DESIGN OF A LOW-COST PROSTHESIS FOR USE IN DEVELOPING REGIONS

Alison J. Sitek
Harrington Department of Bioengineering
Arizona State University
Tempe, AZ 85287-9709

ABSTRACT

The upper limb amputee population in developing regions is steadily increasing. Most of these amputees lack the funds to buy a prosthesis, and are therefore often denied employment. The goal of this project was to design an inexpensive, yet effective, upper extremity prosthesis that could be used in a manual labor or agrarian job. This has been accomplished by developing a new socket fabrication method, a simple locking elbow component, and a terminal device manufactured from Delrin.

BACKGROUND

Because of war, inaccessibility to healthcare, and an unsafe farming environment, the upper limb amputee population in developing countries is growing at an alarming rate. In India alone, it is estimated that the number of amputees needing prostheses increases by 17,000 annually (1). Owning a prosthesis often saves an amputee from a life of begging and facilitates his return to gainful employment. However, a severe lack of funds will prevent most amputees from ever receiving a prosthesis (2). This can be changed through the development of an effective and inexpensive upper limb prosthesis.

STATEMENT OF THE PROBLEM

The aim of this project was to develop a low-cost upper extremity prosthesis. It was designed using the following criteria. The total cost should not exceed $100. It should be easily manufactured and compiled as a kit for easy delivery to developing countries and/or rural America. The socket fabrication process should allow for fitting in the field by those with limited resources and experience. The arm should be durable for use in manual labor, especially in an agrarian environment. It should not be compromised by exposure to dirt and water. The arm should also be easily repaired by someone in the field with limited skills. Finally, the prosthesis should be culturally and aesthetically acceptable by a wide range of amputees.

RATIONALE

For many of the developing world's amputees, a prosthesis is a purchase they will never be able to afford. Although various organizations are involved with distributing used prostheses and manufacturing them at reduced costs, even these are often too expensive to be purchased by the people who need them (3). In addition to cost, there are other barriers that prevent amputees in the developing world from receiving prostheses. There is often a long waiting list for available prostheses, especially in those countries, such as Vietnam, where prosthetic work is filtered through the government. In his 1999 field survey of prosthetic use, Matsen reported a hierarchy favoring North Vietnamese war heroes first, followed by esteemed public officials, other North Vietnamese veterans, women involved in the war, civilian casualties, and "social amputees", those whose amputations were not caused by the war (2). In other cases, prosthetic centers are too remote, and amputees are unable to reach them (3). A prosthesis can enable an amputee to obtain a job, which he most likely will not be able to find without one. There is a need for an inexpensive upper extremity prosthesis that can be both fitted in the field and easily repaired without special equipment.

DEVELOPMENT

In fall 2000, an interdisciplinary team composed of both bioengineering and industrial design graduate students was created. The team sent out surveys to prosthetists working in developing countries to gain feedback on the needs of amputees in those regions. The team also compiled information on the state of prosthetics in developing countries and developed several designs for creating upper extremity prostheses out of locally available materials. In fall 2001, the cold molded socket fabrication method was designed and tested. Feedback on the socket was received from a trans-radial amputee, a local prosthetist, and from several attendees of the 2001 American Orthotic and Prosthetic Association conference. In 2002, the terminal device and elbow component were designed using SolidWorks 2001.

DESIGN

Figure 1: Cold Molded Socket

The arm consists of either two or three main components, depending on whether a trans-humeral or trans-radial amputee will be using it. They are as follows: the socket, the elbow, and the terminal device. The socket is formed by molding two layers of fiberglass casting material over the residual limb and coating it with epoxy to form a smooth surface (please see Figure 1). The elbow is composed of high-density polyethylene (HDPE) and nylon. It locks into various positions of flexion by using the opposite arm to tighten a screw (please see Figure 2). The terminal design is made of Delrin plastic (please see Figure 3). This material was chosen because it is both machinable for prototypes and injection moldable for production. The terminal device was designed using the Hosmer-Dorrance hook as an initial point, because this design has benefited from almost 200 years of modifications. Four major changes were applied: 1) strengthening the hook to allow manufacture from Delrin instead of aluminum, 2) modifying to facilitate easy injection molding, 3) using a common roller blade bearing as opposed to the current specialized bearing, and 4) eliminating the cable, allowing for either actuation by the opposite hand or another surface. This last change was implicated based on data received from the aforementioned international surveys.

Figure 2: Elbow Component

The kits will contain a terminal device with a supply of rubber bands, an elbow component, and the materials to fabricate a socket. These components will be connected by pipe, bamboo, or a similar cylinder provided by the amputee.

EVALUATION

Testing of the prototype will be performed in spring 2003. Both bench-top testing and amputee trials will be conducted. Bench-top tests will be performed to 1) test the terminal device to failure, 2) fatigue the plastic strips of the elbow component to failure, and 3) test the socket-pipe interface to failure. For the amputee trials, 6 amputees will be recruited through local prosthetic clinics. They will be both male and female adults of varied ethnicity. Hopefully, three will have

Figure 3: Terminal Device

experience using a prosthesis and three will not. This will provide an idea of how the changes from the current technology will be accepted by amputees familiar with the current terminal device. The trials will consist of three stages. In stage 1, a prototype will be fabricated and fit for each subject. The subjects will then be videotaped while performing a set of activities of daily living (ADL). During stage 2, the subjects will be asked to use the prosthesis in activities of minimal risk at home/work for one month and to daily record a log of their usage on a provided audiocassette tape. Stage 3 will consist of a second videotaped set of ADL and an interview on the function and appearance of the prototype. Finally, a Failure Mode and Effects Analysis (FMEA) will be conducted to ensure the safety of the prosthesis.

DISCUSSION

An inexpensive upper extremity prosthesis has been designed. It will be tested and refined in spring 2003. The modifications will be used to create beta prototypes. Projected research includes testing these second generation prototypes with the target population in countries around the world.

ACKNOWLEDGMENTS

Thank you to Dr. Gary Yamaguchi, Dr. James Sweeney, and Don Herring for their advice as members of my supervisory committee; to Brian McMahon and James Egan for gathering the survey information; and to Sander Nassan and Bill Atteberry for valuable feedback on the design.

Alison Sitek
Harrington Department of Bioengineering
Arizona State University
Tempe, AZ 85287-9709
480-727-7041
480-727-7624 (fax)
alison.sitek@asu.edu