The Temporary Patellar Tendon Bearing Limb

Frank W. Clippinger, M. D.

One of the chief problems associated with the use of the patellar tendon bearing below-knee prosthesis is that the procurement of a second limb is necessary shortly after the fitting of the initial limb. Usually this necessity for replacement occurs from eight to twelve months after the initial fitting, and is occasioned by shrinkage of the stump and the subsequent loss of fit. The foot is the only salvageable part of the PTB limb and replacement of the remainder of the prosthesis is expensive. The additional expense is a problem not only to private agencies and the individual involved, but also to public agencies with limited funds.

A stump will almost always change size and shape following application of the initial limb, regardless of how faithfully the patient has wrapped the stump during the pre-prosthetic period, how carefully the clinic team has reviewed the fitting problem, or how snugly the prosthetist has made the socket. Since the major stump shrinkage occurs during the first weeks following fitting, it is evident that an inexpensive temporary socket might serve a beneficial purpose in conditioning the stump.

Temporary Pylons

In the past many efforts have been directed toward the use of temporary pylons of various types and these have been prescribed universally. The members of the Duke Orthopedic Amputee Clinic have used above-knee plaster pylons since 1955 and below-knee pylons during the past three years. These prostheses have assisted in speeding stump shrinkage, early ambulation and exercise, and the rapid development of a four-point gait. The above-knee plaster pylon has also been helpful to the clinic team in evaluating the prosthetic potential of elderly amputees with a borderline prognosis. In many instances, it has enabled us to avoid the expenditure of considerable time and money on a permanent limb for a patient who could not manage it.

The crutch-end pylon, although readily adaptable to the above-knee amputee (Fig. 1 ), has proven less successful in the early conditioning of the patient with a below-knee amputation. The margin of weight bearing tolerance is much less in the below-knee patient than in the above-knee and the leverage and torque exerted at heel strike and push-off cannot be tolerated with crutch-tip contact. The abnormal pressures applied to the stump create instability and discomfort of sufficient magnitude as to preclude significant weight bearing.

PTB Socket

In order to overcome these disadvantages, our team utilized a plaster of Paris patellar tendon bearing socket molded directly over the stump and attached to a Hosmer below-knee aluminum pylon with a SACH foot (Fig. 2 and Fig. 3 ).

The socket is made in the same manner as the initial cast for a conventional PTB limb using the VAPC (Veterans Administration Prosthetics Center) molding jig. The plaster is molded directly over a stump sock which, in essence, replaces the liner of the PTB socket. After the plaster has hardened, the adjustable pylon of appropriate length, a SACH foot, and a supracondylar strap are added. Plastic foam is used as a filler between the end of the plaster socket and the pylon to facilitate attachment, increase the durability of the socket, and improve the distribution of forces.

The temporary socket is applied as soon as the operative wound is healed and the patient is able to manage crutches. As yet we have not used the socket as an immediate post-operative dressing.

Unit Instruction

The patient receives initial gait instruction by the physical therapist on the same day that the pylon is made and begins to walk with partial weight bearing on the stump and the assistance of crutches. The frequency of follow-up visits depends on the patient's adaptability but the second visit for adjustment of alignment is usually one week after the application of the socket.

Increased weight bearing is encouraged as rapidly as it can be tolerated. A second and a third wool stump sock is added to compensate for stump shrinkage. When a fourth stump sock is required, a new plaster socket is usually made. No significant problems with pressure points on the stump or wound separation have been experienced to date. An amputee with a tender spot on the stump or incomplete healing cannot tolerate full weight bearing. As pain or a pressure area develops, the patient removes the socket or takes more weight on his crutches.

Anterior-posterior and lateral X-rays are taken of all total contact sockets with the extremity in weight bearing position in order to obtain precise information concerning the accuracy of socket fit. An X-ray is taken on the day of the initial fitting and on subsequent return visits, if the need is apparent.

Patients have worn the plaster pylon for an average of six to twelve weeks. No sockets have had to be replaced because of material failure, all replacements being necessitated by stump shrinkage. No new or unusual gait problems have developed in any of these patients nor in any fitted in the past with above-knee or below-knee plaster pylons with crutch-tip contact. As soon as full weight bearing is established with a permanent limb, the gait pattern is the same as that of any patient wearing a patellar tendon bearing limb.


In summary, temporary patellar tendon bearing plaster pylons have served the following purposes:

  1. Reduced the time required for stump shrinkage.

  2. Provided a means for more active exercise of the hip and thigh musculature.

  3. Provided insight into the patient's ability to utilize the patellar tendon bearing prosthesis.

  4. Assisted in determining the need for the added stability of a knee joint and thigh lacer.

  5. Provided a reasonable resemblance to permanent prosthetic function relatively soon after the amputation.

These, of course, are important but initial or immediate values. A prime question still to be answered is the effectiveness of prior wear of the temporary prosthesis on the prosthetic history after the permanent prosthesis has been applied. Specifically, does this prior wear significantly prolong the period the initial permanent prosthesis can be worn before replacement is necessary? We hope to answer this question as we follow our patients over the next year.

It should be emphasized that the successful use of the pylon depends upon close cooperation between the physician and the prosthetist. Happily, Bert Titus and Robert Gooch of the Duke Prosthetics Unit have provided this cooperation consistently. Mrs. Grace Horton, of the Physical Therapy Department, has worked with all of the patients who have used the temporary pylon and it is her opinion that physical restoration and gait training were somewhat easier for most of them. The cooperation of Mrs. Horton and Messrs. Titus and Gooch has been an important factor in our operation.

Frank Clippinger is Associate Professor, Orthopedic Surgery and Associate Chief, Child Amputee Clinic, Duke University Medical Center, Durham, North Carolina