Silicone-Gel Pads to Improve End-Bearing Tolerance in Lower-Extremity Amputees

BY ALFRED B. SWANSON, M.D., F.A.C.S.


Since 1963 we have been using intramedullary stemmed, silicone-rubber implants to improve the end-bearing characteristics of lower-extremity amputation stumps. This work is part of a nine-year research project supported by the John A. Hartford Foundation, Inc., to develop implants for reconstructive surgery of the extremities. We have designed, tested, and used 23 different implants during this period 2,5,7,8 ( Fig. 1 ).

Implants for finger-joint reconstruction have been used in more than 10,000 patients in our own clinic and in a network of participating Field Clinics throughout the world. It is now well established that flexible implants are well tolerated both biomechanically and physiologically in human tissues. Their use as joint spacers in resection arthroplasty procedures and as cushioning or dampening devices in amputees makes this new concept of reconstructive surgery of great interest to those concerned with the care of patients with crippled or amputated limbs.

Review of Cases

We have recently reviewed our series of 75 cases of lower-extremity amputations in which a heat-molded, intramedullary stemmed, silicone-rubber implant (Silastic 8 , Dow Corning Corp., Midland, Mich.) was used. We have found that the use of an additional cushioning device ( Fig. 2 ) in the socket of the prosthesis further improves the stump's tolerance to end-bearing. Most lower-extremity amputees experience changes in the size of their limbs from day to day and even at different times of the day. The use of shims at the bottom of the socket ( Fig. 3 ) in association with a cushioning device allows the patient to adjust the depth of the socket to obtain the best total-contact fit and to improve end-bearing.

Silicone-Rubber Gel Pads

We have used silicone-rubber gel pads as cushioning devices to achieve maximum tolerance to end-bearing since 1964 1,4,6 . This material acts somewhat like subcutaneous tissue in allowing some mobility of the soft tissues. It also helps distribute weight-bearing forces equally over the end of the stump. We have attempted to enclose silicone gel in a variety of covers including stockinette, leather, and a molded silicone bag 3 . Extrusion and loss of the silicone gel under the forces of weight-bearing was a problem. It would appear that the ideal container for the silicone gel is a tightly stitched soft leather bag (Stryker Corporation, Kalamazoo, Mich.).

Case Report

A 54-year-old farmer sustained a traumatic below-knee amputation in an auto-train crash in 1965. A guillotine amputation was done. This was followed one month later by a stump revision using a silicone-rubber. intramedullary stemmed, end-bearing implant ( Fig. 4 , Figs. 5-A & 5-B ). With this patient the rehabilitation result was excellent as he was able to tolerate between 50-per-cent to 75-per-cent end-bearing. He carries out two jobs-eight hours a day as a security policeman in a factory where he walks one to two miles a shift, and up to 12 hours a day on his farm. He has had no difficulty with his stump in a six-year follow-up period. The skin has become cornified at the end of the stump somewhat similar to a normal heel pad. For many years he has used a silicone cushion and shim pads which he adds or subtracts as his stump swells or shrinks minimally. This patient walks without a noticeable limp, is extremely active, and demonstrates excellent end-bearing characteristics with minimal fatigue, pain, or discomfort. Most of his associates are unaware of his amputation. His prosthesis is simple and he has not had any fitting problems.

Discussion

The benefits of end-bearing for the lower-extremity amputee are well known. Fitting problems are less than with the standard method, prosthetic tolerance is greater, and the gait is better and less fatiguing. It is possible to achieve good end-bearing characteristics in these stumps by using the sili-cone-rubber-implant technique. Bone tolerance to the implant is established. The soft tissue and skin over the stump toughen to withstand weight-bearing not unlike the sole of the foot. Weight-bearing tolerance is improved by the use of cushioning pads of silicone gel. The silicone pad allows cutaneous mobility and simulates the effect of a physiological subcutaneous pad like the heel. Disks of hard rubber can be used as shims to raise or lower the limb in the socket in order to obtain the proper depth in the prosthesis as the stump shrinks or swells.

Summary

A technique for obtaining end-bearing characteristics in the lower-extremity amputee has been presented. The method involves the use of a silicone endoprosthesis to improve the stump end and the use of silicone-gel pads to increase the tolerance of the stump to end-bearing. The use of shim pads under the gel pad to raise or lower the stump in the socket to accommodate stump shrinkage or swelling is discussed.

Consultant, Michigan Area Juvenile Amputee Clinic, and Chief, Orthopaedic Surgery and Orthopaedic Research, Blodgett Memorial Hospital, Grand Rapids, Mich.

References:
1. Swanson, A. B., Improving the end-bearing characteristics of lower extremity amputation stumps-A preliminary report. Inter-Clin. Information Bull., 5:5:1-7, February 1966.
2. Swanson, A. B., A flexible implant for replacement of arthritic or destroyed joints in the hand. Inter-Clin. Information Bull., 6:3:16-19. December 1966.
3. Swanson, A. B., B. L. Hotchkiss, C. H. Frantz. and J. R. Glessner, Jr., Study of end-bearing characteristics in the lower extremity amputee. Scientific Exhibit, American Academy of Orthopaedic Surgeons, San Francisco, January 1967.
4. Swanson, A. B., B. Hotchkiss. and V. Meadows, Improving end-bearing characteristics of lower extremity amputation stumps. Orthop. and Pros. Appl. J., 21:1: 23-26. March 1967.
5. Swanson, A. B., Silicone rubber implants for replacement of arthritic or destroyed joints in the hand. Surg. Clin. N. Amer., 48:1113-1127, October 1968.
6. Swanson, A. B., Improving the end-bearing characteristics of lower extremity amputation stump by the use of silicone rubber implants. Thesis presented to the American Orthopaedic Association, 1969.
7. Swanson, A. B., Finger joint replacement by silicone rubber implants and the concept of implant fixation by encapsulation. International Workshop on Artificial Finger Joints, suppl. to Ann. of Rheum. Dis.. 28:47-55, 1969 (Brit. Med. Assn.).
8. Swanson, A. B.. Bone overgrowth in the juvenile amputee and its control by the use of silicone rubber implants. Inter-Clin. Information Bull., 8:5:9 18, February 1969.