Improving End-Bearing Characteristics Of Lower-Extremity Amputation Stumps

Alfred B. Swanson, M.D. Brian Hotchkiss, M.D. Vance Meadows, CP.

Reprinted with permission from the Orthopedic & Prosthetic Appliance Journal, March 1967.

The skillful application of basic biomechanical principles and the use of new technical advances in limb-making have greatly improved the lot of the modern amputee. In providing for his rehabilitation, major emphasis has been given in recent years to improving the functional characteristics of the prosthesis; the attitude has been to provide a prosthesis which will suit the stump rather than the reverse. Not enough attention has been given to the improvement of surgical techniques which would serve to enhance the functional characteristics of the stump.

We have been very impressed for many years at the tolerance to weight-bearing of our Syme-type patients, of whom there are a considerable number in our amputee clinic. Largely because of its tolerance to end-bearing, the Syme-type stump is accepted in many quarters as the ideal lower-extremity amputation. In consideration of improving the stumps of standard below-knee and above-knee amputations, it seemed obvious that efforts therefore might well be directed toward simulating the functional characteristics of the Syme procedure. This stump has obvious anatomical advantages for weight-bearing, in that the unyielding end of the bony stump is covered with the elastic heel pad. No such specialized skin structure is available in higher ablations. Improvement of the end-bearing characteristics of the standard below-knee and above-knee amputations, therefore, must be achieved by introducing an elastic substance between the skin and the bone end.

We, along with other investigators, have attempted to develop improved surgical amputation techniques in handling skin, bone, and myofascial structures. Esslinger has attempted to produce in animals an externalized surgical device which would provide an attachment for prostheses and also be usable for end-bearing. His interesting experiments stimulated us to undertake a research program to facilitate the concept of end-bearing for the human lower-extremity amputee. This led to the design and development of a mushroom-shaped, intramedullary-stemmed surgical implant.** It is placed internally between the skin and bone end to to act as a stress-absorbing cushion. This report is the outcome of a three-and-a-half-year study of implant design and mechanical testing, the development of surgical techniques and instrumentation, testing of the surgical procedure in animals, application of the techniques in selected human amputees, and improvement of prosthetic design.

**Alfred B. Swanson, M.D., "Improving the End-Bearing Characteristics of Lower-Extremity Amputee Stumps-A Preliminary Report," ICIB, Vol.V, No. 5, February 1966.

The implants used must be stable to the bone, inert, elastic, strong, durable, easy to manufacture, and easy to handle at surgery. Silicone rubber (Dow Corning, Inc., Silastic medical-grade elastomer No. 372) has been used because it has good elastic properties, does not fatigue quickly with repeated bending, and its tissue acceptance has been firmly established. The implants are performed from molds, then heat-vulcanized in a variety of sizes. They can be sterilized by autoclaving. A variety of sizes is necessary, so that reaming of the intramedullary canal of the bone stump is kept to a minimum.

Mechanical testing was performed on a cyclic gait-imitating machine which was designed to subject the implant to repeated stress such as it might endure in the patient. Dynamic calibration of the testing was accomplished with an electronic load cell working on the strain gauge principle. This load cell has also served to demonstrate the force-modifying characteristics of the implants. The implant has proved to be durable under these mechanical testing methods. In fact, one underwent ten million compression repetitions without evidence of breakdown.Image 1

Twenty medium-size adult dogs were used in the development of the surgical procedure. Those cases with satisfactory surgical results were able to bear weight directly on the ends of their stumps. Roentgenograms, dissections, and microscopic sections have demonstrated biological acceptance of the implants. The bone is contiguous with the shaft of the implant. An insignificant amount of foreign body reaction has been found. In fact, an intimate mesotheliallined fibrous capsule forms over the silicone. No bursal formation was noted.

Following successful animal application, the procedure was utilized on 32 patients, including 27 below-knee and 14 above-knee amputations. The surgical procedure is simple and requires a minimum of instrumentation. A set of reamers for shaping the intramedullary canal is necessary. A myoplastic closure is used, the stump is left as long as possible, and where possible, the incision is kept away from the stump end. Relatively long posterior flaps are preferred in below-knee amputations. Longer anterior flaps are used in the above-knee stumps. Summarization of these patients has demonstrated that the majority have been able to tolerate end-bearing without pain, skin breakdown, or bursa formation. A callus-like thickening of the skin occurs over the end of the weight-bearing stump.

Early fitting of patients has been done with several forms of temporary prostheses. Plaster sockets and adjustable plastic socket (U.S. Manufacturing or Fillauer) prostheses have been used to assist in stump shrinkage in the above-knee patients. A modified patellar-tendon-bearing prosthesis has been used with an increasing number of stump socks to accommodate for shrinkage in the below-knee patients. Permanent prostheses have been designed with total contact and end-bearing characteristics. Studies with the electronic load cell have demonstrated axial end-bearing forces ranging from 50 to 75 percent of body weight. A silicone jell pad has been used in the end of the socket on some of the recent cases. It appears that this will also be a useful adjunct in permitting increased end-bearing tolerance .Image 2

The intramedullary-stemmed implant has also been used in the upper- and lower-extremity overgrowth problems of the juvenile amputee. The results to date suggest that the implant prevents the overgrowth problem by allowing the soft tissue to be pushed in front of the implant and thus avoids the spiking and the perforation of the skin which frequently occur.

The first human implantation was performed in May 1964. Because of the small number of human amputations studied, no recommendation is being made at this time for general use of these techniques. Indications and contraindications for the procedure will be worked out on a field clinic trial basis at seven clinics in the United States and three foreign countries before the procedure is recommended for the surgical profession.

Drs. Charles Frantz, James Glessner, Akira Fujiwara, Osamu Kataoka, and Shigeaki Imura, and Mr. Nelson Dupree have also participated in this research program.