In last month’s webinar on the treatment of plantar fasciitis with prefabricated orthosis, a participant asked how rigid should prefabricated orthosis be.

The answer to this is the same as with custom orthoses: they should be rigid enough to reduce stress on the tissue that is being treated.

For example,when treating plantar fasciitis, we want to make sure that the orthosis does not deform under the arch of the foot. If the orthotic shell deforms then the flattening of the device allows the foot to flatten, and and this increases tension on the plantar fascia.

Any orthosis, whether prefab or custom, should have a non-deforming shell for effectively treating plantar fasciitis.

ProLab P3 prefabricated orthoses are made with polypropylene, resulting in an orthosis that has a bit of flex but doesn’t deform during gait. Very heavy patients, over 250 pounds, may find these devices too flexible. However, there are no prefabs that are going to hold up for such a patient and they are likely going to require a custom orthosis.

In general, it’s easier to work with orthoses that are too rigid rather than  too flexible. The polypropylene used in the P3 orthoses is extremely easy to modify. If it is too rigid, grind it slightly thinner from the bottom in order to increase the flexibility. This 10-second adjustment is usually enough to increase flexibility and increase comfort on the rare patient that feels the arch is too rigid or too high.