Evaluation of the Patellar-Tendon-Supracondylar Prosthesis for Children

ARTHUR L. HAUGE, M.D. ARTHUR L. ECKHARDT, M.D. PAUL CAMPBELL, M.D.


In this paper an attempt is made to evaluate the use of the patellar-tendon-su-pracondylar prosthesis for children. Published studies indicate that this prosthesis has many advantages over its predecessor, the patellar-tendon-bearing prosthesis. These reports have been limited almost entirely to experiences in fitting adult patients with little information presented concerning applications to children1,2. Thus, a report dealing exclusively with children seems timely.

History and Terminology

The patellar-tendon-supracondylar prosthesis, commonly referred to as the PTS prosthesis, was developed by Guy Fajal in France in 1964. It was introduced into this country by Marschall and Nitschke4,5 in 1966. This prosthesis is a modification of the commonly used patellar-tendon-bearing (PTB) prosthesis, and derives its name from the fact that the socket encloses the patella in front and the femoral condyles medially and laterally. Other terms, such as modified PTB prosthesis with molded supracondylar-suprapatellar-suspension and patellar-tendon-bearing supracondylar-suprapatellar prosthesis, have been used to describe this prosthesis. However, Fajal's original term, patellar-tendon-supracondylar prosthesis, remains the most common term in use and is the one applied in this article.

Description

The PTS prosthesis might be best described as a PTB prosthesis modified so that (1) the anterior brim line extends above the patella and is reflected in against the quadriceps tendon; (2) the medial and lateral aspects extend above the femoral condyles; and (3) the suprapatellar suspension strap is eliminated ( Fig. 1 , Fig. 2 , Fig. 3 , Fig. 4 .)

The advantages that have been claimed for the PTS prosthesis as compared with the PTB prosthesis are:

  1. The need for a suspension strap is eliminated, hence the possibility of constriction by the suspension strap is also eliminated.
  2. Pistoning is minimal because of the closely fitted high enclosure about the condyles and patella.
  3. Mediolateral stability at the knee is increased by the addition of the high medial and lateral walls.
  4. Since the total-contact area of the socket is increased, pressure over the weight-bearing areas of the stump is decreased.
  5. Shorter stumps can be fitted because of the stability afforded by the high walls and the increased contact area.
  6. Cosmetic appearance is better because of the high anterior brim line and the strapless suspension.

Review of Cases

Over a period of 20 months we have fitted ten patients with PTS prostheses at the Portland Shriners Hospital. All of these prostheses were fabricated by the prosthetist at this hospital. A hard socket was used in all cases. The average length of time these prostheses were worn was 12 months, with a range of one to 20 months. Only one of the patients, however, had worn the prosthesis less than ten months at the time of this study. The patients' ages at the time of initial fittings with PTS prostheses ranged from three to 14 years. All of the patients fitted had been wearing PTB prostheses immediately prior to receiving PTS prostheses. Seven had required some additional above-knee support with their PTB prostheses.

The primary reasons for amputation were:

  • Terminal transverse partial hemimelia (congenital amputation); 5 cases
  • Terminal longitudinal complete paraxial hemimelia; fibular (complete absence of fibula and lateral foot elements); 4 cases
  • Trauma; 1 case

In five cases the fibula was present, and in five it was absent. The stumps ranged in length from four to seven inches and were all in good condition at the time of our most recent evaluation. All of the patients except one, the youngest in the series, have required one or more stump revisions for bony overgrowths or spurs. The activity level of all these patients tended to be quite high, as might be expected for this age group.

The results of this review are presented in Table 1 .

The gait ratings represent the overall opinion of the examiners and are not based on any specific criteria. In the ratings of suspension, a score of good was given if no additional suspensory device was required to hold the prosthesis on the stump. Suspension was rated as fair if the addition of a pelvic belt and elastic strap was required and if this addition kept the prosthesis from falling off. It was rated poor if the pelvic belt with elastic suspension strap did not supply adequate suspension.

In the ratings of overall results, a grade of good was given only if the suspension was adequate, the patient was satisfied with the prosthesis, and there were no significant gait problems. The result was rated as fair if the patient was satisfied with the prosthesis but had difficulty with suspension when the knee was flexed so that an additional suspensory aid was necessary. The result was rated as a failure if suspension was scored as poor and the patient was not satisfied with the prosthesis.

Analysis of Results

The overall results of this study are shown in Table 2

The only patient who was rated as having a good result in this study was the three-year-old boy who had previously required a pelvic belt and suspension strap for his prosthesis. He was now able to run and to ride a tricycle; and was very active in his PTS prosthesis. Of the five patients rated as having a fair result, all had difficulty with the prostheses falling off when the knee was flexed. It was necessary to add a suspensory aid in all cases except one in which suspension was a problem only when sitting. Of the four cases rated as failures, all had poor suspension. In analyzing these results, it is obvious that the major problem with the PTS prosthesis at this institution was inadequate suspension (nine out of ten cases).

An analysis of the results in regard to presence or absence of the fibula is given in Table 3 .

In all cases where the fibula was absent, the child had required the addition of side joints and a thigh lacer to provide adequate mediolateral stability when wearing the PTB prosthesis. We have found that it is difficult to obtain good mediolateral stability in a prosthesis when the fibula is absent. However, although absence of the fibula resulted in a major suspension problem, it is important to note that only one of these patients required the addition of side joints with a thigh lacer to obtain adequate mediolateral stability with the PTS prosthesis. Thus it appears that the PTS prosthesis is an improvement of the PTB in this respect.

Although the number of cases presented in this review is small, it does bring out the significant fact that the suspension afforded by the PTS prosthesis was, in our hands at least, usually inadequate for this age group during knee flexion. Certainly the high activity level of children accentuates this deficiency.

Wedge-Suspension System

Because of the difficulty encountered in obtaining satisfactory suspension with the PTS prosthesis, we are now using a removable fitted wedge, as described by Fillauer 2 . The wedge is placed over the medial femoral condyle after the stump is inserted into the prosthesis ( Fig. 5 and Fig. 6 ). This modification has been referred to as the STP (supracondylar-tibial prosthesis) to distinguish it from the PTS prosthesis described previously. This modification is designed to provide good suspension in flexion as well as in extension, and to increase medioiateral stability by providing a snugger fit over the femoral condyles.

Although the preliminary results have been encouraging, particularly as regards improved suspension, it is far too early to make a meaningful evaluation concerning the use of this modification for children.

Summary

During a period of 20 months ten children with below-knee amputations were fitted with the patellar-tendon-supracondylar prosthesis at the Shriners Hospital, Portland. A review of this limited number of cases reveals that in nine of the ten cases the suspension afforded by the PTS prosthesis was inadequate. A good result was obtained in only one patient. Five had a fair result, and four were rated as failures.

If it is established that the addition of a removable wedge over the medial femoral condyle affords satisfactory suspension, this prosthesis should be significantly better than either the PTS or PTB prosthesis for the child amputee.

Shriners Hospital for Crippled Children Portland, Oregon

References:
1. Allen, R. W., and J. R. Verhoff, Supracondylar suspension patellar tendon bearing prosthesis. Southern Med. J., 63:59-61, Jan. 1970.
2. Fillauer, Carlton, Supracondylar wedge suspension of the P.T.B. prosthesis. Orth. and Pros., 22:2:39-44, June 1968.
3. Hamontree, S. E., H. J. Tyo, and Snowdon Smith, Twenty months experience with the "PTS." Orth. and Pros., 22:1:33 39, Mar. 1968.
4. Marschall, K., and R. Nitschke, The P.T.S. prosthesis. Orthop. and Pros. Appl. J., 20:2:123-126, June 1966.
5. Marschall, K., and R. Nitschke, Principles of the patellar tendon supra-condylar prosthesis. Orthop. and Pros. Appl. J., 21:1:33-38, Mar. 1967.