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Orthotics Biomechanics


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Foot biomechanics simplified, and a close look at the function of foot arch supports.

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Orthotics Biomechanics

  1. 1. Michael E. Graham, DPM, FACFAS, FAENS Macomb, Michigan USA
  2. 2. • Biomechanical principals• What is an arch support/orthosis?• What is its function?• What can it accomplish?• What role does it play in the treatment of flatfoot/talotarsal displacement?
  3. 3. Parts of the gait/walking cycleSWING phase CONTACT phase
  4. 4. We don’t care too much about the swing phase.
  5. 5. We need to focus very much on the contact phase. Let’s take a close look.
  6. 6. It’s not that complicated!
  7. 7. Primary motions of the footduring the contact phase of walking.
  8. 8. Supination• Locks the joints of the foot to create a stable lever-arm.• This should be the dominate position of the talotarsal mechanism – 2/3 motion.
  9. 9. Pronation• Allows the foot to act as a mobile adaptor to the weightbearing surface.• Should only consist of 1/3 total talotarsal motion.
  10. 10. Neutral Position• Part of the stance phase when the foot is neither supinated nor pronated.• Minimal strain on the supporting tissues.
  11. 11. During the Contact Phase• There are certain times when the talotarsal joint needs to be supinating, in neutral position, or pronating.• This is very important for proper biomechanical foot function.• If pronation/supination occur at the wrong time during the walking cycle, compensation of the pathologic strain/forces will be acting on the tissues.• Eventually, critical point is reach where the tissues can no longer handle those forces. The tissues begins to become inflamed and send a warning signal (PAIN) that something is wrong.
  12. 12. Unfortunately, the majority of the medical community is onlyconcerned with covering up the painwithout eliminating what has caused that pain in the first place.
  13. 13. Contact Phase of the Gait Cycle with a Stable Talotarsal Joint Mechanism Heel strike Early Mid-stance Late Mid-stance Heel-lift Toe-off Supinated Slight Supinated pronation Neutral Position
  14. 14. Talar position during the walking/gait cycle Maximally Neutral Maximally Supinated Talotarsal Pronated Displaced Talotarsal Joint Talotarsal Talotarsal Joint Joint Joint
  15. 15. Center Line of Gravity This is the center of forcespassing through the foot.
  16. 16. Normal Center Line of Gravity
  17. 17. Normal Center Line of Gravity Toe off Heel LiftLate Mid-stanceEarly Mid-stance Heel Strike
  18. 18. Talotarsal Joint Displacement• Unlocks the stability of the foot.• When the foot is supposed to be in a supinated position it is in a pronated position.• There is a longer than normal period of pronation = hyperpronation
  19. 19. Stance Phase of the Gait Cycle withDisplacement of Talotarsal Joint Mechanism
  20. 20. What is the role of an arch support?
  21. 21. What is an orthosis?• It is an external appliance/device• Used to provide support• Attempts to prevent or correct for a plantar foot deformity• Tries to improve foot function
  22. 22. What is their function?• Support “fallen” arches• Align- biomechanical defects• Correct- alignment issues• Cushion- bony prominences• Protect-remove pressure from callused/ulcer areas.
  23. 23. Type of foot orthoses• Soft• Semi-flexible/rigid• Rigid
  24. 24. Made of many different materials • Foam • Thermoplastic • Carbon fiber • Hard plastics • Soft plastics
  25. 25. How are they made?
  26. 26. Ideal Method
  27. 27. “Electronic” Methods
  28. 28. “Easy” Method
  29. 29. “Commercial” Method
  30. 30. “Off the shelf”/pre-made generic
  31. 31. Where is the evidence?
  32. 32. Internal imaging.
  33. 33. Is this arch support working?
  34. 34. An arch support, even if custom-made, cannot prevent/stabilize a talotarsal displacement.
  35. 35. They can cushion the plantar aspect of the foot.
  36. 36. They can possibly help to rebalance the center of gravity but the evidence is weak.
  37. 37. Not all patients are surgicalcandidates and something is better than nothing.
  38. 38. Limitations of arch supports• Cannot control talotarsal joint mechanism and therefore have a difficult time realigning foot structure.• Only function when being used, if the patient is not wearing them in their shoes or going barefoot there is not correction.• Have to wear bigger/limited shoe style• Method to make them still isn’t perfected.
  39. 39. The worst of it is that an arch support may give the individual afalse sense of correction- the archsupport really isn’t fixing anything.
  40. 40. Advantages of Arch Supports• Non-surgical option• Can help to off-weight prominent areas to the bottom of the foot.• Can help to re-align the center of gravity through the bottom of the foot.• May give the patient enough correction to alleviate their pain.
  41. 41. Doesn’t an internal deformitydemand internal correction?
  42. 42. Refuse to ignore or cover-up your misaligned feet.
  43. 43. There is an internal option with exploring.
  44. 44. Questions?