Peculiar Orthosis

Members do not see these Ads. Sign Up.

I'm a first time poster but wondered what the community thought of this: I had a new patient attend last week; he had a R/ankle # a few years ago and was prescribed an orthosis to help it heal. He now has plantar fasciitis on the R/foot and came in for advice. The orthosis he has is something I've never seen before. It appears to be a standard carbon fibre shell (probably Langer) and the rearfoot is extrinsically posted on the medial side with a standard EVA material, but the lateral half of the heel has no posting at all, as can hopefully be seen on the attached photo. So the patient has medial rearfoot posting but only the rounded contour of the shell on the lateral half, which to my mind causes considerable instability and may be a causative factor for the plantar fasciitis. I wonder if this orthosis was originally prescribed as a temporary treatment for the original ankle injury and should have been reviewed? The technical staff at my usual orthosis lab are puzzled by this device but the prescribing Podiatrist, who I advised the patient to contact (who seems to be quite highly qualified) scoffed at my comments and told him that "that is how all orthoses are made these days"!

Any thoughts from colleagues would be appreciated!

Many thanks

 

Nothing too peculiar here. This design has been around for some time. By posting only on the medial side of the heel cup, there should be a relative increase in stiffness on the medial side of the heel-cup, this should tend to increase the reaction forces beneath the medial heel and "pull" the centre of pressure more medially.

Can I suggest that the "technical staff" at your usual lab might want to learn something about foot orthoses design before they call themselves "the technical staff"?

See also: J Am Podiatr Med Assoc. 1992 Apr;82(4):202-7.
Extrinsic rearfoot posts.
Blake RL, Ferguson H.

 

Looks OK to me.

Some orthoses have no lateral post and no lateral heel cup contour. Depends on what you are trying to achieve

Not quite sure about the mechanics of this. Are you saying that "lateral instability" is forcing the peroneals to contract in mid to late stance in a form of active pronation which then overloads the plantar fascia. I think I would be paying a little more attention to the sub talar joint axis as a laterally deviated sub talar joint axis is more likely to be a cause of "active pronation" than this particular shell design

 

Its common in this part of the world. One lab has trademarked it as a DC Wedge

 

As Simon said, this device is great for treating problems caused by a high pronation moment from ground reaction force. (Medially positioned STJ axis). Put the device on the table and put two fingers in the heel cup. In an orthosis with a varus wedge modification, the medial finger will be farther from the table than the lateral finger. The difference in post will accentuate this.

However, there are some feet that have late stance phase pronation in gait. These feet often have laterally positioned STJ axes and ehibit pronation caused by the peroneal muscles (as opposed to being caused by the ground). The medial heel skive will make the laterally positioned STJ appear to pronate more. What does he look like walking with and without the orthoses?

Eric

 

Thanks for the feedback - will dig out some biomechanics books and so some research. I consider myself pretty competent and up to date, but maybe these devices are much more widely used in the US and Australia; I can honestly say amongst a survey of several very competent colleagues here in London no-one was familiar with it. My orthoses lab only produces CADCAM devices so this may be why the technical staff were not familiar with this carbon fibre shell type of prescription.

The patient when walking does pronate heavily and I expect the plantar fasciitis may resolve quickly with a more standard type of orthosis; I wondered if this current device he is using could exacerbate the plantar fasciitis?

Thanks for your feedback!

 

MFreedman
Consider this:
What is a standard type of orthosis? Is there a standard design for plantar fasciitis?

The current design may be wrong but, and assuming that it is plantar fasciitis and not something else, you need to assess why there is pathological stress in the PF and design an appropriate orthosis that is not based purely on the observation of 'over or heavy pronation' and some unhelpful idea of standard prescription.

Regards Dave Smith

 

Hi MFreedman

I run a lab and a bit surprised that your lab guys hadn't seen this type of design before - we do a CAD version of this and it is fairly well established as a design.

Re its use, I would like to offer the following anecdotal comments-
The rounded shape of the lateral aspect of the heel section can be unstable - depending on the forces being applied by the upper of the shoe - and if the peroneal reaction times are reduced it can lead to an increased risk of inversion sprains (If the patient has any history associated with 'going over on the heel')

Without complicating things you need to look at GRV and GRF at initial contact and the structures of the foot that are under tension/active. Then see how the instability can impact on them.

I hope I am not being condescending as this is not my intention but don't ignore this orthotic modification as it can be very useful.

Cheers

Phil

 

Hi Phil

Thanks for your thoughts....... can you clarify what GRV and GRF stand for?

Many thanks

Mark Freedman

 

Hi Freedman

As noted above it is common as a heel post option on both CAD and Vac formed devices.

A lot of our customers also use it to aid shoe fit of the heel post when required.

Will put a picture of a DC wedge from OZ in here for you shortly (as discussed above)......when i figure how!

 

Hi

Sorry about that.
GRF = Ground reaction force
GRV = " " vector.

Phil

 

OK, so what you need to think about is what causes plantar fasciitis. Most would probably agree that there is an element of tensile loading at play, some would argue that compressive loading may also be significant. So to answer your question: could the current device he is using exacerbate the plantar fasciitis? Yes, if it increases the tensile and/ or compressive loading on the plantar fascia and takes the loading outside of the tissues zone of optimal stress (ZOOS).

In terms of designing a pathology specific device for plantar fasciitis: there are many, many ways to skin the cat, but basically you need orthoses design features which will lower the tensile and/ or compressive loading on the fascia and place the loading back within it's ZOOS. These may include: heel lift, varus rearfoot post/ medial heel skive (note that this should help with tensile loading, but may increase compression force beneath the medial tubercle of the calcaneus and could potentially exacerbate the problem), cut-out aperture or "sweet spot" in the shell beneath the medial tubercle, horse shoe pad within the heel-cup, plantar-fascial groove, first ray cut-out, valgus forefoot extension, reverse Morton's extension, kinetic wedge, Cluffy wedge, any variety of shell materials, custom or prefabricated, etc. etc. This is not an exhaustive list and I'm sure my colleagues will add and subtract to the content, but you get the idea. Some of these you'd use in concert, others might be an either/ or, some just a secondary option.

 

Mark,

What Simon said is spot on.

I am personally a believer that compressive force beneath the med calc tubercle can affect the outcome of an orthotic device greatly when dealing with plantar fascia pain. I have more recently changed the angulation of the medial heel skive to be a little more "MOSI- like" as it seems to be more comfortable, reducing the feeling of compression directly on to the med calc tubercle.

In answer to your question as to whether this type of device could cause plantar fasciitis, as Simon said, yes it is possible if the load through the tissue exceeds its physiological capapbilites. Do I think it is likely - probably not.

Look at the lateral quarter of the shoe where it meets the sole of the shoe. It may well be curved and accurately match the lateral contour of the device. If this is the case then it is even less likely that the dvice will be unstable and cause plantar fascia symptoms

Also, do not forget other modalities that can reduce compression and tension in the plantar fascia and its origin. Low dye tape for example

It is important that you examine the timing of the gross pronation that you see. At certain points in the stance phase, pronation that you might consider gross can be normal. The later in stance the pronation occurs, the greater the likelihood that the peroneal musculature is actively pronating the foot. Inverting the heel and many of the aforementioned presciption variables may increase the external supination moment forcing an internal pronation moment to be generated by the peroneals and pronating the foot at a less appropriate point in the stance phase that has potential to greatly increase plantar fascia tension.

On re-reading this, it could confuse matters more. Eric needs to paraphrase and sum up everything I am saying in 1 sentence!

 

You will get increased compression under the medial tubercle with that post design though, Robin. And a stress riser in the shell at it's distal margin. To be honest, from the photo it looks like the post has collapsed and is rounded off (maybe it's just the lighting?)- what does that tell us?

 

In some feet (lat deviated STJ axis) the ground causes supination. In response the CNS increases peroneals activity (relative to feet with average axis position) to cause STJ pronation. (The pronation moment from the muscle is greater than the supination moment from the ground.) When you add increased supination moment from the ground (medial heel skive, medial only post) the peroneals will increase activity even more. Pronation of the STJ from any cause, will tend to increase tension in the plantar fascia. Sorry, a little complex for just once sentence.

As Simon pointed out, not all heel pain is from tension, but plantar compression forces can also be a cause of heel pain.

Eric