Welcome to the Podiatry Arena forums

You are currently viewing our podiatry forum as a guest which gives you limited access to view all podiatry discussions and access our other features. By joining our free global community of Podiatrists and other interested foot health care professionals you will have access to post podiatry topics (answer and ask questions), communicate privately with other members, upload content, view attachments, receive a weekly email update of new discussions, access other special features. Registered users do not get displayed the advertisements in posted messages. Registration is fast, simple and absolutely free so please, join our global Podiatry community today!

  1. Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
Dismiss Notice
Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
Dismiss Notice
Have you liked us on Facebook to get our updates? Please do. Click here for our Facebook page.
Dismiss Notice
Do you get the weekly newsletter that Podiatry Arena sends out to update everybody? If not, click here to organise this.

Prescribing Orthoses: Has Tissue Stress Theory Supplanted Root Theory?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Apr 1, 2015.

Thread Status:
Not open for further replies.
  1. Nope, I guess it could be down to measurement error, or down to plastic deformation, but she had an inverted forefoot to rearfoot when the subtalar joint is in "neutral". Is this another problem with a rigid theory, or just the measurement error of a highly experienced clinician trying to apply such a theory? Viva variation. Either way, neither of these measurments really had any impact on my successfull orthosis prescription. Ain't it a bummer when individuals don't fit a model that relies upon individuals fitting a model? Nope- treat that patient in front of you- the tissue stress approach.

    Maybe it was due to plastic deformation of the medial column as weight transferred medially toward the opposite limb during terminal stance?
     
  2. Jeff Root

    Jeff Root Well-Known Member

    It depends on the amount of tibial varum and rearfoot varus. Can the heel get to vertical? If not, the heel would be posted inverted but maximally pronated since the STJ ROM will not allow it to reach vertical. In that case, you use a very high lateral heel cup and a lateral post flare. And if the forefoot is inverted to the rearfoot when the MTJ is maximally pronated, then the forefoot would be posted inverted since there is no more eversion ROM. If the patient has an uncompensated forefoot varus, this creates an eversion moment at the STJ. But if the STJ is maximally pronated, then how can the medial forefoot get to the ground? Subluxation. That is why we would post the forefoot inverted. And this would reduce compression in the sinus tarsi since the STJ would not be attempting to pronate past its end ROM.

    Jeff

    corrected typo: changed about to amount
     
  3. I don't remember reading anything like that in your dads books. Regardless, are we talking rearfoot varus post, or valgus post with a reafoot varus? And we still going to post the forefoot inverted even in the patient with chronic lateral ankle instability. K? And increase the STJ supination moment in the process. Moreover, let us be cognisant of the FACT: this patient got better even though I didn't follow a Root approach to foot orthoses prescription- could be due to many reasons- it wasn't due to Root.
     
  4. Jeff Root

    Jeff Root Well-Known Member

    I don't like the term rearfoot varus post but in my Rx the heel bisection would be corrected inverted, what some call a varus rearfoot post. I use the term reafoot post only to describe an extrinsic rearfoot post and use the heel bisection angle to describe inverted or everted angle of the heel in the corrected cast from which the orthosis if made. At Root Lab we use intrinsic cast correction as our default, so I we say that we balanced the cast with the heel X degrees inverted or everted or to vertical.

    I think we also need to consider the possibility that this patient may have a forefoot supinatus secondary to rearfoot varus as a result of firing their anterior tibial in an effort to resist STJ pronation that will result in stj subluxation. Again, I would want to know the heel bisection angle when the patient is maximally pronated. As for your last sentence, I see a Root type extrinsic rearfoot post so I think it is fair to say that there is some Root influence in your treatment.

    Jeff
     
  5. drhunt1

    drhunt1 Well-Known Member

    Hogwash. And therein lies the problem, folks. We have biomechanics "gurus" that are traveling around the world, lecturing to other Pods about a "new" theory, and yet they can't determine the difference between extensor and flexor contractions.

    How many of you following this post agree with Simon's assessment...that the lady he showed a pic above in static stance demonstrates extensor, (EDL), contraction?
     
  6. efuller

    efuller MVP

    When looking at the picture you can clearly see the long exenstors contracting. However, as you look at the toes you can see that they are pressed into the ground with hyperextension of the dipj which would only happen with contraction of the flexors.

    Although we shouldn't be over thinking a single snapshot. We don't know if this picture is representative of what is happening most of the time.
    Eric
     
    Last edited: Apr 3, 2015
  7. Jeff Root

    Jeff Root Well-Known Member

    Looking at the right foot in particular, it appears to me that she is firing her flexors resulting in dorsiflexion of the proximal phalanx, plantarflexion of the intermediate phalanx and dorsiflexion of the distal phalanx on 2-4. You can easily replicate this effect by holding your hand firmly on the table top and flexing your digits.

    Jeff
     
  8. efuller

    efuller MVP

    I created a mechanical model where a tendon that curled around a "cuboid" was attached to a first ray that could plantar flex. In a more medially positioned STJ axis the STJ pronated with such force that it dorsiflexed the first ray even though the tendon was attempting to plantar flex the first ray. Ground reaction force attempting to dorsiflex the metatarsal was greater than the plantar flexion moment from the tendon.

    In a centrally positioned STJ axis, pull on the tendon caused the STJ to evert, but the first ray stayed in the same position.

    In a laterally positioned STJ axis, the first ray plantar flexed and caused STJ supination even though the pull of the tendon around the cuboid created a pronation moment. The supination moment from the medial shift of center of pressure was greater than the pronation moment from the pull of the tendon.

    So, the position of the STJ axis is important for understanding peroneal function and the muscle functions differently in feet with different STJ axis positions.

    Eric
     
  9. drhunt1

    drhunt1 Well-Known Member

    In an earlier post, Simon asked Jeff Root what his father would order for the orthotics on Simon's patient, which is a ridiculous question for a number of reasons. First, Simon doesn't give very much information, other than to initially write that the patient had lateral instability and shows a pic of her in RCSP. He stated that the orthotic he either made, or had made, sufficed in resolving her symptoms...even with the abducted device. I'm sure Dr. Root would've been MUCH more complete in his presentation here, than Simon has been. Second, Merton only had rohadur to work with...not the polypropylene devices with durable and absorptive top covers available. Simon finally admits that the patient had a forefoot varus, (inverted position)...which can be assumed looking at the pic, but would've been MUCH easier to discern had he also provided a pic of the patient in NCSP...especially from the rear. But where he really makes a grave error is to write that the patients' lesser digits are contracted secondary to extensor involvement. Ooops! Big mistake.

    So using Root biomechanics, here's what I would've ordered the patient. 6 degree inverted Rx for the rearfoot, with little to no lateral skive on the rear post, add a lateral clip, order the orthotic wide, and have the lab build a crepe arch fill with a 6-8 degree forefoot varus extension carried out to the end of the toes. Extrinsic correction. The orthotic would look similar to this, with not quite as much forefoot varus extrinsic correction.
     
  10. Indeed. Yet when the patient stood in front of me, her toes were rarely stationary as she was constantly fighting the lateral instability with her toes intermittantly being raised off of the floor as the extensors fired every few seconds.
     

  11. So, you'd use an inverted, varus posted device to treat a patient that presented with chronic lateral ankle instability?

    Lets go back to the start, why did I post up the photo's that I did of a female squash player who'd had a history of chronic lateral ankle instability that was successfully treated using orthosis which were designed to increase the pronation moment acting about the STJ axis? It was because it is this kind of case which shows the difference between the Root approach to foot orthosis design and the tissue stress approach to orthosis design. The Root approach would have us design a foot orthosis which would increase supination moments, whereas the tissue stress approach would have us design an orthosis that should increase pronation moments. I know that the tissue approach was successful in this case, I do not believe a Root approach would have been, which is further evidenced by the fact that when I initially saw this patient she had a pair of foot orthoses which had been prescribed using a Root philosophy which had made the problem worse. Why would anyone choose to design a foot orthosis which increased the external supination moment about the STJ axis in a patient that already has an excess of supination moment? It just doesn't make any sense at all. So go ahead, pick faults, argue over the lack of photo's taken from behind, the STJ neutral position, the RCSP, the forefoot to rearfoot alignment, whether the flexors are firing or the extensors are firing, whether the orthoses "look good", all you want, but the fact remains, following a Root philosophy should result in an orthosis which should be virtually mechanically opposite to what was successful here- and that's the point.
     
  12. Don ESWT

    Don ESWT Active Member

    Pictures posted at 10:29 3rd April are interesting, should we not be concerned with the reduction in vascular supply as it clearly shows in the second picture blanching of the soft tissue and that is before the foot is in-cased in footwear. If this person as poor foot function(CMT) are you not increasing the forces be applied to the base of the 1st met and cuneiform, thus creating a knife edge which may result in an ulcer due to inadequate soft.
     
  13. This picture? There does appear to be a lot of blanching particularly on the left foot. Perhaps there was inadequate expansion applied to the heel section of the positive cast. Or maybe he's putting more weight through the left leg, that's the trouble with photographs, it's difficult to tell what's really happening.
     

    Attached Files:

  14. Are you talking about the section I've highlighted with a red circle? It's difficult to say because we don't have an image of the unloaded device and the photo is taken standing on carpet rather than a hard surface, but it does look as if the shell is undergoing a fair amount of displacement in this area given the rather "wavy" edge.

    There also seems to be some black marking on the leg which looks like felt-tip pen lines, I've highlighted with the blue circle- not sure what this is because an anterior photograph wasn't provided.
     

    Attached Files:

  15. Jeff Root

    Jeff Root Well-Known Member

    Simon,

    We need to clarify some terminology at this point. I was talking about a foot that has a reafoot varus (or RFV and tibial varum) that causes the heel remain inverted when the STJ is maximally pronated.

    Lets use some hypothetical numbers here to give it more meaning. Lets assume that our subject has eight degrees of tibial varum. And lets also assume that the STJ demonstrates 20 degrees of inversion (using the distal 1/3 of the tibia as a reference) with maximum STJ supination and one degree of eversion with maximum STJ pronation, giving us a total ROM of 21 degrees. So in our open chain examination we determine that the heel, with maximum STJ pronation remains 7 degrees inverted to the plane of the ground (8 degrees tibial varum minus 1 degree of available heel eversion). And lets also assume that we get a RCSP of five degrees inverted due to some additional heel eversion during stance (subluxation, measurement error or something). And lets also assume that when we attempt to have the patient attempt to further pronate their foot we get no additional heel eversion so we know that the five degree inverted heel is the maximally everted position of the heel.

    Now let's assume we cast the patient in STJ neutral or even maximally pronated, and then correct the heel of the cast anywhere between 5 to 7 degrees inverted. These are our two maximally pronated (everted) positions we measured. Although the heel of the cast is inverted to the ground, it is supporting the heel (STJ) in its maximally pronated position. This would not increase the external supination moment about the STJ axis as you suggested. The STJ has no additional eversion (pronation) ROM, so please explain how supporting the foot maximally pronated could possibly increase the STJ external supination moment. And what is the logic of using a device that attempts to pronate the STJ beyond its pronation end ROM and encourages STJ subluxation?

    Regardless of what we do, these patients will have a tendency for inversion instability because the foot is so inverted. But, we are reducing it by attempting to keep the foot from inverting by supporting it in a maximally pronated position. And we are reducing sinus tarsi compression force by resisting STJ subluxation in the direction of pronation.

    Jeff
     
  16. Jeff Root

    Jeff Root Well-Known Member

    The devices are 5/16 polypropylene. I used a more flexible shell because this is an employee and we can easily make him a more rigid pair if these are too flexible, which in fact they probably are. This is why his bony prominence, which we did not accommodate, is causing deflection in his orthotic shell.

    The line on the anterior tibia and dorsum of the foot was drawn with the patient supine, the STJ in neutral and the MTJ fully pronated. His tibia internally rotates and his arch collapses during weightbearing. I drew the line to demonstrate to students how the orthosis reduces the amount of internal tibial rotation as compared to the non-weightbearing foot. So we get frontal plane changes (a reduced angle of heel eversion) and transverse plane changes (reduced internal tibial rotation) when this subject wears his orthoses.

    Jeff
     
  17. So, you've pushed the foot with your hand to "know where it's end of range is"(- really?), then you've got varus posted orthoses which "increase the pronation moment"? I don't think so, Jeff. :rolleyes: Devices provide reaction forces Jeff, they don't hold the foot in any position, they merely push back when the foot pushes against them. 1 degree of posting certainly does not = 1 degree of positional change in the foot. Varus posting certainly does tend to increase the supination moment by shifting the centre of pressure medially when the foot is in contact with the superior surface of the shell- or are you suggesting the foot is never in contact with the shell because you made it with the foot in it's maximally pronated position as measured when you pushed the foot with your hand as oppossed to when a couple of times body weight was acting through it?

    "keep the foot from inverting by supporting it in it's maximally pronated position And we are reducing sinus tarsi compression force by resisting STJ subluxation in the direction of pronation."- come on. Lets say it is in it's maximally pronated position, the varus post may not change the kinematics, but it will change the kinetics decreasing the sinus tarsi compression- that's what you are saying- right?. How can it reduce sinus tarsi compression without increasing supination moment? It can't- end of story. And if it's increasing supination moment- which it is, how is this influencing the stress in the tissues that resist supination in a patient with chronic lateral ankle instability? That's right- it's increasing stress in these tissues because that's how physics works.

    For those following that don't understand: imagine we have a see-saw and we put a fat kid on one end, the see-saw moves (pronates) to it's end of range and touches the floor (the talus compresses against the floor of the sinus tarsi). The floor (of the sinus tarsi) pushes back with an equal and opposite force (against the talus) (Newton's 3rd). Now we add another fat kid to the same side of the see-saw, there is little obvious change in position of the see-saw. However the compressional forces at the interface (talus against floor of sinus tarsi) have increased (more force pushing the see-saw into the ground from the additonal fat kid- more force pushing the talus against the floor of the sinus tarsi). Now, how can we decrease the compression between the see-saw and the floor (talus against the floor of the sinus tarsi)? Let's place a small baby on the other end of the see-saw, the see-saw does not change position, it's still maximally pronated, but the compression force is now lower. Viz. by adding a supination force (small baby) the "residual" pronation moment has been reduced. In order to reduce the compression at the floor of the sinus tarsi, supination moment must be increased, yet Jeff claims his devices "would not increase the external supination moment about the STJ axis as you suggested." yet at the same time he believes: "we are reducing sinus tarsi compression force". Impossible. There is no argument here, what Jeff is suggesting is simply impossible. I know that might be tricky for those that don't understand the difference between kinematics and kinetics, nor physics and biomechanics from Root, but there you go- you really do need to understand the difference since foot orthoses alter kinetics; kinetics drive kinematics but foot orthoses only ever directly alter kinetics; Rootian philosophy would have us breaking the laws of physics- never going to happen.

    You respect Kevin, right? Why do you think he employs valgus posted devices to treat chronic lateral ankle instability?

    *Lots of edits because I was thinking and typing on the fly- sorry.
     
  18. drhunt1

    drhunt1 Well-Known Member

    What Simon also doesn't discuss, (it is no surprise to me), is that above he states that his orthotics increase the pronatory moment for the squash player. Considering that she is probably functioning at her pronatory end of ROM at the STJ at midstance, how is this possible unless one holds the calcaneus at a slightly more inverted position, ie., more neutral? Simon's orthotics abduct the forefoot, which is obvious from the pics he shows. What he has not done, however, is show the squash players' foot from different angles, with and without the orthotics at static stance. If he didn't have me on ignore, he could address these issues. But 'out of sight, is out of mind' for Simon. Tsk, tsk.
     
  19. Jeff:

    Let me try to clarify some terminology that seems to be preventing you and Simon from totally understanding each other. When Simon saysthat his foot orthosis with a lateral heel skive and valgus forefoot wedge "increases the external subtalar joint (STJ) pronation moment", what he means is that his specific orthosis modifications increase the STJ pronation moment acting on the plantar foot (i.e. an external moment) when compared to the balance of STJ pronation-supination moments which the ground or a non-lateral heel skived or non-valgus wedged foot orthosis would produce. This would be true if the STJ is maximally pronated, 2 degrees supinated from maximally pronated or in STJ neutral since Simon's "valgus orthosis modifications" will cause a shift in the center of pressure (CoP) laterally which, by definition, will cause an increase in external STJ pronation moment.

    The logic of applying an additional amount of external STJ pronation moment to a foot which is suffering from symptoms caused by excessive magnitudes of STJ supination moment should be self explanatory using STJ Axis Location and Rotational Equilibrium (SALRE) Theory (Kirby KA: Methods for determination of positional variations in the subtalar joint axis. JAPMA, 77: 228-234, 1987; Kirby KA: Rotational equilibrium across the subtalar joint axis. JAPMA, 79: 1-14, 1989; Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001).

    Simon knew that his patient's symptoms were caused by excessive STJ supination moment due to her lateral ankle instability. He also knew, from SALRE theory, that the addition of more STJ pronation moment to the foot would decrease the abnormal magnitudes of STJ supination moments and decrease her tendency to undergo inversion ankle sprains. Therefore, he chose the most logical path by which to make the patient's foot orthoses. Would you think it better to increase the patient's STJ supination moments by making a varus wedged orthosis? A varus wedged orthosis for this patient makes absolutely no sense to me.

    In addition, your suggestion that somehow using an orthosis that shifts the plantar reaction forces laterally or, in your words, "that attempts to pronate the STJ beyond its pronation end ROM and encourages STJ subluxation", will cause "STJ subluxation" is erroneous and is another podiatric myth that still persists. I've been using valgus wedged foot orthoses for these patients for over a quarter century and never once saw a patient that had appropriately valgus-wedged orthoses develop a "STJ subluxation". In fact, they generally come back for more orthoses of the same design every four to five years since these lateral heel skived-valgus wedged orthoses are the only devices that have made them asymptomatic.

    And as a further note, these patients with supination-related pathologies such as peroneal tendinopathy and chronic lateral ankle instability generally also come to me with a bag full of "Root-inspired orthoses" with varus rearfoot posts, vertical heel balancing, no lateral heel skive, no intrinsic forefoot valgus corrections, and no valgus forefoot extensions which have either made their problem worse or no better. Why did these orthoses fail? Because these orthoses didn't have lateral heel skives, valgus intrinsic wedges and valgus forefoot extensions which would have been necessary to counteract the excessive STJ supination moments which were causing the patient's symptoms.

    I'll see you in Vancouver in a few weeks at the PFOLA seminar and we will discuss these topics further.
     
  20. Jeff Root

    Jeff Root Well-Known Member

    Forefoot valgus is very common, so we would need to know if Kevin's patient had a ff varus or a ff valgus. Maybe Kevin can comment on how he would treat a RF varus with a FF varus versus a RF varus with a FF valgus. We also need to recognize that a varus or valgus forefoot extension attached to the top cover is different than intrinsic or extrinsic correction (posting) of the orthotic shell. Most individuals with chronic lateral ankle instability have a forefoot valgus, so in the majority of casts I would use an orthotic with intrinsic forefoot valgus correction and possibly an extrinsic forefoot valgus extension.

    When we create a positive cast of the foot for producing a functional orthosis, the frontal plane orientation of the cast is the only plane that we modify. It doesn't make any difference if we adduct or abduct the cast on the countertop, it won't change anything. And the contact point at the heel and under the met heads determines the sagittal plane orientation of the cast (note: we can add ff or rf lifts to alter the sagittal plane orientation of the orthotic shell). So the one plane we determine in the Rx is the frontal plane position or orientation of the positive cast (or the orthotic shell with extrinsic posting). The terminology and techniques that I am discussing are conventional techniques used by virtually every commercial foot orthotic laboratory.

    I guess there is no end ROM of any joint is the force applied can be infinitely increased, but that doesn't happen in the real world which is why we want to know the functional end ROM. Time now to go enjoy my Saturday!

    Jeff
     
  21. But that doesn't make them the best way, nor right. Happy Easter, Jeff.
     
  22. And how many degrees of change in his body did you get for the number of degrees of change in the orthoses? Moreover, what about the "blanching" of the heel tissues?
     
  23. drhunt1

    drhunt1 Well-Known Member

    Kevin-I'll make this brief....you're using your own newsletters to "prove" a point? Hmmm....

    If the STJ is maximally pronated at static stance to begin with, how does a lateral skive offer the patient an increase in the pronatory "moment"?

    Just because the prior Podiatrists used Root biomechanics, either by telling you that, or by your own assumptions, and have supposedly failed said patient, doesn't mean that those Podiatrists accurately diagnosed and/or prescribed an orthotic. Suffice it to write, that I'm using Root biomechanics more now then ever. Why? Because it works and because Merton was right. With a few modifications, I've discovered and successfully treated the cause of growing pains in children and RLS in adults. My next project is identifying and resolving DJD of the knee, using the same biomechanic precepts discussed by Merton Root and John Weed.

    Please let me know when the tissue stress theory accomplishes the same end points.

    Happy Easter.
     
  24. Jeff:

    I don't treat "rearfoot varus" or "rearfoot valgus". I don't treat "forefoot valgus" or "forefoot varus". However, I do treat symptoms and gait abnormalities in my patients that may occur as a result of a multitude of structural and/or functional variables in my patients. Therefore, since I now use Tissue Stress Theory to guide my foot orthosis prescriptions versus the Subtalar Joint (STJ) Neutral Theory that I was taught at CCPM by your father, John Weed and all the rest of the CCPM Biomechanics Faculty, I don't treat "foot deformities", as you suggest, I treat pathologies. And, by the way, I don't consider a "rearfoot varus", "forefoot valgus" or a "forefoot varus" either a "pathology" or a "foot deformity", they are rather variations in foot structure.

    The difference here, Jeff, between your reliance on STJ Neutral Theory and my reliance on Tissue Stress Theory is that I would treat the chronic lateral instability with some type of valgus orthosis modification that would redirect ground reaction force (GRF) more laterally on the plantar foot regardless of whether the patient had a "forefoot valgus", a "forefoot varus" , a "rearfoot varus", or a "rearfoot valgus". All I need to do with a foot orthosis using Tissue Stress Theory with chronic lateral ankle instability to be successful is to:

    1. Increase the external STJ pronation moment acting on the foot to reduce the symptoms;
    2. Prevent other pathologies from occurring, and
    3. Optimize the gait function of the patient.

    The amount of valgus wedging (i.e. lateral heel skive, arch filler plantar to the lateral arch of the orthosis, intrinsic forefoot valgus correction, and/or valgus forefoot extension) may vary from foot to foot to be successful. However, I really don't need to draw a heel bisection on the foot and used a goniometer to tell me what my patient's "rearfoot deformity" or "forefoot deformity" is in order to be successful with foot orthoses. This is especially true since heel bisections, STJ neutral and determination of Z"rearfoot deformities" and "forefoot deformities" are extremely unreliable from one practitioner to another.

    Agreed.

    I agree that it is important to know what the end range of motion of the STJ is, especially in a weightbearing setting. That is why I perform the Maximum Pronation Test on my patients. [The Maximum Pronation Test was first described in my book chapter with Donald Green, DPM 23 years ago: Kirby KA, Green DR: Evaluation and Nonoperative Management of Pes Valgus, pp. 295-327, in DeValentine, S.(ed), Foot and Ankle Disorders in Children. Churchill-Livingstone, New York, 1992.]

    I quit measuring the neutral calcaneal stance position (NCSP) in my patients 25 years ago since the Maximum Pronation Test gives me much more useful information as to where the STJ is within its range of motion during weightbearing activities.

    Happy Easter, Jeff. Looking forward to seeing you in Vancouver.:drinks
     
  25. Jeff Root

    Jeff Root Well-Known Member

    So how much external STJ pronation moment is necessary to eliminate the patient's lateral postural instability and how do you measure it? Did my Rx with a maximally pronated STJ have enough? Is more simply better? Perhaps your device with a lateral heel skive etc. is insufficient too. Have you ever had to use an ankle brace like the ASO (http://www.asoankle.com/index.cfm?fuseaction=information.ShowAsoInformation) in conjunction with a functional foot orthosis to prevent inversion ankle sprains in an athlete because the moment arm of the orthosis is too short?

    I do recommend lateral heel skives on orthoses when indicated. I find it very interesting that Simon keeps telling me how ineffective Root type functional orthoses are. I don't feel the same need to prove his methodology wrong. I just try to discuss the reasoning and logic of the techniques that I feel are valid and I share my concerns with theories that may not seem logical or practical to me.

    For example, we recently had a significant amount of discussion about whether or not the Root casting technique fully pronates the MTJ. Would not a valgus FF extension, in order to produce a pronation moment at the STJ, have to first produce a pronation moment at the MTJ? And if Simon is correct that the Root technique doesn't fully pronate the MTJ since it can be further pronated if you apply enough force, how do you know that the valgus wedge increased the STJ pronation moment? Perhaps it only increase the pronation moment at the MTJ.

    I think there are elements of the tissue stress theory that make a lot of sense. In many cases they are compatible with Root theory. I see flaws in both theories. For the record, I detest both of these labels because I think they hinder progress and create unnecessary division within the profession. If kind of reminds me of hearing a Ford and Chevrolet enthusiast debate which brand of cars is better. Personally I'm a Ford guy but I won't get caught up in a silly debate about which is better. Can we use the data and evidence to determine which line of cars is better? No!

    Jeff
     
  26. Just like in STJ Neutral Theory, the Tissue Stress Approach to orthosis prescription will involve some trial and error. Both objective findings and subjective findings are used to determine how well the orthoses are working. I do use ankle strapping and/or ankle bracing both with and without foot orthoses in order to prevent inversion ankle sprains, along with sometimes a change in shoe gear, strengthening of the peroneals, etc. All of these treatment methods have their pros and cons. However, I always make orthoses for patients that suffer from inversion ankle sprains with some form of valgus forefoot extension on the orthosis (i.e. my orthoses for these patients are always full length). The reason for this is two-fold. First of all, the 5th metatarsal head has the largest pronation moment arm to the STJ axis of all the plantar weightbearing structures of the foot. Secondly, once the heel lifts off the ground during propulsion or in a maneuver where the heel never touches the ground, a valgus forefoot extension is still doing its job causing a STJ pronation moment, whereas the rest of the orthosis plate is doing little to prevent an inversion ankle sprain.

    I suspect that some of Simon's frustration is not directed to you, Jeff, but to others that are trying to support you within this thread.

    I use the lateral heel skive modification on my prescription foot orthoses to treat chronic lateral ankle instability, peroneal tendinopathy, 5th metatarsal head plantar lesions, lateral dorsal midfoot interosseous compression syndrome (lateral DMICS) and any time the patient is exhibiting signs of excessive STJ supination during gait.

    If the forefoot valgus wedge shifts the ground reaction force (GRF) laterally on the forefoot (which it should), then this lateral shift in GRF would simultaneously cause an increase in external STJ supination moment and an increase in external eversion moment at the midtarsal joint (MTJ). A change in MTJ kinetics does not occur without a change in STJ kinetics by increased lateral positioning of GRF from a forefoot valgus-wedged orthosis. In other words, one does not occur without the other and one does not occur before or after the other. In addition, by definition, as soon as the more laterally-directed forefoot GRF is applied to the plantar foot, not only are the kinetics of the STJ and MTJ simultaneously affected, but the kinetics of the ankle joint, knee joint and hip joint are also simultaneously affected. This can easily be demonstrated using Newton's Third Law of Motion and with proper modelling of the foot and/or lower extremity.

    The labels of STJ Neutral Theory and Tissue Stress Theory are necessary to enable more coherent and logical discussions of both theories. There is no proven rights nor wrongs at this point in time with the two theories. The labels given to these theories do enable better communication which, in turn, allows more clear discussions regarding the pros and cons of both theories so that further development of even better theory may be achieved.

    I agree that both some components of STJ Neutral Theory can be effectively combined with Tissue Stress Theory to order custom foot orthoses. I believe that the combination of the two can be effective since this is the way I have practiced and the way I have taught the many podiatric surgical residents I have trained over the past 28 years for the Scripps/Kaiser Sacramento Residency Program.

    However, also, there are parts of STJ Neutral Theory that are wrong and should not be taught since they are erroneous. I do also believe that Tissue Stress Theory is a work in progress, but it is still complete enough now to be taught as an effective method by which to more optimally design foot orthoses for patients with any mechanically-based foot and/or lower extremity pathology. For me, Tissue Stress Theory has a bright future as long as the practicing clinicians that are using it to order custom foot orthoses understand its concepts, its limitations and its practical application in the treatment of mechanically-based foot and ankle pathologies.

    Good discussion!:drinks
     
  27. Jeff Root

    Jeff Root Well-Known Member

    I was recently watching a television program about the use of Polio virus to treat brain tumors. There was success until too much Polio virus was used which resulted in edema and death. If foot conditions were terminal, we would have much more funding for research and we would better understand our treatment approaches as a result. But look at how many people's quality of life is adversely impacted by foot conditions. But because it isn't a terminal condition in most cases, we don't get the funding for research. Too bad!

    Looking forward to seeing you in Vancouver! :drinks

    Jeff
     
  28. efuller

    efuller MVP

    Whether or not you have added enough pronation moment is determined by the patient. If they say these inserts feel great and I'm not having any problems then it was enough. If they say I need more, then going to an ankle brace is reasonable. (The ankle brace can also increase pronation moment) We don't really need to measure how much the pronation moment from the ground has changed. If we did we would also have to know the amount of change that we need. We just need to know that we do need to increase pronation moment for someone with lateral ankle instability and peroneal tendonitis. We then increase the pronation moment, with various methods, till it feels better.

    What is the logic for the use of a lateral heel skive? Does this logic come from neutral position theory? Or is the lateral heel skive used because it works? I've had adherents of neutral position theory complain to me that "a valgus heel wedge will be bad because it will pronate the foot. Pronation is bad because it will unlock the foot." Yet, the logic of a lateral heel skive is quite simple. There is an "over" supination problem, so you do need to pronate it more.

    I do believe that we need a theoretical framework for designing an orthosis. In neutral position theory, there is not really a coherent framework for designing orthotics. When we look at Root theory there are a couple of concepts used to make orthoses. One is the need to push the foot toward an idealized neutral position. The other is that the forefoot to rearfoot deformity needs to be supported. I would agree that in the majority of cases the STJ should be pushed toward neutral position. However, the peroneal tendonitis, lateral ankle instability case is one where the STJ should be pushed toward pronation. So, to stay within neutral position theory, do we add an exception for lateral instability.

    When people thought the Earth was center of the universe they looked at the stars. As they looked more closely they saw planets that apparently moved in ways that were difficult to explain with the Earth as the center. So, they changed their theory so that some of the celestial bodies had exceptions (epicycles) that allowed them to, sort of, predict future motions of the planets. Then someone figured out that you could get better predictions if you changed the theory to the Sun is the center of the solar system. These are two different explanations for the same celestial observations. One is better than the other.

    Yes, we do need to keep some of the neutral position ideas. A partially compensated varus is an important concept to understand. An intrinsic forefoot valgus post is a useful tool for changing the forces under the foot. However, if we neglect to choose the better theory there will be confused practitioners of the art. On this very thread, we have people suggesting that you should give someone with lateral ankle instability and a varus forefoot to rearfoot measurement, a forefoot varus wedge. We should treat the problem that the patient has and not some measurement (that just can't be done accurately).

    We need to choose a coherent theoretical framework with which to design our orthotics. Yes we had a lot of success with the old framework. The same could be said for sailors who thought the Earth was flat. The vast majority of them made it back to port. That is no reason not reject the notion that the Earth is flat.

    Eric
     
  29. drhunt1

    drhunt1 Well-Known Member

    Eric-in many cases I've seen in the office, the patient with a barely, or uncompensated rear foot varus, for example, is already at their eversion, (pronation), end of ROM of the STJ. I'm suspecting this is the case with the squash player that Simon gave pics of above. If she's already fully pronated at static stance, how does any further pronatory device solve this problem? It doesn't. I've asked Kevin this same question several times above and he either has me on ignore, or refuses to answer such a simple question. Instead, many of the proponents of tissue stress theory are using terms like "moment"...and I'm assuming it's to appear more like engineers, then Podiatrists. Oh well. Why not just discuss "motion"? Orthotics are very good at limiting excessive motion and/or redirecting GRF's. Excessive calcaneal motion is best controlled at midstance when the orthotic obtains full purchase...less so at heel strike. But once the heel comes off the ground as the patient enters into forefoot loading and propulsive phase of gait, that's where we, as a profession, have not provided useful data. I aim to change that.

    Even the orthos have backed away from forefoot valgus extensions to control medial knee pain...probably because it only worked for a limited number of patients, and many others, made worse. There's a reason why...and I aim to demonstrate that as well. Wish me luck. The resolution of growing pains in children and the tie to RLS in adults is just the beginning.
     
  30. efuller

    efuller MVP

    I did a study on 30 asymptomatic podiatry students and all of them were within 3 degrees of maximally pronated. There are some patients that rest more inverted than that, but they are rare. Looking at the picture that Simon gave, I would give that foot a 50% chance of resting more inverted than 3 degrees from maximally pronated. Every patient I give orthotics to, I assess how much eversion range of motion they have. I can't tell from across the room, or from a picture, which feet will have more eversion range of motion. Why do you think the foot in that picture is nearly maximally pronated?

    Matt, you do know that moment is the same as torque, right? To cause a rotation you need a moment or torque. Newton's 2nd law for angular motion is net moment = moment of inertia x angular acceleration. So, if you want to know what you are doing when you try and change foot motion, you need to understand moments. Yes, you can change motion without knowing about moments, but you are just guessing what you are doing. So there is really no point to discussing motion without discussing moments.

    So, if you had a foot that was laterally unstable and maximally pronated: Lateral instability is a tendency to invert at the STJ. Why do some feet tend to pronate in response to ground reaction force and other feet tend to supinate? Well you have to understand how ground reaction force causes a moment about the STJ to understand that. Yes, you can talk about "foot deformities", but you still don't have the full picture of why a particular deformity will tend to cause pronation or supination if you don't look at moments.

    The reason that a partially compensated varus might be laterally unstable is that the heel sits markedly inverted and the contact pointh (center of pressure) of the heel would be far medial to the STJ axis. It is possible to have an inverted heel and center of pressure relatively far lateral and this foot is much more likely to have a pronation moment from the ground. The important thing is where the center of pressure of the heel is and not where the heel bisection is.

    So, if you understand that there is a moment from ground reaction force. And that a foot with lateral instability has a very small pronation moment, or even a supination moment from ground reaction force, it is very easy to understand how an increase in pronation moment will decrease the tendency to lateral instability, even if the foot is near maximal pronation.


    Did you read the abstract of one of the most recent articles posted in the thread on lateral wedging for medial knee OA. It noted that eversion range of motion was an important factor in whether a valgus wedge was going to be effective in relieving medial knee OA. It all makes perfect sense if you understand the physics of the situation. In a leg with tibial varum the center of pressure under the tibia will be medial to center of pressure of the knee. In the frontal plane when the force from the femur applied to the tibia is lateral to the force from the ground applied to the foot, there will be an external adduction moment on the tibia. An external adduction moment on the tibia must be resisted by compression forces in the medial compartment of the knee and tension forces in the lateral ligaments. To treat this you want to reduce the adduction moment by moving the center of pressure of ground reaction force more lateral. If the wedge is not big enough to do this you will not get the effect that you want. Some feet have a greater eversion range of motion than others. If you give all feet the same size wedge, some will have their center of pressure shifted and others won't. This a very good explanation of why the data on wedging and medial knee OA has been inconsistent and has been effective in some people. Understanding physics of treatments is important. You shouldn't give up on a treatment because orthos are giving up on a treatment. You shouldn't think the world is flat just because all of other people do. Matt, you should trust in science and not deride people for using the term moment.

    Eric
     
  31. But it is also important to understand that you can change the moments without any obvious observable change in position nor motion.
     
  32. Trevor Prior

    Trevor Prior Active Member

    This has been a really interesting discussion although at times, it drifts from discussion to argument which is a shame.

    However, I think Eric provides some a very good summary when he indicates certain structural alignments are important yet applying the principles of physics to dynamic motion moves us on from the original theory proposed by Root et al.

    I have said, somewhat glibly in the past, that I have concerns about tissue stress, and I am aware that I have not articulated this well. It is my opinion that we all apply a tissue stress approach because we are trying to reduce load and relieve symptoms. It is how this is achieved that is different.

    I recently read the roundtable discussion that Kevin and Simon produced for Foot & Ankle specialist and there was a very pertinent comment from Simon. When referring to using orthoses to return the loading on a tissue to its zone of optimum stress, he notes ‘…allowing it to heal, and without inadvertently exposing other tissues to deleterious loading levels.’

    It is this concept that I believe to be key and, to date, I have seen relatively little that explains how this is determined. We have all judged our success or not of orthoses on the degree of symptom relief achieved but how do we determine if another structure may develop injury as a result but in the future?

    To my mind, any theory has to be developed such that it can be taught to students so that they have a framework to provide care. Much of these concepts are already in place but it seems to fall short on the point above. I can easily teach someone how to offload a structure but how do I teach them to try and determine the potential detriment of an intervention?

    If we believe that orthoses can be positive, then there must be the potential for them to be negative and we have all had patients who have developed problems. I am not aware of any other area of our practice where we would not provide the student with a framework for determining they may cause a problem. If we can provide criteria for this, I believe we would have made a significant step forward in our understanding and thus management.

    My assessment and management approach is in keeping with Simon, Kevin etc. Although I may assess and treat in slightly different ways, it is essentially similar. That I still consider some of the structural alignments from Root et al is simply because I use these as part of the jigsaw. It has developed with evolving philosophies and experience but I am acutely aware, is largely unproven.

    I believe the biggest problem we have had with research to date is the role of more proximal function on foot function. Looking at the proximal drivers has the potential to explain some of the function we observe and can alter the loading of the foot irrespective of range of motion / alignment etc. Of course, these are important factors but only part of the jigsaw. If we can develop a method of a broader assessment of function, treatment will follow, utilising the principles discussed for altering load but, more importantly in my opinion, allow us to make an assessment of the potential negative effects or the limitations of the treatment we have provided.

    I have recently submitted a couple of guest blogs that relate to some of these thoughts and will happily post a link when they are up if anyone is interested.
     
  33. It's all about what Craig terms "load management" in a "zero net game", that is if we reduce the moment in one direction with a foot orthosis, we increase it in the opposite direction. So lets say we design an orthosis to reduce the stress in a tissue which provides internal supination moment by introducing a foot orthoses with provides additional external supination moment, in so doing we will have increased the stress in the tissues which resist pronation moment. How do we know if the additional stress on the tissues that resist pronation moment is too much? Glibly, the same way we know whether or not our orthoses are successful, the degree of symptoms, i.e. if a patient develops pain in the peroneal musculo-tendon units after the introduction of an orthoses designed to increase external supination moment, there is a good chance that the orthoses is increasing the supination moment by too much. So, we model the joints and identify which tissues are providing which moments, we model our foot orthoses and understand how their design influences the external moments acting via the foot-orthosis interface; if we know what the tissues do and we know what our foot orthoses do, we can predict the tissues which our orthoses may potentially overload.

    We should also understand that the orthosis is only one tool in the load-management strategy and load can be managed by other methods. This is why orthoses may only be required temporarilly. We also must realise that the zone of optimal stress (ZOOS) is dynamic; controlled loading over time will increase the threshold boundaries of the ZOOS. So in the same way that `'too much, too soon" can create injuries in the athete that over-trains, "too much, too soon" can also be applied to foot orthoses and it may be that a gradual, graded approach should be required in terms of the foot orthosis prescription.

    One of the other main problems we have is something I also addressed in the paper you referred to, that the modern podiatrist understands that foot orthoses work by altering kinetics, but we are not prescribing foot orthoses using enough kinetic testing. Tests like supination resistance have scratched the surface, but we need better, more accessible kinetic testing systems.

    Regardless, I'm comfortable that the tissue stress framework can be taught to students, my colleagues and I have been doing it for the last couple of decades.

    I look forward to reading your blogs. Link here to the paper Trevor mentioned: http://www.sportspodiatryinfo.co.uk/wp-content/uploads/2013/09/orthoses2012.pdf
     
  34. drhunt1

    drhunt1 Well-Known Member

    I speculated that the squash player had a barely compensated rear foot varus deformity simply because of her lateral instability. She also, it appears, has a forefoot varus deformity from the pics Simon offered, and finally, because he admitted to that. In my world, that is called a skewfoot deformity. I've seen it before. In fact, I offered pics to show that, and even used my patient in a video with animated overlays to demonstrate this, as well. I also provided you with a lateral plain film x-ray...which is much more than most pundits here ever offer.

    Kevin refuses to engage my simple questions to him. Like I wrote above, perhaps because he has placed me on ignore again, or he is just refusing to answer the question. Either way...tsk, tsk.

    One of the problems as I perceive it, is that the orthos and many biomechanics "gurus" here believe that the problems created in the knee are purely a frontal, (coronal), plane problem...it is not, and that's what my new research is aimed to show.

    If the STJ is maximally everted at mid/static stance, then the patient cannot compensate to resist supinatory forces, ie., irregular terrain or forces applied to the subject from above in closed kinetic chain. In your study, 3 degrees is sufficient, IMO, to accomplish this task. As I produce the necessary videos that demonstrate the cause of all of this, I will make them available.
     
  35. Jeff Root

    Jeff Root Well-Known Member

    So what if my device using the Root approach and Simon's device using the Tissue Stress approach both feel equally good to the patient? Simon contends his device produces a greater external STJ pronation moment but we can't measure this nor can we observe any difference in function because the patient is already and their eversion end ROM. As a result, all we can do is debate about which approach might be better based on theory.

    In the case of the patient I posted pictures of, I made two pairs of orthoses off of the same positive cast. The first pair was manufactured with the heel corrected to vertical, the ff varus intrinsically corrected, minimal medial arch fill, an 18mm heel cup and a flat rearfoot post. The second pair was manufactured by with the heel five degrees inverted and had a 3mm medial heel skive added to it. All other Rx variables were the same.

    The patient felt that the first device (with vertical heel) was more comfortable than the second device (with heel inverted and medial heel skive). Had I not made two pairs of orthoses, the patient would not have had the ability to compare them. And had the only device manufactured been the one with the inverted heel and the medial heel skive , the patient would have had to try to wear them or I would have had to modify them to reduce the external supination moments from the device. Based on his gross pronation, my tissue stress based device would seem to be most logical because it should produce a greater external supination moment. But in actuality, it was less comfortable because it produced too much supination moment. So if more pronation moment is theoretically better in Simon's patient with lateral ankle instability, then why is more supination moment not better in my patient with sever medial ankle instability? I'm not attempting to use my experience here to discredit the TS approach, but it does demonstrate a point.

    Jeff
     
  36. Depends where they were uncomfortable. If you are trying to push too hard in the medial longitudinal arch area where the STJ axis envelope is, then you are likely exerting too much compression since by pushing directly into the axis, all we get is compression. Try adding more arch filll or using a stiffer material medial to the axis ending roughly 10mm from it with a more compliant material lateral to the axis forming the rest of the shell. Also you can generally use a more compliant shell, but employ a medial oblique rearfoot stabilizer, also drop the heel cup height on the medial side a little as this will act as a rib stiffening the medial longitudinal arch of the device. Lots of ways to differentially change foot orthosis stiffness to pull the high forces where you want them to be and not where you don't. These are just a few examples. Perhaps it is your lack of experience in designing foot orthoses using a tissue stress approach that resulted in a lack of comfort? Where did he find them uncomfortable?

    It was clear from the pictures you posted there was an awful lot of blanching in the skin of the heel- what do you think was causing this?
     
  37. Jeff:

    I have had plenty of failures with custom orthoses designed using my understanding of subtalar joint (STJ) axis location and rotational equilibrium and using the concepts of Tissue Stress Theory. However, the successes I have had with this approach far outweigh the failures I have had with this approach. Designing foot orthoses with the goal to reduce the pathological internal forces which are causing the pathology rather than designing foot orthoses to "hold the STJ in neutral position" or to "prevent abnormal compensation", as I was taught as a podiatry student, certainly seems more biomechanically logical to me.

    I don' t believe there is one best approach to prescribing foot orthoses, but I do believe the Tissue Stress Approach gives us much greater ability to design orthoses with the correct prescription variables necessary for success with orthosis treatment. Treat the patient to get rid of their symptoms with foot orthoses and, if at first you don't succeed, then adjust the orthoses until the symptoms improve or are eliminated, without causing any other symptoms. Seems like a logical approach to me, and one that has served me well for 30 years and over 15,000 patients that I've made foot orthoses for during that time.
     
  38. ~Sorry mistake in there, it should read:

    So lets say we design an orthosis to reduce the stress in a tissue which provides internal supination moment by introducing a foot orthoses with provides additional external supination moment, in so doing we will have increased the stress in the tissues which provides internal pronation moment. How do we know if the additional stress on the tissues that provides internal pronation moment is too much?
     
  39. efuller

    efuller MVP

    With the tissue stress approach to orthotic design, you know where you are trying to increase force and where you are trying to reduce force. I had a patient who had lateral instability and I made an orthosis that tried to increase force on the lateral forefoot. She came back and she said they were uncomfortable, because there was too much force under the lateral forefoot. Another example, I had a patient with sinus tarsi syndrome and a significant genu varum. To treat the foot, I wanted to shift the center of pressure under the foot more medially. Looking up the leg to the knee, shifting the center of pressure more medially would tend to increase compression of the medial compartment of the knee. His knee started to hurt. Going back and forth we eventually got to the point where he would tape a coin under the medial side of the rearfoot post when his foot hurt and take it out when his knee hurt.

    This is an advantage of the tissue strress approach. You know where you are trying to push. If you do a mechanical anaysis you can predict what will go wrong if you push too far.

    Eric
     
  40. efuller

    efuller MVP

    You do point out a problem from learning from orthoses. You have to make more than one to compare. As Simon pointed out, you did two things to this device, you added a medial heel skive and inverted it. Would you be willing to make a device with just the medial heel skive added?

    As I pointed out in an earlier post, we know where we are pushing with the tissue stress approach. As Simon pointed out when you push, with a higher arch, you may not be getting the effect you want because the push is directly underneath the STJ axis.

    Eric
     
Loading...
Thread Status:
Not open for further replies.

Share This Page