Improving The End-Bearing Characteristics Of Lower Extremity Amputation Stumps - A Preliminary Report

Alfred B. Swanson, M.D.

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.

Syme-Tvpe Stumps

Because of its tolerance to end-bearing, a Syme-type stump is accepted in many quarters as the ideal lower extremity amputation. Efforts at improving lower extremity amputation stumps generally, 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.

Other Studies

Several 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 usa-ble for end-bearing.1 His interesting experiments have stimulated us to undertake a research program, the goal of which is the development of a surgical procedure to improve the end-bearing characteristics of lower extremity stumps. The research is supported by a John A. Hartford Foundation grant.2

This preliminary report is the outcome of three years' study in implant design and mechanical testing, the development of surgical techniques and instrumentation, prosthetic design, and application of procedures in animals. The procedure has also been utilized in selected human cases following the successful application to animals.

Use of Silastic

The implants to be used must obviously be inert, elastic, strong, durable, easy to manufacture, and easy to handle at surgery. In our experience to date an implant (Fig. 1 ) of a silicone rubber (Dow Corning Silastic, medical grade #372) has proved to be quite satisfactory. It has elastic qualities which allow the skin of the ordinary amputation stump to tolerate much greater end-bearing loads. The implant is tolerated by the bone and soft tissue structures surrounding it and has not been rejected as a foreign body even in some cases which have developed postoperative drainage and wound infection. The intramedullary insertion is surgically simple. Several reaming drills to accommodate the intramedullary canal to the mold size are the only additional surgical tools required.

Stress Testing

A gait machine (Figure 2A ) was designed to subject the implant to repeated stress such as it might endure in the patient. The implant has proven to be durable under these mechanical testing methods (Fig. 2B and Fig. 2C ).

Development of Surgical Procedures

Twenty medium sized dogs (30 to 50 pounds) have been used in the development of the surgical procedure. Those cases in which satisfactory surgical results were achieved were able to tolerate direct end-bearing (Fig. 3 and Fig. 4 ). Microscopic studies of the reaction of bone and soft tissue to the implant are being conducted on both short and long term bases.

Following successful animal application, the procedure was utilized on 13 patients who had below-knee amputations; one case was bilateral. Three patients with above-knee amputations have also had the procedures applied. Early evaluation of these patients suggests that their stumps (Fig. 5 and Fig. 5B ) are improved; being characteristically smooth, pain-free, and capable of tolerating increased end-bearing loads. Further long range evaluation of these cases is obviously necessary before the procedure can be recommended for general use.

Prosthetic Design

Our studies of prosthetic design have been concerned primarily with the utilization of such modern concepts of socket design as total contact and patellar tendon-bearing in relation to end-bearing function. The goal has been to improve the patient's tolerance to weight-bearing in the prosthesis ({popup9] ). The extent to which the load is being borne on the end of the stump is being studied with strain gauges. Some patients state that their prostheses are mostly end-bearing, and that the load can be tolerated without difficulty.

Relation to Overgrowth

The intramedullary stemmed silastic surgical implant also has been applied to the problem of overgrowth of the diaphysis of long bones in juvenile amputees. Early evaluation of these cases would suggest that the problem of bony overgrowth can be controlled by use of this procedure.

Future Plans This research study will continue to:

  1. Study the design and characteristics of the implant by mechanical testing; and in applications to animal and human patients.

  2. Study the surgical amputation technique, including consideration of the vascular adequacy of long posterior skin flaps, the myofascial covering of the implant, and standardizing of implant insertion procedures.

  3. Evaluate the patient's tolerance to end-bearing and to the implant; improve prosthetic limb design to provide increased end-bearing.

Alfred B. Swanson, M.D. is associated with the Area Child Amputee Center Grand Rapids, Michigan

1 John O. Esslinger, M.D., Birmingham, Michigan - Veterans Administration Research Contract: "Semiburied Implants for the Attachment of External Prostheses". (See Page 8, Editor) 
2 Experiments reported are being conducted at Blodgett Memorial Hospital, Grand Rapids, under the direction of Alfred B. Swanson, M.D.