Robert D Phillips, DPM gives a simplified approach to analyzing why an orthotic is not working for the patient, by breaking it down into 4 steps. The important thing to remember is that the steps have to be taken in the proper order. Once an issue has been identified for the patient, then solutions to solving that issue are given. The viewer of the lecture will find many ways to increase by simple means the number of patients who are satisfied with orthotic therapy.
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Robert Phillips, DPM
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Dr. Daryl Phillips: Hello, I'm Daryl Phillips, and I practice Podiatric Medicine full-time at the Orlando Veterans Administration Medical Center in Orlando Florida. One of the big problems of everyday clinical practice is the custom-made orthotic that is not working for your patient. It makes little sense to go through the process and incurring the cost of making such an orthotic if it is uncomfortable to wear, or if it doesn't make the patient feel better. In either case the patient will probably not continue to wear such an orthotic. And in essence money has been wasted.
This lecture will give you the busy clinician some additional tools to solve many of the problems your patient is having with orthotics and improve your success rate. My disclosure is that I own a computer program called CoM'nalysis which I wrote to calculate the vertical movement of the center of body mass using [Indiscernible] [0:01:06] graphic data. It is currently licensed and sold by Tekscan, Inc. of Boston Massachusetts.
This lecture has no relationship to my interests. This lecture breaks down four basic steps in diagnosing and solving various orthotic problems. At the end of the lecture you'll be able to follow these steps in their proper order and give examples of solutions within each step. Fortunately when we prescribe orthotics there are great many things we still cannot measure, therefore it is important that we disclose to our patients the fact that we estimate many of the prescription variables, and there is usually a period of time in which adjustments may need to be made to that prescription to get the results that are desired. Proper patient expectations are therefore essential to achieving success.
It is important for you the clinician to remember that you are not selling the orthotic product but you are selling the service that will allow the product to do what it is intended. For this reason a good biomechanical practitioner will have a space in the office where minor orthotic adjustments can be made. There are several reasons that patients do not continue to wear their orthotics. The four major ones are: the orthotics aren’t comfortable to wear; I have found over the years that very little braking time is needed for good orthotics. If my patient cannot wear their orthotics comfortably all day within one week I start looking for reasons why. The orthotics do not relieve the symptoms for which they were prescribed. The orthotics are creating new symptoms. The orthotics do not work with the shoes that the patient wants to wear.
Complexity of orthotic therapy it is extremely frustrating to the clinician to try to remember all the variables that may produce problems. Therefore I've developed a four-step algorithm that if followed in this order solves the vast majority of the orthotic problems. These steps in the proper order are: first, ensure the orthotic has the proper shape; if this is not correct, trying to fix any of the other things will most likely meet with failure. Second, ensure that the orthotic has the proper balance; these are extrinsic things that are done to tilt the orthotic. Third, ensure that the orthotic has the proper flexibility properties. And forth, ensure that the orthotic is functioning well inside the shoe.
We will now consider each of these. The item to assess is whether the orthotic has the proper shape. It is important to remember that the orthotic is nothing more than a complex curved material that pushes up against the bottom of the foot. In order for it to push up against the bottom of the foot, it has to make contact with the bottom of the foot. Most of the orthotics we make are intended to push the foot to its neutral position. Therefore if you want the foot to be in neutral position when the patient stands on the orthotic, the orthotic must have the shape of the neutral foot.
It is for this reason that the non-weightbearing casting technique was developed to capture the shape of the neutral foot when there was no compression on any of the soft tissues. Weight-bearing or semi weight-bearing casting techniques compress soft tissues especially under the heel pad and metatarsal heads. If these pads are compressed, you decrease the likelihood of capturing the full height of the arch.
When I begin the process of evaluating the orthotic shape, I place the patient's foot in its neutral casting position with the patient sitting in the supine position. I put my thumb against the fourth and fifth metatarsal heads and gently dorsiflex until I meet a very gentle resistance. I then place the orthotic against the plantar surface of the foot with the top surface of the orthotic barely touching the skin surface, making sure that there is no pressure between the skin surface and the orthotic.
I want to see total contact with the plantar surface of the foot with the following exceptions. Number one, a very mild gapping, a maximum of 1 cm of the orthotic from the medial arch that is medial to the medial slip of plantar fascia. Number two, if the patient has a forefoot varus, a gap of the orthotic from just the first metatarsal head, this gapping should be about 1 mm for every degree of forefoot varus. Number three, if the patient has a forefoot valgus, a gap of the orthotic from the fifth metatarsal head.
It should be noted that there should be no gapping from the fifth metatarsal shaft. One important place that there should not be any gapping even a very slight gap is under the calcaneocuboid joint. If you see even a very small gap then the orthotic is going to allow the calcaneal inclination angle to fall, which means that the patient will pronate on the orthotic. The place to check for gapping is under the sustentaculum tali, because the orthotic is responsible for supporting the calcaneal inclination angle on the medial side as well as the lateral side. If the orthotic gap is here the patient will pronate on the orthotic.
Pronation on the orthotic is one of the most common causes of arch pain when the orthotic is worn. Another area to check for gapping is under the central metatarsal heads. A common error that some labs make for a patient with the plantarflexed first metatarsal is to fill the dell between the first and fifth metatarsal heads with plaster. For ease of illustration I've placed an orthotic against the original mold of the foot where it does not make adequate contact with the second, third, and fourth metatarsal heads. If this happens then the orthotic does not allow the first metatarsal head to sit in its neutral position of being plantar flexed relative to the second metatarsal head.
The first metatarsal will tend to dorsiflex, and the foot may pronated. It will also decrease the propulsion and may cause the second metatarsal to plantar flex. Here we see an orthotic that was made over pronated cast of the foot. Note that the orthotic has significant gapping from the medial column of the foot. However, when I placed the subtalar joint in its fully pronated position, the orthotic fits much closer. This tells me that the original cast was taken with the subtalar joint pronated, and it also means that the orthotic cannot push the foot out of its fully pronated position when the patient stands on it.
Unfortunately, the only thing you can do is apologize to the patient that there was an error in the casting and that you will have to take a whole new cast of the patient's foot. We see another very badly fitting orthotic. Note the large gap in between the orthotic and the neutral foot. Normally there should be total contact with the middle and lateral slips of the plantar fascia, the entire length of the orthotic, and gapping from the medial slip only if there is bowstringing of the plantar fascia and the hallux is dorsiflexed.
If the gapping is very mild I may be able to fix it enough by spot heating and reforming the device, but many times it's easier to recast the patient. You should never see gapping between all of the metatarsal heads and the anterior edge of the orthotic. If you do, the patient is probably complaining of pain across the mid-arch. If the gapping is very mild, say less than a quarter inch, you may be able to make the patient comfortable by adding felt on top of the orthotic to fill in the gapping. However, most of the time you need to recast the patient. [Indiscernible] [0:09:14] the orthotic just from the first metatarsal head is acceptable only if the orthotic was intrinsically posted for forefoot varus.
A general rule of thumb I use is to allow for about 2 mm of gapping for every 3-degrees a forefoot varus. If you see more than this then it is most likely that the original cast was taken with the long axis of the midtarsal joint supinated which would result in the patient complaining that the arch feels too high.
One way to fix mild cases of this problem is to heat the medial arch and lower it, and then to add additional felt on top of the orthotic under the lateral metatarsals to evert the forefoot to the rear foot. Moderate or severe gapping should be corrected by recasting the foot, and the fifth metatarsal head should be seen only if the laboratory has intrinsically corrected for a forefoot valgus deformity.
Again the same rule of about 2 mm for every 3-degrees of forefoot valgus is a good rule of thumb. If you see more than this, then you can usually assume that the casting was made with the subtalar joint pronated. Usually the best solution is to recast the patient. [Indiscernible] [0:10:20] complaining of arch pain, ask them if they feel it more as they come down on the orthotic or as they start to push forward with the orthotic. If they tell you that it is more as they start to push forward, the most likely cause is irritation of the medial band of the plantar fascia by the orthotic.
Test for this by holding the orthotic lightly against the bottom of the foot with the subtalar joint neutral, and then dorsiflex the first metatarsophalangeal joint. If the plantar fascial band bowstrings and pushes the orthotic away from the foot, then you know that the cause is plantar fascial band irritation. Mark on the orthotic the place where the plantar fascial band makes contact. If there is only a few millimeters of bowstringing, and if the orthotic material is cork or a homogenous plastic such as polypropylene or acrylic, then you can use a small Dremel sander to carve a groove into the top surface of the orthotic for the plantar fascial band.
If the bowstring is greater than the thickness of the orthotic, or if you are dealing with a fiber composite material you will have to reorder the orthotic made with the plantar fascial band accommodation built into the cast over which the orthotic was pressed. If you are satisfied with the shape of the orthotic then the next item to check on the list is what I call the orthotic balancing. These are extrinsic additions or modifications made to the orthotic that change the tilt or rocking of the orthotic.
There are many aspects of orthotic balancing which can make a big difference in how the orthotic feels and functions. The first balancing property I check is for inversion and eversion stability. To do this, I set the orthotic on a flat surface and see if the anterior edge of the orthotic shows the medial anterior corner, and the lateral anterior corner touching the ground. At no time do I accept an orthotic that does not show these corners touch the ground simultaneously.
If I see any gapping, even a millimeter, I know that the orthotic is unstable. I can usually fix this in the office with a small filler with cork or crepe to prevent rocking on the center of the anterior edge. You will be surprised that the way that eliminating just a very tiny bit of rocking makes the orthotic feel so much better. I next check the heel post for any abnormal valgus rocking. With the orthotic sitting on a flat surface the medial side of the heel post should be flat on the ground. If it is not, then when you push down on the medial side of the heel cup you'll see the orthotic valgus rock, and the lateral anterior corner lift from the ground.
This may be the cause of the person pronating on the orthotic inside the shoe. If you see this valgus rocking of the heel post, I advise that you use a small piece of cork to fill in this gap so that the orthotic cannot valgus rock when pressure is concentrated down on the medial side of the heel seat. Again I emphasize that if the patient is complaining of arch pain with the orthotic, and you are satisfied with its shape, then the next place I look is for signs if the patient is pronating on the orthotic.
An important place to look is inside the shoe. I've pulled the insoles out of the shoe for ease of illustrating the indent pattern that the orthotic makes at the anterior edge and also the heel post indent pattern. You can usually feel this with your fingers easier than you can see it. The indent pattern on the anterior edge should be even on the lateral and medial corners. Likewise the indent pattern of the heel post should be even on the medial and lateral sides. If the medial corner has a deeper indent than the lateral corner, then you can conclude that the patient is pronating excessively.
An easy way to fix a patient pronating on the orthotic is to add a forefoot varus wedge under the anterior edge of the orthotic. It is sometimes amazing how often just the various wedge makes the orthotic feel so much better. Here a 1/8th inch cork wedge is added which inverts the entire orthotic. Note that I also had to add a small wedge under the medial side of the heel post to prevent the orthotic from valgus rocking on the heel post. [Indiscernible] [0:14:36] look for while the orthotic is sitting on a flat surface is whether the lowest point of the heel seat is in the middle of the orthotic. If it is slightly offset medially then there is a high probability that the orthotic is not providing enough supination torque against the rear foot, and the foot will pronate.
This is an example of an orthotic that the point of contact of the heel cup is slightly medial to the center of the heel cup. When I push down in the center of the heel cup I see the medial anterior edge rise off the ground. I will fix this by adding a small amount of cork under the anterior medial edge to fill this gap at an orthotic pushing against the bottom of the foot, remember that at each point the orthotic pushes perpendicular to the tangent line at that point.
Here you see various points across the heel cup in the direction they push. Heel cup hype can be used to also change the pronation or supination torques on the heel. If you see the foot sliding laterally during stance or gait, you can decrease the height of the heel cup on the medial side. If you see the foot pronating, you may increase the supination force by decreasing the lateral heel cup height.
Heel post motion can play a very important part of whether your orthotic is working well. The average person should have 4-degrees of varus rock when you push down on the lateral side of the heel post. However if the patient has a high amount of transverse plane movement of the foot, you may need less than 4-degrees at motion. If the patient has a high degree of frontal plane motion of the foot, you may need more than 4-degrees at motion. The general rule I use is if the patient starts having knee symptoms within a short time after starting to wear their orthotic, I know I need either more or less heel post motion.
For a normal foot the center of the bottom of the heel should be in line with the center of the leg. However in some people the center of the heel may be medial or lateral to the center of the leg. If the heel is medial then the force of the ground will try to invert the heel; if the deal is lateral then the force of the ground will try to evert the heel. A goal of orthotic therapy is to produce equal inversion and eversion forces on the heel.
Normally the center of force should be under the center of the heel. However if the patient has a laterally displaced calcaneus, then I want to create an orthotic such that the center of the bottom of the heel is under the center of the leg. For mild cases I order the heel post layered medially.
Here on the right I've made this adjustment myself. For mild cases of the heel being displaced medially, I need to flare the heel post laterally. For severe cases of medially or laterally displaced calcaneus, you can shift the center of force more by flaring the soles of the shoes.
When you are satisfied that you've done everything possible to solve the balancing and posting, the next thing to consider is flexibility properties of the orthotic. Again it is important to remember that an orthotic has to generate an upward force in order to generate an effect on the foot. In order to understand that upward force we will need to first review what we know about material stress and strain.
All orthotics are made from some type of material that has a specific stress-strain curve. In engineering this is represented on a graph where strain or deformation is put on the x-axis and the stress or force is put on the y-axis. The more stress that is applied the more the material deforms. As long as the material stays in its elastic region, the material will return to its original shape when the stress is removed. If the material is deformed beyond its yield point, it enters its plastic region where it stays deformed after the stress is removed.
Now, for materials like concrete there is very little strain for a lot of stress. However for a rubber band there is a lot of strain for a small amount of stress. No matter what material you are dealing with, the slope of the stress-strain curve is called Young's modulus of elasticity. By knowing Young's modulus, if you know the amount of stress being put on the orthotic you know how much it is bending; and if you know how much it is bending you know how much force it is supporting at that point.
This is a typical graph of the total force under the foot during the stance phase of gait. Note the two peaks of force at the end of contact and also in propulsion. I have also plotted the amount of force that is being placed on top of the orthotic. When we take a neutral shape orthotic it is only in that neutral shape when there is no force being exerted on it. During contact phase we want the foot to pronate about 4-degrees. The force on the top of the orthotic reaches about 120% body weight, and so we want the orthotic to deform to the shape of the foot that it has at 4-degrees of pronation.
During midstance the force on the top of the orthotic starts decreasing, and we want the orthotic to rebound toward the neutral shape. Remember that the subtalar joint should reach its neutral shape at the moment the heel comes off the ground.
Some important principles about materials that you need to remember. First, the flexibility of the material is proportional to the cube of its length. Remember that an orthotic is like a bridge supported at each end. This means that if you double the length of an orthotic it will be eight times more flexible. If you decrease the length of an orthotic by 25% you will double its rigidity. You will quickly appreciate that an orthotic made for a person with a size-12 foot which is only 1 inch longer than a size 9 foot will be much more flexible.
Of course you can make an orthotic more rigid by increasing its thickness. Just as flexibility increases by the cube of the length so rigidity increases by the cube of the thickness. This means that an orthotic that is 4 mm thick will be eight times more rigid than an orthotic that is 2 mm thick; and an orthotic that is 5 mm there will be two times more rigid than an orthotic that is 4 mm thick.
My experiences been that a great many orthotics that aren’t working properly in that [Indiscernible] [0:21:26] actually too flexible. I often look for this by putting the orthotic on the floor and ask the patient to stand on the orthotic. I feel the height of the arch on the medial and lateral sides just before the patient stands on it. When the patient stands on the orthotic I then feel how much the orthotic bends. If I feel it flex a lot I will often try to stiffen the orthotic. The most common way I stiffen an orthotic is to add extra material under the orthotic between the heel post and the anterior edge.
If I want just a little bit of stiffening I will use a soft material like PORON. If I want a moderate amount of stiffening I’ll use a material like cork or crepe. You'll be surprised at how just 1/8 inch of material addition will increase the stiffness of the orthotic. And most of the time the patient will tell you that it feels more comfortable. Stiffness of the orthotic is not only determined by the length and thickness of the material but also by the curvature of the material. The greater the curvature of the material the stiffer it is. And if you want to make it stiffer yet, put a curve in both the longitudinal and transverse directions.
One quickly appreciates that an orthotic fit to a low arched foot will be much more flexible than an orthotic fit to a high arched foot. So take that into consideration when prescribing the orthotic. A higher arched foot will probably need an orthotic made from a thinner material and a low arched foot will need an orthotic made from a thicker material. [Indiscernible] [0:22:59] orthotics show the medial side has a higher curvature than the lateral side. This means that the lateral side of the orthotic will flex easier than the medial side of the orthotic.
If the patient is collapsing the lateral side of the orthotic too much, you may observe the patient rolling lateral-ward, or the patient may feel peroneal symptoms along the lateral side of the foot, or they may feel that the arch is too high. You can increase the stiffness of the orthotic just under the lateral side by adding a reinforcer under the lateral side of the orthotic. You'll find that the patient not only feels more balanced when walking but that the arch doesn't feel as high.
Things to remember is that orthotics not only flex but they also twist. When the front part of the orthotic inverts to the rear part of the orthotic, it allows the rear foot to pronate which will bring the arch of the foot down against the medial arch of the orthotic. You'll find that this is a bigger problem in orthotic materials that have fibers such as TL-2100, polycarbonate, and DBX6. The ways I've found to increase the torsional stiffness of orthotics is to increase the length of the heel post along the medial side of the orthotic.
Notice that I've made this addition with a small piece of cork that is about 1 to 2 cm long that I smoothed out to blend in with the heel post in the plastic material. [Indiscernible] [0:24:27] risers can produce areas where the patient feels excessive pressure points. A stress riser occurs at a point where there is a sudden change in the flexibility of the orthotic. For example, at the anterior edge of the heel post. The patient may complain of pressure or even pain at the proximal area of the arch.
The solution to this problem is to bevel the anterior edge so that the change in the thickness at the distal edge of the heel post is more gradual. After you have addressed the shape, the balancing, and the flexibility properties of the orthotic, the final step is to address the fit of the orthotic inside the shoe. This can be one of the toughest issues because patients don't always wear the shoes we want them to wear.
Sometimes the issue is a work-related constraint on the patient, sometimes there are economic constraints, and sometimes there are just personal preferences that have to do with self-image and tastes. Diplomacy can be very delicate at times as you the practitioner must become a very close listener to what the patient says about their shoe needs, their desires, and constraints.
When the patient comes to the office I make a point of looking at the shoes they're wearing. You need to question them about the styles of shoes they wear most of the time. You may also asked them whether they would be resistant to any suggestions that you may make about the type of shoe they wear. My personal opinion is that it is very inconsiderate for a physician to demand a patient toss away all their current shoes. And most of the time the patient will respond by tossing away the orthotics before they switch styles of shoes. I would rather have a patient who needs orthotics wear an orthotic that is doing half the job than to have them wear no orthotic at all.
This is a picture of some of the many styles of shoes that I have successfully fit orthotics in. The important things to teach your patient no matter what type of shoe they wear, is they need to pick a shoe made on the proper shape [Indiscernible] [0:26:26]. If a person with an adducted forefoot type wears a straight-last shoe they will pronate off the orthotic. Note that a sign of this is the orthotic sliding medially in the shoe.
If the person with a straight forefoot type wears an adducted shoe, the patient will push the upper of the shoe laterally. I teach my patients proper last selection by having them sit and place their foot lightly on a piece of paper with the subtalar joint in neutral position. I trace the shape of their foot and then mark on the drawing two lines, the first bisecting the rear foot to the center of the arch, and the second from the end of the second toe back to the center of the arch.
I show the angle that this makes. I then turn the shoes over and make the same two lines bisecting the center of the rear foot to the center of the arch, and from the end of the second toe to the center of the arch. The angle on the bottom of the shoe and the angle that I drew on the tracing of the shoe should match. I give the drawing of the foot to the patient and tell them to take it with them when they buy shoes to get the shoe made on the right last.
Those of you who have patients who like to wear sandals, this is no longer a problem. I personally wear sandals here in Florida when I am outside. The key is to find a sandal that has a small lip around the back that the heel post can sit against. I personally find this type of sandal in my local sports shop. There are also a wide selection of dress sandals that have removable foot beds that can be replaced with orthotics.
If a person has a sandal that has no back on it, I will put Velcro on the bottom of the heel post and on the sandal to prevent it from sliding when the patient wears it. The simple fact is that your orthotic and the foot must be able to get into the shoe. Don't be afraid to cut the orthotic down to fit the width of the shoe in the forefoot. When you decrease the width of the orthotic in the anterior aspect, always cut it from the medial side. Remember that the first [Indiscernible] [0:28:49] has to be able to move up and down, so it's okay if the orthotic doesn't come all the way medial under the first metatarsal.
The two basic causes of the patient's heel slipping up and down in the shoe when they wear their orthotics. The first is that the orthotic is too wide for the heel counter of the shoe, and it pushes the sides of the counter outward away from the patient's heel. The second is that the orthotic is pushing the foot forward away from the back of the counter. In the first case cut the heel cup of the orthotic down until it fits easily inside the shoe. You also need to cut the orthotic heel cup down so that fits easily all the way back into the heel counter of the shoe.
When I tilt the shoe backward I should see the orthotic slide all the way back to the back of the shoe. If it doesn't, then there is a high likelihood that the patient will be complaining that the shoe is sliding up and down on their heel when they wear their orthotics.
In summary I've covered some things that can fix a great many of the orthotic problems that you will encounter. Orthotic work is like any other skill – the more you do the better you get at it. Your attitude about it will determine your patient's attitude. If you demonstrate a humble yet eager to please attitude with your patient, your patient will probably be very cooperative in working with you until you are both satisfied.
I have never learned anything when the patient states that they are 100% satisfied the moment they put the orthotic on. It is only in the solving of patient dissatisfactions that I've learned more about how orthotics function. As I tell patients, orthotic work is the hardest thing I do; yet it is the most rewarding experience when you do solve a difficult problem. I wish you many great successes as you prescribe and follow your patients who may benefit from wearing orthotics. If any of you have any questions, please feel free to contact me.