Clinical Evaluation Of Prosthetic Hands

Germain Boivin, M.D. Maurice Mongeau, M.D. Jeannette Hutchison, P/O.T. Reg.


The purpose of this article is to describe briefly a method of clinical evaluation of prosthetic hands which has become an actual project at the Rehabilitation Institute of Montreal.

Considering that prosthetic hands aim at restoring both function and cosmesis, it is evident that both these factors have to be assessed in such a project.

It must be made clear that this study involves an assessment of prosthetic hands only, and not entire upper-extremity prostheses. The hands are considered as terminal devices only and are being tested according to their capability of grasping, holding and releasing objects, and their resemblance to the normal hand. To achieve this specific goal we voluntarily ignore, in one important part of the project, many factors that influence the functional level of an amputee wearing a prosthesis, such as age, and sex; whether the amputation is congenital or acquired and unilateral or bilateral; as well as educational level, occupation, and other considerations. We even ignore sources of energy, control systems and proximal positioning joints in order to obtain an exact and true picture of the grasping, holding and releasing capabilities of the hand considered solely as a separate entity of an upper extremity prosthesis.

Instrumentation And Working Method

Functional Evaluation

A total of 14 different prosthetic hands have been chosen for this evaluation. The selection will include:

  1. Five mechanical (conventional) adult hands - Dorrance, APRL, Becker Imperial, Becker Plylite, and Robin-Aids.

  2. Five externally-powered adult hands - Viennatone, Belgrade, Otto Bock Z6, Russian and Otto Bock Pneumatic.

  3. Four externally-powered children's hands - Otto Bock Pneumatic, Northern Electric Electro-Mechanical; and two Northern Electric prototype Hydraulic Units, differing slightly in design from each other.

The functional evaluation will be conducted in two series of experiments: (1) the free hand evaluation, and (2) the amputee evaluation.

Free Hand Evaluation

A special testing handle has been designed so that a normal experimenter can hold and control the hand in order to grasp, hold and release different objects (Fig. 1 ). This testing handle can be connected to any type of prosthetic hand. The control of the conventional or mechanical hands involves a foot pedal which transmits the opening forces through a conventional cable and housing system (Fig. 2 ). Electric and pneumatic hands will be controlled by a lever switch adapted to the testing handle.

A dual-axis goniometer (Fig. 1 ) is included within the testing handle in order to secure an easy reading of the angle of approach of the hand to the object, considering the long and transverse axes of the hand in relation to the vertical or horizontal plane.

A large spectrum of objects to be grasped is being collected. These objects are divided into two categories: (a) experimental objects, characterized by their different sizes and shapes, e.g., flat, cuboid, spherical, cylindrical, conical and discoid objects (Fig. 3 ); and (b) objects of daily use, that is, those objects that we currently hold and manipulate in activities of daily living, such as cups, plates, utensils, faucets, door handles, shoe laces, keys, etc.

As a first step, the capability of the hand in grasping each of these different objects will be tested and the angles of approach and the prehension pattern will be recorded.

In the second step, the stability of the object grasped by the hand will be checked by recording the tension needed to displace the object from the hand, using special instrumentation (Fig. 4 ). This tension will be tested in relation to both the long and the transverse axes of the hand.

In dealing with cylinders and discs, the torque required to rotate the objects within the hand will be tested and recorded.

All of the experimental objects are made of aluminum and therefore have the same texture and surfaces. All the prosthetic hands will be covered with a cosmetic glove. In some aspects of the testing program the holding surfaces of the hand may be padded with different materials, such as sandpaper or foam rubber, to simulate situations in which objects of different textures are grasped.

Amputee Evaluation

To reduce the influence of the proximal joints on prosthetic-hand function, a decision was reached to choose below-elbow amputees only. Furthermore, in order not to disturb the amputees by a change in the control system, subjects who are accustomed to controlling the prosthetic hand with a cable and harness system will try the conventional mechanical hands, the Belgrade hand and the CO2 hands. Patients who are used to the myoelectric system will try the Russian hand, the Viennatone and the Model Z6 Otto Bock hand.

A total of four adults and two children will be chosen in the following way: for the adults, one bilateral and one unilateral amputee currently fitted with a cable and harness system and one unilateral and one bilateral presently fitted with a myoelectric system. For the children, only one bilateral and one unilateral amputee fitted with conventional systems will be selected. Prehension tests will be carried out on experimental and daily-use objects in the same manner as for the freehand experimentation except that only experimental objects of minimal and maximal size will be checked. However, all the daily-use objects will be included. We will not have to test the angle of approach; and the displacing tensions will not be measured.

Once all the tests are completed with the wearer's own prosthetic hand, the same tests will be carried out with other types of hands.

Whereas the speed of operation was not considered in the free-hand evaluation, it will be in the amputee evaluation. The assessment of the amputee performance will be both objective and subjective; the objective criteria being the number of objects being picked up and moved, the speed, the accuracy of operation and the number of errors, the degree of independence achieved in activities of daily living and all of the objective tests carried out in our usual amputee evaluation. Subjective criteria will consider such factors as amputee reactions to noise, weight, ease of operation, special difficulties, etc.

Cosmetic Evaluation

This procedure will take into consideration the points of resemblance between the artificial hand and the normal, and will be divided into two parts: (A) static cosmesis, and (B) dynamic cosmesis.

  1. Static cosmesis. In static cosmesis we will consider the rest posture, shape, texture, abnormal projections; and the gloves.

  2. Dynamic cosmesis. In dynamic cosmesis we will consider the appearance of the hand in motion, the changes in finger alignment as they move, the normality or abnormality of the combination of joint motions, and other factors.

Technical Evaluation

The technical evaluation will be limited to the following aspects: the absolute weight of the hand and its relative weight in relation to volume, the pinching force, the maximum opening, and the speed of the closing and opening phases. These technical data will be correlated with the cosmetic and functional evaluations previously described.

Anticipated Results

It was decided not to compare prosthetic hands with prosthetic hooks, since the purpose of this project is to determine the differences between different prosthetic hands considered as terminal prehension devices. It is anticipated that this work will help us to determine whether it is really useful to have more than one prehension pattern in a prosthetic hand, whether the finger alignment and padding are more important than the pinching force, whether multiple linkage fingers are more functional than rigid semiflexed fingers, and whether it is functionally significant to have active fourth and fifth fingers as compared to passive ones. It is envisaged that recording the angles of approach of the prosthetic hands to the objects will help to determine the importance of easy hand positioning through suitable wrist units.

It is hoped that a preliminary report of our results will be available in approximately six months.

Germain Boivin, M.D., Maurice Mongeau, M.D. and Jeannette Hutchison, P/O.T. Reg. are associated with the Rehabilitation Institute of Montreal Department of Research Montreal, Quebec, Canada