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Biomechanical principles of orthotics

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Biomechanical principles of orthotics

  1. 1. 1
  2. 2. THESE PRINCIPLES ARE :- PRESSURE EQUILIBRIUM THE LEVER ARM 2
  3. 3. The pressure is equal to the total force per unit area.  [ P= F/A ] where  F = force, A= area of application It means that the larger the area of a pad or plastic shell of an Orthosis is, the less force will be placed on the skin. 3
  4. 4. It says the sum of the forces and the bending forces created must be equal to zero. This means that three-point pressure system or loading system occurs when three forces are applied to a segment in such a way that a single primary force is applied b/w two additional counter forces with the sum of all three forces equalizing zero. 4
  5. 5. The farther the point of force from the joint is, the greater will be the moment arm and the smaller the magnitude of force is required to produce a given torque at the joint. THIS IS WHY MOST ORTHOSIS ARE DESIGNED WITH LONG METAL BARS OR PLASTIC SHELL THAT ARE THE LENGTH OF ADJACENT SEGMENT. 5
  6. 6.  So while designing or evaluating the orthotic device, we should check that- 1. There is adequate padding covering the greatest area possible for comfort. 2. The total force acting on the involved segment is equal to zero or there is equal pressure throughout the Orthosis and no areas of skin irritation. 3. The length of the Orthosis is suitable to provide an adequate force to create the desired effect and to avoid increased transmission of shear forces against the anatomic tissues. 6

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