Knee Disarticulation Successfully Fitted with a PTS Socket

Knee Disarticulation Successfully Fitted with a PTS Socket JOHN N. PIERCE, CO.


Introduction

On December 27, 1974, W. F., a 3-year-old female, was admitted with a diagnosis of chicken pox of one week's duration and a 12-to-24-hour history of purpura and more recently hematuria. As a result of varicella gangrenosa, a complication of chicken pox, she lost the right leg through the knee and the left leg at a very high thigh level ( Figure 1-A , Figure 1-B and Figure 2 ). This case and a discussion of the entity were detailed in the Inter-Clinic Information Bulletin in 1969 1 . Our purpose now is to describe the success we have had in fitting the right knee disarticulation with a patellar-tendon-supracondylar socket after years of using bilateral above-knee prostheses ( Figure 3 and Figure 4 ).

Case Report

For a number of years we had treated this 16-year-old girl with bilateral above-knee prostheses for a very short 10-cm (4-in.) above-knee amputation on the left and a knee disarticulation on the right. Having observed a patellar excursion of approximately 40 degrees, we were prompted to think of fitting a PTS prosthesis, modular design, thereby reducing the weight of prosthetic apparel and possibly reducing the abducted gait caused by the volume of bilateral above-knee prostheses. We also recommended weight reduction. We took the necessary measurements and modified the cast as usual. We then prepared a Lexan check socket and proceeded to the fitting ( Figure 3 and Figure 4 ).

We had, of course, expected a great deal of instability due to the lack of tone in the thigh muscles and also the small amount of purchase the socket provided. We were pleasantly surprised to find that the patient was able to ambulate much better than we had expected. The fitting proceeded normally with the exception of a decision to raise the proximal socket brim an additional 2.5 cm (1 in.) to increase stability in all planes.

The patient is now seven months postfitting, and most of the abducted gait has disappeared - an added bonus in this particular case. She is delighted with the prosthesis. When the knee-disarticulation amputation was performed, the patellar tendon was sutured to the hamstrings, allowing excursion of the patella. This affords the patient limited powers of flexion and extension.

A very important aspect in the preparation of the socket is that the diagonal-posterior-trim-line procedure must be used to ensure retention of the prosthesis when the knee is flexed, as in sitting. This procedure has been reported previously 2 , and we use it routinely in our office ( Figure 5 ).

This is the first time that we have tried to fit a knee disarticulation with the PTS socket, and we were pleasantly surprised to find that it is indeed possible. We feel that this procedure may be applicable to other patients with knee disarticulations.

References:
1. Hagen, Arthur R., Joseph G. Matthews, and Joseph J. Nixon, Varicella gangrenosa. Inter-Clin Inform Bull, 8:8:9-19, May 1969.

2. Thranhardt, H. E., and S. W. Walker, Diagonal-posterior-brim below-knee prosthesis. Presented at American Orthotic and Prosthetic Association National Assembly, Atlanta, Georgia, October 1974.