Notes From The Prosthetics Research Program

Continuing the series of abstracts from reports of prosthetic research projects in the United States and Canada, the material which follows summarizes the second part of the July 1 to November 30, 1967, report issued by the Prosthetics Research Study in Seattle, Washington. Ernest M. Burgess, M.D., is the principal investigator, Robert L. Romano, M.D., the associate investigator, and Joseph H. Zettl, the director, of this VA-sponsored research project. The first part of the Seattle Report, which dealt with prosthetic activities, was presented in the April 1968 issue of the Inter-Clinic Information Bulletin.

- Editor

Surgical Research

The use of rigid postsurgical dressings with a compressible interface (the immediate postsurgical "socket"), combined with controlled early ambulation, is thought to minimize edema, promote improved wound healing, and hasten stump maturation. Our experience at the clinical level supports this view. Improved wound healing should permit a lower level of amputation in patients with impaired circulation; hence, salvage of the knee has increasingly been our goal. It appears at this time that the below-knee amputation used in our study can be successfully employed in more than 75 percent of all vascular patients requiring amputation of a lower extremity.

A number of methods are being developed to obtain more accurate preoperative assessment of extremity blood flow, especially skin circulation. These methods include interarterial fluorescein with skin mapping (Fulford), the use of radioactive xenon 133 with local tissue perfusion thermography with the Barnes technique, transcutaneous Doppler recordings (Fig. 1), and others. Effective use of such methods should assist in achieving an even higher percentage of successful below-knee amputations.

Surgery at the below-knee level for ischemic disease is technically precise. The below-knee amputation which has evolved in this project (Seattle technique) has several specific elements :

  1. The level is short (3 1/2 to 4 1/2 inches from the tibial plateau).

  2. The skin and supportive soft tissues are handled with absolute gentleness-plastic surgery instruments and techniques prevail.

  3. The anterior skin flap is short, at the level of the bone section, and essentially transverse. The posterior flap is long (5 1/2 to 6 inches) and is also relatively transverse (Fig. 2 ). The resulting lateral and medial "dog ears" of skin are not tailored too severely, thus leaving some final stump shaping to be achieved by the immediate postsurgical cast (Fig. 3 ). Deep fascia is left attached to skin.

  4. When adequate blood supply to muscle is present, the muscles are stabilized under mild tension by appropriate contouring and suturing to bone or to periosteum and adjacent opposing muscle groups-myodesis or myoplasty (Fig. 4 andFig. 5 ). The long posterior gastrocnemius-soleus muscle flap is feathered, resected,or thinned as necessary to bring it forward over the tibia for stabilizing sutures.

  5. The tibia is meticulously beveled with a short, rounded anterior and medial border; a long bevel is undesirable (Fig. 6 ). With skin drawn over the tibia, no rough areas or prominent ridges should be felt, since all immediate and definitive prostheses will be total contact. The fibula is divided transversely no more than one-half inch above the tibial section. It is not cut short, nor is tibiofibular osteosynostosis performed.

  6. Hemostasis is achieved by fine absorbable suture; nerves are ligated and sectioned high without crushing, cauterizing, or injecting.

  7. Subcutaneous sutures are not used. Skin is closed by interrupted fine suture deep enough to support the subcutaneous tissues. The skin closure is made without tension but firm enough to prevent wrinkling and redundancy (Fig. 7 and Fig. 8 ).

  8. Wounds are drained to bone for 48 hours.

The immediate postsurgical prosthesis is applied (Fig. 9 ).

This amputation provides a firm, nicely shaped, cylindrical stump, which is comfortable, stable, and eminently suited to the modern below-knee prosthesis (Fig. 10 ). In our experience this below-knee amputation will heal promptly and permanently in a far larger number of ischemic patients than is the case when the so-called routine or conventional below-knee amputation is used.

The project has developed additional surgical modifications and improved techniques, particularly in muscle stabilization at the above-knee and conventional (nonischemic) below-knee level. A combination of myoplasty and myodesis is used for muscle stability. Myodesis and myoplasty have also been routinely employed in upper-extremity amputees.

Prosthetic Research

The maintenance of appropriate pressures at the stump end remains a major problem. The correct pressure required to best control edema and hasten healing is unknown, as are the answers to many other questions: Should the pressure be relatively constant or should it be intermittent? How narrow or wide a variation can be tolerated to insure optimum healing, yet avoid tissue death? What are the time requirements of pressures as plotted against wound healing? How wide a variability is created by individual patient and tissue characteristics?

At present we continue to use clinical experience as a guide to cast application and suspension. The very small number of complications resulting from excessive pressures (tissue necrosis) or inadequate pressures (edema, congestion, stasis, blistering) indicate that effective pressure relationships are being generally obtained. In-depth study of the basic physiological questions requires instrumentation not now available to our project. Such studies have great implication clinically in all areas of tissue inflammation and healing. Peizer at the Veterans Administration Prosthetic Center, New York University, and Alcock at the newly completed Biomechanical Research and Development Unit, Roehampton, London, are actively investigating pressure relationships at the basic science level in immediate postsurgical prosthetic fitting by using transducers implanted in the walls of the socket. We propose to maintain constant contact with these research groups and correlate their information with our clinical experience.

Investigations concerning various types of interface materials are continuing. In clinical applications, the following materials (Fig. 11 ) are being evaluated and their effectiveness is being studied:

  • Fluffed gauze Lambs wool Stryker gel

  • Steel wool in three grades of coarseness

  • Brass wool

  • Foam pads

  • Polyurethane pads

Polyurethane pads in three different densities have shown an excellent porosity but have required shaping to conform to irregular surfaces. Efforts to eliminate this problem are under way.

At present, four custom-made sizes of perforated foam pads are being tested clinically and have shown promising results. Steel and brass wool have excellent compression qualities. However, in one patient some temporary wound irritation was noted, and it was suspected that splinters which penetrated the Orlon-Spandex sock and the initial fluffed gauze were responsible.

The use of the Stryker gel and lambs wool was discontinued, as the latter was found to lack sufficient compressive qualities, and the Stryker pads were nonabsorbable and uneconomical.

Fluffed gauze gives some initial compression quality. However, this is quickly lost when fluids are absorbed, and the gauze dries into a hard, crusty mass.

Our technique in evaluating the various materials is to cover the wound with a nonadherent silk dressing and then apply an Orlon-Spandex stump sock of a corresponding size and hold it firmly in place. The polyurethane pads, Stryker gel pads, steel and brass wool, etc., are then located against the distal stump end, and a thin cast sock is pulled on to hold them in their predetermined position. Next we proceed to locate the felt relief pads and continue the cast socket in the usual manner.

Foam pads, consisting of one part Silastic 386 Foam Elastomer and one part Silastic 388 Denture Release, were prefabricated in four sizes. Molds were made of plaster of paris, and a plastic cap was fitted over them to create a 3/4-inch-thick space. Nails driven into the mold at predetermined intervals give the pads absorbability by creating vent holes in the foam (Fig. 12 andFig. 13 ). Prior to foaming, a thin cast sock pulled over the mold facilitates adherence of the foam and creates a very thin feathered edge all around the pad without crumbling. The cast sock with attached foam pad can be gas-sterilized. It is pulled over the Orlon-Spandex sock and held suspended with it until casting of the stump is completed. Further clinical evaluation on this approach is indicated.

The Prosthetics Research Study above-knee casting fixture was further improved by the addition of an interchangeable adjustable lateral wall (Fig. 14 ). This worthwhile feature can be added to any existing casting fixture very simply. It should be available from the manufacturer in the very near future. An inexpensive adjustable casting stand (Fig. 15 ) was also fabricated to enable us to use the PRS casting fixture for every routine stump casting for a definitive above-knee prosthesis.

The present suspension technique of the above-knee procedure is being studied with a view to possible improvements (Fig. 16 ).

One item needed for some time and finally completed is the PRS adjustable Syme's unit (Fig. 17 and Fig. 18 ). With this item, the prosthetist can use a Syme's foot of a corresponding size on an immediate postsurgical cast socket and make any required adjustment by simply loosening the foot bolt and moving the foot a maximum of 3/4 inch in any direction. The foot bolt is then tightened to hold the new adjustment. The unit is 5/16 inch thick and weighs less than 200 grams. The Syme's foot can be reused later in the definitive prosthesis.

Ambulation of the Postsurgical Amputee

The advantages of ambulation and postsurgical activity in the vertical position are obvious. However, excessive wound stress must be avoided, particularly in the elderly and in the patient with circulatory deficits. In several instances, unsupported walking the day following surgery has been inadvertently permitted by attending hospital personnel. This activity has not resulted in wound breakdown, significant pain, or delayed healing. We have, however, encountered one or two instances where delayed healing could be attributed to excessive and too enthusiastic early weight-bearing. This acceleration of activity cannot be recommended, even in children. Guarded standing and assisted walking up to no more than 25 pounds of weight-bearing prior to the initial cast change is the rule (Fig. 19 ). Patients who are debilitated or ill can achieve the benefit of the stance position by using the tilt table, Vitali bed, or circular bed.

Stump-socket pressure relationships require study during both the stance and swing phases. Subjective reports of comfort received from many patients while standing indicate that they derive certain benefits from pressure. In fact, patients fitted in the immediate postsurgical program will occasionally ask the nurse to allow them to stand at night to relieve aching and discomfort.

The Ischemic Lower-Extremity Amputee

An estimated 80 percent of elective civilian lower-extremity amputations result from ischemia. The Prosthetics Research Study is now conducting a precoded statistical study of an unselected consecutive group of 100 of these patients. Information obtained from this study will be incorporated in subsequent reports.