O&P Library > Orthotics and Prosthetics > 1979, Vol 33, Num 2 > pp. 45 - 53

Orthotics and ProstheticsThis journal was digitally reproduced with permission from the American Orthotic & Prosthetic Association (AOPA).

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Evaluation of an Ultralight Below-Knee Prosthesis

Brian Reed, R.P.T. *
A. Bennett Wilson, JR. *
Charles Pritham, C.P.O. *

This work was carried out with fiscal support from the Veterans Administration under Contract V101(134)P-576.

This is a report on experience gained since publication of the article by Wilson and Stills 1 in the March 1976 issue of "Orthotics and Prosthetics" on ultralight prostheses for below-knee amputees made by vacuum-forming sheet polypropylene (Fig. 1 ). The design resulted in a prosthesis that weighs one-third of the more conventional PTB prosthesis, with essentially the same function, depending upon the treatment of the sole and heel. In addition to offering the possibility of a decrease in energy requirements, suspension problems might be reduced. In the article it was stated that the Rehabilitation Engineering Center would welcome other groups to participate in the development of this concept.

With partial support from the Veterans Administration work on this project was continued and although the original aim of the project was to provide a better prosthesis for the geriatric patient, it was found that the active patient also appreciated advantages offered by the new design. By March 1976 a draft of a manual was sufficiently complete so that it was practical to invite prosthetists from each of the Rehabilitation Engineering Centers, the Veterans Administration Prosthetics Center, and several privately practicing prosthetists to Northwestern University to become acquainted with the technique so that it could be applied in their own setting and provide information useful in making the technique as practical as possible.

With the help of the participants the original fabrication technique was modified to use hand draping of the polypropylene to mold the shank to provide more uniform wall thickness and an anterior seam. An alternate method of fabricating the foot was also introduced (Fig. 2 ). During the fall of 1976 a fabrication manual 2 was prepared and submitted to the VA with the suggestion that the ultralight below-knee prosthesis be evaluated nationwide through the VA outpatient amputee clinics.

Instead of acting upon this suggestion, the VA requested a proposal from us for the conduct of clinical trials through the Philadelphia Regional Office Amputee Clinic. The proposal was accepted by the VA, and the program was initiated in January 1978.


Seven Philadelphia-area prosthetic firms agreed to participate in the study. The prosthesis design selected was the one using the rigid toe section since it was the lightest of the two designs. The prosthetists were instructed in the fabrication and fitting of the ultralight prosthesis in a twelve-hour course at the Rehabilitation Engineering Center of Moss Rehabilitation Hospital in January 1978. The prosthetists then fitted amputees from the VA Regional Office Amputee Clinics, and from their own private practices who were referred to the study from two other local clinics. Amputees who were receiving their first definitive prosthesis as well as amputees who already were successful PTB users were included in the study. Data were collected by means of questionnaires (Appendix A and Appendix B ). For the former PTB users, one questionnaire was administered before fitting and another one was administered two weeks after a "satisfactory" fit was obtained. A "satisfactory" fit was one which was agreeable to both the patient and prosthetist. In addition, an unannounced followup was done one month after the final fitting in order to determine if the subjects were still using the ultralight prosthesis or if they had gone back to their conventional prosthesis. At this time the subjects were also asked whether they liked the lightness of the prosthesis, other factors aside. The prosthetists were given a questionnaire (Appendix C ) after all patients had been fitted in order to assess fabrication and fitting problems and the applicability of the device as a first definitive prosthesis versus a PTB replacement. Data in this respect were not collected on the new amputees since they had no prosthetic experience on which to base a comparison.

To date (January 1979), the sample consists of thirty-six patients who have been fitted with the ultralight prosthesis. Of that number, four are receiving it as their first definitive prosthesis. Of the remaining thirty-two patients, complete data have been obtained on fourteen. All but one are male. One patient died during the course of the study from an unrelated cause.


The patient data are presented in Fig. 3. The responses of one patient, H.G., need to be considered in light of the fact that shortly after receiving the prosthesis he moved out of state. He then had a structural failure of the foot of the prosthesis which altered its cosmesis, fit, and alignment. He indicated that this was the reason for his unfavorable response to several of the questions. Those responses are circled. He was unable to return to Philadelphia to be fitted with another ultralight prosthesis.

The following general conslusions can be drawn from this preliminary data:

  1.  Although wearing time and walking distance do not appear to increase when the lighter prosthesis is used the overwhelming majority of the subjects felt that the lighter prosthesis requires less energy to walk with than a conventional prosthesis.
  2.  Opinions were mixed regarding which prosthesis is easiest to control and which one was the most comfortable to walk on. In both cases, however, the majority favored the experimental prosthesis.
  3.  The majority of the subjects felt that conventional prostheses are more cosmetically acceptable than the ultralight (polypropylene) model.
  4.  For the most part, either there was no difference in ease of donning and doffing, or else the lighter prosthesis was slightly superior in this area.
  5.  The overall preference was overwhelming for the ultralight prosthesis. The two who preferred their conventional prosthesis both liked the lightness of the experimental prosthesis, but they were very dissatisfied with the foot action.
  6.  There were six incidences of structural failure. Three were fractures of the polypropylene at the toe area of the foot. Two other cases involved crushing of the internal keel foot. The other failure was a subluxation of the socket within the shank. The first two problems were corrected by using an external keel foot. The socket problem was solved by using a heavier guage polypropylene and meticulous welding at the brim. It may be noted that structural failures occurred with both of the bilateral amputees. Structural failure also occurred most frequently in patients who subjected the prosthesis to extreme stress, as would be expected.
  7.  All but three subjects were using the ultralight prosthesis at follow-up. Of the three who did not, two gave their reasons as dissatisfaction with the "fit" that they had as a result of the rigid foot. The third subject (H.G.) was not wearing his prosthesis because the crushed foot precluded its use.
  8.  The subjects were unanimous in their approval of the lightness of the prosthesis.
  9.  Half of the patients commented that they disliked the rigid foot of the prosthesis, and there were some interesting comments about the light weight of the prosthesis. Two subjects (L.B. and J.C.) commented that the lighter weight noticeably reduced pistoning of the stump in the socket. Two others (A.W. and H.G.) stated that they had found the leg useful for work in and around water. A.W. also Commented that his stump was in better condition than it had ever been before. R.S. felt that the lightweight legs were superior to his conventional ones in every way except durability. Data from the prosthetists's questionnaires has not been compiled yet since some subjects are still undergoing fitting modifications. From informal communication, however, the principal complaints of the prosthetists are: (a) that the ultralight prosthesis is difficult to modify once it is made; (b) structural failures, especially at the foot, pose a problem.


The preliminary data seem to indicate that the concept of an extremely light below-knee prosthesis is valid. The model used for this study seems to be inferior to conventional below-knee prostheses only in the areas of adjustability, durability, and, in some cases, function of the foot. Half of the patients sampled complained about action provided by the rigid foot. Most frequently the complaint was that heel-strike was jarring, and that it was hard to walk up inclines because of difficulty in "rolling over" the foot. The complaints about the rigid foot may be simply a matter of "getting used to it," especially after being used to a SACH foot. Nevertheless, the rigidity of the foot as well as its structural weakness can probably be solved by the incorporation of an external keel foot, a possibility now being considered by the REC. It is estimated that an external keel foot would add about 8 oz. to the prosthesis. Regarding cosmesis, the REC is now investigating the use of prosthetic skins that have been developed elsewhere. The current model is probably best used with patients who do not subject the prosthesis to extreme stress. It is of potential benefit to amputees of all ages, but it may be particularly indicated for patients with cardio-vascular impairments.

A final report on this project will be issued toward the end of 1979. Meanwhile a new fabrication manual will be published, and it is hoped that the American Academy of Orthotists and Prosthetists will undertake a nationwide clinical evaluation of this technique on behalf of the Veterans Administration.

The authors wish to express the sincerest of appreciation for the cooperation and assistance provided by Dr. Howard Zeidman, Chief, Prosthetics Clinic Team, VARO, Philadelphia, Edward Vargo, Prosthetics Representative, VARO, and the following prosthetists :

  • Joseph Botkin, J.E. Hanger of Philadelphia
  • Frank N. Cocco, Cocco Brothers
  • Virgil Faulkner and Amin K. Hajj, INA O&P Research Laboratory, University of Pennsylvania Hospital
  • Harry J. Lawall, Harry Lawall and Son
  • Harry J. Lawall, Jr., Harry Lawall and Son
  • Frank J. Malone, Jr., Frank Malone and Son, Inc.
  • Edward F. Moran, Cocco Brothers
  • Blondell Smith, Nu-Way Limb and Brace, Inc.
  • Thomas Sulima, Modern Limb and Brace Co.
  • John Swoyer, Modern Limb and Brace Co.
  • Charles Wright, J.E. Hanger of Philadelphia
  • Without their unselfish help and open minds this study could not have been carried out.

Literature Cited

  1.  Wilson, A. Bennett, Jr., and Melvin Stills, Ultralight prostheses for below-knee amputees, Orthotics and Prosthetics 30:1, 43-47, March 1976.
  2.  Wilson, A. Bennett, Jr., Charles Pritham, and Melvin Stills, Manual for an ultralight below-knee prosthesis, Rehabilitation Engineering Center, Moss Rehabilitation Hospital-Temple University-Drexel University (1977).

O&P Library > Orthotics and Prosthetics > 1979, Vol 33, Num 2 > pp. 45 - 53

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