An Above-Knee Training Prosthesis For Physical Therapists

Hans Hillander


The invaluable assistance rendered by Mr. R. Setzer, Prosthetist, Sunnyview Rehabilitation Center Brace Shop is gratefully acknowledged. Without his skill, craftmanship, and patience in a difficult assignment this training prosthesis would not have materialized.

An idea was born the day the nervous patient assailed me and said, "It's all right for you to say it's easy. You'd think differently if you had only one leg!" I realized then that I knew very little about the patient's problems and feelings. How would it be possible to simulate an amputee's infirmity, despite the presence of my own two "normal" legs and thus understand his lack of confidence, his fears, and his insecurity?

Rehabilitation Studies

Sunnyview Rehabilitation Center, Schenectady, New York has been a recognized Amputee Center since 1957 and conducts clinics twice monthly. It was from Sunnyview that this therapist, an orthopedic surgeon, and a physiatrist went to New York university to take a course in amputee rehabilitation.

Most of the problems to be encountered were covered thoroughly in the course, with amputees on hand to demonstrate their functional ability with the then new quadrilateral socket. The socket and other developments, including alignment jigs, constant and variable friction knee units, conventional ankle and SACH foot were adequately presented. Gait deviations, as well as their causes and methods of prevention, were also discussed. Theoretically we had all the know-how we needed to conduct effective treatment. But there was a missing link: practical experience on the part of a non-amputee therapist.

Non-Amputee "Training Prosthesis"

With the cooperation of the prosthetist associated with our clinic, plans for a training prosthesis to be worn by a non-amputee were developed. These had to take into account the problems of construction, alignment and suspension. Our guide to adequacy was the Check-out Form from the NYU training course.

The major difficulty, obviously, was to construct a prosthesis that could be worn by a therapist yet with the normal function of the intact leg rendered ineffective. If the project was to be a success the therapist must be forced to rely upon the artificial device as a means of ambulation and be subjected to the typical pressures, loss of balance and loss of sensory perception experienced by an amputee. During the development of the prototype limb it was discovered that the socket had to be made as a separate unit (which was applied first), following which the knee unit and attached calf and foot were added.

The training unit consisted of a quadrilateral socket, a knee unit, a calf section (lower leg) and a conventional single axis ankle-foot assembly. Accessory suspension devices were not required because of a snug fit and apparent expansion of the quadriceps muscles during swing phase.

Standard below-knee joints were used with the distal straps attached to the lower leg and the proximal straps fitted into slots in the thigh (socket) unit. The therapist's normal leg was suspended in sling fashion at approximately 90° of knee flexion by use of dacron straps attached to the medial and lateral areas of the posterior aspect of the socket, as shown in Fig. 1 .

Donning the Prosthesis

No assistance and less than a minute of time is needed in donning the prosthesis. Once the socket is in place, with the ischial seat accurately located, the lower unit (knee, shin and foot) is attached using single screws on the lateral and medial sides to join the two parts securely. The dacron sling is then fastened to the ankle and attached to the socket.

Experiences in Use

When wearing the "trainer" the therapist's initial reaction was that the normal center of balance had moved approximately two inches towards the "non-amputated" side. Balancing in the normal manner by pushing the foot against the floor was now a problem and the hip seemed to be the only stable area. In swaying from side to side (weight on one leg, then the other) the hip or lower trunk seemed to collapse and the shoulder on the same side dropped down. Lateral trunk bending while walking may be the outcome of this collapsing tendency.

Walking without support at this time seemed utterly impossible. Initially a four-point gait pattern in the parallel bars proved to be the best method. Later a cane was used, and then nothing. The wearer noticed a tendency to over-swing the "prosthesis". This caused the push-off on the normal leg to be inadequate or out of phase. Since the body weight was not completely over the hip on the "prosthetic" side, knee instability leading to short steps with the "normal" leg seemed unavoidable.

One of the amputee's greatest obstacles is lack of assurance that the prosthetic knee is fully extended and fear that it will "buckle" when the normal leg is in "toe-off" position. The tendency is to depend on terminal swing impact, i.e., the sound associated with full knee extension as an indication that the knee is stable. Thudding into full knee extension gave this therapist the assurance that it was safe to push off on the normal leg. Construction of a training leg with a variable friction knee or elastic extension aid was not achieved in this initial project.

Result of the Project

The writer feels that he gained an immeasurably valuable experience in wearing and using the training prosthesis. It provided greater understanding of the problems confronting an amputee following the major trauma of amputation.

Normal balance and sensory feedback from the floor to the bottom of the foot were lost with the training leg. The quadriceps muscles could not be used in the normal manner to "lock" the knee, making it necessary to press back with thigh extensors to assure knee stability. The unusual role of the hip and lower trunk musculature on the "amputated" side in maintaining balance during swing-thru with the "normal" leg, was noted. Similarly revealing was the stress and work load imposed on the remaining leg, especially the calf muscles, during the balance and push-off phase of walking. This additional stress might be crucial for an individual who has either weakness or vascular involvement of the part.

Also important was the first-hand experience with ischial seat pressures which caused pain and soreness that lasted for days. However, the residual soreness from one day to the next was tolerable and at no time interfered with use of the training leg.

Typical gait deviations such as lateral trunk bending, terminal swing impact, uneven timing, and circumduction were encountered initially and only time, and a great deal of gait training, reduced, but did not eliminate them completely.

The "trainer" forcefully demonstrated that a great deal of time was needed to teach the amputee to use his prosthesis successfully. By subjecting himself to difficulties similar to those encountered by the amputee, the therapist was able to approach the problems with more insight and understanding.

Conclusions

Experience with an above-knee training prosthesis provides the therapist with a greater awareness and understanding of the amputee's problems. This insight contributed to a more meaningful and convincing program of gait instruction. The importance of pre-prosthetic training, including exercises to attain maximum agility and strength to meet the great physical and emotional demands on a new prosthesis wearer were underscored. This training should include the remaining (intact) extremity, because of the exceptional demands on its calf musculature. Training with a pylon to introduce the amputee to two-legged activity and to develop the lower trunk and hip musculature for their supporting function would seem well worthwhile.

Greater understanding of these problems by prosthetic clinic teams and especially by the therapist who will train the amputee, should contribute to successful amputee rehabilitation.

Hans Hillander is a Physical Therapist at Sunnyview Rehabilitation Center in Schenectady, New York