Direct Mechanical vs. Neuromotor Effects of Foot Orthoses

Graham:

Alas, the intoxicating effects of my personality.....and my orthoses....do eventually wear off so I seriously doubt that the patient would be so numbed in the weeks, months and years after receiving my orthoses that they would not be able to feel any eventual symptoms that may result.


Also, I didn't know that in-shoe pressure analysis was able to predict injury....I suppose I missed that important piece of research also.....I'm waiting again for you to provide to me with the reference for this research so I can learn of the amazing predictive values of in-shoe pressure analysis....again....I won't hold my breath.:drinks

 

Kevin,

A

It can't predict but it at least demonstrates the possibility of less harm than blindly administering a device based on assumptional theory.

Kevin, you are fully aware of the research done using In-Shoe force measurement and the theoretical development of Sagittal plane facilitation both by Howard and Craig. None of which has professed to predict anything, merely to demonstrate the effect of a foot orthoses on observed multiple gait parameters.

This is how the theory was developed. In-shoe observations of "conventional" devices did not result in improved function. oce a device was made to improve function it could not be explained using conventional "wisdom" unlike your theories, which profess to predict improvement of function based on theoretical application without testing pre and post orthoses in shoe.

After all, this is where the action is!

I have attached an article I wrote many moons ago for a prosthetics & Orthotics magazine for you assassination.

Regards,

 

Lawrence,

Changes in foot function brought about by changes in neuromuscular function changes gait parameters and thus may reduce/increase the control/facilitation for which the orthotic should be designed.

For instance, lowering an arch height or adding a heel lift or softening a shell for a subject with ankle equinus would not be necessary if you first performed a manipulation of the ankle and resolved the equinus. Also, when treating equinus, one of the "side effects" is a return to normal facilitation of the peroneals, leading to a foot that is far less inverted. This would require a change in the orthotic Rx as well. In addition, the use of foot manipulation prior to orthotic casting does make for a far less rigid structure and one that is much easier to cast in the appropriate position.

On a different note, and joining the "friendly" discussion between Graham and Kevin, the use of in-shoe pressure testing does change the way in which orthotics are fabricated. With "eyeball" technique, by the time changes are visible in function from an orthotic post, there is a high likelihood of overcorrection. Over my many years using F-scan, I have been amazed as to the limited amounts of correction with orthotic posts/material hardness/additional functional adaptions necessary to accomplish the effect I used to think needed high amounts of posting. My outcomes have definitely improved (and I have published these in the past) as a result. I do use the F-scan less that before as my experience has allowed me to determine what it usually required. There are, however, the unusual patient with some strange deformation either congenital or due to trauma where predicting what the orthotic device will accomplish is simply too difficult to determine without an objective method of analysis. In these cases, F-scan and similar devices are extremely valuable.

Howard

 

Dear Kevin
As stated in another rather heated forum I use pressure plates as one of the biomechanical tools used to evaluate the postural effects of orthotics. I have come across a similar problem to the one you describe above...
"What I did say was that Dr. Blake and I, including many others who have used inverted orthoses for many years, have noticed that inverted foot orthoses may actually cause increased STJ pronation motion, especially in the late midstance phase of walking gait, if the inversion correction is too great and causes STJ supination instability. The point of making this comment was to emphasize that we must be very careful when discussing the kinematic effects of foot orthoses on the rearfoot and/or tibia in that we are very specific as to when the rearfoot/tibial motion is occurring within the stance phase of either the running"

IMHO I think this is because the first ray has been lifted of the floor and in late stance phase the foot will pronate to get this proprioceptive and propulsive met on the deck.
Clinically I will use more midfoot support ,less rearfoot support and perhaps a mortons extension to the end of the first toe. All acheived effortlessly using Neil Smiths "casting Machine"
Kind Regards
Gavin Johnston

 

How does ankle manipulation improve ankle RoM? By a mechanical or neurological effect?

If I get the patient to stretch their calves that changes the Rx because the calves are either longer or more elastic. Thats a mechanical effect, no?

How does the observation that there is neurological control of gait and that orthotics may have neuro input , change my orthotic prescription? In any other way apart from "it means you need to prescribe...less"?

 

Hi Everyone

The discussion over mechanical vs neuromotor effects of FOs is great to read. My interest lies more towards the impact of FOs on postural stability and lower limb muscle measurements. However the impact of manipulation as an alternative or working in conjunction with FOs is iteresting.

Does anyone know of any research relating to manipulation with or without FOs on the mechanical/neuromotor effects? If there is limited research, like many issues with podiatry, could this be the bases for future research and funding?

 

Lawrence,

Manipulation has a dual effect. It can increase ROM of the ankle joint itself, as well as create a facilitation to the peroneal muscles. Neither stretching or surgical gastrox lengthening has this dual outcome. In fact, if someone has a restricted ankle joint, and motion is simply not available...then I am not so sure that stretching is even beneficial. Are you really lengthening the Achilles tendon and associated muscles, or simply stressing the joint capsule of the ankle? This is not to say that stretching is not important, its just that when restriction is present, manually releasing it and then stretching has led to far better outcomes in my experience.

As far as orthotic Rx is concerned, if you are treating a patient with equinus, but a rigid device is not tolerable, then you will need some type of accommodation to allow this patient to wear them. This may mean adding heel lifts, softening the shell, decreasing the posts, etc. If however, you initially manipulate their ankles and resolve the equinus, the type of device you ultimately prescribe will not need to accommodate the equinus....

Alternatively, if you have a patient with equinus, but the issue with which they present is chronic inversion type sprains, this may very well be a direct result of chronic peroneal inhibition. You will need a lot less valgus posting and deep heel cupping for this patient if manipulation is performed, and peroneal inhibition is successfully facililtated and normal strength returns.

Howard

 

This was VERY early on in this thread but I would like to contribute my clinical observations along with the scientific basis of neuromotor changes stemming from the feet. Also, as manipulation benefits have been raised, I could no longer be a passive observer...

Craig, will you accept clinical observation as evidence or does it have to pass through a double blind peer reviewed process to be acceptable? If you are open to the former, try this clinical test:

Have your subject simply walk up and down on the spot for 6 or so steps.
Ask them to stop and extend one arm to horizontal.
Using a gradually increasing force, gently push down on that extended arm and observe the 'quality of response and resistance'.

You are establishing a baseline reference for muscle response of a muscle group involved in gait; (the deltoids with arm swing). This is not about 'strength', it is about quality of response (v. important!)

Now place 1 pencil under the 1st ray and 1 under the 5th ray and ask your subject to place normal weightbearing load on both feet. This will artificially 'sublux' the transverse metatarsal arch and cause aberrant proprioceptive feedback to the brain which will respond in an aberrant response to associated muscles of which the deltoids are one such group.

Repeat the extended arm 'quality of resistance' test. You will notice a weakened or altered quality of resistance due to the altered proprioceptive feedback caused by the pencil 'subluxation' set up.

I believe we can deductively extrapolate that if an artificial 'subluxation set up' can cause an alteration in the neurophysiological response pattern, then orthoses can also cause an alteration in neurophysiological responses. I'm convinced, but I haven't seen a rigorous study conduct this test.

The neurology however, is explained in Enoka's Neuromechanical Basis of Kinesiology (2nd Ed) p142,175.

I am aware of 'fringe' health practitioners who take Kinesiology to the 'nth' degree however, in terms of pure biomechanics and neurophysiological responses, I don't think it's too big a concept to grasp.

What say you?

Ted.


PS Lawrence, this has changed my orthotic prescribing by ensuring a metatarsal dome is built into CFO's to stimulate the proprioceptive feedback from the metatarsal arches when required.

 

Ted - I have no doubt that there are neuromotor effects from foot orthoses - I just remain to be convinced what those effects have to do with how orthotics work (ie how they make patients better).

I am travelling at the moment and have ONE book with me --> the new edition of Enoka! (makes the luggage heavy!)

If a patient has "typical" overuse symptoms, there is only one possible way foot orthoses can work and that is by reducing the forces in the injured tissue. The only way it can do that is via reducing kinetic parameters. For eg if someone has post tib tendon symptoms, then the only way an orthotic can help is by reducing the ankle inversion moment, so the post tib muscle does not have to work as hard. I just do not see how any neuromotor or neuromechanical or neurowhatever effect can reduce that ankle inversion moment.

It is possible that if a pronated foot is "corrected" by a "neuromotor" effect, then the only way that this can happen is via the post tib muscle contracting more (pretty disastrous if the patient has post tib symptoms) or the gluteal muscles externally rotating the limb. In both situations this will lead to increased muscle activity which surely has to be a bad thing? ...and even if the gluteal muscles everted the limb more to "correct" a pronated foot, that is still no guarantee that the ankle inversion moment has been decreased.

 

I don't think the above is a good example, or rather an explanation of the example. Standing on a pencil will not sublux the bones of the foot. It will be very uncomfortable to stand on. When someone pushes down on your outsretced hands your body will tend to rotate forward. To prevet forward rotation you attempt to plantar flex your ankle and shift your center of pressure forwar. If you did this with a pencil under your met heads it would hurt more. Try repeating the "subluxation" with a wide pile of 35 durometer EVA.

On the other hand, I have seen clinical neuromuscular changes that remain after removal of the orthosis for a short period of time. Specifically, a patient at the two week follow up after getting orthosis the patient walke with more resupination with the orthotic in the shoes. Then removed shoes and orthotic and for 2-3 trips up and down the hall the resupination was still present and then the patient reverted back to the more pronated pattern for the subsequent trips up and down the hall while barefoot.

Heck I remember this kind of effect after I got my own orthoses. I remember walking into the bathroom a couple of weeks after getting my orthotics and realizing that I was holding my foot in a more supinated postion and then deciding to relax my foot and noticing that did not feel as good for my then symptomatic 1st mpj.

Cheers,

Eric

 

I agree that increasing posterior tibial muscle activity is a bad thing for someone with posterior tibial dysfunction. However, is so bad for someone with 1st MPJ symptoms? I had one PT dysfunction pateint who came back after she got her orthotics complaining of increased pain. I made her a pair of lower arched devices and her pain resolved. She came back six months later and asked if it would be ok if she wore the high arced ones. I was about to say no, but she told me she already had been wearing them for 3 weeks and she liked them better. And her tendon did not hurt.

Regards,

Eric

 

The reason I see increased muscle activity as bad, is that is probably represents an inefficient gait and will lead to an increased energy consumption --- I just see that as not being a good thing.

 

I agree Craig. I wouldn't want to increase Post Tib activity in a hyper-active/tonic Tibialis Posterior muscle.

What about the under active Tib Post though? Clinically, I have tested for muscle strength in a Tib Post that shows clinical signs of reduced activity at the required phase of gait. The muscle is so strong that I cannot over power it, yet, it is not contributing to the stability of the medial column.

Stimulate the related proprioceptors of the STJ and TNJ with an Activator, and the firing activity of the Tib Post changes noticeably immediately. It is postulated that the mechanosensitive receptors are frequency & speed dependent which might explain why this neuromotor response is more consistently obvious with an Activator rather than a manual manipulation only. The human thrust (200-240ms) cannot get close to the speed and frequency of an Activator (40ms).

Maybe some chiropractors are on to something...?
Keller et al Validation of the Force Frequency Characteristics of the Activator Adjusting Instrument JMPT 22:2 Feb 1999

Eric, you raised the exact point of why I was reluctant to use the 'artificial subluxation' example. The elements the practitioner must use ensure any postural compensation in the test are minimised to avoid your proposed 'forward rotation of the body' and other practitioner induced results. The pencils are not to cause discomfort, only a change in position, otherwise you will induce a nociceptive response which is a whole other neuromotor response pattern. Your EVA idea could be just the thing. Have you tried it?

Our clients/patients regularly regularly report changes in their gait patterns as you described. I'm of the opinion this is a neuromotor change to prescribed & delivered mobilisation/manipulation and Activator application.

Cheers,
Ted.

 

I think this is the key difference in what has been going on in this thread. If this effect happens (or dosen't happen), the kinetic parameters still have to be altered (ie tissue loads) or the patient does not get better. Alteration in kinematic parameters (ie motion) does not imply or mean the kinetic parameters have been reduced. Thats the basis of my argument against the neuro-whatever or sensory effects. I don't deny they happen, I just need to be convinced that the kinetic parameters get lowered via those mechanisms (the post tib eg given above is a simplistic eg).

 

I agree that increased muscle activity can lead to increased inefficiency. However, there can be a trade off with pain or injury avoidance. For example when a foot is injured the preferred movement pathway is to limp. Limping is more energy intensive, but the brain overrides the efficiency concern with the pain avoidance concern. I will bet that the "within the head" efficiency versus pain avoidance equation is not constant. At times efficiency will be more important, at others stress reduction on a particular structure will be more important.

Cheers,

Eric Fuller

 

Ted, I'm not sure of what you are saying. The tendency to rotate forward is a simple problem. Standing with your hands outstretched, your hands will be anterior to the tips of your feet. When you push straight down on the hands and ground reaction force pushes straight upward at the location of center of pressure under the feet, a force couple will be created that will tend to cause the body to rotate forward. I'm not sure what you meant by postural compensations.

Cheers,

Eric

 

I'm sorry Eric, to clarify, do you have the subject's arm stretched out in the sagittal plane? In this case, the hand is certainly anterior to the feet. My test is having the subject's arm stretched out in the frontal plane so that the hand is in the same plane as the COG and no forward motion of the body would be induced. Make sense?

Craig, I agree your attempt to reconcile the kinetic parameters with patients getting better is a very difficult case to empirically demonstrate. I was hoping that my simple example of the hypoactive tib post would clarify my point.

Ol' Einstein said it well (and I guess I didn't) when he said:

Cheers,
Ted