No, it has not been proven that custom devices are better.
By Eric Fuller, DPM

I would like to make it clear that I'm not saying custom orthoses do not work. I believe custom orthoses work very well and I actually wear them. The question is: Are they worth the additional cost when you compare them to over-the-counter (OTC) devices? Custom devices may indeed be worth more than over-the-counter devices, but I think we need to see better outcomes from custom-made orthoses in order to justify this additional cost.

There are many ways to look at the question of whether prefabricated orthoses are better than custom-made devices. I think it's important to examine the theory behind neutral position casting and custom-made orthoses, because that is the rationale docs often use to say why custom orthoses are better than OTC orthoses. Those who argue for custom orthoses usually maintain that you have to hold the foot in a certain position for optimal function. It has never been proven that the foot has to be held in this position while on top of custom orthoses.

I firmly believe that you can modify OTC devices so they work as well as custom-made devices. It is important to note that, in many cases, you should modify OTC devices. I believe orthoses work because of how they alter the forces under the foot. Both custom orthoses and OTC devices can alter the forces under the foot with wedging. A generic OTC device will probably be less effective than one that you modify with wedging.

Additionally, if you use OTC devices, you need to be reimbursed for the time and knowledge that is required to assess whether or not wedging is needed (biomechanical examination), and the time that is required to add the wedging to the OTC device. This cost benefit argument is a tricky one. Sometimes, the trial and error required to determine what is the best wedging may take longer than the manufacture of custom-made orthoses.

While I concede that a custom-made orthosis may produce an effective treatment faster than experimenting with wedging, I don't think this is true all of the time. Remember, custom devices don't always work the first time either. We need to evaluate the protocol for either approach. I believe that a protocol can be devised that will produce a correct formula for adding wedges to OTC devices, and that DPMs will be able to use the same protocol for custom-made as well as OTC devices. I described the protocol that I use in a previous article for Podiatry Today (see "Reinventing Biomechanics" in the December 2000 issue).

Addressing The Assumptions Of Neutral Position Theory

There are two schools of thought in neutral position theory. The first one says we need to hold the foot in neutral position because this is a position of stability. The extension of this theory is that pathology occurs because the foot is not in neutral position. Therefore, according to the theory, you would relieve pain by creating an orthosis from a neutral position cast and then have the foot stand on this orthosis. Yet the proponents of this school of thought admit the foot never does get into neutral position but only moves closer to neutral position.

The second school of thought, under neutral position theory, is that you should provide support for rearfoot deformities or forefoot deformities. You're looking at a rearfoot deformity when the patient is standing in a relaxed position and the subtalar joint neutral position is not vertical. A forefoot deformity occurs when the plane of the metatarsals is not perpendicular to the calcaneal bisection when you place the foot in neutral position, and the midtarsal joints are maximally pronated. In theory, when you provide support for these deformities, you should be able to prevent abnormal compensation.

There are many problems with neutral position theory. In one study, researchers compared the position of the foot during gait to neutral position. They found that 100 percent of this asymptomatic population, in stance and in gait, was in a position more pronated than neutral position. My clinical observations concur with the study's finding that the vast majority of feet stand and walk at or near maximal pronation of the subtalar joint. If you go by neutral position theory, these feet should all be unstable and should all have pathology. The problem with the theory is no one has ever correlated pathology with an absence of standing in neutral position.

It is also questionable as to whether these feet would be better off in neutral position. Keep in mind that most feet, when they're placed in neutral position, will have their first metatarsal off of the ground. Will people be less likely to develop pathology if they walk with their forefoot significantly inverted to the level ground? This does not seem like a position of stability.

Do You Believe In 'Voodoo Biomechanics'?

In neutral position theory, you would take a negative cast of the patient's foot in neutral position. Then you would make a positive cast from the negative cast. The perception is that the orthosis made from this negative cast will put the foot in neutral position or the orthosis will move the heel to the same position that the positive cast was balanced in. This is what I call voodoo biomechanics.

Just because you capture the plantar contour of the arch with a negative cast does not mean that the orthosis will put the joints of the foot in the same position when the foot is on the orthosis. While neutral position theorists think they have captured the osseous relationships with this cast, the reality is there is about an inch of compressible soft tissue between the plantar skin and the bones of the medial arch in most feet. It is usually quite painful to apply a significant amount of force to this tissue as anyone who has spent a significant amount of time on a ladder in soft shoes can tell you.

For this reason, it is doubtful whether pressure in the medial arch is directly and entirely responsible for moving a pronated subtalar joint toward neutral position. Pressure in the medial arch may cause the muscles to work differently so the foot does change position on top of these orthoses. This is probably the major reason that patients need to "break in" newly dispensed orthoses.

Other Key Pointers

The neutral position theory assumptions continue with the notion that the heel cup is supposed to hold the heel in the position that you request in your custom orthosis prescription. The obvious problem with this is you can easily move your foot while standing on top of a pair of orthoses. Keep in mind that the heel cup of an orthosis is not capable of holding the heel in a selected position.

One concept that I have never accepted the explanation for is the idea of an orthosis, which ends just proximal to the metatarsal heads, supporting a forefoot varus throughout gait. Once the heel leaves the ground, the first metatarsal head is no longer supported and the STJ should pronate because all of the ground reactive force should be on the lateral metatarsals.

Another problem with neutral position theory is the lack of agreement among practitioners on the measurements they see. I once had 30 experienced DPMs measure the same foot and there was a ten degree range in the forefoot to rearfoot relationship they saw in this foot. One practitioner might see and treat a forefoot varus and another DPM could look at the same foot, seeing and treating a forefoot valgus. They both would claim to have success with their treatment.

Neutral position theory looks at the positions of joints and not necessarily the forces that alter those positions. Joint position does not necessarily correlate with force on anatomical structures. After all, it's not the pronation that hurts, it's the stopping of pronation that hurts. When you use wedging under the medial heel, it has been shown to slow the velocity of pronation. You can use this wedging with both OTC devices and custom orthoses in order to reduce the risk of injury when pronation stops.

Final Notes

Eventually, it may be proven that custom orthoses are better than OTC devices, but the proof simply cannot come from neutral position theory. I believe that orthoses made from a neutral position cast work because there is an arch support and there is an alteration in the location of ground reactive force with wedging.
While other theories are emerging from the literature about why orthoses work, I hope to soon publish one based on mechanical modeling and force analysis. I believe the shape of the orthosis is critical in determining whether you can achieve symptom relief. However, there is no reason why you cannot obtain this shape (or a close enough shape) with OTC devices.

Dr. Fuller is an Associate Professor of Biomechanics and Podiatric Medicine at the California College of Podiatric Medicine.