Partial Foot Amputation - A Case Study

Partial Foot Amputation - A Case Study

Charles H. Pritham C.P.O. *

Traditionally amputations through the foot have been held in poor repute for a variety of reasons, chief among them being the equinus deformity that can result from an imbalance between the intact triceps surae and the severed anterior muscles. In addition, the poor quality of socket fit that often occurs with older styles of fabrication can be cited as a contributing factor for the low esteem in which tarsal and mid-tarsal amputations are held.

In recent years there has been an ever increasing emphasis on more distal level of amputation for peripheral vascular disease and the advantages to be accrued. Thus, today, below-knee amputations and disarticulations at the knee have supplanted to a large measure above-knee amputations. In a similar fashion Syme's and partial foot amputations are being performed by some to ensure the patients the advantages of full limb length, distal end-bearing, retention of proprioception, and a long lever arm. The trend has gained impetus from such improved methods of predicting successful amputation levels as Xenon Radiography, and differential pulse ratios to predict accurately stump viability as well as such improved methods of surgical technique as fixation of the pretibial muscles for Chopart and Lisfranc amputations, heel pad fixation for the Syme's, and the use of rigid dressings for all levels of amputation .

It, thus, seems correct to conclude that an increasing number of partial foot amputations for vascular insufficiency will be seen by prosthetists in the years to come. The challenge to the prosthetist, therefore, is to maximize the advantages cited by using the best products of the latest available technology. One example of this can be found in the use of a modified plastic ankle-foot orthosis with a toe filler distal to the stump in those cases where stump length is adequate to ensure proper control and fit of the shoe . Numerous variations of the basic theme exist, and are well known. Karl Fillauer has reported recently on his experience with a prosthesis that totally encompasses the stump below the malleoli and permits tree motion of the ankle . To the extent of the author's knowledge, neither of these designs have ever been subjected to formal evaluation and while experience has been gained by many prosthetists with the first design, little is known objectively about the latter. Both designs appear to work well in selected cases, but neither design appears to provide for the broadest possible distribution of pressure (or in the case of a modified AFO, the most accurate distribution) to protect the fragile, sensitive, and often partially anesthetic skin over the dorsal surface of the remainder of the foot . The purpose of this paper is to discuss one possible solution to this problem.

Case Report

W.M. is a 62-year-old male Caucasian, who sustained a right Chopart amputation in 1972, secondary to peripheral vascular disease and necrosis of the forefoot (Fig. 1). He was subsequently fitted with a prosthesis which he wore until April 1977 (Fig. 2). The prosthesis was fabricated of polyester lamination with a posterior opening and metal reinforcing elements. Because of subsequent failure an additional steel armature was added externally, and the weight of the unit when seen by us had crept to 5 lb. 4 oz. Over the years sufficient change had taken place in contour of the stump so that W.M. was experiencing pain on the distal-lateral and anterior aspects of the stump, and he walked slowly with the use of a cane. Our initial attempt to fit the patient was made with a molded ankle-foot orthosis with a toe filler, but the patient obtained no relief from the pain, and the situation was re-evaluated.

After due deliberation, the patient was cast in the weight-bearing position, tracings were taken of both feet and vertical reference lines drawn (Fig. 3). With the tracing as a guide, a proper sized SACH foot was selected for the forefoot extension to the positive model of the stump, overwhich a polyethelene form of the heel and sole could be vacuum molded. The positive model of the stump was positioned inside the polyethelene form and the tracing and reference lines were used as guides to establish proper alignment. After plaster had been poured in the form and blended into the stump model, 1/4-in. thick polypropylene was vacuum formed about the extended model and subsequently modified to establish an AFO-type of socket with maximum rigidity about the ankle and anterior lever arm. A Plastizote interface was molded to the anterior aspect of the stump model and mated to a toe filler shaped from SACH-foot heel-cushion stock.

Fig. 3. Outline of feet during weight-bearing to provide references for fabrication and alignment of the molded prosthesis.

The semi-completed prosthesis was fitted to the patient so that adequacy of fit and alignment could be checked. Ambulation by the patient revealed that he still experienced some pain, which was relieved by using adhesive tape to strap the shin firmly into the prosthesis and thus distribute the pressure over a broader area. While the patient was standing, strapped in the prosthesis, splints were used to cast the limb for an anterior shell that would match properly with the posterior element. Polyethelene was vacuum formed over the model to form an anterior shell that was lined with Plastizote. The two elements were then fitted to the patient and fastened proximally with "PTB-type" buttons in a fashion identical to the tibial fracture orthosis reported by Stills . The finished prosthesis (Fig. 4, Fig. 5, Fig. 6) weighed 18 ounces and fitted more loosely in the shoe than the older prosthesis. The patient reported total comfort in the prosthesis during walking and considered the vastly decreased weight an important advantage.

References:

1. Alidredge, R. FF, and E. F. Murphy, The influence of new developments on amputation surgery. In: Human Limbs and their Substitutes. New York, McGraw Hill Co., Inc. 1954.
2. Anderson, M. H., J. J. Bray, and C. A. Hennessey, The construction and fitting of lower-extremity prostheses. In: Orthopaedic Appliances Atlas. Ann Arbor, ). W. Edwards, 1960.
3. Bingham, J. The surgery for partial foot amputations. In: Prosthetic and Orthotic Practice. London, Edward Arnold Ltd., 1970.
4. Condie, D. N. Biomechanics of the partial foot amputation. In: Prosthetic and Orthotic Practice. London, Edward Arnold Ltd., 1970,
5. El-Sharkaw, A., H. Abdel-Farrar, H. El-Hadidi, and M. Abdel-Hafez, A reconsideration of tarsal amputations with a new approach to the problem of equinus deformity. In: Proceedings of the International Conference, Cairo and Alexandria, Egypt, May 1- 1 1, 1972. Sponsored by Social and Rehabilitation Service, DHEW, USA and International Society-tor Prosthetics and Orthotics.
6. Eillauer, K. A prosthesis tor foot amputation near the tarsal-metatarsal junction. Orthotics and Prosthetics 30 (3): 9-11, September 1976.
7. Rubenstein, H. J., G. J. Sweeney, P. Strong, and C. Durrett, A foot amputation orthosis-prosthesis. Inter-Clinic Information Bulletin 14(4), April 1975.
8. Rubin, G., and M. Daniso, Functional partial foot prosthesis. Bulletin of Prosthetic Research 10-16: 149-152, Fall 1971.
9. Rubin, C, and M. Daniso, A functional Chopart prosthesis. Inter-clinic Information Bulletin 11(6), March 1972.
10. Stills, M. Vacuum-formed orthoses for fracture of the tibia. Orthotics and Prosthetics 30(2): 43-55, June 1976.
11. Wagner, W. Instructional Course in Amputation Surgery and Post-Op Care. ISPO World Congress. New York, May 1977