Using computed tomography and 3D printing to construct custom prosthetics attachments and devices
© The Author(s) 2017
Received: 12 May 2017
Accepted: 17 July 2017
Published: 22 August 2017
The prosthetic devices the military uses to restore function and mobility to our wounded warriors are highly advanced, and in many instances not publically available. There is considerable research aimed at this population of young patients who are extremely active and desire to take part in numerous complex activities. While prosthetists design and manufacture numerous devices with standard materials and limb assemblies, patients often require individualized prosthetic design and/or modifications to enable them to participate fully in complex activities.
Prosthetists and engineers perform research and implement digitally designs in collaboration to generate equipment for their patient’s rehabilitation needs. 3D printing allows for these devices to be manufactured from an array of materials ranging from plastic to titanium alloy. Many designs require form fitting to a prosthetic socket or a complex surface geometry. Specialty items can be scanned using computed tomography and digitally reconstructed to produce a virtual 3D model the engineer can use to design the necessary features of the desired prosthetic, device, or attachment. Completed devices are tested for fit and function.
Numerous custom prostheses and attachments have been successfully translated from the research domain to clinical reality, in particular, those that feature the use of computed tomography (CT) reconstructions. The purpose of this project is to describe the research pathways to implementation for the following clinical designs: sets of bilateral hockey skates; custom weightlifting prosthetic hands; and a wine glass holder.
This article will demonstrate how to incorporate CT imaging and 3D printing in the design and manufacturing process of custom attachments and assistive technology devices. Even though some of these prosthesis attachments may be relatively simple in design to an engineer, they have an enormous impact on the lives of our wounded warriors.
An estimated 1.9 million amputees in the United States  sustained their amputations from trauma and vascular disease. The United States military care system has seen an increase in the number of amputees since the beginning of the conflict overseas. Over 1600 service members have lost limbs since 2001, with over 300 members having lost multiple limbs. Over 40,000 veterans with limb loss also receive care for their amputations within the DOD/VA system .
‘The art and science of prostheses’ dates back over 100 years , when a split tree trunk with leather straps was the best replacement leg. The methodology and technology to rehabilitate amputees has evolved over the years from muscle transplant to biomechanical manipulation and now to 3D printing technologies. Although 3D printing is a little over three decades old, it is now revolutionizing the inception and delivery of devices in rehabilitation medicine . Major advances in medicine occur when medical specialties, biomedical engineers, and technologists collaborate, and the field of prosthetics is no different. Several recent manuscripts, abstracts, and case reports describing original contributions in robotic prostheses to improving 3D printing for prosthesis have been published [5–11], to. There have been many recent review articles about 3D printing and the contributions of several medical specialties ranging from physiatrists to radiologists towards improving prosthetic devices and the rehabilitation process [4, 12–15].
The United States military has been at the forefront of these new technologies and working to bring about major advances in prosthetics (e.g. extending battery life, water resistance, and improved control schemes). The majority of military amputees differ from the dysvascular amputees of the general population in that they are generally young and extremely active individuals. Military amputees are driven individuals who take part in complex activities such as kayaking, skiing, climbing, swimming, mechanical maintenance, and team sports. The age and active lifestyle of these patients are something the DOD/VA will be dealing with for the next several decades.
Currently, at WRNMMC, conventional technologies are used for socket construction. Our lab and the prosthetic service focuses on specialty attachments to reduce limitations of current prosthetic terminal device and allow individuals to once again take part in activities they desire. In this manuscript, we present examples and methods for using computed tomography and additive manufacturing to construct custom prosthetics attachments and devices.
3D printing and prosthetics
3D printing, also referred to as additive manufacturing, is a process that uses a layer-by-layer approach to build an object from a digital file. In this process each subsequent layer bonds to the previous layer by means of heat, energy, or binders. This manufacturing process can be used with an array of different materials, ranging from plastics to metals. This method of manufacturing allows for production in small quantities and parts with intricate or unique geometries. Most prosthesis can be designed and manufactured with standard materials and limb assemblies that are currently available on the market. When desired specialty devices are not available, these devices can be custom designed and manufactured using digital technology and 3D printing, if an appropriate methodology has been developed.
Computed tomography utilization
Computed tomography (CT) is a powerful tool in the development of custom prosthetics. Traditional production methods for complex objects rely on labor-intensive direct measurements with calipers or rulers and the translation of that data into CAD/3D reconstruction software. Surface scanning systems using optical image capture are one option, however they typically require dedicated equipment and often require dedicated physical space. Both of these traditional methods for capturing spatial data are limited by object complexity. Specific barriers include undercuts, complex internal and external surfaces, and glossy finishes. Capturing spatial data on CT overcomes all of these barriers and has significant additional advantages. First, images are high-resolution and rapidly acquired, by-passing the need for direct measurement and eliminating translation error. Second, reconstructing scan data into digital 3D objects using specialized software allows for the seamless reconstruction of organic shapes that are not easily modeled in CAD software. Finally, acquisition techniques such as dual energy CT may also allow for the scanning of metal parts, a previous barrier to CT.
Creating devices using CT first requires acquiring a CT scan of the device’s articulating surface or area of interest. The recommended CT acquisition parameters depend on the object scanned, with z-axis resolution determined by the smallest physical detail of the object necessary to print. Generally, a reconstruction thickness of 0.625–1.25 mm will suffice. Note that these methodologies may not be sufficient for objects with critical details smaller than 0.625 mm. After acquisition of the scan, a series would then be imported into MIMICS Medical v17 (Materialise), a 3D reconstruction software that produces 3D data from the CT scan. The component is then exported and additional computer aided design would then be performed to create the device. Once the organic shape is digitized, it is possible to create custom designs that articulate with the complex geometry of the prosthetic component. Objects dependent on direct measurements would be designed in a CAD package such as Solidworks (Dassault Systemes) and then registered to the reconstruction of the articulating surface. Organic structures would be designed in a program like Freeform Plus (3D systems). The pieces and 3D reconstruction of the surface would then be registered and all the pieces aligned.
The remainder of this manuscript will discuss, in detail, three example methodologies where computed tomography was essential to the device development and construction: a weight lifting hand, hockey skate adapters, and a wine glass holder.
Example 1: Weightlifting adapter
Example 2: Hockey skate adapters
Example 3: Wine glass holder
Results and discussion
In this manuscript, we researched and presented several methodologies to construct personalized examples highlighting the benefits CT reconstructions and the 3D printing process provide in successfully manufacturing prosthetic devices in limited quantities. These are but a few examples of the applications of this technique. Three-dimensional reconstructions from computed tomography create an accurate starting geometry for designing custom prosthetic attachment and devices when barriers to traditional design processes and production methods exist. Once 3D reconstructions were obtained anywhere from thirty minutes (Wine Glass Holder) to three hours (Hockey Skate Adapters) were spent on the digital design process. 3D Printing has created new opportunities for the production of prosthetic devices and allows for the creation of unique, customized devices. Some limiting factors of these developed methodologies include the availability of equipment and materials, software, scanners, CT scan expenses, 3D printers, and experienced staff.
Materials for these prosthetic components were chosen based on the technologies and materials available at the institution. Preliminary results show that the titanium alloy used has allowed for large safety factors, greater than 2.5, on prosthetic attachments analyzed. Future endeavors include 3D printing a mold for to manufacture the Wine Glass Holder from silicone rubber. For less complex designs conventional machining could also be utilized if the facility had in-house capabilities or outsourcing could be more economical. For these particular project and other similar projects, the cost of outsourcing these components would have been higher than the cost of in-house production. CT scanning cost will differ by the institution; however, these objects do not require the radiologist reading.
Using CT in conjunction with digital design and 3D printing can be utilized to create custom rehabilitation devices. Facility resources and knowledge can be limiting factors. 3D printing has created new opportunities previously unavailable to prosthetics, occupational therapy, and assistive technology departments. This methodology continues to be utilized when conventional techniques are limiting or suboptimal. Interprofessional collaboration, imaging, and digital manufacturing expertise are vital to the successful form, fit, and function of these devices.
The authors would like to thank our Service Members for allowing us to feature several of the photographs in this manuscript. We would also like to thank the CT technologists in the Department of Radiology for assistance with image acquisitions.
No funding was used in the in completing this study.
Availability of data and materials
Data is available by contacting the corresponding author.
The identification of specific products or scientific instrumentation is considered an integral part of the scientific endeavor and does not constitute endorsement or implied endorsement on the part of the author, DoD, or any component agency. The views expressed in this manuscript are those of the author and do not reflect the official policy of the Department of Army/Navy/Air Force, Department of Defense, or U.S. Government.
L: Study design, Data Acquisition, Digital Design, Drafting and revision of manuscript. S: Drafting and revision of manuscript. B: Prosthetist for weightlifting adapter and wine glass holder, Study design, revision of manuscript. S: Prosthetist for hockey skate adapter, Study design, revision of manuscript. H: Revision of manuscript. L: Drafting and revision of manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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