Rancho Rehabilitation Engineering Program: Project 1

Project 1 -- A Body Powered Hand for Toddlers:
Easy Feed Hands for the Growing Child

STAFF:

Samuel E. Landsberger, ScD
Pierre Leung, MSME
Somboon Maneekobkunwong, MSME
Grigor Kerdanyan, MSME
Roger Weber, CPO
Julie Shaperman, MSPH, OTR

What is an EASY FEED Hand?

The design builds on observations of children's natural hand use patterns and their cognitive skills. Young children frequently transfer objects from hand to hand. The Easy-Feed Hand takes advantage of this hand use pattern as children transfer objects to the prosthesis with the sound hand. A young child wearing a prosthesis usually picks up an object with the sound hand and transfers it to the terminal device (hand or other). This method is fast and simple since it requires no prosthetic hand pre-positioning - a constant requirement for picking up objects from a container or table surface with a terminal device. Children with absence of one hand tend to use the prosthesis as a non-dominant hand,

THE DESIGN CONCEPT OF THE EASY-FEED HAND: When a person pushes an object against the thumb and finger tips, the Easy-Feed Hand opens to receive the object. Kinematics of Easy Feed The placement of the pivots, and the configuration of the fingers facilitate this opening motion. Spring action closes the hand automatically.

To assure secure grip on objects, the Easy-Feed Hand incorporates a feature called Self-Energizing Grasp Geometry (SEGG). This feature restrains the object in the hand for secure grip. The hand acts something like a one-way valve. Passive springs molded directly into the mechanism act as a safety valve to release grip when a reasonable withdrawal force is applied to the object.

The system is called Easy Feed since the hand operates (opens and closes) in response to objects used to perform activities, without requiring an auxiliary operating system, e.g. body powered harness and cable. The child does not need to manually open or close the hand. As children become more adept at pre-positioning, and wish to grasp objects from a surface, they may find it useful to have a body-powered control system added. The mechanism for including a voluntary opening or voluntary closing system is incorporated into the Toddler Easy-Feed Hand design. The Easy-Feed Design has a patent pending.

Why is the Easy-Feed Hand Important?

For Young Children:
Parents of infants and toddlers with an upper limb absence usually want a hand for their child. Existing body-powered hands require higher operating forces than young children can produce until they reach school age. Voluntary opening body-powered hands that operate with little effort do not give firm grip on objects. Young children using voluntary closing operation forget to maintain cable tension to keep the hand closed. Externally powered hands give good early function, but are not appropriate or available to all children. Passive hands do not teach young children that their prosthesis holds objects, and may delay the development of early bi-manual hand use patterns. The Infant and Toddler Easy-Feed Hands offer a low cost, lightweight, rugged alternative that has good appearance to meet this need.

For Teens and Young Adults:
Clinicians report that teenagers often ask for cosmetic hands; some teens are even willing to forgo their functional prosthesis in order to look more like their peers. Many functional hands available to them are heavy and don't appear as cosmetic as they would like. An objective of this project is to produce a highly cosmetic hand that incorporates the Easy-Feed feature to offer some function but without requiring a harness and cable, along with good appearance to meet needs of teens and young adults.

For Young People in Underdeveloped Countries:
Children in underdeveloped countries who need a prosthetic hand often do not have access to expensive technology and skilled prosthetists nearby who can fit and repair their prostheses. Since the Easy-Feed Hand functions without a control system, the hand could be applied by persons who have no special training. The hand screws into any standard (1/2 - 20) threaded wrist connector that is part of whatever socket and forearm they are able to fashion. An objective of this project is to produce a very durable, low cost Easy-Feed Hand that will be usable by these children. This will be called the Appropriate Technology Easy-Feed Hand. Work on this hand will begin when the toddler and teen hands are available. We are working with the Rehabilitation Engineering Center for Improved Technology Access for Land Mine Survivors on this aspect of the project. (For more information on the land mine project, see www.banmines.org/)

What is the current status of the Easy-Feed Hand?

The Infant Easy-Feed Hand

An Infant Easy-Feed Hand has been designed and developed. The hand is produced by TRS, Inc. of Boulder, CO. and is called "Lil EZ." Early prototypes were evaluated and the hand was improved before the current clinical field evaluation.

Easy Feed Hand Fig. 4 Easy Feed Hand Fig. 5 Easy Feed Hand Fig. 6

Ten children evaluated the Infant hands in six centers in North America. Evaluation results show that the hand met its design goals for structural durability and ease of installation. Maintenance was easy, but some active users showed some stains after three months. Acceptance was excellent. Children all became aware that their hand could hold objects and they placed objects into the hand through the space between index finger and thumb. While adults could feed objects into the hand through the tips, children found the target too precise and used the alternate insertion method Easy Feed Hand Fig. 7

The Toddler Easy-Feed Hand

Development of the Toddler Easy-Feed Hand has been the major focus of this year. Designs for the internal mechanism have been revised several times to meet requirements for function, size, and mating with the glove. The size for two to four year olds is close to that of a two-year old since a prosthetic hand that is larger than the sound hand is unacceptable to families, while a prosthetic hand that is slightly smaller is more acceptable. A model of the outer shape and size of the glove was finalized and work has been in progress with glove-makers in Hong Kong and the USA who use a very durable silicone material that looks very life-like and should wear well. Several trials with the glove form were needed to arrive at one that was the proper size and appearance. The glove design is unique in that it includes "pleats" to allow stretch and compression on hand opening and closing while retaining good appearance. This is needed because the Easy-Feed Hand has a wide span at full opening.

An inner-sleeve that will fill the space between the mechanism and the glove is made of a neoprene material otherwise used in wetsuits. The inner sleeve must be durable, give a soft feel, and not restrict movement for functional activities. The inner sleeve has openings at points where finger tips bend. Another solution for the inner sleeve involves a series of ribs that compress under the pressure of an object in the hand and resume their original shape when the object is released. These approaches are also tested in the laboratory.

Preliminary evaluation of the Toddler Easy-Feed Hand had promising results and identified a few features that would make it easier for local prosthetists to install and maintain the hand. Easy Feed Hand Extra1-3

In the coming year, twelve prototype hands will be developed for clinical evaluation. Initially, one or two hands will be evaluated locally at the Los Angeles Shriners Hospital. If results are promising, wider clinical evaluation will follow. In preparation for wider clinical evaluation of the Toddler Hand, applications have been approved by institutional review boards in four other pediatric amputee treatment centers.

It is hoped that the Toddler Easy-Feed Hand will become available to limb deficient children everywhere through a manufacturer on completion of this project.

Appropriate Technology Hands

In preparation for development of the Easy-Feed Appropriate Technology Hand, a survey was conducted by e-mail of centers in Central America and Asia. Contacts were arranged through USAID and the RERC on Improved Technology Access for Land Mine Survivors.

Your questions, comments and suggestions on the Easy-Feed Hands are welcome. Our e-mail address is: info@ranchorep.org

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Last modified: Mar. 07, 2005