Poster V15 - A 3D-printed carbon fiber weightlifting prosthesis for people with partial finger amputation

Introduction: Complete or partial finger amputations comprise 10-15% of the 2.1 million people living with limb loss in the United States. To help restore basic hand functionality and help users perform daily tasks, new prosthetic technologies are leveraging 3D printing to create cost-effective prosthetics customized for a user’s specific hand anatomy. These devices are body-powered, solely relying on user movements for prosthesis control. Although they have the potential to restore function, it is difficult to design these prosthetics to be durable, comfortable, and versatile. For example, individuals with distal partial finger amputations have limited prosthetic options given that they maintain most of their finger function and require assistance with only a few, specific tasks. Devices such as Naked Prosthetics’ PIPDriver enable users to perform dexterous tasks, such as typing and writing, but are not intended for load bearing. Products that provide greater load strength are designed for users with complete finger amputation, such as Naked Prosthetics’ GripLock Finger, and therefore are not as useful for those with amputations past the proximal interphalangeal (PIP) joint. Thus, it remains challenging for users with partial finger amputation to use these prosthetic devices during load-bearing tasks, such as weightlifting or rowing. The objective of this study was to determine the design of a load-bearing exercise prosthesis for an individual with partial finger amputation.

Materials and

Methods: One individual with partial amputation of the right index, middle, ring, and little fingers participated in this study (male, age: 25, weight: 225 lbs). He reported difficulty performing exercises such as pull-ups, deadlifts, and rowing with the impaired hand. Through user interviews, we determined the prosthesis needed to be strong enough to support a maximum of 250 lbs, be lightweight, be easy to put on and take off, and be comfortable for the user while allowing him to regain his confidence and abilities in the gym. We chose to form the prosthesis as a hook with an inner diameter matched to fit a standard gym dumbbell (1.2 in) and sized to match the user’s hand dimensions (4 in wide, 5.03 in tall). The device is worn on the palmar side of the hand, with a wrist strap to secure the device to the anterior part of the wrist (Fig. 1). A thumb cutout was added to improve dexterity and overall grip. The curved wrist seat allows for a more comfortable fit, while the tapered angle of the seat’s sides allows for radial and ulnar deviation during exercises. We 3D printed the prosthesis using MakerBot Method Nylon Carbon Fiber Filament, chosen for its high tensile strength (7.33 GPa) and Young’s Modulus (225.4 GPa). These material properties ensure the device will maintain its shape without deformation and provide consistent support under heavy loads. We tested the prosthesis for durability and functional use.

Results, Conclusions, and Discussions: The prosthesis showed no visible deformation or fractures after dropping a 10 kg weight on it from a height of 3 feet, demonstrating the material’s ability to withstand substantial force (maximum energy absorbance of 89.61 Joules). User functionality testing consisted of the user completing pull-ups, deadlifts, and rowing to simulate the device’s intended use. We observed the user could perform pull-ups, deadlifts, rowing, and dumbbell lifting with no fracture or deformation of the device. The user reported the thumb cutout enabled him to achieve a secure grip on the rowing machine handle and the dumbbells, allowing him to increase the intensity of these exercises for more difficult training. The user was able to lift 70-lb dumbbells using the prosthesis, which he previously could not do. However, we observed that when lifting heavier dumbells, the prosthesis pulled away from the wrist when using an elastic wrist strap but not with the nylon wrist strap (Fig. 1). The user reported that the device was comfortable to wear, easy to put on, take off, and clean and allowed him to regain confidence and ability in the gym. We evaluated the prosthesis in a real-world gym setting, ensuring the final product met and exceeded the user’s expectations, giving him the confidence to perform his desired exercise without restriction. Our results demonstrate the strong potential for entirely 3D-printed, customizable exercise prostheses for partial finger amputees. The techniques used to create this device could be applied to create more personalized, durable prosthetic devices that empower users to engage in a wide range of physical activities with comfort and confidence.

Acknowledgements (Optional): Efforts are sponsored by George Mason University Bioengineering Department and Quality of Life Plus.