A Foot Amputation Orthosis-Prosthesis

H. Jay Rubenstein, PH.D. Garnett J. Sweeney, MD. Pamela Strong, L.P.T. Gregory Durrett, A.A.S.


With the advent of plastic lower-limb orthoses, it has become evident that reconsideration of the classical management of several levels of foot amputation is in order. These levels include the transmetatarsal, midtarsal (Chopart's) and tarsometatarsal (Lisfranc's) articulations.

With transmetatarsal amputation, there is a loss of the metatarsal heads which function as a fulcrum and a loss of push-off resulting in some gait impairment. Additionally, an equinovarus deformity usually develops following Lisfranc's and Chopart's amputations. The disability resulting from these two levels of disarticulation and the lack of an adequate stump for weight-bearing usually suggests to the orthopaedic surgeon the desirability of a revision to the Syme's (transmalleolar) amputation and the fitting of the appropriate prosthesis1. In at least one study, it has been shown that a functional orthotic-prosthetic device could be fabricated and successfully applied in the case of a Chopart amputation3 without revising the amputation level. In this paper, we will present a similar case in support of a more conservative mode of treatment and rehabilitation.

Case History

The subject, a 9-year-old black male, received a partial-foot amputation at the tarsometatarsal level in an automobile accident. The amputation was surgically completed and a split thickness skin graft was subsequently applied to the stump. The X-ray (Fig. 1 ) reveals an amputation through the tarsometatarsal area, i.e., essentially a Lisfranc's procedure, with only a very thin layer of soft tissue present. In one area the thickness measures no more than 1.5 mm. Fig. 2 shows the appearance of the stump following healing of the grafted skin.

Local care was given until all areas of granulated tissue had completely epithelialized and an Orthoplast splint was fitted to prevent the residual foot from developing an equinovarus deformity during healing and the construction of the prosthesis (Fig. 3 ).

Design and Fabrication of the Prosthesis

The remnant of the patient's lower limb was molded with plaster bandages with the foot in a neutral position, in preparation for the positive model from which the prosthesis would be formed (Fig. 4 ). The model was modified by the addition of plaster to simulate the amputated mid- and forefoot. Following modification, a sheet of heated 1/8-in. polypropylene was draped over the model and trimmed according to the method of Engen2. Fig. 5 shows the completed orthosis-prosthesis. A soft plastic material (polyurethane) was applied proximal to the stump to protect the patient's skin. Distally a cork shoe filler was added but was subsequently replaced by Silastic elastomer to allow more natural toe-off during gait. Silastic, in monomer form, was poured into the toe of the shoe and then polymerized by the addition of a catalyst. Fig. 6 shows the relationship between the completed device and the stump. The final fitting with the shoe is illustrated in Fig. 7 .

The patient was able to ambulate immediately following application of the prosthesis and attained an almost normal gait pattern with a week of training. As of this writing, the patient has experienced no complications during six months of use.

Discussion

The design of this device affords a normal gait pattern as it restricts unwanted motion in the mediolateral (M-L) plane while allowing controlled anteropostenor (A-P) motion. It also prevents the residual foot from acquiring an equinovarus deformity.

It is the opinion of the authors that this method of treatment has many advantages over a Syme's revision. The prosthesis is certainly lighter, less cumbersome, and less expensive. There is no leg-length discrepancy when the device is removed. The patient retains proprioception and skin sensation from the time of heel strike. There is no need for the risk and the possibility of increased disability resulting from further surgical procedures. There are several common complications of the Syme's procedure, including slough of the heel flap following injury to the posterior tibial artery and a distorted heel pad resulting from displacement of the plan tar flap. Shifting of the heel pad on weight-bearing may occur if the cut surface of the tibia is not parallel to the ground1.

Conclusion

In summary, it is felt that this method is a viable alternative to the classical management of selected foot disarticulations and should be considered in the treatment of cases resulting from diabetes and arteriosclerosis as well as trauma.

Kosair Crippled Children Hospital and University of Louisville, School of Medicine, Louisville, Kentucky

References:
1. DuVries, Henri L., Surgery of the Foot. The C. V. Mosby Co., St. Louis, pp. 558 564, 1965.
2. Engen, Thorkild, The TIRR polypropylene orthoses. Orth. and Pros., 26:4:1 15, December 1972.
3. Rubin, Gustav, and Michael Danisi, A functional Chopart prosthesis. Inter-Clin. Inform. Bull., 11:6:3 5, March 1972.