By Terrell S. Tate, BOCP,CO
In 2012, I entered the digital world of orthotics and prosthetics (O&P), but did not fully understand the potential. The practice was a traditional brick and mortar O&P company with a satellite location. The business was built around spinal orthotics, but prosthetics was the target for future growth as the demand for spine bracing continued to decline. As a co-owner, we talked about changing to outsource fabrication as a means to contain costs. But the idea of outsourcing fabrication was very difficult to consider since the practice was built around in-house fabrication for 95% of all orthotics and prosthetics. After making the decision to close in-house fabrication, we shifted our workflows away from traditional hand-casting with plaster model rectification and began to scan all impressions for lower extremity orthotics and digitally scan all amputees.
We utilized one person to scan all of the impressions for LE orthotics and then he and I shared the digital modeling responsibilities. However, as the only prosthetist, the design work for prosthetics was all my responsibility. This was my tutorial: trial and error. Since we outsourced all fabrication, I had to evaluate the fitting problems and decide if they were design flaws or technical fabrication flaws.Early on, the errors were mostly design and my responsibility. However, I was able to learn and understand how the scan and design combine to create a finished product that was more accurate and precise than what I could achieve using traditional methods.
After gaining an understanding of better shape-capture technique, and then some basic rule sets for model design, there was only one aspect of fabrication that was inconsistent. The alignment of the adapter was at times perfect and other times off by a small amount. And though this small amount could be corrected with an alignment adapter, I understood the potential for achieving a socket that would be perfect. At that time, the outsource partner was carving the model and then manually placing the adapter. I wanted to eliminate the technical possibility for human error.
3D printing was able to finally provide the last element of control that I desired. Admittedly, I am very picky about alignment. Especially on a patient that is atypical and I have already been through the learning curve to understand the alignment. My thought was this: if I can see the perfect alignment in the design software, then I should be able to have a perfectly fitting finished product.
When I am able to place the adapter in position during the model design phase, I have found that I have little to no adjustments to make during dynamic alignment. The power of this aspect of 3D-printed test sockets is, to my mind, what will truly save time and money in clinical practice. While some consider the fabrication process simplicity of 3D-printed test sockets, reduced manual labor, and reduced material cost to be the key to time and money, I believe that a test socket which is perfect in shape, soft tissue tension value, and alignment to offer the greatest value. Clinician time is a premium, and the value of maximizing this time offers the greatest potential for effecting business in total.
For those clinicians and business owners who have also realized this potential, many question the reliability of 3D-printed sockets. This is a legitimate concern. I have experienced separation between the inner and outer walls, failure of the z axis, and improper wall thickness. Some of this was due to the nature of FDM (formed deposition modeling) as a 3D-print method. Other was due to my shell creation. I currently use Ossur Design Studio (Ossur Americas, Orange County, CA) for model design. I have found great success in shape design. However, in my experience, the shell creation tool has a limitation in that it does not always generate a structurally sound design.
Fabrication partners, such as Extremiti3D LLC (Johns Island, SC), have tested their designs for the structural integrity needed to safely ambulate on a test socket. Barry Hand, mechanical engineer and founder of Extremiti3D, presented a research study at the American Academy of Orthotists and Prosthetists annual meeting titled, Strength Testing of Definitive 3D-printed Transtibial Prosthetic Sockets (now in print at J Prosthet Orthot. 2020;32(4):295-300). Interestingly, they learned that there is little to no evidence for strength-testing prosthetic sockets fabricated using conventional methods. The international ISO standards for structural integrity were used in the non-patient research to test the structural integrity of their design. The design was tested using ISO10328 cyclic testing and did not fail testing to 3 million cycles. The significance is that in a digitally printed socket, the validation of strength is possible because the design is reproducible and exactly the same, just under different specifications. Could more research like this be utilized to test the failure rate of socket designs in the future? Of course, and this would also lead to a new set of standards for socket manufacturing.
Current technology in 3D printing offers many new business solutions and design/manufacturing possibilities. PVA Med (Cohoes, NY) has a pre-integrated, standards-based solution for scanning, model design, and check socket fabrication. They utilize preconfigured profiles that simplify slicing (the parameters are understood by the printer for building the check socket layer by layer) to create the check socket design which can be sent directly to the PVA printer with the click of a button. The PVA Med approach is focused on simplification, repeatability, and ease of use. Most clinicians can adapt to the digital design world as we understand the positive plaster model and can transport that knowledge to the computer screen. However, the software expertise needed to design the actual socket in CAD is not a common part of our knowledge set. Although this is not native to prosthetists, several clinicians have dived deeply into digital socket manufacturing.
Brent Wright, CPO, formed Additive America (Kinston, NC). At Additive America, they are printing parts with the HP Multi Jet Fusion (Palo Alto, CA) and using Geomagic Freeform (3D Systems, Rock Hill, SC) as the software for socket design. Brent wants to help bridge the gap and serve as a resource to others who want to have 3D printed test and definitive sockets. Additive America offers socket design and definitive socket fabrication for all clinicians and Brent is very open to sharing how he uses these digital tools. The technology for multi jet fusion offers a much stronger link in the z axis which has a general strength advantage over FDM methods thus producing a reproducible product with low failure rate.
The 3D printing technology is growing quickly and through discourse, research, and collaboration we will all be able to offer socket designs that are not possible with conventional methods. The next generation digital prosthetist will be able to scan, design, and fabricate with greater precision and ultimately lead to better patient compliance and outcomes.
Terrell S. Tate, BOCP, CO, is founder and chief executive officer of MPower Health in Memphis, TN. Terry has been a prosthetist for more than 15 years and an orthotist for more than 25. He’ll be using this space on a regular basis to discuss all things technology related to the lower extremity. Reach him on LinkedIn for more about digital O&P technology.