Parameters to Consider For Prosthetic and Orthotic Workflow

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Over the past 25 years, we have witnessed a move toward Prosthetic and Orthotic digital workflows. This interest has prompted some in-depth research that verifies the clinical validity of 3D-printed devices. However, research takes time and there is still a lot that needs to be studied in terms of the best process or parameters to get to these devices. This means that a reoccurring challenge for 3D adoption amongst clinicians is deciding which software offers these digital tools and which is better for their use cases.

The question hence is what digital workflow parameters should you look at to pick a complete solution that’s right for you? 

In this article, we will address the following:

  • Why use digital tools in O&P
  • The four basic parameters to validate a digital workflow
  • How do digital tools work? 
    • Scan (Shape Capturing)
    • Model
    • 3D Print
  • Next steps: choosing the right digital workflow

Why use digital tools in O&P 

For centuries, manual craftsmanship in O&P has been the hallmark of the profession with advances in techniques, materials, and quality of products. Colloquially known as braces, orthoses are assistive devices that provide stability and enhance mobility for people with neuromuscular and musculoskeletal impairments. 


All the way through most of the 20th century, orthoses produced by skilled craftsmen were mostly bulky devices made with metal and leather and customized with padding. A shift came in the 1970s with the introduction of thermosetting resins for lower-limb orthotics. Soon, these thermoplastics became mainstream as technicians found they could vary trimlines, contour ,and cross section of the components thus modifying the functionality they provided.  Patients also found them more aesthetically pleasing and more comfortable.

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Figure 1 Orthotic fabrication timeline

This changed the industry more than we could have anticipated. Technicians saw the direct benefits of a shift in fabrication methods as the new technique set a quality standard (customization, lightweight, thermoformability) that was inconceivable before (Condie, n.d.). Following the newly developed standards, researchers undertook studies, which led to a complete revision of the literature and resources. 

We are anticipating a similar change as the field now shifts towards 3D-printed orthoses. The change comes as patient needs have increased and the population of individuals seeking personalized care has skyrocketed. Clinicians face an insurmountable task of providing quality, evidence-based, patient-centered care with an overstretched workforce. 

Thus, 3D digital tools, from scanning to modeling to printing, are being seen as the light bulb moment that will enhance patient care. As adoption has increased, 3D printing technology has reached academic and clinical research institutions, subsequently becoming not only a vital tool to aid research but becoming the subject of research itself (Jakus, 2019).

There has already been quite some research conducted that shows 3D-printed devices are effective. However, there is little research on the process itself. 

If we can take the thermoplastic brace shift in the 1970s as an example, we think that next there will be many more studies done to validate the process – both as a whole and the individual steps.

But then what parameters should we look at now when validating digital workflows?

The four basic parameters to validate a digital workflow

So far, the main research into the digital workflow was conducted by Hale and colleagues in 2020. They mapped the digital workflow for the fabrication of bespoke orthoses and found the workflow to be feasible and potentially faster than traditional methods with quantifiable clinical and patient benefits (Hale et al., 2020).

They recognized that using procedural or parametric software to create customized semi-automated process enabled the rapid generation of 3D-printable geometry (less than 3 minutes). 

At Spentys, we have identified four key parameters based on our research that validates the clinical efficacy and usability of a digital workflow.  They include: 

  • Repeatability: This is defined as the variation in output data over time from a stationary or fixed target.
  • Reliability: The degree to which the result of a measurement, calculation, or specification can be depended on to be accurate
  • Accuracy: How close a measurement is to true value 
  • Final Fit: How well does the final printed device fit

Based on these four parameters, we will walk you through current digital workflows and tools and highlight how you can access the validity of the workflow you decide to use. 

How do digital tools work? 

Across the board, healthcare delivery is going digital because it is more efficient, minimizes human error and improves patient outcomes.

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In O&P, digital tools have gone beyond only manufacturing, which was mainly the 3D printing of the device. This means, solutions cater specifically to orthotic shape capturing and modeling to aid clinicians in designing 3D-printed orthoses. 

While many solutions have now adapted the Spentys scan-model-print approach, we are constantly optimizing the selection of tools available on the platform and simplifying it to its core functions. This basic tenet is founded on the four parameters as is explained below.

Scan (Shape Capturing)

An orthosis is made to fit exact to a patient’s specific anatomy. Therefore, to design an orthosis you first need to capture the exact shape of a patient’s body. 

While many clinicians still employ a hands-on approach with plaster of Paris, 3D scanners have become more commonplace. Few of these scanners on the market offer enhanced 3D visualization of the shape and even texture of the limb.

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To validate the clinical efficiency of a shape capture method, a clinician must be confident that it will increase the chances of attaining a well-fitted device. 

A good rule of thumb to evaluate this would be to use the parameters and ask the following questions:

  • Is it repeatable? That is, will this method give me the same geometric shape for the same patient when used multiple times? 
  • Is it reliable? What is the likelihood that the method will have a high degree of error in any given circumstance? 
  • Will it give an accurate result?
  • Will it lead to a good final fit?

Current scanning devices can accurately capture numerous scans, of the same shape, because of the underlying principle of light scanning technology. Since infrared rays map can calculate the distance between an object and the camera, it is not subject to human expertise to take an impression. This shape capture method makes the entire process repeatable, and less prone to human error. 

Reliability and accuracy tie into a clinician’s ability to produce repeatable results. The clinician must verify that a digital scan is the same and variation in techniques to obtain the scan does not affect its results. The final fit is not solely dependent on the initial shape capture, as other factors must tie into this. However, if there isn’t a good scan from the start then the final fit will be sub-optimal.

Experts find 3D scanning to be faster than plaster casting for capturing the foot and ankle, especially for those experienced in 3D scanning. In the context of foot orthoses, 3D scanning of the foot is comparable in accuracy and reliability to traditional methods. (Farhan et al., 2021)

In another study, de Mits and colleagues evaluated the validity of 3D scanning measurements using comparisons with X-rays and manual instruments. The results showed that 3D scanning provided good validity when scanning participants. (de Mits et al., 2010)

Model 

In the digital workflow, the ‘modeling’ step has two components which include;

  • Rectification (scan correction)
  • Device Design

 Rectification/modification/scan correction tools in CAD software modify the form of digital anatomical models. In a traditional workflow, this process mainly depends on the clinician’s skill and expertise, a series of plaster subtraction and addition aids the clinician to achieve the final form of the positive mold. However, in a digital workflow, there are tools that aid in sculpting, remeshing, and smoothening out the 3D model.

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As far repeatability as goes, these digital tools are designed with an underlying algorithm that ensures that the same action occurs every time a tool is used. A great example would be with Spentys scan correction step where in a clean-up tool can automatically remove and smoothen out every unwanted fragment that may have been included in the scan. Regardless of how many times this tool is used, the results are always the same.

Modification maps (highlights of addition and subtraction using different colors on the 3D model) show areas of change which enable clinicians to visualize accurately the pressure sensitive and pressure tolerant areas. Since every modification is recognizable and can be measured to 0.1mm, high level of precision is achieved, and this ultimately leads to a perfect final fit. 

Although these tools provide the foundation for a good final fit, a major bottleneck for clinicians who are accustomed to verifying the accuracy of modification with their hands would be deciding if the visual representation of the corrected scan is truly accurate after modification. One way to ensure this is:

  1. Avoid complex software. Complexity isn’t a benefit, as it will lead to a long and steep learning curve. Using software with many features can be nice to have but make it very easy to make mistakes since the process can be complicated.
  2. Stick with a simple 3-step workflow. The goal of digital tools is not to replicate the laborious traditional modification process but to optimize it. Rectification on a digital platform should have fewer targeted steps that address all key biomechanical principles.

The 3D device design process as opposed to traditional workflow, allows for more freedom of creativity. With the ability to vary materials, thickness, and rigidity, there is more freedom in orthotic device designs. 

As mentioned earlier, CAD software designed for O&Ps work with algorithms that facilitate repeatability in outcome and overall are reliable in their estimation of dimensions. Unlike traditional workflow where it is impossible to visualize and adjust the final design before manufacture, digital tools offer the flexibility to do this. Adjustments can be done throughout the design phase thus ensuring reliable outcomes as every step can be tracked.

According to Wang (Wang et al., 2021), they found repeatable patterns in the traditional workflow that could be mirrored with digital tools. Expert articles (Fantini et al., 2017; Shih et al., 2017) highlight the benefit of digital modification: 

  1. Reversibility: with the original digital scan saved, modifications can be undone and redone, and the design of the device can be re-iterated many times, both pre-production and postproduction. 
  2. Saves material: There is no waste of materials in the modification process.

3D Print

Nowadays, 3D-printed lower limb orthoses are manufactured using powder-based multi-jet fusion (MJF) and fused deposition modeling (FDM). These techniques determine what materials are used and influence the cost and time, which are vital factors for clinicians to consider. 

To ensure that the final fit of the end devices is accurate, there are 3D printing machine parameters (especially for the FDM process) that are considered. These parameters affect athe ccuracy and the reliability of the mechanical properties of the final print. 

  • Repeatability is built into the 3D printing process. Instead of having to start from measurements for each device, a technician can have a digital design sent to a 3D printer to have multiple prints of the orthoses.
  • Structural-based parameters range from layer thickness, number of layers, infill density, etc. All these affect the reliability of the device. If any of the print settings are wrong the device is prone to breakage. 
  • Geometry-based parameters that include the nozzle size and filament size play a major role in ensuring accuracy through cthe onsistent quality of the surface finish and material integrity.
  • Process-based parameters focus on the temperatures and printing speed. These will affect the final fit of the device. If the temperatures of the melted filament and bed are not in order, the chances of deformation are high.
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Central fabrication labs now exist to aid precise and quality 3D printing thereby easing the process for clinicians. Spentys works with a number of expert 3D printing partners who ensure that all print parameters are consistently maintained during manufacturing. 

It is also worthy to note that in-hospital 3D printing is a better alternative as it allows for more manufacture control and quality assurance in-house. Factor et al., 2022 found that in-hospital manufacture to be highly feasible and relatively fast. In some cases, two casts were printed simultaneously without extending the printing time. With an ideal configuration, it is possible to print as many as up to four casts at once, making the process even more effective.

Next steps: choosing the right digital workflow

Spentys is taking the lead in making streamlined O&P digital workflow software accessible to more clinicians and driving the integration for large healthcare provider through partnerships and intensive research development. 

The four parameters: Repeatability, Reliability, Accuracy, and Final Fit, have been used when creating our Spentys workflow. We base our solution on research and constantly reiterate based on O&P usage so that it is always customized to the users’ needs.

This is where we want the industry to go – a collaborative cloud-based solution designed for O&P that enhances usability and meets these parameters highlighted in this article.

So that in the long run, clinicians will have access to digital tools in one place that can easily evaluate patient needs and improve long term clinical outcomes without friction.  

Barrios-Muriel summarized it nicely in his paper: 

The application of these [3D] technologies may lead to a significant improvement in the orthotic manufacturing process as production times are lower, morphology acquisition is faster and more pleasant for the patient, plaster molds are suppressed, and manufacturing errors are minimized.

In the near future, a single hospital visit will be all it takes to provide a customized and personalized device for each patient using a solution that the practitioners and patients can trust.

References:

Condie, D. N. (n.d.). The modern era of orthotics. https://doi.org/10.1080/03093640802113006

de Mits, S., Coorevits, P., de Clercq, D., Elewaut, D., Woodburn, J. J., & Roosen, P. (2010). Reliability and validity of the Infoot 3D foot digitizer for normal healthy adults. Footwear Science, 2(2), 65–75. https://doi.org/10.1080/19424281003685694

Factor, S., Atlan, F., Pritsch, T., Rumack, N., Golden, E., & Dadia, S. (2022). In-hospital production of 3D-printed casts for non-displaced wrist and hand fractures. SICOT-J, 8, 20. https://doi.org/10.1051/SICOTJ/2022021

Fantini, M., Crescenzio, F. de, Brognara, L., & Baldini, N. (2017). MANUFACTURING OF CUSTOMISED FOOT ORTHOSES BY 3D SCANNING AND 3D PRINTING TECHNOLOGIES. In Journal of Bone and Joint Surgery-british Volume.

Farhan, M., Wang, J. Z., Bray, P., Burns, J., & Cheng, T. L. (2021). Comparison of 3D scanning versus traditional methods of capturing foot and ankle morphology for the fabrication of orthoses: a systematic review. Journal of Foot and Ankle Research, 14(1). https://doi.org/10.1186/S13047-020-00442-8

Hale, L., Linley, E., & Kalaskar, D. M. (2020). A digital workflow for design and fabrication of bespoke orthoses using 3D scanning and 3D printing, a patient-based case study. Scientific Reports, 10(1). https://doi.org/10.1038/S41598-020-63937-1

Jakus, A. E. (2019). An Introduction to 3D Printing—Past, Present, and Future Promise. 3D Printing in Orthopaedic Surgery, 1–15. https://doi.org/10.1016/B978-0-323-58118-9.00001-4

Shih, A., Park, D. W., Yang, Y. Y., Chisena, R., & Wu, D. (2017). Cloud-based Design and Additive Manufacturing of Custom Orthoses. Procedia CIRP, 63, 156–160. https://doi.org/10.1016/J.PROCIR.2017.03.355

Wang, J. Z., Lillia, J., Farhan, M., Bi, L., Kim, J., Burns, J., & Cheng, T. L. (2021). Digital mapping of a manual fabrication method for paediatric ankle–foot orthoses. Scientific Reports 2021 11:1, 11(1), 1–8. https://doi.org/10.1038/s41598-021-98786-z

About the Author: 

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Louis-Philippe Broze

Co-founder & CEO of Spentys

“I’m the CEO & co-founder of Spentys, a European-based startup specializing in the mass-customization of orthopedic immobilization devices through the use of 3D technologies. We set up the company in late 2017 with my co-founder Florian De Boeck. We are active throughout Europe and outside, with production facilities across 5 countries. We firmly believe that the future of health lies in the mass personalization of care, which will have an added value for every citizen in our societies. We want to be an active actor of this societal change.”

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