Prosthetic Research And Training Unit

Colin A. McLaurin, B.A.Sc, P.Eng.


The Prosthetic Research and Training Unit (PRTU) functions under a Medical Advisory Board of which Dr. John E. Hall is chairman. The Unit relates very closely to the Amputee Clinic at the Ontario Crippled Children's Centre, its functions being (1) to advise the chief clinician, particularly with respect to engineering considerations; (2) to assist the commercial limb shops in adopting new devices and techniques; (3) to design and develop specific prostheses when these cannot be obtained elsewhere; and (4) to become familiar with patient problems so that research activities can be directed most fruitfully.

As the name implies, the general purposes of the PRTU are research and training activities in the field of prosthetics. This article presents a brief report of current research projects. The staff member associated with each item is indicated.

Swivel Walker (Wallace Motloch)*

*student prosthetist

Two patients have been fitted with the swivel walker developed at the Centre. This device is designed for patients who functionally are hip disarticulation amputees and whose arms are inadequate for crutch or cane use. Both these children originally used rockers (both the fore-and-aft and lateral types) as an aid in developing balance. In the lateral-type rocker the body weight is shifted from one side to the other. The swivel walker also incorporates this lateral motion, and in addition the body may be swiveled forward about a vertical axis on the stance foot for ambulation purposes. The principle is illustrated in Fig. 1

Fig. 2 shows a child wearing an early-type swivel walker, and Fig. 3 shows a newer type, in which the swivel mechanism is mounted entirely in the ankle.

These swivel walkers have been in use for more than a year, and the children wearing them are proficient in walking forward and backward and even up ramps, but not on rough ground. The step length is about 3 inches and the walking speed is 120 paces per minute. A manual describing the fitting of swivel walkers and the training of children in their use is available upon request. Although drawings of the ankle mechanism have been made, arrangements for their manufacture have not yet been completed.

Electrically Powered Components

The electrically powered prosthetic components designed and developed at this Centre are the two-fingered electric hook, the electric elbow, the electric wrist rotator, and a coordinated preschool electric arm.

Electric Hook (Kaare Lind)*

*design and development technologist

Following trials with six models of the two-fingered hook (Fig. 4 ) 36 have now been manufactured by Sunny-brook Prosthetic Services. These hooks will be used for further clinical testing at this Centre and elsewhere.

To date the hooks have been fitted to five amputees-two above elbow, two shoulder disarticulation, and one below elbow. In the latter fitting, the socket is of the "Muenster type," and hence no cables or suspension straps are required (Fig. 5 ). The 5-ounce battery pack is incorporated in the forearm, and the device is operated by distal stump rotation, which presses a lever.

Electric Elbow (Kaare Lind)

Only one unit of the electric elbow has been made and fitted (Fig. 6 ). However, a dozen more have been ordered, and delivery is expected very shortly. This unit is slightly larger than the Hosmer child-size elbow (E-50) and is made to fit a standard forearm. The motor projects above the elbow unit and in long stumps must be mounted parallel to the socket. In the unit fitted, operation is by a rocker switch mounted on the medial side of the upper arm and controlled by pressure against the side of the body. The lifting force is approximately 7 pounds. A safety clutch prevents gear damage from excessive external loads.

Electric Wrist (Kaare Lind)

Only one wrist unit has been fitted, and this to an above-elbow patient (Fig. 7 ). The unit is controlled by means of a University of New Brunswick three-state myoelectric control system. The wrist unit is used with a standard hook and is simple and rugged in construction, but somewhat heavy. Six additional units have been made up and are now ready for fitting.

Coordinated Preschool Electric Arm (Kaare Lind)

The first prototype of the coordinated arm was recently finished and fitted to a bilateral phocomelic patient (Fig. 8 ). One motor powers the shoulder unit, which is mechanically linked to the elbow so that the arm moves in a physiological fashion from the area of the mouth down to the table level and then continues through to the back of the body. The motor unit is essentially the same as in the elbow mentioned above and holds the arm in any position when the motor is stopped.

The forearm contains the hook mechanism, which is identical to that used in the two-fingered hook. The terminal device is a three-fingered hook, the design of which was motivated by a desire to avoid the need for wrist rotation. In the clinical tests conducted thus far this goal seems to have been achieved. The arm appears to be useful for eating, picking up objects at table-type play, painting, carrying, sweeping, etc. (Fig. 9 ).

Although it reaches behind the buttocks, the coordinated arm has not yet been tried for toilet care. When fitted bilaterally, this device provides bimanual grasping of bulky objects. Control of the arm is by simple rocker switches, which in the case fitted are actuated by the child's phocomelic fingers. Control of the terminal device is by a simple lever switch. Drawings of these items have been made, and efforts are being made to obtain a suitable manufacturer.

Myoelectric Control

In cooperation with the University of New Brunswick, we are trying their three-state myoelectric control unit (Fig. 10 ) with several patients in an effort to determine specific applications for this type of control and to compare it with biomechanical or simple switch-type controls. It is interesting to note that congenital child amputees have little difficulty in getting good control of the myoelectric system in a matter of minutes. In the very limited service application of this type of control, it appears that inadvertent operation is the most serious problem.

Activated Spatula

A fair percentage of the case load for this device consists of acheiria- or adactylia-type anomalies where some carpal elements are usually present, so that some motion of the distal portion in the stump is possible. In the past these patient: have been fitted with a socket and a terminal device similar to that used for a wrist disarticulation amputee, or with a spatula fastened to a wrist cuff to provide apposition to the distal motion of the stump. In an attempt to give the prehension advantage of a voluntary-opening hook and the sensory advantage of the spatula, several patients have been fitted with the activated spatula. In this device the apposition post is spring-loaded to oppose the distal end of the stump and is connected with a standard below-elbow harness system so that it may be voluntarily opened like a hook finger (Fig. 11 ). Some 15 patients have been so fitted apparently they prefer the activated spatula to the types of prostheses previously worn.

In an attempt to increase the stability of the apposition post, a second model was designed to provide automatic locking, so that the post would not open except when pulled by the control cable (Fig. 12 ). Six of these units have been fitted, and 20 more have been ordered from the manufacturer (Sunnybrook Prosthetic Services). The advantages and disadvantages of the locking type have not yet been established. A third and simpler design of a nonlocking device for infants has also been produced (Fig. 13 ).

Slip Socket (Bill Sauter)*

*chief prosthetist

A bilateral below-knee patient seen in the clinic had extensive skin grafts which covered much of the surface area of one limb. Attempts at fitting a standard prosthesis always resulted in breakdown of the skin in the socket almost immediately.

A satisfactory solution to the problem was achieved by the use of a plastic quadrilateral weight-bearing thigh section plus a spring-loaded slip socket padded internally with a half-inch of soft foam rubber. The slip socket is supported on a vertical shaft which slides with very little friction in ball-bearing-type axial bushings located in the lower part of the shin (Fig. 14 ). A steel spring maintains a pressure of a few pounds between the stump and the socket. The socket pistons in the shank about 1 1/2 inches, but pistoning between the socket and the stump is practically nonexistent. After six months the stump had improved so much that the soft foam lining was no longer necessary. However, the slip-socket mechanism has been retained.

Winnipeg Instant Sockets

In an attempt to provide faster prosthetic service for traumatic above-knee amputees, the Winnipeg* prefabricated adjustable plastic quadrilateral sockets have been used. They have been mounted on adjustable pylons with SACH feet attached. By means of a lap joint in the lateral wall, the socket can be adjusted to the patient's individual measurements with hose clamps. Foam Silastic has been injected into the distal end of the socket to provide total contact. The sockets have been used (usually for several weeks) until shrinkage was essentially complete. They have required only routine adjustments proximally and distally. In each case the permanent prosthesis was fabricated from a cast taken directly from the temporary socket. Three or four cases have been fitted to date, and the fit achieved with these standard sockets appears to be as good as that obtained with those that are custom-made in the conventional way. The chief difficulty experienced has been obtaining suitable suspension when fitting is attempted before reduction of excessive swelling from edema.

*Prosthetics/Orthotics R&D Unit, Manitoba Rehabilitation Hospital, Winnipeg, Canada.

Above-Elbow Sockets (Bill Sauter)

Because of difficulties encountered in obtaining adequate suspension and stability in conventional above-elbow sockets, particularly with infant children, new methods of fitting have been attempted. Informal experiments have led to the present socket design, which employs a snug fit in the axilla with a large cutout on the lateral proximal wall and a strap applied directly over the shoulder for suspension (Fig. 15 and 16 ). A flexible plastic, particularly "Polysar," cast is the socket material of choice.

The distal circumference of the socket may be made oversized so that it may be split and adjusted by overlapping and fastening with Velcro or a similar material. The preferred harness pattern is one that is similar to the saddle or chest strap type fastened to the anterior and posterior horns of the socket. The results achieved to date have been encouraging, and use of the method is becoming routine at the Centre.

"Polysar" Cast (Bill Sauter)

"Polysar" cast is an experimental plastic developed by Polymer Corporation, Sarnia, Ontario. When heated to 140° F., it may readily be formed until it cools to 95° F. Because of this low-forming temperature, it can be formed in direct contact with the patient's skin. It can also be readily welded at this temperature. "Polysar" is slightly more flexible than polyethylene. It appears to be tougher, has a flat, opaque finish, and can be pigmented almost any color.

Because of the broad temperature range for forming, local areas can be heated and reformed much more readily than polyethylene.

Experimental Applications

So far, this material has been use experimentally to produce above-elbow, below-elbow, shoulder disarticulation, and elbow disarticulation sockets; spatula cuffs; below-knee and knee disarticulation sockets. These items have been made from flat sheets approximately 1/8 inch in thickness. A thicker material would be suitable for above-knee and po sibly hip disarticulation sockets.

A typical and satisfactory means om making a socket is to heat the material in the oven, in hot water, or with a heat gun and then apply it directly to the stump, pulling it into place with a elastic bandage. The procedure is quite compatible with the Northwestern sling-type casting procedure for below-knee sockets. The time required to make a socket is about the same as that needed for taking a plaster cast. Modification to accommodate the patellar tendon shell, etc., can be readily made after the socket is removed from the stump.

Many Possible Uses

In addition to the prosthetic applications mentioned above, "Polysar" cast, has been used for custom-formed contour chairs, scoliosis braces, arm splints, chest panels, contour pads for long-leg braces, and quadriplegic hand splints (Fig. 17 and 18 ).

Although the flexibility and ease of adjustment characteristic of this material are unique in themselves, its most significant attribute is that sockets or splints can be produced in a time comparable to that for cast taking in the old system. Thus with a stock of pylons, feet, elbows, terminal devices, and other components, it is possible to custom-fit and fabricate either an upper-extremity or a lower-extremity prosthesis in a few hours.

Our biggest apprehension in the use of the material has been concern that deformation will occur from the constant loading and excessively hot conditions, but so far, problems from this factor have not developed.

Colin A. McLaurin, B.A.Sc, P.Eng.is the Project Director Prosthetic Research and Training Unit Ontario Crippled Children's Centre Toronto, Ontario