Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) in Prosthetics and Orthotics

Original Editor - Nicolette Chamberlain-Simon

Top Contributors - Nicolette Chamberlain-Simon  

Introduction[edit | edit source]

The field of prosthetics and orthotics (P&O) utilises a wide variety of methods to provide custom devices to patients. Similar to how thermoplastics revolutionised a field mostly grounded in wood carving, leatherwork, and metal bending[1], digitisation introduced a new strategy for fabricating P&O devices.

Computer-aided design and computer-aided manufacturing (CAD/CAM) is an umbrella term for many technologies that use computer software to design and manufacture both prototypes and definitive devices. In P&O, CAD/CAM technologies include:

  • 3D scanners
  • 3D visualisation softwares
  • CAD software
    • Can be specifically designed to perform prosthetic/orthotic modifications
    • Can include finite element analysis (FEA)
  • 3D carvers or subtractive manufacturing
  • 3D printers or additive manufacturing

History[edit | edit source]

CAD/CAM was introduced to P&O over three decades ago. One of the first reports of CAD/CAM, published in 1985, described a “software package” for the manufacture of transtibial sockets[2]. The second author of this publication went on to develop Vorum, the first and longest-standing CAD/CAM company dedicated to P&O. Vorum was initially focused on 3D carvers, which uses a milling machine to carve a foam block based on a CAD drawing[3].

The first attempts of 3D printing in a P&O-specific application were reported in the early 1990s, about a decade after the first published patent of any 3D printing technology. These studies described the fabrication of transtibial socket using stereolithography (SLA), and fused deposition modelling (FDM) with the Squirt-Shape(™) printer.[4]

The prevalence of CAD/CAM technologies in P&O has grown over the past decades with the advent of new scanners, modification softwares, 3D carvers, 3D printers, and printing materials. Though many view 3D scanning and printing as a way to reduce costs and increase access to P&O devices, CAD/CAM is not always synonymous with lower cost.[5]

Current literature indicates a steady increase in adoption of CAD/CAM technologies, but not to the point of overtaking traditional methods. A 2021 study indicates increased interest in CAD/CAM from both developed and developing countries. However, developing countries have faced challenges in adoption such as accessibility, resources, qualified practitioners, and gaps in knowledge.[6] In the United States, the 2022 Practice Analysis indicates that 30% of prostheses incorporate CAD/CAM, increasing from 23% in the 2015 study[7].

Current Applications[edit | edit source]

Currently, CAD/CAM technologies are used in the fabrication of all kinds of diagnostic and definitive devices, including:

  • Lower limb prostheses
  • Upper limb prostheses
  • Custom prosthetic covers
  • Lower limb orthoses
  • Upper limb orthoses
  • Scoliosis braces
  • Other spinal orthoses
  • Cranial remolding orthoses (CROs)
  • Other

Process[edit | edit source]

The process for creating a prosthesis or orthosis with CAD/CAM can be broken into four parts:

  1. 3D scanning
  2. Digital modification
  3. Slicing
  4. Printing or carving

For a practitioner to incorporate CAD/CAM into their practice, they do not have to use all three parts of the process. For example, a prosthetist may fit a 3D printed diagnostic socket made from a scan of a modified plaster model. An orthotist or technician may pull plastic (using traditional methods) over a carved foam model for a scoliosis brace.

Scanning[edit | edit source]

Several types of scanners can be used to capture an impression of a patient’s limb or anatomical feature. Two commonly used technologies in P&O are:

  1. Structured light scanners (ie Structure Sensor)
  2. Laser-based 3D scanners, or LiDAR (ie Comb P&O)

Some are used independently as a handheld or stationary scanner, and some work in conjunction with an iPhone, iPad, or other device.

Several studies have confirmed the reliability of capturing limb shape compared to traditional methods.[8] [9]

Digital Modifications[edit | edit source]

In order for a scan to be turned into a printable prosthesis or orthosis, it must be modified using CAD software. While there are P&O-specific programs for digital modifications, some use other design programs such as Autodesk Meshmixer, Autodesk Fusion 360, Dassault Systemes SolidWorks, etc.

There are several platforms for performing modifications, including:

  • Design suites purchased through a subscription
  • Cloud-based software through an internet browser
  • A phone or tablet app
Slicing[edit | edit source]

Before sending a modified scan to print or carve, the file must be prepared for the specific manufacturing technology. For 3D printing, this process is usually called “slicing.” This can sometimes be performed in the same CAD program for modifications, but generally the design file is saved as a .stl or .obj and imported to a separate slicing software.

Printing/Carving[edit | edit source]

CAM technologies can be divided into carving (subtractive manufacturing) and 3D printing (additive manufacturing).

There are many different 3D printing technologies, but three are predominantly used in P&O:[10]

  1. Fused deposition modelling (FDM)
  2. Selective laser sintering (SLS)
  3. Powder bed and inkjet head 3D printing (3DP)

The selected printer, print properties and material determine ultimate properties of the prosthesis and orthosis.

A systematic review by Kim et al. reports that transtibial sockets made with 3D printing show promise as definitive sockets based on ISO standard testing methods.[11]

Clinical Impact[edit | edit source]

Few studies have evaluated the overall clinical impact of CAD/CAM in P&O. One study reported that transtibial sockets manufactured with CAD/CAM resulted in better quality of life than those manufactured by traditional methods[12]. However, due to low standardisation and quantification of methods in P&O, this can be a difficult conclusion to draw.

Some groups are trying to use CAD and 3D printing to improve access to P&O worldwide. One group defined a method to provide 3D printed prostheses to patients in Sierra Leone in order to address an unmet global health need[13]. A different group cites 3D printing as a way to incorporate low cost materials and rapid prototyping to increase access to prostheses[6].

Most of the research analysing CAD/CAM for upper limb (UL) prostheses has focused on paediatrics. 75% of the prostheses developed for children were made using FDM. A review of 3D printed UL prostheses reported that evidence regarding durability, functionality and user acceptance is lacking.[5]

There is little evidence to indicate whether or not the CAD/CAM method is more efficient than traditional methods. However, one advantage is the ability to save an impression or mold on a computer vs. store within a fabrication lab. This allows duplication of devices and fast comparison between scans (such as a patient’s residual limb one year post-amputation vs. three months post-amputation).

Potential Applications[edit | edit source]

Printing strategies[edit | edit source]
  • Different materials within the same part
    • ex:) provide rigidity in pressure tolerant areas, and flexibility in pressure intolerant areas
  • Hybrid materials
    • ex:) use carbon fiber-reinforced filaments to increase part strength[11]
  • Incorporate textures
    • ex:) add ridges inside a prosthetic socket to reduce rotation over the residual limb[14]
Automation & Parametric Designs[edit | edit source]
  • Personalised prosthetic feet based on anthropometrics[15]
  • Automated modification software

Resources[edit | edit source]

  • bulleted list
  • x

or

  1. numbered list
  2. x

References[edit | edit source]

  1. ↑ Condie DN. The modern era of orthotics. Prosthetics and orthotics international. 2008 Sep;32(3):313-23.
  2. ↑ Dean D, Saunders CG. A software package for design and manufacture of prosthetic sockets for transtibial amputees. IEEE transactions on biomedical engineering. 1985 Apr(4):257-62.
  3. ↑ Vorum Research Corp. About us - CAD CAM for prosthetics & orthotics. Available from: https://vorum.com/about/ (accessed 17 Oct 2022).
  4. ↑ Rogers B, Bosker GW, Crawford RH, Faustini MC, Neptune RR, Walden G, Gitter AJ. Advanced trans-tibial socket fabrication using selective laser sintering. Prosthetics and orthotics international. 2007 Mar;31(1):88-100.
  5. ↑ 5.0 5.1 Ten Kate J, Smit G, Breedveld P. 3D-printed upper limb prostheses: a review. Disability and Rehabilitation: Assistive Technology. 2017 Apr 3;12(3):300-14.
  6. ↑ 6.0 6.1 Silva K, Rand S, Cancel D, Chen Y, Kathirithamby R, Stern M. Three-dimensional (3-D) printing: a cost-effective solution for improving global accessibility to prostheses. PM&R. 2015 Dec 1;7(12):1312-4.
  7. ↑ American Board for Certification in Orthotics, Prosthetics & Pedorthics. Practice analysis of certified practitioners in the disciplines of orthotics and prosthetics. Available from: https://www.abcop.org/publication/section/practitioner-practice-analysis/results-related-to-professional-background-work-setting-and-demographic-information-22 (accessed 17 Oct 2022).
  8. ↑ Kofman R, Beekman AM, Emmelot CH, Geertzen JH, Dijkstra PU. Measurement properties and usability of non-contact scanners for measuring transtibial residual limb volume. Prosthetics and orthotics international. 2018 Jun;42(3):280-7.
  9. ↑ Dickinson AS, Donovan-Hall MK, Kheng S, Bou K, Tech A, Steer JW, Metcalf CD, Worsley PR. Selecting appropriate 3D scanning technologies for prosthetic socket design and transtibial residual limb shape characterization. JPO: Journal of Prosthetics and Orthotics. 2022 Jan 1;34(1):33-43.
  10. ↑ Barrios-Muriel J, Romero-Sánchez F, Alonso-Sánchez FJ, Salgado DR. Advances in orthotic and prosthetic manufacturing: A technology review. Materials. 2020 Jan 9;13(2):295.
  11. ↑ 11.0 11.1 Kim S, Yalla S, Shetty S, Rosenblatt NJ. 3D printed transtibial prosthetic sockets: A systematic review. PloS one. 2022 Oct 10;17(10):e0275161.
  12. ↑ Karakoç M, Batmaz I, Sariyildiz MA, Yazmalar L, Aydin A, Em S. Sockets manufactured by CAD/CAM method have positive effects on the quality of life of patients with transtibial amputation. American journal of physical medicine & rehabilitation. 2017 Aug 1;96(8):578-81.
  13. ↑ van der Stelt M, Grobusch MP, Koroma AR, et al. 3D prosthesis printing research group. Pioneering low-cost 3D-printed transtibial prosthetics to serve a rural population in Sierra Leone–an observational cohort study. EClinicalMedicine. 2021 May 1;35:100874.
  14. ↑ Quinlan J, Subramanian V, Yohay J, Poziembo B, Fatone S. Using mechanical testing to assess texturing of prosthetic sockets to improve suspension in the transverse plane and reduce rotation. PloS one. 2020 Jun 11;15(6):e0233148.
  15. ↑ Prost V, Johnson WB, Kent JA, Major MJ, Winter AG. Biomechanical evaluation over level ground walking of user-specific prosthetic feet designed using the lower leg trajectory error framework. Scientific reports. 2022 Mar 29;12(1):1-5.
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