3D Printing And Orthotics: A Roundtable Discussion

How is three-dimensional printing changing orthotic dispensing? Is 3D scanning as accurate as plaster casting? Are commercial orthotic labs becoming obsolete? These expert panelists discuss the realities and potential of 3D-printed orthoses.

Offering a closer look at materials, scanning methods and industry trends, these panelists assess the current and future impact of 3D printing on the development of custom orthoses, and how it may affect podiatry.

Q:

What are the various materials that practitioners have to choose from for orthotics? What is the durability of the various materials? How do the various materials compare with current heat-molded and 3D subtraction materials? How does the practitioner decide which material to use?

A:

James McGuire, DPM, notes that two of the most common current methods for 3D printed foot orthoses are selective laser sintering (SLS) and fused filament fabrication (FFF), both of which work by raising the temperature of a thermoplastic material to the point that the molecules flow together and bond. He says the most commonly used material in SLS is nylon, which one may modify with additives such as glass fibers. Dr. McGuire says nylon is also available for use in fused filament fabrication as are other materials such as polystyrene and rubber. He adds that nylon has greater stiffness and tensile strength than the equivalent thickness of either polypropylene, polyethylene or copolymer, which are thermoplastics used in traditional heat molding and 3D subtraction processes.

Bruce Williams, DPM, notes Hewlett-Packard uses polyamide 11 (PA 11) or polyamide 12 (PA 12), derivatives of castor oil, in 3D printers. He says carbon fiber can also be 3D printed. Although this material may last forever, Dr. Williams cautions that it can break. As Konrad Job (BPod) notes, the majority of commercial laboratories appear to be utilizing SLS technology and printing with PA11 or PA12. The tensile strength of PA11 and PA12 appears to be good after manufacturing but Mr. Job says the hygroscopic nature of polyamides can lead to changes in the long-term dimensional stability due to the material’s moisture absorption within a humid in-shoe environment. At this early stage of 3D printing, he would advise practitioners to base material selection on the ability of printed orthoses to retain their structural integrity over time.

Mr. Job has also encountered a number of individuals printing with thermoplastic polyurethane (TPU) filaments via fused deposition modeling (FDM) technology. Dr. Williams cautions that thermoplastic polyurethane is not rigid enough in a thin form but clinicians can use it for foot beds in sandals and shoes.

Ethylene vinyl acetate (EVA), polypropylene and carbon fiber are the most common materials used presently for 3D orthoses, says Dr. Williams. He notes EVA will last one to two years or more depending on its overall usage. He says polypropylene “will essentially last forever” depending on the thickness or stiffness of the device, and the weight of the patient. Dr. Williams adds that usage and heat can affect polypropylene.

Paul Langer, DPM, cites 3D materials ranging from flexible rubber-like thermoplastic elastomers to rigid material filled with carbon fiber. One of the flexible materials he is using, TPU, was tested under lab conditions by a footwear manufacturer and did not break down after 100,000 flexes. As with current orthotic materials, Dr. Langer says the practitioner decides on the appropriate material based on the needs of the individual patient.

“While there are not as many options for materials for 3D printing yet, the options are growing very quickly,” says Dr. Langer. “Currently, there are materials suitable for both accommodative and functional foot orthotics.”

John Stimpson says the materials available will vary from one printing technology to another in regard to the desired performance properties. He cites a large number of materials that can be 3D printed. However, when looking at production level, biocompatibility and high quality parts, Mr. Stimpson says the list of materials narrows significantly to a small number of polymers of different grades. Given this reality, the most likely manufacturing method will be single material orthosis shells (with or without plantar surface posting), which he says will have variable densities (apertures, covers, etc.) incorporated via traditional techniques.

Mr. Stimpson notes the material he and his colleagues chose compared favorably to the heat-molded material that they utilized in regard to the key performance indicators of strength and durability. He cites a difference in appearance as the 3D printed shell is opaque (white) while the previous heat-molded shell was semi-translucent with a skin tone color.

Mr. Stimpson’s company has only ever offered a single material to its clients so the only option DPMs have had is to choose from a limited number of thicknesses. He says it is much the same with 3D printing with the exception that the number of different thicknesses possible is greater.

Dr. Williams has not had much opportunity to test many of the new orthotic materials. In general, he has found the nylon to be amazingly durable but also very expensive. He says polyamide materials are similar to polypropylene but can break like carbon fiber if they bend the wrong way.

Q:

What are the reasons that more companies aren’t producing 3D printed orthotics?

A:

As Mr. Job explains, industrial grade selective laser sintering printing hardware is a costly investment.
“With a rapidly changing landscape, it appears many commercial laboratories are waiting for further validation and acceptance of methods and materials from the broader community,” notes Mr. Job.

Mr. Job adds that no orthotic specific manufacturing expertise is required to operate hardware so many laboratories can use third-party printing services at increasingly competitive rates.

“The most compelling reasons to convert to 3D printing are precision, production scalability and a really significant, positive ecological impact,” says Mr. Stimpson.

However, as Mr. Stimpson notes, cost savings are not a major factor in companies printing 3D orthoses. As he says, the equipment and software for 3D printing are sophisticated and expensive, and the choice of material requires a degree of expertise not readily available in the market. The reason that established labs have hesitated to make the shift to 3D printing, Mr. Stimpson suspects, is mostly the difficulty for companies to realize an acceptable return on a major investment without significant cost savings. He notes newcomers to the industry are more open to making the investment with very different business models often driven by companies whose stock in trade is selling technology.

Dr. McGuire says time and cost have always been two of the main factors limiting widespread acceptance of 3D-printed orthoses. While manufacturing time has improved significantly in recent years, with some printers capable of printing a pair of orthoses within an hour, he notes cost can still be an issue. While certain desktop 3D printers are available for well under $10,000, Dr. McGuire says the mass production of orthoses would require multiple printers or larger printers, which can cost over $100,000. He notes this is not to mention the cost of the scanning hardware and computer-aided design (CAD) software required to create the 3D printable model.

In addition to the cost of printers, Dr. Williams notes it is expensive to retool a whole operation for 3D printing and it will cost jobs. He says new 3D printers can make 40 to 50 or more orthoses a day with a competitive price point and multiple printers only need one person to run with perhaps a few more employees to help with gluing of topcovers and other modifications.

Dr. Langer cites several factors that make 3D printing less attractive for orthotic labs. He notes 3D printing for orthotics is very good for on-site or localized manufacturing but all the orthotic labs are using centralized manufacturing. Dr. Langer points out that three-dimensional printing is much slower than computer numerical control (CNC) machining and all orthotic labs have already invested heavily into CNC milling machineries so it will be very difficult to make a switch to 3D.

In contrast, Dr. Langer cites benefits for 3D printing: a turnaround time of a few hours, a cost of one-third or one-fourth that of an orthotic lab and that 3D printers can print multiple devices to make corrections incrementally. If 3D-printed foot orthotics can meet the requirements of practitioners regarding the material and prescription options, he feels 3D printed foot orthotics will make their way into clinics.

Dr. Langer explains that CNC machines can manufacture each pair of orthotics faster than 3D printers but because orthotic labs have large volumes and have to ship orthotics, podiatrists end up waiting two to four weeks to get their orthotics back. He says 3D printing is slower per pair but because orthotics can be manufactured in clinic and an individual clinic may make five to 10 orthotics per week, a podiatrist could get his orthotics to his patients faster.

“I think we are approaching the tipping point where this technology will be more rapidly adopted in clinics and in retail,” says Dr. Langer.

Q:

Does 3D printing offer the practitioner more control or less control over the prescription? Is there a possibility that orthotic labs could utilize individual practitioners’ offices for their printing sites to decrease the turnaround time for the patient?

A:

Depending on the programming offered by the lab, Dr. Williams says physicians should have an opportunity for significantly increased control over the orthoses. He explains the costs to add accommodations to the arch, or to add heel lifts and other postings, should be negligible as the machine will 3D-print exactly what the doctor programs in.

“This is a big change from ticking off a box on a piece of paper and hoping that your orthotic lab will get the modification that you may be paying extra for exactly the way you want it done,” says Dr. Williams.

Practitioners can now have as much control over 3D printed orthoses as they want, says Dr. Langer. In fact, he notes the more control physicians take, the more money they can save themselves on the cost of the orthotic. Physicians can scan and have the lab model and manufacture the devices, says Dr. Langer, or physicians can scan, model and print the devices on site in their clinic if they wish. He notes practitioners can buy their own scanners and printers, and use the lab only to model the orthotic for a small fee. Dr. Langer says the clinic can scale up the manufacturing process as needed. As he notes, the cost of printers is decreasing so adding printers as orthotic volume increases could be relatively inexpensive.

Dr. McGuire notes 3D printing offers practitioners more control over the orthotic prescription than both traditional manufacturing methods and 3D subtraction methods. However, he says in the most common prescriptions, the difference in customization between 3D printing and 3D subtraction may not be clinically significant as one can carve a variety of reinforcements, cutouts or grooves from the plastic block with current milling technology.

“It is inevitable that as the cost of 3D printing technology continues to decline, there will eventually come a point that orthotic labs will be able to provide clinicians with 3D printers linked directly to that lab, similar to how some labs already provide clinicians with 3D scanning equipment,” says Dr. McGuire.

Mr. Job says practitioners have yet to explore the array of options within subtractive, let alone additive, manufacturing. He says the control over prescriptions largely depends on the aptitude of the practitioner to utilize CAD/computer-manufactured design (CAM) software, noting the ability to work in a CAD environment is almost fundamental if physicians are trying to conceptualize CAD/CAM specific design variables. Mr. Job is optimistic that there will be an increase in the availability of CAD/CAM specific prescription options by laboratories.

“It is likely inevitable that in-office 3D printers will begin to appear within the profession,” says Mr. Job. “However, it remains to be seen whether the traditional laboratory will have any involvement at such a time. Hardware implementation in-clinic is also inextricably linked to the availability, cost and reliability of hardware. In an ideal scenario, a clinician may design and print the device using their own hardware with no laboratory involvement. However, very few clinicians currently possess the hardware or have the incentive to undertake this endeavor.”

Mr. Stimpson notes that from the perspective of producing a more precise orthotic device, it only really makes sense to have an end-to-end 3D process, consisting of 3D scanning in the clinic and 3D production technology in the lab. He says the variability inherent in physical casting in the clinic and traditional production methods in the lab will “nullify” any precision gains if a lab uses 3D technology only on one end of the process.

An end-to-end 3D process will give the practitioner more control over the prescription, according to Mr. Stimpson. With greater precision, he says the practitioner can produce true custom plantar surfaces and foot contours while choosing from multiple thicknesses of the material. He notes this allows more refined control over the flexibility of the orthotic depending on the desired outcome for the patient. In addition, Mr. Stimpson says the repeatability of the process brings predictability for health care professionals, who can ensure they are getting exactly what they ask for.

In regard to orthotic labs using podiatric offices as printing sites to decrease turnaround time, Dr. Williams acknowledges it is possible but unlikely. He says there will be an increase in the number of central printing sites all over the country and there will likely be agreements to post at different sites with different labs using or renting the printers as needed to make shipping local and cheaper whenever possible. Dr. Williams says this should shorten delivery time over time.

Mr. Stimpson suggests that, given the complexity, it would require “a certain know-how and a certain volume” to make 3D printing work in the clinic. He cautions that different 3D printing technologies are required to print the shell, the top covering and the posting materials of the orthosis. Not unlike the decision for physicians to produce their own orthotics now, he says the decision to use 3D printing will come down to “a trade-off between time and effort in the clinic versus time and effort managing a production workshop.”   

Q:

How does the accuracy of various scanning methods compare with the accuracy of traditional casting techniques? Are there adjustments that need to be made by the laboratory for distortions in scanning techniques?

A:

Three-dimensional scanners are generally accurate to within 1 mm or less, which Dr. McGuire says is for all intents and purposes clinically no different than traditional casting methods in terms of capturing the shapes it is meant to capture. However, he notes traditional methods such as plaster casting have the advantage of allowing the manipulation of soft tissues while capturing a model of the foot. Dr. McGuire notes examples such as allowing the clinician to reshape the calcaneal fat pad, heighten the lateral arch or press into the groove of the tarsal tunnel (e.g. for a UCBL-type device) at the time of casting. As with traditional casting methods, Dr. McGuire cites the potential for artifacts on scans, which the orthotic lab will need to be able to recognize and correct.

Ideally, Mr. Job says the lab should not be adjusting or interpreting anything, and if a 3D scanner is requiring adjustments, then one should not use the scanner.

“A high-quality 3D scanner engineered specifically to capture the foot will likely offer the clinician a greater level of accuracy and reliability than the suspension cast method,” maintains Mr. Job.

Accuracy depends on the quality of the scanning technology one is using, according to Mr. Stimpson. He notes a wide range of technologies starting at a few hundred dollars and going up to over $100,000 with the main differentiating factors being accuracy and the integrity of the image. Although all of the technologies can legally claim to be 3D, Mr. Stimpson cites distinctions among them. At the lower end, he says the images produced are typically high resolution with low accuracy (plus or minus 4 mm) and there are likely distortions in scale and geometry. As the cost of the technology climbs and the complexity of the scanner increases (multiple camera systems), he notes the inverse tends to be true. There is lower resolution but much higher accuracy (plus or minus 0.5 mm) with zero distortion. For these technologies, Mr. Stimpson says the price of a 3D scanner runs upward of $10,000.

If the objective of the clinician is simply to replace the traditional casting method in the clinic and go with 3D printing, Mr. Stimpson says the lower accuracy and distortion may not be issues, adding that the variability of one technique will be about the same as the other. However, if the objective is to obtain a more precise, more effective custom orthotic, he notes this requires a larger investment. Unfortunately, Mr. Stimpson says the large number of relatively low-cost scanning options in the market, which have suggested higher accuracy than they are able to deliver, has led to many questions about the quality of 3D technology. He adds that the practice of producing from a database of similar foot shapes in many labs has created an additional level of distortion.

“In the ideal world of quality 3D technology in both the clinic and the lab, the new reality will be minimal involvement by the lab with the potential to eliminate adjustments altogether,” says Mr. Stimpson. “In the real world, inaccurate and distorted scans are an all too common problem for which lab intervention is required and which may also explain the wide use of databases to find an approximation of the foot shapes required.”

Dr. Williams stresses that all major labs scan the foam boxes or plaster casts they receive. He notes that few, if any, labs work with traditional plaster positive casts, saying the plaster process is not fast or efficient enough to keep up anymore. He says most labs use CAD/CAM systems and scan the non-digital casts they receive.

Dr. Williams cites “essentially no difference” in comparing scanned plaster casts or scanned foam boxes or foot scans with similarly casted feet in plaster of Paris.

“Scanning is not the issue,” maintains Dr. Williams. “Positioning by the practitioners is more important.”

Mr. Job says a scanner should allow for non-weightbearing, semi-weightbearing and weightbearing scans with the patient either prone or supine. He stresses it is fundamental to have a non-proprietary per-vertex color format (VRML, PLY, OBJ) that allows the scanner to utilize reference markings during the CAD process.

Dr. Langer says tablet scanners are proving to be accurate enough to be suitable in orthotic manufacturing. However, he says the photogrammetry programs that rely on pictures taken with a phone or tablet are not adequate. He says tablet scanners have to model the foot and “clean up” the files before printing.

Mr. Job says handheld scanners have recently become accepted due to their low cost, simple integration with mobile applications and convenience, largely driven by laboratories providing this technology at no charge to practitioners, which he calls “a clear conflict of interest.” Mr. Job notes that many clinicians are also neglecting to position the foot during 3D capture, requiring more subjectivity in CAD.

Q:

With the advent of department stores selling 3D insole printers and with home printers, is the commercial orthotic lab becoming obsolete?

A:

Calling 3D printing a “disruptive technology,” Dr. Langer sees the traditional orthotic lab business model as well as the footwear retail model changing dramatically in the next five to 10 years. He thinks the barriers to entering the orthotic manufacturing and custom footwear businesses will fall. No longer will physicians need a large investment of capital or years of training to start an orthotic lab or footwear company. For less than $10,000, Dr. Langer says a store, clinic or other interested party can purchase the technology, and become a manufacturer.

“This is both good and bad, of course, because you will have businesses entering a market they know little about and they will not be capable of providing the high level of service or quality products,” says Dr. Langer. “But unfortunately, this is also a normal part of the process when disruptive technologies start to become more widely adopted.”

As long as people view orthotics as a one-time product purchase for which ongoing, structured follow-up care is not required, Mr. Stimpson says this opens the door for new price competition for both the lab and the clinic. For clinics to face these new competitors, he suggests that DPMs evolve to a model that offers an enhanced perception of value.

To create a greater perception of value, DPMs will be able to distinguish themselves from other entities using 3D orthotics by leveraging their expertise in biomechanical correction and their ability to offer ongoing care, says Mr. Stimpson. In doing so and working with their orthotic lab partner, he notes physicians can ensure prescribing the most appropriate device for optimal correction and sustained well-being for their patients.

For orthotic labs, Mr. Stimpson says the advent of 3D technologies will bring about “great disruption” whether it is due to “mall-based competitors” or because the era of outdated and outmoded production methods is ending. For the time being, he says the cost to make the switch to 3D may be prohibitive but that will change.

“In the meantime, the industry worldwide will be ripe for consolidation as the physical foot cast disappears and production scalability at the lab will be a simple question of investment dollars,” says Mr. Stimpson. “The hundreds of regional players around the world will be replaced by a handful of more sophisticated players who will have mastered the new technologies and will bring them to bear on a global scale.”

Dr. McGuire says 3D orthotic printers in department stores and in homes can potentially provide the population with quasi-prescription orthotic devices. He emphasizes that while such devices may be customized to the patient’s anatomy, they likely lack expert, adequate customization for the patient’s pathology via a podiatrist, orthotist or pedorthist.

In addition, Dr. McGuire says devices that are 3D printed at a department store or from home currently and will likely continue to have a price tag somewhere between prefabricated foot orthoses and prescription custom foot orthoses.

“While these devices will not completely obviate the need for prefabricated or prescription foot orthoses, they will give the patient another option along the orthotic spectrum—both in terms of probable outcomes as well as in terms of price,” notes Dr. McGuire.

Without having specific experience with such systems or knowledge on proprietary algorithms utilized by all-in-one 3D scanning, gait analysis and manufacturing systems, Mr. Job says it is difficult to accurately evaluate.

“One can assume that such systems run on the assumption that extrapolations from normative data offer an appropriate prescription paradigm. This potentially conflicts with the tissue stress model of orthosis design although more information is required,” explains Mr. Job. “The orthotic laboratory and practitioner that do not value a patient specific approach both appear to be at risk of redundancy with the advent of such systems.”

Commercial orthotic labs are not obsolete, “not yet, anyway,” opines Dr. Williams. He stresses the importance of positioning for orthotic scanning. Dr. Williams says people scanning their own feet don’t know how to position their feet to get the best scan, something practitioners can usually do better. He adds that the kiosks and store scanners/printers won’t allow patients to program many, if any, prescriptive elements into their devices as that can cross a line into the medical world and can then open kiosk owners up to liability claims.

“Kiosks will sell ‘comfort’ orthotics but if you need a posting at the heel or forefoot, a heel lift or first ray cutout, then you need to see a medical practitioner,” says Dr. Williams.

Mr. Job is a podiatrist in private practice at Rise Allied Health and a Technical Adviser at LaserCAM Orthotics in Australia.

Dr. Langer is in private practice at Twin Cities Orthopedics in Minneapolis. He is an Adjunct Clinical Professor at the University of Minnesota Medical School and a board member of the American Academy of Podiatric Sports Medicine.

Dr. McGuire is a Clinical Professor in the Departments of Podiatric Medicine and Podiatric Biomechanics at the Temple University School of Podiatric Medicine. He is the Director of the Leonard S. Abrams Center for Advanced Wound Healing in Philadelphia.

Mr. Stimpson is the President of Cryos Technologies, Inc. in Montreal.

Dr. Williams is the Director of Gait Analysis Studies at the Weil Foot & Ankle Institute. He is a Past President and Fellow of the American Academy of Podiatric Sports Medicine. Dr. Williams is the Past President and Fellow of the American Academy of Podiatric Sports Medicine. He is the Director of Breakthrough Sports Performance, LLC in Chicago.

Dr. Phillips is affiliated with the Orlando Veterans Affairs Medical Center in Orlando, Fla. He is a Diplomate of the American Board of Foot and Ankle Surgery, and the American Board of Podiatric Medicine. Dr. Phillips is a Professor of Podiatric Medicine with the College of Medicine at the University of Central Florida. He is also a member of the American Society of Biomechanics.