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Functional forefoot extensions and accommodative orthoses

Discussion in 'Biomechanics, Sports and Foot orthoses' started by admin, Sep 12, 2006.

  1. admin

    admin Administrator Staff Member

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    I am grateful to Kevin Kirby and Precision Intricast for permission to reproduce this March 1990 Newsletter (you can buy the 2 books of newsletters off Precision Intricast):

    The use of forefoot extensions in foot orthoses has been around since the days when Levy molds were used to accommodate isolated painful plantar tylomas under the metatarsal heads. Unfortunately, somewhere along the evolutionary line from the era of "balancing the foot" with cork and leather to "controlling the foot" with Rohadur functional foot orthoses, the art and science of using forefoot extensions on foot orthoses has been somehow misplaced.

    From my own personal experiences and education at the California College of Podiatric Medicine, I observed the lack of integration of ideas between thermoplastic foot orthoses and accommodative orthoses. As a student, biomechanical foot therapy meant a Rohadur orthosis with a rearfoot post and an intrinsically balanced forefoot post. In all of the pairs of thermoplastic orthoses that I saw being dispensed as a student, only a few of them had crudely constructed forefoot extensions.

    In fact, forefoot extensions were almost never mentioned in the same breath with biomechanical foot orthosis therapy. They were not meant to be part of a "functional" orthosis. In fact, my distinct impression was that by putting a forefoot extension on a thermoplastic orthosis, the orthosis somehow became less functional!

    As a graduating senior from C.C.P.M., my understanding of mechanical foot therapy was that if you wanted to control the abnormal motion of the foot, you used an intrinsically balanced Rohadur orthosis with a rearfoot post. However, if you wanted to accommodate a forefoot lesion you would use a cork and leather orthosis or one of the many other types of accommodative orthoses. In my days as a student, you simply did not mix the features of a "functional" orthosis with the features of an "accommodative" orthosis.

    The idea that foot orthoses should be strictly dichotomized into functional and accommodative types is an idea whose time should quickly come to an end. There is no reason why one can't make a "functional" foot orthosis from cork and leather and there is no reason why one can't incorporate metatarsal pads and lesion accommodations into a rigid thermoplastic orthosis. The truth of the matter is that the distinction between functional and accommodative orthoses should not be black and white, it should be a blending of many different shades of gray.

    One of the first indications that I possibly didn't know the whole story about the biomechanics of foot orthoses upon graduating from C.C.P.M. was when I attended a lecture on shank dependent and shank independent types of orthosis materials given by Dr. Michael Burns, former Chairman of the Department of Orthopedics at the Pennsylvania College of Podiatric Medicine.

    Dr. Burns classified flexible orthosis materials such as cork and leather or the thin, flexible thermoplastics as being shank dependent materials. In other words, in order to make the flexible materials rigid enough to control abnormal motion of the foot inside a shoe, they need to be shaped so that their plantar aspects exactly match the contours of the shank of the shoe. Therefore, a cork and leather device can be just as rigid as a Rohadur device inside a shoe, however the rigidity of the cork and leather orthosis is dependent on how well the cork filler contours the shank of the shoe. Shank independent materials include the thermoplastics such as Rohadur and polypropylene and the composite orthoses (e.g. graphite) since they all hold their shape well without support from the shank of the shoe.

    The point that Dr. Burns made which I thought made so much sense in regards to the great "functional vs. accommodative orthosis" debate was that the material which the orthosis was constructed of made little difference whether that orthosis was functional or not. It is actually the shape of the superior surface of the orthosis and the resistance of the orthosis to deformation inside of the shoe which determine how functional the orthosis is. Even though I heard this lecture over five years ago, I still feel the ideas that Dr. Burns presented are of great importance to any podiatrist involved in mechanical foot therapy.

    Another problem with the avoidance of mixing accommodative orthosis technology in with thermoplastic orthoses is that forefoot extensions have been nearly forgotten. Since I have become enlightened as to the usefulness of forefoot extensions, it has bothered me that I did not learn about them sooner as a student.

    I remember being lectured to as a student by a nationally known expert in podiatric biomechanics who said that a congenital plantarflexed 3rd ray cannot be treated with a functional orthosis unless the 3rd ray is first surgically elevated. However, I found through trial and error that simple application of the time tested accommodative forefoot extension to my otherwise "functional" foot orthosis allowed the third metatarsal head to "drop into a hole" to relieve the pain from a plantar tyloma caused by a plantarflexed third metatarsal.

    Unfortunately, as a student you practically have to believe everything you hear from your professors (especially the famous ones) since you have yet to gain the practical knowledge required to decipher fact from fiction. This just goes to show you that you can't believe everything you were taught during podiatry school, even if it comes from one of the guys who wrote the book.

    In fact, after continuous experimentations with forefoot extensions on my patients' "functional" foot orthoses now for over six years I have learned another of the great truths regarding foot orthosis therapy. The best foot orthosis is one which has a forefoot extension to modify the ground reactive forces on the metatarsal heads during midstance and propulsion. If you are not using forefoot extensions on your "functional" orthoses, and are not taking advantage of the years of "balancing" that your podiatric forefathers did with their patients' Levy molds, then your orthoses will not be as good as they could be at relieving your patients' mechanical foot problems.
    [Reprinted with permission from: Kirby KA.: Foot and Lower Extremity Biomechanics: A Ten Year Collection of Precision Intricast Newsletters. Precision Intricast, Inc., Payson, AZ, 1997, pp. 75-76.]
  2. Thanks to Craig for posting the above Precision Intricast Newsletter from 16 years ago.

    To add to the subject of forefoot extensions and shank dependent/independent orthoses:

    I will be giving a lecture titled "Successful Conservative Treatment of Peroneal Muscle/Tendon Disorders Using Subtalar Joint Axis Location/Rotational Equilibrium Theory" at the Podiatry Institute Reconstructive Surgery of the Foot and Ankle Annual San Diego Seminar this weekend. The attached figure is a diagram that I just prepared for the lecture showing an orthosis that I commonly use for chronic peroneal tendinitis which has a "shank dependent" lateral arch and "shank independent" medial arch (along with other modifications such as a flat rearfoot post, increased everted balancing position, lateral heel skive, and valgus forefoot extension) to increase the STJ pronation moment in these patients that excessive STJ supination moments.

    By the way, this type of orthosis would never have been thought of if one were to simply follow the teachings of STJ neutral theory. Understanding the importance of STJ spatial location and its effects on STJ moments allows the clinician to mechanically rationalize this type of orthosis for patients with symptoms caused by excessive STJ supination moments, such as chronic peroneal tendinitis/tendinopathy.

    Attached Files:

  3. Lawrence Bevan

    Lawrence Bevan Active Member


    The one problem I know I would have in these circumstances would be the height of the medial arch, particularly with shank independent materials.

    I would more likely use shank dependent for the whole orthosis, filling the lateral underside and hollowing out the medial underside dependent on the ability of the device to comfortably supply enough supination moment.

    Open to suggestions
  4. Stanley

    Stanley Well-Known Member


    I have to agree with you on this. As a student from 1972-1976, Dick Schuster taught these exact concepts. He made leather orthotics that extended to the sulcus or full length. He accomodated the metatarsals exactly by reading the leather, which was an improvement over the Turchin balance padding of earlier years. As far as the function, he would fill the arch with either rubber butter (a latex cork dust mixture) or additional pieces of leather. If he wanted rigidity, he used fiberglass between the leather and the bulk filler. I had the oppurtunity to visit CCPM in 1976 during my fellowship, and I agree with you that they totally seperated the functional from the accomodative orthotics. They did not understand the concept of bulk supporting the flexible orthotics.

    Regarding your orthotic for the peroneal tendonitis: I agree with what you are doing, but just as an aside, if the orthotic was truly rigid (shank independent), then you wouldn't need to place anything under the cuboid area. If you remember when the Sporthotics from Langer first came out (they were the first semi rigid orthotics), there were many "lateral arch" problems. Later models had fillers placed in them, and this reduced the problems. There is no 100% rigid shank independent orthotic. They act more like springs, and the spring constant is dictated by the material, the thickness of the material, and the length of the foot. They bend when there is weight on them. I have seem broken steel orthotics as a result of the bending over time. On the other hand a bulk device can be non compressible. I had a patient in a bulk device whose foot was run over by a school bus. Outside of the skin being ripped apart, there was no bone breakage.


  5. Steve The Footman

    Steve The Footman Active Member

    There seems to be a value judgement by most podiatrists that functional devices are better than accomodative. There is also the belief amongst most pods that orthoses must be three quarter rigid devices to be functional.

    My question is how can you create a functional change in propulsion with a three quarter device when your heel is off the ground and there is no ground reaction force?

    An easy test for the control available at the MLA of an orthoses is to push down on the arch and see how easy it is to deform. Many so called controlling functional devices can be completely flattened with a bit of palm pressure while soft, full length, accomodative, comfortable and flexible devices offer much better resistance to compression.

    My own orthotic prescription methodology has been hugely influenced by the articles such as the above by Kevin Kirby in his intricast books. In particular thinking about foot function during the whole gait cycle and not just an instant in time at mid stance. I would just like to thank him publicly for sending me off in the right direction after university.
  6. pgcarter

    pgcarter Well-Known Member

    I use combinations of EVA ,poron, etc and polypro or similar of various thicknesses and rigidities in order to use the behavioural characteristics to suit the job intended by blending a group of materials into the finished article. I'm a bit of a fan of dynamic support as provided by a plate that flexes as distinct from the previously discussed "bulk" device which offers no resistance at all until it is grounded between the foot and shoe....and then any flex is due to its compressability, which is usually not very dynamic and has very little "travel", otherwise they wear out pretty quickly.
    So a plate to the met heads and other stuff on top and distal to the met heads.
    Phill Carter
  7. Stanley

    Stanley Well-Known Member


    Would you then make the arch higher so that it can dynamically bend down to "neutral" or make it at "neutral" and allow the foot to "pronate into it". The point I am trying to make is that most orthotics are tolerated to a certain arch height. A little more feels like a rock. How do you guess the amount of arch height that would be required? How do you compensate for different materials, thicknesses, and body weight, and activities?


  8. pgcarter

    pgcarter Well-Known Member

    I think tolerance is also a function of degree of "hardness"....hence the desire to allow the foot to function across a range of positions, not hold it rigidly in one position either at the supinated or neutral or pronated end of its possible envelop of motion. I tend to look at the individual anatomy and decide what "envelope" of motion is probably going to work best for that foot and then try to encourage it to do that.
    As far as "reaching up" to a really high arched cavus foot type in order to influence it's function before it has flattened a great deal....yes I am a fan of that...you just have to be careful which material you select and how much and how hard any heel post is......you want tolerance ....and change....there is usually an achievable balance in there somewhere. My 15-20 year background fitting ski and trekking boots probably taught me more about what feet will or won't tolerate than my pod training, it is the art side of things to some extent...trial and error till you start getting it right most of the time. Very difficult to teach and lots of folks don't see it as important anyway..."get a lab to do it"
    regards Phill
  9. Stanley,

    Thanks for your comments. Shank independent does not mean "rigid". It simply means that the stiffness of the orthosis is not affected by shoe shank morphology. All materials will bend when a load is placed on them. The terms "rigid" and "flexible" in regard to orthosis stiffness are basically undefinable, useless terms that should be discarded from our podiatric lexicon. Otherwise, thanks for confirming what I have already discussed before in my newsletters and newsletter books over the past two decades regarding the parameters that affect orthosis stiffness.
    Last edited: Oct 2, 2006
  10. Steve,

    The purpose of the Precision Intricast Newsletter books was to make sure that the knowledge that I gained during my CCPM Biomechanics Fellowship, studying under some of the most knowledgeable podiatrists in the world in foot biomechanics, and that I gained during in my practice and research,was shared with a much larger audience than would have been possible otherwise. Your acknowledgement of their worth to your clinical development means very much to me. And after having written these newsletters for 20 years now, I appreciate the compliments no less than I did two decades ago. Thank you.
  11. Scorpio622

    Scorpio622 Active Member

    I usually add a lateral rearfoot flair and lateral clip to increase the pronatory moment. Do you think this is effective/worth doing?? I also increase the arch fill to lower the arch height.

    We tend to think of functional orthoses as anti-pronation devices, and little is talked about regarding situations such as peroneal tendonitis where we try to control supination.

    To echo others, I have gained much from your newsletters, well worth the price. I find practical advice helps my patients more than hard science. Although we need both. Thanks for sharing.

    How do you make your diagrams, such as the one in the above posting??

    Last edited by a moderator: Oct 3, 2006
  12. A lateral rearfoot flare makes sense but probably the same effect may be designed into the orthosis by using a deep heel cup and straight ground lateral rearfoot post. I don't know how a lateral clip would help produce STJ pronation moment. I use extra medial expansion thickness also and hold the medial column of the foot in a dorsiflexed position during negative casting to lower arch height of orthosis in patients with symptoms caused by excessive STJ supination moments.

    Your point about anti-supination effects being ignored by podiatry is a point I have been making for some time now. Just read the article by the financial interests of SoleSupports, Inc in this month's Biomechanics Magazine to see how they think that all injuries need maximum arch congruency to achieve therapeutic success. Shows how little some podiatrists understand STJ axis location/rotational equilibrium theory.

    I use CorelDraw to make all my drawings. Now, after using it for 20 years of newsletters, I think I am getting pretty good at it. ;)
  13. efuller

    efuller MVP

    A lateral flare added to the post of the orthosis may make shoe fitting dificult, especially in individuals with wider than usual heels. I often have enough trouble getting the width of the heel cup to fit into the shoe and there is not enough room for any additional width. It is good in theory though.


  14. Try the external oblique post design we described here:
    Paton J., Spooner S.K.: Effect of Extrinsic Rearfoot Post Design on the Lateral-to-Medial Position and Velocity of the Center of Pressure
    J Am Podiatr Med Assoc 2006 96: 383-392.
  15. javier

    javier Senior Member

    What is the difference between this Extrinsic Rearfoot Post Design and a Thomas heel?

  16. Thomas heel is applied to a shoe. This is more analogous to a reverse Thomas heel. But the mechanical principle is the same, just applied to the orthoses, rather than the shoe.
  17. javier

    javier Senior Member

    It is obvious.

    But, why do you want to add a Thomas heel or a reverse Thomas heel to a polypropylene shell? Leaving aside the bulk from the device, you can achieve the same result by a shank dependent orthosis made of EVA, can not you?
  18. From the abstract of our paper:
    "Findings from investigations of the effects of external forefoot and rearfoot posts added to foot orthoses have been inconclusive. This study was undertaken to examine the effects of rearfoot post design on the lateral-to-medial position and velocity of the center-of-pressure path. Four identical pairs of neutral-cast polypropylene orthotic shells were constructed; three pairs had a rearfoot post of specified design added. The fourth pair, the control, did not have a post added. Stance period data were broken down into four functional phases, and the statistically significant differences between the experimental conditions were calculated and analyzed. The addition of a rearfoot post to an orthotic shell affects center-of-pressure lateral-to-medial position and velocity. Although the effect of the post designs seemed to provide reasonably predictable changes in center-of-pressure position, the effect on center-of-pressure velocity was variable and inconsistent. The effect of the orthotic post was dependent on design and phase of gait. The addition of a rearfoot post and, specifically, the design of the post can probably be used to alter the center-of-pressure position and velocity. (J Am Podiatr Med Assoc 96(5): 383–392, 2006)"

    In other words by manipulating the shape of the rearfoot post it may be possible to alter the CoP position at distinct phases of gait over and above that achieved by the shell alone. Don't you add rearfoot posts/ stabilizers to your polyprop shells?

    You can skin a cat many ways Javier, however the discussion point here was about modifications to rearfoot posts used to treat peroneal tendonitis. To gain the same control with the EVA device that could be achieved with the polyprop would require a very thick EVA device, but in theory you could do a lateral heel skive or a rearfoot valgus post and/ or a forefoot valgus post.

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