Balanced Force Arm Resistance Arm RF A
    • 51. Balance with MoreForce Arm Resistance Arm RF A
    • 52. Balanced with Less Force Arm Resistance Arm RF A
    • 53. Factors In Use ofAnatomical Levers
    • 54. Factors In Use of Anatomical LeversA lever system can become unbalance when enough torque is produced
    • 55. Factors In Use of Anatomical LeversA lever system can become unbalance when enough torque is producedTorque is the turning effect of a force; inside the body it caused rotation around a joint.
    • 56. Factors In Use of Anatomical LeversA lever system can become unbalance when enough torque is producedTorque is the turning effect of a force; inside the body it caused rotation around a joint.Torque = Force (from the muscle) x Force Arm (distance from muscle insertion from the joint)
    • 57. Practical Application Resistance Force
    • 58. Practical ApplicationForce is produced by the muscle Resistance Force
    • 59. Practical ApplicationForce is produced by the muscleFA the distance from Resistance Force joint (i.e. axis or folcrum) to insertion of the force
    • 60. Practical ApplicationForce is produced by the muscleFA the distance from Resistance Force joint (i.e. axis or folcrum) to insertion of the forceResistance could be a weight, gravity, etc.
    • 61. Practical ApplicationForce is produced by the muscleFA the distance from Resistance Force joint (i.e. axis or folcrum) to insertion of the forceResistance could be a weight, gravity, etc.RA the distance from joint to the center of the resistance
    • 62. Examples Resistance Force
    • 63. Examples1. How much torque needs to be produced to move 45 kg when the RA is 0.25 m and the FA is 0.1 Resistance Force meters?
    • 64. Examples1. How much torque needs to be produced to move 45 kg when the RA is 0.25 m and the FA is 0.1 Resistance Force meters?Use the formula F x FA = R x RA
    • 65. Examples1. How much torque needs to be produced to move 45 kg when the RA is 0.25 m and the FA is 0.1 Resistance Force meters?Use the formula F x FA = R x RANote: A Newton is the unit of force required to accelerate a mass of one kilogram one meter per second per second.
    • 66. Example 1 RA = 0.25FA = 0.1 ? 45A
    • 67. Example 1F x 0.1 meters = 45 Kg x 0.25 meters RA = 0.25 FA = 0.1 ? 45 A
    • 68. Example 1F x 0.1 meters = 45 Kg x 0.25 metersF x 0.1 kg = 11.25 Kg-meters RA = 0.25 FA = 0.1 ? 45 A
    • 69. Example 1F x 0.1 meters = 45 Kg x 0.25 metersF x 0.1 kg = 11.25 Kg-metersF = 112.5 Kg RA = 0.25 FA = 0.1 ? 45 A
    • 70. Example 2: Increasing the FA RA = 0.25FA = 0.15 ? 45A
    • 71. Example 2: Increasing the FA2. What if the FA was increased to 0.15 meters? RA = 0.25 FA = 0.15 ? 45 A
    • 72. Example 2: Increasing the FA2. What if the FA was increased to 0.15 meters?F x 0.15 meters = 45 Kg x 0.25 meters RA = 0.25 FA = 0.15 ? 45 A
    • 73. Example 2: Increasing the FA2. What if the FA was increased to 0.15 meters?F x 0.15 meters = 45 Kg x 0.25 metersF x 0.15 = 11.25 Kg-meters RA = 0.25 FA = 0.15 ? 45 A
    • 74. Example 2: Increasing the FA2. What if the FA was increased to 0.15 meters?F x 0.15 meters = 45 Kg x 0.25 metersF x 0.15 = 11.25 Kg-metersF = 75 Kg RA = 0.25 FA = 0.15 ? 45 A
    • 75. Example 3: Decreasing the RA RA = 0.2FA = 0.1 ? 45A
    • 76. Example 3: Decreasing the RA3. What if the RA was decreased to 0.2 meters? RA = 0.2 FA = 0.1 ? 45 A
    • 77. Example 3: Decreasing the RA3. What if the RA was decreased to 0.2 meters?F x 0.1 meters = 45 Kg x 0.2 meters RA = 0.2 FA = 0.1 ? 45 A
    • 78. Example 3: Decreasing the RA3. What if the RA was decreased to 0.2 meters?F x 0.1 meters = 45 Kg x 0.2 metersF x 0.1 = 9 Kg-meters RA = 0.2 FA = 0.1 ? 45 A
    • 79. Example 3: Decreasing the RA3. What if the RA was decreased to 0.2 meters?F x 0.1 meters = 45 Kg x 0.2 metersF x 0.1 = 9 Kg-metersF = 90 Kg RA = 0.2 FA = 0.1 ? 45 A
    • 80. Summary
    • 81. Summary• The actual torque needed to move a given resistance depends on the length of the FA and RA
    • 82. Summary• The actual torque needed to move a given resistance depends on the length of the FA and RA• As the FA increases or RA decreases, the required torque decreases.
    • 83. Summary• The actual torque needed to move a given resistance depends on the length of the FA and RA• As the FA increases or RA decreases, the required torque decreases.• As the FA decreases or RA increases, the required torque
    • 84. Levers Continued
    • 85. Levers ContinuedInside the body, several joints can be “added” together to increase leverage (e.g. shoulder, elbow, and wrist.
    • 86. Levers ContinuedInside the body, several joints can be “added” together to increase leverage (e.g. shoulder, elbow, and wrist.An increase in leverage can increase velocity
    • 87. Lever Length Z’ S’ S Z
    • 88. Lever LengthWhere is the velocity or speed the greatest; at S’ or Z’? Z’ S’ S Z
    • 89. Lever LengthWhere is the velocity or speed the greatest; at S’ or Z’? Z’ S’ S Z
    • 90. Lever LengthWhere is the velocity or speed the greatest; at S’ or Z’? Z’ S’ S Z
    • 91. Lever LengthWhere is the velocity or speed the greatest; at S’ or Z’? Z’ S’ S Z
    • 92. Lever LengthWhere is the velocity or speed the greatest; at S’ or Z’? Z’ S’ S Z
    • 93. Lever LengthWhere is the velocity or speed the greatest; at S’ or Z’? Z’ S’ S Z
    • 94. Lever LengthWhere is the velocity or speed the greatest; at S’ or Z’? Z’ S’ S ZHow can this principle be applied to tennis?
    • 95. LeverLength
    • 96. Lever LengthA longer lever would increase speed at the end of the racquet unless the extra weight was too great. Then the speed may actually be slower.
    • 97. Wheels and Axles R = 3” R = 1”
    • 98. Wheels and AxlesWheels and axles can enhance speed and R = 3” range of motion R = 1”
    • 99. Wheels and AxlesWheels and axles can enhance speed and R = 3” range of motionThey function as a form of lever R = 1”
    • 100. Wheels and AxlesWheels and axles can enhance speed and R = 3” range of motionThey function as a form of leverMechanical advantage = radius of wheel / radius of axle R = 1”
    • 101. Wheels and Axles H
    • 102. Wheels and AxlesConsider the humerus as an axle and the forearm/hand as the wheel H
    • 103. Wheels and AxlesConsider the humerus as an axle and the forearm/hand as the wheelThe rotator cuff muscles inward rotate the humerus a small amount H
    • 104. Wheels and AxlesConsider the humerus as an axle and the forearm/hand as the wheelThe rotator cuff muscles inward rotate the humerus a small amountThe hand will travel a large amount H
    • 105. Wheels and AxlesConsider the humerus as an axle and the forearm/hand as the wheelThe rotator cuff muscles inward rotate the humerus a small amountThe hand will travel a large amountA little effort to rotate the humerus, results in a significant amount of movement at the hand H
    • 106. Joints and momentsNote, as a joint moves through its ROM, two things change: – Instantaneous Center of Rotation • Rotation • Sliding • Rolling – Muscle Line of ActionThese combine to change the moment arm
    • 107. lenfunk@shoulderdoc.co.uk

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