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A Volume-Adaptable Prosthesis for Ankle Disarticulation

Michael S. Pinzur, MD
John A. Angelico, CP
Michael J. Quigley, CPO

ABSTRACT

Ankle disarticulation amputation in patients with peripheral vascular disease is sometimes complicated by delayed healing or residual limb volume fluctuation. This change in shape and contour presents several challenges to the prosthetist charged with producing a static prosthesis that must meet the demands of a constantly changing residual limb.

This article describes a method of producing a preparatory ankle disarticulation prosthesis that can be quickly and inexpensively fabricated, and can adapt to changing residual limb size and shape.

Introduction

Patients who have ankle disarticulation amputations walk with far more energy efficiency than do patients who have experienced transtibial amputations (1,2). Amputation by disarticulation allows direct load transfer, i.e., end-bearing, in the prosthetic socket, which makes intimate socket fit less crucial than in through-bone amputations where indirect load transfer, i.e., total contact, is essential to accomplish functional load transfer (3). Many experienced prosthetists and physicians who treat amputees believe the direct load transfer available in disarticulation prostheses allows improved "sense-of-feel" and proprioception as compared with load transfer where the terminal residual limb is unloaded.

Until recently, ankle disarticulation was reserved for cases of nonsalvageable traumatic injury and rarely used for patients with peripheral vascular disease. Several authors have shown ankle disarticulation can be successfully used in patients with peripheral vascular disease, insulin-requiring diabetes and even in the presence of an insensate heel pad (4,5,6).

Rehabilitation in peripheral vascular disease ankle disarticulation amputees sometimes is delayed due to postoperative infection or delayed healing. Some patients have large residual limb volume fluctuations from day to day (and from early to late in the same day) due to cardiac insufficiency and/or renal failure. Some also have a very limited life expectancy, which may not warrant the expense of definitive prosthetic limb fabrication (5). A removable weightbearing cast is adequate, but it is heavy, cumbersome, and retains wound secretions and odors (7).

These complex ankle disarticulation patients present several challenges in prosthetic design. Significant residual limb volume fluctuation and changes in geometry normally require frequent adjustments by the prosthetist and compliance by the patient. Altering the number of prosthetic socks is generally used to provide some measure of volume adaptability; however, when the number of prosthetic socks used is increased, pistoning and shearing also increase, further stressing a compromised, healing surgical wound. The potential morbidity related to these residual limb size and shape changes can be decreased by providing volume adaptability and using flexible materials in fabricating the prosthetic socket.

Prostheses fabricated in the early postoperative period need to be made rapidly and inexpensively. This article presents guidelines for producing a lightweight, sturdy, volume- and shape-adaptable temporary/preparatory prosthesis constructed¹ of copolymer plastic (3/16-to 1/4-inch thick depending on the patient's size) that can be molded quickly and inexpensively to approximate the smallest volume of the patient's residual limb (see Figure 1 ).

Method

A standard Syme's casting technique was used to obtain an impression from the residual limb (8). (This cast was removed either by cutting it off posteriorly or by cutting out a medial door.) The positive model was then modified by using patellar-tendon-bearing modifications proximally with increased distal end weightbearing (9). The prosthesis was fabricated with a posterior opening design in which a Gillette ankle joint² was incorporated into the posterior distal door, creating a "clamshell"-type prosthetic socket that used a Velcro? closure to ensure volume adaptability. The lightweight, somewhat flexible copolymer plastic used in fabricating the prosthetic socket also allowed some adaptability.

The weightbearing distal end of the socket was lined with a pressure-dissipating material, such as PPT foam³ (1/4 inch thick). The prosthetic foot was initially carved from crepe then bonded to the prosthetic socket and covered with leather⁴. A Syme's SACH foot and attachment plate⁵ were used to increase the strength of the prosthetic foot attachment as well as improve walking stability and cosmesis.

Patients generally use this prosthesis until their wounds are fully healed and residual limbs have "matured" sufficiently to allow definitive limb fabrication. In patients with profound residual limb volume fluctuation, limited walking or limited life expectancy, this prosthesis can be used permanently.

Conclusion

This report describes a lightweight, comfortable preparatory ankle disarticulation prosthesis that can be used in complex cases following ankle disarticulation amputation. It allows patients the functional ambulatory benefits of a definitive-type prosthesis while preserving wound access and adaptability to residual limb volume and geometric fluctuation.

Michael S. Pinzur, MD, is with Loyola University Medical Center, Maywood Ill.

John A. Angelico, CP, is with Scheck & Siress Orthotics and Prosthetics Inc., 1141 Madison St., Oak Park, IL 60302.

Michael J. Quigley, CPO, is with Oakbrook Orthopaedic Services Ltd., 1S224 Summit Ave., Suite 104, Oakbrook Terrace, IL 60181.

References:

1. Pinzur MS, Gold J, Schwartz D, Gross N. Energy demands for walking in dysvascular amputees related to the level of amputation. Orthopaedics 1992; 15:1033-7.
2. Waters RL. Perry J, Antonelli D, et at. Energy cost of walking of amputees: the influence of level of amputation. JBJS 1976; 58A:42-6.
3. Pinzur MS. New concepts in lower-limb amputation and prosthetic management. AAOS Instructional Course Lectures 1990; 39: 361-6.
4. Dickaut SC, DeLee JC, Page CP. Nutritional status: importance in predicting wound healing after amputation. JBJS 1984; 66A:71-5.
5. Pinzur MS, Morrison C, Sage R, Stuck R, Osterman H. Syme's two-stage amputation in insulin-requiring diabetics with gangrene of the forefoot. Foot and Ankle 1991; 11:394-6.
6. Wagner FWW, Jr. Management of the diabetic-neurotrophic foot. Part II. A classification and treatment program for diabetic, neuropathic and dysvascular foot problems. In: Instructional Course Lectures, The American Academy of Orthopaedic Surgeons. Vol. 28; C.V. Mosby, St. Louis, 1979; 143-165.
7. Rooney JE, Pinzur MS. An easy-to-fabricate temporary Syme's prosthesis. J of Prosthetics and Orthotics 1989; 1:211-2.
8. VAPC technique for fabrication of Syme's prosthesis with medial opening. New York University Prosthetics and Orthotics Training Manual, 1969.
9. Northwestern University Prosthetics & Orthotics (NUPOC) Training Manual for Below-Knee Prostheses. Northwestern University Prosthetics and Orthotics Center.

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