Aug
6
Written by:
Larry Huppin, DPM
8/6/2009 1:49 PM
A loose definition of a flexible orthosis is one where the arch collapses about halfway to the ground under the weight of a particular patient. A semi-rigid orthosis is one that shows a minimal amount of deformation under a patient's weight and a rigid device is one that does not deform at all.
The flexibility of an orthosis is dependent on a number of factors, including:
- Orthosis material: Some materials are simply more rigid than others. Read more here.
- Material thickness: Thicker materials are more rigid
- Patient weight: An orthosis that is rigid for a 100lb patient would be "flexible" for a 250 lb patient.
- Patient arch height: Increased curvature increases rigidity. For example, a polypropylene shell that is flexible for a low-arched foot might be rigid for a high-arched foot.
- Heel cup height: The increased shell curvature increases rigidity
- Cast fill: A minimum fill results in a higher arch and greater rigidity than a standard or maximum fill
- Post: Adding a post increases rigidity
- Post material: More rigid materials (polypropylene vs. EVA) increase orthosis rigidity
When prescribing polypropylene orthoses using our prescription form you can choose either material thickness or a rigidity. If you choose a rigidity, we will take all of the above factors into consideration in order to give you the rigidity you prescribed.
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