Are Static Measurements Of Foot Morphology Necessary To Create Custom Foot Orthoses

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From Podiatry Today:
Are Static Measurements Of Foot Morphology Necessary To Create Custom Foot Orthoses

Point-Counterpoint: Robert D. Phillips, DPM vs Eric Fuller, DPM

 

Same old stuff again

My response to Jeff

Jeff, Thanks for your comments. You seem to be criticizing my maximum eversion height measurement when you said: "Subtalar joint pronation occurs in conjunction with internal rotation of the lower leg. Advocating a method of assessing heel eversion (i.e. STJ pronation) in stance that does not involve internally rotating the lower leg seems completely illogical since the heel will potentially evert farther if the lower leg is allowed to internally rotate." When I ask patients to use their muscles to evert their foot, the leg will internally rotate. There is no problem with this. We both agree that you should not attempt to evert the entire foot farther than it can go. My measurement is looking directly at how much eversion range of motion there is in stance. Using the calcaneal bisection to assess for eversion is fraught with problems. There is the problem of inaccuracy of the bisection itself. There is the problem of skin movement that occurs more in some people than others upon weight bearing. There is the problem of only looking at the heel and not the range of motion available of the forefoot. The heel cup of the orthotic is not as important as how much intrinsic forefoot valgus post there is in determining whether or not the orthotic will attempt to evert the STJ and MTJ farther than their available range of motion.

There is more than one way to determine the amount of intrinsic forefoot valgus post there is in a cast that will be used to make an orthotic. When you place a nail in the plantar surface of the fifth metatarsal head of a cast, the amount of height that nail sticks out of the cast will determine the number of decrees that a heel bisection is everted. You don't have to look at the heel bisection, you could just look at the height. When you perform the maximum eversion height measurement you know the maximum height the nail can stick out of the cast without attempting to evert the foot farther than it can go. You don't need to use heel bisection to determine how much forefoot valgus wedge you have put in your orthotic. Wedge can be measured in height as well as degrees. The maximum eversion height is a better measure than using the heel bisection because it measures, directly, what you want to measure. If you are worried about attempting to evert the foot farther than it can go you should look directly at how far it can go when standing. You should also look directly at how far the orthotic will attempt to evert the foot. Looking at the nail height does that.

Jeff, you asked, without measurement how can we determine whether or not a sub talar joint in pronated, neutral or supinated. In response, I ask you why do we need to know this. I once took 30 aysmptomatic podiatry students and assessed their STJ position in stance. All of them stood more pronated than neutral position. The asymptomatic feet looked very similar in distribution when compared to my patient's feet. Not standing in neutral position has nothing to do with pathology in the foot. Why do we need to know about neutral position? We can learn what we need to know about the foot without making heel and leg bisections. It is about time we get away from the magical thinking that making an orthotic from a cast that was inverted one degree will cause the foot to be one degree inverrted when standing on the orthotic made from that cast. The argument that patients got better when heel bisections were used is not a good one. They got better in spite of heel bisections being used. Orthotics work and we have different explanations of why they work.

When you ask neutral position proponents how an orthotic works you tend to get two different answers and neither of them make much sense. One is that casting the foot in neutral position will tend to make the foot move toward neutral position when the foot is on top of an orthotic made from that cast. If you feel that the heel bisection of the cast is important in moving the STJ toward neutral position then you should not balance it vertical when neutral position is not vertical. The vast majority of people are not vertical when they are in neutral position. It doesn't make sense. The other common explanation of how orthotics work is that it supports the deformity. But, the deformity is measured in neutral position and when the foot stands in a position pronated from neutral the increased range of motion of the MTJ will cause a change in the forefoot to rearfoot relationship. So, when a foot stands pronated from neutral its forefoot to rearfoot relationship is not what it was in neutral position. How, does an orthotic made from a neutral position cast support the deformity? I believe we should move to more of an engineering approach to how orthotics work. We can model anatomical structures and design the orthotic to reduce load on those anatomical structures. It's more about the force on anatomical structues and less about the position that they are in.

Eric Fuller, DPM