Are You Getting A Custom Orthotic From The Lab?

When the lab sends back an orthotic based upon your custom orthotic prescription, is it truly a custom orthotic that meets the specific needs of the patient? Drawing upon his experience, this author discusses compromises that may happen at the orthotic laboratory and what steps podiatrists can take to cast orthoses more accurately.

Physicians use foot orthotics to treat and prevent a wide range of foot and related disorders. Despite some of the rhetoric and propaganda in social media, I believe orthoses have a positive effect on outcomes.

For clinicians, there are a substantial variety of foot orthotics and pathways to prescribe, use and manufacture the devices. At one end of that pathway, the clinician has options ranging from the prefabricated orthoses to the library devices to the custom-made devices at the other end.

If one is going down the custom-made pathway, the clinician has many options to take a model of the foot and send that model to a orthotic fabrication laboratory or facility to get custom orthoses. I estimate there are probably just over 200 orthotic laboratories globally that make custom orthoses. At the manufacturing laboratory, they have a range of options for design and manufacturing of the foot orthotic devices.

Due to that range and diversity of pathways from the “foot” to the finished foot orthotic device, one needs to consider this question: are you getting a custom orthotic from the lab?
What follows is a personal reflection on the topic after being involved in, observing, teaching and commenting on the industry for over 30 years.

In order to achieve a certain clinical outcome, the orthotic device must have certain design features. Different feet and different symptoms need different design features. If one achieves the right design features for that purpose, then the “what” and “how” of the type of foot orthotic and the manufacturing process are secondary considerations. The primary decision is what design features are necessary. The secondary decisions are how and what is the best way to deliver those design features.

For example, take someone with symptomatic posterior tibial tendinopathy. One of the primary functions of the posterior tibial tendon is to provide an inversion moment at the rearfoot so the clinician needs a design feature to reduce that inversion moment so the muscles do not put so much load on the tendon. The most effective design feature to accomplish this goal is having the bulk of the material of the device on the medial side of the subtalar joint axis. Additionally, any sort of arch support design feature has the potential to counter the bulk of the material on the medial side of the subtalar joint axis, depending on the location of the subtalar joint axis (for some clinicians, the “arch support” is lateral to the joint axis).

The clinician then needs to decide which sort of foot orthotic best provides those design features. Sometimes a prefabricated device, perhaps with some extra medial heel wedging, can meet those needs. In other cases, a custom-made device is necessary to get the design features. There is likely to be a clinical failure if the foot orthotic does not have the design feature to reduce that rearfoot inversion moment. It is not a matter of which type of device is better but it is a matter of which orthotic delivers the types of design features that are needed.

A Critical Look At A Meta-Analysis Comparing Custom Orthoses And Prefabricated Orthoses

Is the evidence of any use in helping make clinical decisions as to which is the most appropriate foot orthosis? The published scientific evidence is clear that there is no difference in outcomes between what the studies call “custom-made foot orthotics” and prefabricated foot orthotics. A systematic review of the evidence by Collins and colleagues concluded there was no difference between custom-made and prefabricated foot orthoses on clinical outcomes.¹ Since that time, that is probably still the consensus based on a superficial review and understanding of the evidence.

It always makes for interesting analysis to follow commentary and views on the differences between different types of devices and their clinical usefulness. Previously held biases and agendas often factor into those commentaries and views (and I am not different in that regard). The question then becomes: do we accept that evidence and use it to support our clinical practice protocols, or do we dig deeper? The outcome of those studies and systematic reviews already has had a significant impact on clinical practice, but should it have?

The question to start with, for the purpose of this commentary, is to ask about the appropriateness of the custom-made foot orthotic prescription, design and manufacture used in the studies in the review.¹ Did the orthoses have the design features that would commonly be in use in clinical practice? I would have to say no as almost all of the orthoses used in the studies for this systematic review are not of the prescription and design that are commonly used in clinical practice. This raises questions of the validity of the study comparing custom-made orthoses to prefabricated designs.

Let me cite just a few examples of these disparities. A custom-made foot orthotic design adjusts the thickness and rigidity of the material based on body weight (none of the studies in the review did that).¹ A custom-made design would use a heel raise if the calf muscles are tight (none of the studies did that). A custom-made design would use features such as a kinetic wedge or first ray cutout if a functional hallux limitus is present (none of the studies did that).

To be clear, that does not mean that the studies comparing custom-made designs to prefabricated designs would still not have the same outcomes if the studies used a true custom-made device incorporating the design features I just mentioned. However, based on the previously published studies, we do not know if this is the case or not.

Another way of looking at this is to look at the shapes of the custom-made devices used in almost all of the clinical studies and compare those shapes to the prefabricated designs the study authors used.¹ Generally, the studies used a very generic prescription and design for the custom-made designs and their shapes did not differ much, if at all, from the prefabricated designs. That lack of differences in the shapes of the foot orthotic devices could easily account for the lack of differences in outcomes between the groups using the different devices. However, at this stage, it is only speculation that there would be different outcomes if the studies used true custom-made foot orthotic designs rather than a generic custom-molded device.

What Happens At The Foot Orthotic Laboratory?

For a custom-made device, the foot orthotic laboratory receives from the clinician a negative model (plaster cast, foam box or digital scan) and a prescription from which it designs and then manufactures the final device. There are many steps and procedures in that process that can be compromised so the final product may become a very generic shape, meaning that one might as well have used a prefabricated device.

First, it starts with the quality of the negative cast model from the clinician. I have visited many labs all over the world and never cease to be amazed at the generally poor quality of what the labs receive. As a result of that, they need to make compromises. For example, in a plaster-based lab, the lab is going to modify the shape by adding extra plaster to the positive cast to account for the poor casting technique used for the negative cast. This type of compromise probably means a more generically shaped device is the final outcome.

Next, with the model of the positive cast, either in plaster or a computer-aided design (CAD) program, labs make modifications to the shape according to the prescription from the clinician, but also from the lab’s discretion. A typical example here is the amount of “arch fill,” which will affect the arch profile for the final device. Different labs do that differently. Some of those devices, due to the nature and amount of what the labs do, could end up looking pretty similar and generically shaped. One common problem with labs that use plaster for the positive models is the plaster additions that labs typically make to each device have a tendency to make the shape of the device more generic. Lab technicians commonly make comments about how similar plaster additions start to look when you have done thousands of them.

A particular problem with the CAD design systems is that it takes time to follow a good prescription from a clinician properly and do all the designs on the computer. Time is money and this can add to the laboratory’s cost structure if this is not controlled properly. To get around this problem and save time, one commercially available design system has emerged and it creates several “blanks” of generic orthotic shapes. The design system superimposes these blanks on the negative model of the foot to jump over a lot of design steps before sending the final design to manufacturing. The cynic would say: if you are going to use such generic shapes, then why not use a prefabricated device?

Another problem is the concept of “mirroring” of the left and right foot devices. Have you ever noticed how often when a pair of foot orthotics comes back from the orthotic lab that the left orthotic looks the same as the right orthotic? If the left and right foot are different and the orthotics are supposed to be truly custom, then shouldn’t the left orthotic look different than the right orthotic?

Labs use this mirroring during the positive model design to make designs look the same or similar. Most CAD systems allow the design of one foot orthotic and then you just “flip” that design to the other foot to save time. These systems do this for aesthetic reasons and for a belief that patients and clinicians want the devices to look the same. What was the point of using custom-made orthotics if a compromise like this has to be made?

The final issue is the use of library devices by the foot orthotic laboratory. Library devices are mass produced, prefabricated orthotic shells that labs either match to the negative model when it arrives at the laboratory or to the positive model after the design process. This skips several steps in the manufacturing process to produce a more economical device.

I do not have a problem with this if the laboratory explicitly explains to the clinician that it is doing this. In the past, I have found there has been more than one example of this happening but outside of the laboratory, no one knew they were getting library devices. Problems can also arise if the range of library devices is limited.

KLM Orthotics has an extensive library system with a range of devices. With such an extensive range, you would probably end up with an exact same-shaped device using the library shell as you would if the lab made the orthotic shell via the typical manufacturing process. With a more limited range of library devices, there is more likely to be a compromise and you might as well use a prefabricated device. The success or failure of a library device will depend on the range of shells at the laboratory’s disposal.

In Conclusion
Personally, I do not think the evidence supports the similarity in outcomes between custom-made and prefabricated foot orthotics. That will be an unpopular view with my academic colleagues. The evidence does support no differences in outcomes between generically shaped custom-made devices and prefabricated devices.¹ The question to resolve is that if patients use truly custom-made foot orthotics, without all the compromises in the manufacturing processes, will the outcomes be different? We do not have the answer to this yet.

Clinicians prescribing custom-made foot orthotics do need to be aware of the issues I raised and how the manufacturing facility that they use deals with these issues. They need to ask questions of their facilities so there are fewer compromises in the process. At the same time, clinicians need to take good negative models to send to the lab so the lab does not have to make compromises.

Are you getting a custom orthotic from the lab? The answer is probably yes. However, given the potential compromises in the design and manufacturing process, are you actually getting orthoses that are closer to prefabricated devices when these compromises occur with your custom orthotic prescriptions?

Dr. Payne was previously a Professor in the Department of Podiatry at LaTrobe University in Melbourne, Australia and now teaches online course in foot orthotic and foot biomechanics.

Reference

1. Collins N, Bisset L, McPoil T, Vicenzino B. Foot orthoses in lower limb overuse conditions: a systematic review and meta-analysis. Foot Ankle Int. 2007;28(3):396-412.

For further reading, see “Current Insights On Functional Foot Orthotics And Choosing A Lab” in the April 2015 issue of Podiatry Today, “Point-Counterpoint: Are Static Measurements Of Foot Morphology Necessary To Create Custom Foot Orthoses?” in the May 2016 issue, or the DPM Blog “Is Your Custom Orthosis Really Custom?” at https://tinyurl.com/o4zy4jo.

For more insights on custom orthoses, attend the lecture “Biomechanics of Plantar Fasciitis: Custom-Molded Orthotic or Insole?” by James McGuire, DPM, PT, CPed, FAPWHc at the inaugural Advance by Podiatry Today meeting Oct. 13–15 in Chicago. To register, visit www.podiatrytoday.com/advance/register.