The Patellar-Tendon-Supracondylar (PTS) Prosthesis: Report Of A Preliminary Study

C. B. Taft


This study was conducted under the general supervision of Sidney Fishman, Ph.D., Project Director, New York University Prosthetics and Orthotics, with financial support provided by a special grant from the Children's Bureau, Department of Health, Education, and Welfare.

In recent years the patellar-tendon-bearing (PTB) prosthesis has been widely applied to below-knee amputees and has had a high degree of general acceptance by amputees and prosthetists alike. However, this prosthesis does not entirely solve some problems encountered in certain types of amputation stumps, e.g. extremely short stumps, despite the adjunctive use of the usual suspension and other aids (supracondylar strap, side joints and lacer, waist belt) in these cases.

During the past few years, two types of suspensionless below-knee prostheses have been introduced which appear to offer certain advantages over the PTB prosthesis in fitting these problem cases. Both of these new fitting methods involve a more intimate encapsulation of the stump and eliminate the need for any further suspension aid above the knee. One method, developed by Dr. G. G. Kuhn at the Research Institute in Muenster, Germany, and called the KBM (Kondylen-Bein-Muenster) method, provides high enclosure of the femoral condyles but exposure of the patella. The other method, developed by Guy Fajal of Nancy, France, and first introduced in 1964 at the International Seminar on Prosthetics in Copenhagen, Denmark, involves complete enclosure of the patella and the medial and lateral femoral condyles-the patellar-tendon-supracondylar (PTS) method (Fig. 1-3 ).

Two recent papers by Marschall and Nitschke1,2 discuss the PTS prosthesis and their adaptation of it. Basically this prosthesis combines the distinctive features and advantages of the PTB prosthesis with the use of a higher brimline. The authors claim the following advantages for the PTS prosthesis :

  1. Relationship between stump and socket. The socket of the PTS prosthesis completely encloses the patella frontally and the femoral condyles medially and laterally. The anterior brimline is brought in direct contact with the tendon of the quadriceps, thus eliminating the need for any suspension above this level.

  2. Increased knee stability. It is this intimate, intricate, and high enclosure that affords piston-action-free contact with the stump and a maximum of medial and lateral knee stability. It provides the patient with the incalculable comfort of not being restricted above socket level while standing, walking, or sitting.

  3. Normal knee flexion and swing-through. The correct fitting of the area of the quadriceps tendon as a main source of suspension cannot be stressed enough. Its proper flare contributes to a smooth swing-through and normal knee flexion in the stance phase.

  4. Ideal for short stumps. The high walls decrease the amount of pressure taken per square inch of stump surface. Stumps of extreme shortness, which frequently were rejected for fitting with a PTB, can be accommodated with the PTS prosthesis in most cases. Also, we found it advantageous to use this type socket for fitting the below-knee amputee with a temporary prosthesis.

  5. Cosmesis. Due to its high brim line and strapless suspension, the PTS is excellent in its cosmetic appearance and should appeal especially to young girls and women."

Following a visit to the New York University laboratory by Mr. Nitschke to demonstrate the fabrication and fitting of the PTS prosthesis, a pilot study was undertaken to evaluate the technique. The purpose of the study was to obtain experience with this fitting method, which would be used as a basis for a possible expanded study of the prosthesis at a future date.

The Sample

Four wearers of conventional PTB prostheses constituted the study sample (Fig. 3-5 ). The physical and prosthetic characteristics of the sample (two unilateral and two bilateral below-knee amputees) are presented Table 1 .

Methodology

The evaluative procedures followed in this study had five major foci, as follows:

  1. The fabrication and fitting of the experimental limb.

  2. Amputee subjective reactions to the experimental limb.

  3. Performance evaluation.

  4. Comparisons with the PTB prosthesis.

  5. Maintenance requirements.

Results

Fabrication and fitting process. As noted above, the fabrication and fitting processes for the PTS prosthesis were demonstrated by Mr. Nitschke. The subsequent fittings undertaken at this center were generally in accord with these instructions and the detailed procedures described in the article by Marschall and Nitschke, with the following exceptions :

  1. Veterans Administration below-knee calipers were used to establish anteroposterior and mediola-teral measurements because of the unavailability of the authors' measuring device.

  2. Instead of the authors' compression device, the standard procedure (use of fingers) was employed in obtaining compression of the patellar tendon and the popliteal area of the stump after application of the plaster cast.

  3. Nonelastic bandage was wrapped over the elastic bandage in order to reinforce the latter and prevent any distortion of the cast on its removal from the stump.

No problems were encountered in the fabrication and fitting process; however, one of the bilateral amputees, subject TM, was unable to adjust to the PTS prostheses with respect to ambulation, as discussed below.

Amputees' subjective reactions. The reactions and opinions of each subject concerning the comfort, cosmesis, etc., of the experimental prosthesis were obtained at various intervals following delivery of the limb. After wear periods of one or two months, the Prosthesis Evaluation Scale3 Questionnaire, involving such factors as comfort, cosmesis, effort, extent of use, and general acceptance, was administered to three of the four subjects. Subject TM was not included in this aspect of the study because of her inability to adjust satisfactorily to the PTS prosthesis. In general, the subjects found the PTS prosthesis highly acceptable. Heat and perspiration discomfort were the only complaints expressed by the three subjects .

Performance evaluation. After a wear period of two months, a gait analysis and observations of knee stability during level walking, plus ramp and stair ascent and descent, were recorded, and knee flexion during sitting and standing were noted, for each of these patients. Comparison of these results and those noted previously with the prior-worn prostheses indicated that improved gait and knee stability were obtained in three cases. However, knee flexion on sitting was decreased for two subjects-T.M. and G.V.

As noted previously, subject T.M. was unable to adjust to the PTS prostheses because they put her knees in more flexion than was the case with her conventional (PTB) prostheses. Her PTB prostheses allowed full extension and even recurvatum. Using the PTS prostheses she felt insecure, adopting an unnatural gait, with postural compensation (increased lordosis) and a restricted, scuffing gait (short stride length). The effects of this knee flexion characteristic were particularly disadvantageous on ramp descent, since she could not lock her knees in extension and felt propelled forward.

4. Comparison with the PTB prosthesis. A questionnaire involving the same factors of comfort, cosmesis, effort, extent of use,and general acceptance previously mentioned was administered to each of the subjects to obtain their reactions comparing the PTS prosthesis to the prior-worn PTB limb. Three of the subjects rated the PTS better than the PTB in all areas except heat. Subject T.M. rated the PTS better in all areas except for the problem with knee extension noted above.

5. Maintenance requirements. To date, no significant maintenance problems have been encountered in any of the PTS prostheses, which have been worn by three of the subjects for periods of nine, eight, and three months respectively.

Discussion

The results obtained in these preliminary studies of the PTS prosthesis tended to support some of the claimed advantages over the PTB prosthesis. Socket retention was good in all cases without resort to any suspension aids; piston action also appeared to be decreased. Increased comfort was reported by all four subjects, and three subjects reported improved cosmesis, lower effort requirements, and more general acceptance of the PTS limb. Improved gait was noted in three cases, and three cases showed increased knee stability, with less lateral thurst. Knee flexion on sitting was unchanged for the two unilateral amputees but somewhat decreased for the two bilateral amputees.

The advantage of the PTS prosthesis over the PTB for very short stumps was demonstrated in the case of subject G.V., whose left stump is only 3 1/2 inches long. With his prior prosthesis adequate knee stability was attained only by using side bars and a thigh corset. The PTS, on the other hand, provided generally good stability without using these adjunctive aids, afforded satisfactory socket retention with less piston action, and resulted in an improved gait.

One of the bilateral amputees, subject T.M. (Fig. 6 ), was unable to adjust to the PTS for ambulation because of inability to obtain the knee hyperextension to which she was accustomed with her PTB prostheses. Both of her PTS prostheses were modified by removing a wedge-shaped portion of the socket from the anterior brimline to the mid-patella point, exposing the area over the quadriceps tendon and the upper half of the patella (Fig. 7 and 8 ). Using an additional player of KEMBLO above her prominent condyles (for ease of donning), she was able then to obtain greater knee extension on standing and walking and some increased knee flexion on sitting. This modification provided her with all the advantages of the PTS prosthesis plus increased knee extension and flexion and thus far has proved highly satisfactory in all respects.

Summary and Recommendations

Favorable results were obtained in a preliminary study of the PTS prosthesis as presented by Marschall and Nitschke. The small sample of subjects fitted in this study tended to confirm the advantages claimed for the PTS and also suggested the desirability of certain modifications which might further improve this type of prosthesis. Accordingly it is recommended that the study be extended to a larger and more diverse sample to (1) obtain a fuller evaluation of the contribution of this socket to amputee comfort and function and (2) explore more fully some ideas for modifications along the lines of the procedures followed in the case of subject T.M. and the Muenster technique (KBM) previously cited.

C. B. Taft is a Research Scientist at the Prosthetics and Orthotics New York University Post-Graduate Medical School New York, New York

References:
1. Marschall, Kurt, and Nitschke, Robert, "The P.T.S. Prosthesis (Complete enclosure of patella and femoral condyles in below knee fitting)," Orthopedic and Prosthetic Appliance Journal, 20:123-126 (June) 1966. 
2. Marschall, Kurt, and Nitschke, Robert, "Principles of the Patellar Tendon Supra-Condylar Prosthesis," Orthopedic and Prosthetic Appliance Journal, 21:33-38 (March) 1967. 
3. Fishman, Sidney, "The Prosthesis Evaluation Scale," New York University Prosthetic and Orthotic Studies, June 1966.