October 2015

3D printing of orthotic devices: Evidence from the literature

SOLS-blogBy Shalmali Pal

In the past two decades, additive manufacturing—commonly known as 3D printing—has evolved from a bleeding-edge, high-priced prototype with limited compositional materials to moderately priced systems with a wealth of manufacturing possibilities. Manufacturers of foot orthoses and ankle foot orthoses (AFOs) are taking advantage of this new technology, particularly as 3D printing’s price point of entry has decreased while its capabilities have increased.

Now biomechanics researchers are beginning to test the effects of new orthotic designs that take advantage of 3D printing capabilities, and to compare additive devices with their subtractive counterparts.1, 2, 3, 4, 5, 6, 7

Subtractive techniques for creating foot orthoses and AFOs are limited due to the conventional technologies used in their manufacture, particularly when it comes to customizing or innovating new features during fabrication.

On the other hand, 3D printing offers design freedom and the ability to develop customized, innovative orthotic designs that offer a vast range of prescription options to clinicians, according to one study.

Scott Telfer, PhD, a biomechanics researcher at Glasgow Caledonian University in Scotland, and colleagues examined this issue in a 2012 single-subject study6 that evaluated 3D printing of foot orthoses and AFOs. They wrote the technology “may allow novel personalized orthotic devices to be produced which are beyond the current state of the art.”

He and his team used 3D printing technology to create a three-quarter length foot orthosis with adjustable metatarsal support elements (threaded to be adjustable with a screwdriver) to relieve pressure at the metatarsal heads, as well as an AFO designed to have adjustable stiffness levels in the sagittal plane. The foot orthosis was based on a direct scan of the participant’s foot, while the AFO was based on a 3D surface scan of a plaster cast.

Additive manufacturing allowed the AFO’s four components—a shank section, strut, foot section, and slider—to be composited separately and then assembled. Device stiffness was controlled by adjusting the pressure in two gas springs attached to the posterior aspect. The geometry of the strut section was designed to allow for adjustment of the foot to shank angle while maintaining the stiffness required to withstand the forces generated during gait. Both of these adjustability features would be difficult to create using traditional manufacturing methods, the authors wrote.

A man aged 29 years tested both devices at Glasgow Caledonian University motion analysis lab. As expected, the foot orthosis could be adjusted to significantly reduce peak plantar pressures under the second and third metatarsal heads during gait—reductions similar to those associated with conventionally manufactured foot orthoses in an earlier study.8 However, peak pressure reduction under the first metatarsal head was not statistically significant, and the peak pressures under the fourth and fifth metatarsal heads unexpectedly increased, leading the authors to suggest that some aspects of the device design need to be reevaluated.

The AFO tests confirmed that adjusting the device’s stiffness was associated with significantly different levels of plantar flexion during early stance. The authors believe that it may be possible to use this type of device to allow patients to tailor the support needed for different activities.

Telfer told LER that “in the 2012 paper, the material used for both foot orthoses and AFOs [Nylon 12] was somewhere between polypropylene and carbon fiber in terms of stiffness. It’s possible that this affected the results; however, when walking with devices, we weren’t able to tell the difference between the printed foot orthoses and standard ones.”

In the three years since the study came out, Telfer noted that “along with new printers, new materials seem to be released every week, so even with low-cost machines, it’s now possible to get a closer match to a standard range of materials than when we carried out the study. Beyond this, several printers now allow the actual properties of the material used to be programmed in at the design stage, and it’s now even feasible to use this in order to print a single device in one build that has regions with different material properties.”

A 2014 study took a comparative approach, using conventional and 3D printing methods to create foot molds, from which otherwise identical orthoses were made. Colin Dombroski, PhD, clinical and lab placement instructor in the Diploma of Pedorthics Program at the University of Western Ontario in London, Canada, and colleagues compared the arch height index (AHI) of custom foot orthoses manufactured using either additive or subtractive methods. They found that AHI was similar for the two devices.7

A 3D scan was taken of the participant’s right foot and ankle, and a foot mold was created of acrylonitrile butadiene styrene filament, layered at 2 microns. A second foot impression was acquired using traditional plaster casting, and a positive foot mold was made of gauging plaster.

Custom-made orthoses were fabricated from both molds. The researchers then assessed AHI during gait in a healthy young adult man while he wore shoes only, followed by wearing shoes with each type of orthosis. Although the findings indicated minimal differences in AHI (within .8 mm) among the control (shod) and the two orthotic conditions, the researchers noted the sample size of one prevented statistical analysis and called for further research with additional participants.

Dombroski’s group pointed out that “if proven successful in the future, this model could be a low cost method of custom foot orthotic manufacturing, thus controlling the ultimate cost to the clinician and end user.”

Wenjay Sung, DPM, a foot and ankle surgeon in Los Angeles and consultant podiatrist for the Los Angeles Dodgers, said he believes that research such as Telfer’s and Dombroski’s can help encourage the acceptance of 3D printed orthoses by practitioners and patients.

“These papers are good examples of momentum building,” Sung told LER.

“The feasibility of fabrication with 3D printed structures has already been proven in many industries including aerospace and medicine,” he added. “Now that the fabrication is not such a big challenge, the anatomical design-to-fabrication steps are currently the greatest opportunity to explore different methodologies.”

Future research will not necessarily be limited to the laboratory, Sung said, since the open nature of the 3D printing community will facilitate organic efforts to explore ways the technology will fit into current practice.

Shalmali Pal is a freelance writer based in Tucson, AZ.

  1. Harper N, Russell E, Wilken J, et al. Selective laser sintered versus carbon fiber passive-dynamic ankle-foot orthoses: a comparison of patient walking performance. J Biomech Eng 2014;136(9):09100.
  2. Creylman V, Muraru L, Pallari J, et al. Gait assessment during the initial fitting of customized selective laser sintering ankle foot orthoses in subjects with drop foot. Prosthet Orthot Int 2013;37(2):132-138.
  3. Mavroidis C, Ranky R, Sivak M, et al. Patient specific ankle-foot orthoses using rapid prototyping. J NeuroEng Rehabil 2011;8:1.
  4. Pallari JH, Dalgarno KW, Woodburn J. Mass customization of foot orthoses for rheumatoid arthritis using selective laser sintering. IEEE Trans Biomed Eng 2010;57(7):1750-1756.
  5. Gibson KS, Woodburn J, Porter D, et al. Functionally optimized orthoses for early rheumatoid arthritis foot disease: a study of mechanisms and patient experience. Arthritis Care Res 2014;66(10):1456-1464.
  6. Telfer S, Pallari J, Munguia J, et al. Embracing additive manufacture: implications for foot and ankle orthosis design. BMC Musculoskelet Disord 2012;13:84.
  7. Dombroski C, Balsdon M, Froats A. The use of a low cost 3D scanning and printing tool in the manufacture of custom-made foot orthoses: a preliminary study. BMC Research Notes 2014;7:443.
  8. Postema K, Burm PE, Zande ME, Limbeek JV. Primary metatarsalgia: the influence of a custom-moulded insole and a rocker bar on plantar pressure. Prosthet Orthot Int 1998;22(1):35-44.
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3 Responses to 3D printing of orthotic devices: Evidence from the literature

  1. Harvey Johnson C.O. says:

    The author references and quotes “Scott Telfer, PhD, a biomechanics researcher at Glasgow Caledonian University in Scotland, and colleagues examined this issue in a 2012 single-subject study6 that evaluated 3D printing of foot orthoses and AFOs. They wrote the technology “may allow novel personalized orthotic devices to be produced which are beyond the current state of the art.”
    “He and his team used 3D printing technology to create a three-quarter length foot orthosis with adjustable metatarsal support elements (threaded to be adjustable with a screwdriver) to relieve pressure at the metatarsal heads, as well as an AFO designed to have adjustable stiffness levels in the sagittal plane.”
    I fail to understand how a “3/4 length” orthotic can be designed (3D or otherwise) that will unload a single metatarsal head through the full gait cycle. 3/4 length orthotics cannot unload a metatarsal head once the heel lift occurs. Once the heel lift occurs the 3/4 orthotic looses its mechanical lever arm and the metatarsal heads contact the insole. The believe that a 3/4 length insole can unload a metatarsal head at heel off through terminal stance is false. Even if the clinician makes a 3/4 orthotic that provides enough lift to the metatarsal shafts during early stance and foot flat the purchase/lift is lost as soon as heel lift occurs. The orthotic has to be full length and the offending metatarsal head has to have “well or divot” to insure unloading of the metatarsal head continues from heel off to terminal stance as well as a metatarsal bar on the plantar surface of the orthotic that terminates at the very proximal/posterior edge of the met head.
    As for the comment the technology “may allow novel personalized orthotic devices to be produced which are beyond the current state of the art” I welcome them to my lab anytime to see how truly customized hand crafted and designed multi density full length foot orthotics can be made for high end athletes to the little old arthritic lady. 3D does have its place in our field of orthotics, prosthetics and pedorthotics but there are some things they will never accomplish. Call me old school but I’ll take my custom hand fabricated multi-denisty foot orthotics and put them up agains any 3D product on the market.

  2. Teri Green says:

    Most podiatrists were taught to cast the patients for custom orthotics. It allows the practitioner to truly customize the device by manipulating the cast to achieve the desired effect. For those patients with out insurance coverage or unwilling to pay, there is an alternative that seems to get great results. It is a heat moldable orthotic. With a heat moldable orthotics the shell is heated and the patient steps on the device. They can be modified to achieve the podiatrist’s desired device. They are inexpensive and easy to fabricate. More practitioners should look in to such a device in my humble opinion.

    Great article overall, learned a lot.

    Teri Green
    Atlas Biomechanics

  3. Harvey Johnson C.O. says:

    As a certified orthotist in the late 1980s I experimented with warm & form foot orthotics as well as foam box impression techniques. IMHO opinion the first mistake any practitioner makes is to use a semi weigh bearing technique like warm and form orthotics or foam boxes and then proceed to build an new device from a poorly formed mold and or modify a prefab worm and form product. I have made a very good living off people walking into my lab with bags of poorly designed, fabricated and or otherwise inferior orthotics who have essentially been nickel and dimed to death. I gladly give a 100% unconditional money back guarantee on my product.
    Given the life expectancy of my product for the average (not athletic person who has disposable income) my patients can expect a minimum 5-7 life expectancy. Amortize 7 years into the original cost (oh did I mention no charge for adjust for the first 6 months) and the patient gets a great value for the dollar. IMHO opinion anybody claiming to make a custom foot orthotic by sticking a warm and form material under the arch and call that a custom foot orthotic is fooling themselves never mind advertising doing it in 10 minutes.
    The foot is an extraordinary complex part of the human anatomy. Within the foot the energy of forward motion begins with vertical loading in the subtalar joint gets transferred into the horizontal platform in the mid-foot/midtarsal joints and then forward to the long lever arms of the metatarsal shafts is truly a remarkable feet (pun intended) of engineering. There are a few week links especially for the athlete, after all we did not evolve playing soccer, basketball and the whole variety of sports stressing the lower extremities. But even then the foot often but not always needs intervention that is sophisticated as the foot. Arch supports may be a quick a dirty functional economical for some but my experience has revealed that even the average Jane needs something more that a warm and form product.

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