3D-printed solutions in upper-limb prosthetic care continue to garner attention. While traditional prosthetic approaches persist as a mainstay in adult care, several entities have argued the value of low-cost, scalable 3D-devices for children, particularly those from families with low income or without insurance. While the bulk of the narrative surrounding 3D-printed prosthetic solutions has taken place in the popular media outlets of newspapers, websites, and various forms of social media, several reports have recently appeared in peer-reviewed literature. This article summarizes the content of these reports with a particular interest in perceived potential value of these solutions for children.
An introduction to the use of 3D-printed prosthetic hand mechanisms is found in a recent publication of the Journal of Hand Surgery.1 Co-authored by physicians from the Department of Orthopedic Surgery at Houston Methodist Hospital and Shriners Hospitals for Children - Houston, the article begins with an explanation of the unique challenges of managing pediatric limb deficiencies. The requirements for such devices are that they be durable, inexpensive, customizable, and easy to fix when broken or outgrown.1
From a functional standpoint, children need prostheses that allow them to more easily participate in tasks or activities that matter to them. Psychosocial considerations are important but highly variable according to the child's age, emotional development, and personality.1 Some children may want something visually compelling that stands out to their friends and peers, while others may desire something as inconspicuous as possible to be more comfortable in social settings. Thus, the individual child's personality, his or her functional goals, and his or her psychosocial preferences will determine the optimal solution.
In addition to these considerations, providers must acknowledge and address the current abandonment rates of pediatric upper-limb prostheses, particularly for children with deficiencies distal to the wrist. Children reject prostheses for being uncomfortable, too heavy, visually unattractive, and having limited functionality.1
Coupled with these concerns are the financial realities of traditional prosthetic care. The authors cite reasonable cost ranges of $4,000- $8,000 for body-powered devices, and $25,000-$50,000 for myoelectric devices. Depending on available health insurance resources, these costs can be overwhelming for families as one-time costs, let alone as cumulative costs that occur with iterative growth, usage, repair, and replacement.1
Abandoning the notion of a one-size-fits-all approach to pediatric upper-limb deficiencies, the authors summarize that "a prosthesis or assistive hand is only useful if it provides enough benefits to outweigh the disadvantages, yet this is a highly individual-dependent assessment."1 While 3D printing does not yet address all the requirements and concerns introduced by the authors, it is put forward as a tool for quickly and inexpensively producing devices that are optimally designed using wearer-specific feedback.1
For these authors, the indications for 3D-printed solutions include children with unilateral reduction deficiencies at the carpal or transmetacarpal level and active wrist motion of at least 30 degrees. This is argued, in part, because of the limited conventional treatment options available at these relatively distal levels of limb deficiency. While these children are generally quite functional without equipment, it is still common for them and their parents to pursue some mechanism to facilitate grasping capabilities with the compromised arm.1
By contrast, contraindications include a lack of sufficient strength and active range of motion (ROM) of the wrist or a very small residual carpal segment distal to the wrist joint. Further, the presence of partial fingers is viewed as a contraindication since existing 3D-printed designs do not accommodate them.1
Several open-source hand models are freely available, including the Robohand, Raptor Hand, Flexy Hand, and Cyborg Beast.1 Common elements include a somewhat anthropometric appearance in which the tenodesis effect is used to translate wrist extension into digital prehension. A dorsal hand piece articulates with a proximal dorsal forearm gauntlet. Nonelastic cords are used to transfer the excursion created with wrist extension into digital prehension while dorsally positioned elastic elements restore extension of the digits in the absence of wrist extension.1
The first authors to describe a 3D-printed design in the academic literature were Jorge Zuniga, PhD, of Creighton University, and his collaborators. This initial publication describes the Cyborg Beast hand design and its application among 11 children, ranging from three to 16 years of age, with unilateral congenital or acquired carpal-level limb deficiencies.2
Prior to printing the devices, sizing was customized using anthropometric measurements and age-based scaling, with older subjects fitted with larger devices. Measurements were taken of all children, either in person or from scaled photographs, and included hand length, palm width, forearm length, and forearm width.2
Zuniga et al. additionally report on utilization of the devices one to three months after their provision. Nine children reported one to two hours of use per day, three subjects reported more than two hours of daily use, and a final subject reported use "only when needed." Usage environments and activities included "just for fun" (n = 10), for activities at home (n = 9), for school activities (n = 4), and to perform sports (n = 2).2
Of note in Zuniga et al.'s report was that the team was able to compare on-site measurements with those obtained photographically and verify their similarities. This validation suggests that the eventual recipients of such hand systems need not be physically present to initiate fabrication, nor would they need to be in the same location as the 3D-printing equipment. This model may represent a distance-fitting technique that would make prosthetic devices available to children around the globe who would otherwise lack access to prosthetic care.2
In addition to their potential benefits in less-resourced international settings, in a subsequent publication, Zuniga et al. explore the potential value of such devices as transitional tools that might prepare their users for adept use of more sophisticated devices at a later date.3 To do so, five children between the ages of three and ten with unilateral congenital or acquired carpal deficiencies were fitted with individually scaled Cyborg Beast hand prostheses and were assessed before and after six months of use. During that period, the children's average maximal forearm circumference increased significantly, from 16.7cm to 17.8cm, approximating the circumference of the sound side forearm (18.7cm). Significant improvements were also seen in average wrist flexion and wrist extension ROM (Table 1).
Similarly, dynamometry was used to monitor wrist flexor and extensor strength. While the improvements failed to reach statistical significance, increases in average demonstrated strength were observed in both motions. The same survey described in Zuniga et al.'s earlier publication was reiterated in this effort. After the extended period of utilization, four of the children were using their devices one to two hours per day, the remaining subject reported four to six hours of daily use, and subjects continued to report utilization of their devices for fun (n = 5), for play (n = 5), for activities in the home (n = 4), and for school activities (n = 4).3
Given the beneficial effects observed regarding muscle mass, wrist joint mobility, and wrist strength with limited use of their devices, the use of 3D-printed training/transitional prostheses would appear to have reasonable merit.
MORE PROXIMAL PROTOTYPE
Shortly after their academic review of the Cyborg Beast, Zuniga et al. followed up with a published technical note that describes fitting a more elaborate 3D-printed prosthesis to a seven-year-old boy with a congenital left shoulder disarticulation deficiency.4 The device fabrication began with a custommade Aquaplast® socket suspended by chest-strap harnessing techniques. Passive locking joints were integrated into the remaining device to permit locking the glenohumeral joint and elbow flexion as well as glenohumeral internal and external rotation and wrist pronation and supination. The only element in the prosthesis under active control was the voluntary closing hand, actuated by protraction of the sound side shoulder.4
The observed benefits of the device were preliminary, citing improvements in posture with the weight of the device offsetting the weight of the sound side limb, improved balance, and some bimanual functional activities such as holding a large ball. Unilateral function was limited by the low grip strength afforded by the device.4
Zuniga et al.'s publication was not blind to some of the limitations of 3D-printed prosthetic solutions, citing durability concerns, environmental considerations, and the current lack of printing standards as factors that warrant consideration. Further, they acknowledge that the gripping strength of the device was roughly one-tenth of that demonstrated by the sound side limb.4
However, the authors present several complementary rationales for the continued development and applications of such devices. In some instances, there are many children in developing countries who may lack access to trained clinical professionals or more traditional prosthetic resources. Alternately, in more resourced areas, a lightweight, rapid-prototype prosthesis might represent a transitional device that affords children an opportunity to perform basic bimanual tasks or lowimpact unilateral gripping activities in preparation for fitting with more sophisticated prosthetic options.4
In a similar technical note from the same journal, Gretsch et al. describe the novel integration of external power to a 3D-printed prosthetic hand.5 The authors describe two limitations with body-powered printed prostheses, exemplified by the Robohand. First, the technology requires active wrist motion and strength to activate the fingers. Second, the technology ties the movement of all five digits to its control motions, precluding individual activation of the thumb.
Their response to these limitations was the fabrication of a shoulder-controlled, externally powered 3D-printed prosthetic arm with a voluntary opening terminal device. The fingers of the hand are pulled closed at rest by internal elastic cables. Individual microservo motors are installed within each of the fingers. The microservo motors, powered by a nine-volt lithium ion battery, open the fingers when activated. The activation signals are drawn from an inertial measurement unit that reads the relative position of the shoulder. The device was programmed so that shoulder elevation opened the fingers, and shoulder depression allowed them to close. Opening of the thumb was attained by moving the shoulder forward twice. Similarly, moving the shoulder backward twice allowed the thumb to close.5
This prototype was evaluated on a 13-year-old patient with a traumatic transradial amputation. The patient found value in the ability to generate independent thumb motions and the low weight of the device. However, it was not without substantial limitations due to low battery life, noisy motors, low grip strength, and low durability.5 As such, it can only be viewed as a rough, preliminary prototype, but it represents a novel addition of external power to such systems.
FILLING FUNCTIONAL GAPS
In contrast to the increasing sophistication introduced in the Gretsch et al. article, a final article documents the attainment of a desired objective through a simple application.6 In this effort, the authors describe their process of using 3D printing and other prototyping materials to fabricate an activity-specific adaptive terminal device to allow a nine-year-old cellist with a transradial amputation to better hold the instrument's bow.6
Particularly for a child, the likelihood of prosthetic acceptance increases when the prosthesis addresses a specific gap in function or a targeted activity, something traditional terminal devices may or may not do. In this subject's case, he had a voluntary closing prosthetic hand that had been repurposed into a passive device to hold the bow. However, the socket, presumably outgrown, was ill-fitting and the grip on the bow was loose and generally ineffective.
In this case, 3D printing was used to create a prototype socket and bow holder, allowing the child to trial various lengths and angles to attain an appropriate alignment of the bow hold relative to his residual limb. The authors even describe incorporating Lego bricks into the interim prototype to allow the boy to adapt its overall length to an optimized position before printing the final, activity-specific device.6
As the momentum around such 3D-printed solutions appears to be growing, a few clinical caveats warrant mentioning. Burns et al. describe their use of a custom-fabricated Orthoplast® inner socket mounted within the dorsal hand shell to increase comfort and ensure that more of the user's wrist force is translated into prosthetic joint movement.1 Zuniga's devices were all fitted with the assistance of an occupational therapist and a prosthetist, with his protocols recommending the inclusion of clinical experts in the fitting process "to avoid skin abrasions or breakdown due to improper fit."3 The Aquaplast socket described in Zuniga et al.'s shoulder disarticulation prosthesis was fabricated by a certified prosthetist, and the authors restated that "inclusion of a certified prosthetist or upper-limb specialist on a research team is crucial for the proper development, fitting, and use of upperlimb 3D-printed prostheses."4 In the work of Gretsch et al., the emphasis was on the robotic hand mechanism, with the socket fabricated, at least in part, by a certified prosthetist.4 Thus, the published efforts in this space have occurred through beneficial interactions between printing engineers and trained clinicians. While the role of trained, certified prosthetists in the provision of 3D-printed solutions is still uncertain, it is clear that they can be valuable resources to successful designs and outcomes.
Phil Stevens, MEd, CPO, FAAOP, is in clinical practice with Hanger Clinic, Salt Lake City. He can be contacted at .
- Burns, M. B., T. Anderson, and G. R. Gogola. 2016. Three-dimensional printing of prosthetic hands for children. Journal of Hand Surgery 41 (5):e103-9.
- Zuniga, J., D. Katsavelis, J. Peck, et al. 2015. Cyborg beast: A low-cost 3d-printed prosthetic hand for children with upper-limb differences. BMC Research Notes 8:10.
- Zuniga, J. M., J. Peck, R. Srivastava, D. Katsavelis, and A. Carson. 2016. An open source 3D-printed transitional hand prosthesis for children. Journal of Prosthetics and Orthotics 28 (3):103-8.
- Zuniga, J. M., A. M. Carson, J. M. Peck, T. Kalina, R. M. Srivastava, and K. Peck. 2016. The development of a low-cost three-dimensional printed shoulder, arm, and hand prostheses for children. Prosthetics and Orthotics International. DOI 10.1177/0309364616640947
- Gretsch, K. F. H. D. Lather, K. V. Peddada, C. R. Deeken, L. B. Wall, and C. A. Goldfarb. 2016. Development of novel 3D-printed robotic prosthetic for transradial amputees. Prosthetics and Orthotics International 40 (3):400-3.
- Hoffmann, M., J. Harris, S. E. Hudson, and J. Mankoff. 2016. Helping hands: Requirements for a prototyping methodology for upper-limb prosthetics users. Proceedings of the 2016 CHI Conference on Human Factors in Computing Systems, 1769-80. DOI: 10.1145/2858036.2858340