Plantar Fascia Grooves in Foot Orthoses cont..

Karpel-Bargess et al (1998) showed that when the onset of the windlass was delayed, there was more pronation of the rearfoot. The second characteristic that our work has identified is that the force needed to establish the windlass varies widely between people. In some people, the force needed is low and in others it is very high.

In reality it is speculated that what was previously considered as a functional hallux limitus is probably a combination of the timing of windlass initiation and the force needed to get it established. These exist on a continuum with, at one extreme there being a delay in windlass initiation and a high force needed to establish it, which is probably what functional hallux limitus is. At the other extreme there is an immediate onset of the windlass with heel lift and a low force to establish it.

As this windlass mechanism is important for normal function and can increase the risk for tissue damage if it is not functioning properly, it is important that foot orthoses or supports do not inhibit this mechanism and, preferably, enhance it. Our preliminary unpublished work has shown that in general foot orthoses do reduce the force needed to establish the windlass, but not all foot orthoses do this. It has been possible to identify the design features of foot orthoses that do result in a reduction in the force needed to establish the windlass mechanism and assist in earlier initiation of the windlass mechanism. This work is ongoing and will be published soon.

One design feature that has been used in foot orthoses is a groove (or ‘channel’) to accommodate the plantar fascia. In the past this has been mostly used as a comfort measure in those who have a very prominent plantar fascia in the arch area. Our work has shown the groove, that is traditionally placed in the midfoot area can lower the force needed to establish the windlass mechanism. However, this did not occur in all subjects. Some subjects responded to the groove in the midfoot and some when the groove was located further forward. Further work will try to identify why some responded and some did not.

As it is pretty clear that windlass function is very important to foot function and a plantar fascia groove should be incorporated into a foot orthoses, it would make sense that the groove should both be in the midfoot as well as further forward to achieve optimum function of the windlass mechanism.
Current research into this includes the ongoing work mentioned above, as well as a clinical trial comparing outcomes between patients using an orthoses with a full length plantar fascial groove and an orthoses with no groove.

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