Designing a Fully Oppositional Prosthesis for People with Finger Amputations

Department of Bioengineering

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Project Abstract

Partial hand amputations affect many people across the world; in the United States alone, as many as 45,000 partial hand amputations occur annually [1]. Point Designs LLC is an American based company that produces prosthetic fingers for people with finger amputations to give function and form. The company has an already established customer base in the United States with plans to expand into the European market. To expand, the prosthesis must be narrowed on the lateral sides of the proximal phalanx and be produced at a lower cost. This will allow the prosthesis to be sold at a competitive price point while also allowing it to function in a cosmetic covering. The purpose of this project is to design and fabricate an affordable and realistic prosthesis for Point Designs LLC at a price reduction of 30-50%.

The Point Digit is a mechanically-based finger with ten different lockable positions. A torsion spring is located in the proximal interphalangeal (PIP) joint to return the finger from any flexed position back to its original position. The finger can return to its original position once fully flexed or with the use of the spring back button located on the proximal phalange. This prosthesis should share the same functionality as the current Point Digit from Point Designs LLC.

Additionally, this new prosthesis will be designed to be functional in a cosmetic covering. To achieve this, the PIP and metacarpophalangeal (MCP) joints will be redesigned to be more life-like inside a cosmetic covering as shown in Figure 3. Redesigning the prosthesis will also allow the spring-back mechanism to function properly within the cosmetic covering, as the current version cannot overcome the additional resistance of the cosmetic covering.     

The prosthesis is designed to minimize cost and maximize the compatibility with a cosmetic covering. The new design features flat steel plates for the medial and distal portions that can be easily manufactured. This reduces the manufacturing cost along with making the device lighter. Plastic pieces surround the medial and distal sections of the design which eliminates pinch points. A newly designed spring can store ~300% more energy in full flexion than the original spring; this will allow the device to overcome the resistance provided by the cosmetic covering. The volume of the prosthesis is reduced by ~30%. This not only improves the function within a cosmetic covering but also reduces the cost of manufacturing.

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