X-Rays As An Adjunct To Pateliar-Tendon-Bearing Fitting

Richard E. King, M.D.


Our clinic team has long felt the need for a positive means of checking the fit and alignment of a patellar-tendon-bearing prosthesis.

Murphy and Wilson1 have pointed out that: "Stability is provided most often by encasing the stump in a socket to a point near the first proximal joint. The soft tissues of the stump are not especially ideal for providing resistance to the torques and movements imposed on them by a socket during use of a prosthesis. If the tissues are compressed in an attempt to provide maximum stability, circulation will be impaired; if the socket is too loose, a false-joint effect is produced resulting in abnormally high unit pressures at proximal and distal points, chafing and a reduction in ability to control the prosthesis. Thus, extreme care must be exercised in socket design and fabrication if the optimum condition is to be obtained."

All too often we have undertaken extensive modifications of a PTB prosthesis on a trial and error basis - an expensive process and a discouraging one for the patient. However, after we introduced the use of X-rays to help determine total contact, fit and alignment, we found that it was no longer necessary to retain the patient in the hospital while adjustments were made. It is our feeling that the use of X-rays offers a positive and significant approach to fitting problems and also reduces the amount of time a patient spends visiting the pros-thetist for adjustments.

Ideally, X-rays should be taken in all phases of gait, i.e., heel contact, total stance and push off, but this has not yet been feasible although we are currently evaluating the adaptation of cineradiography for this purpose. At present we are making antero-posterior and lateral X-rays in total stance phase. and have found these to be helpful in the following ways:

  1. Determination of Total Contact

    Case One - Whaley

    Problem:

    1. Distal stump irritation relative to fibular overgrowth (despite synostosis).

    2. Excessive piston action was a secondary problem. The patient was originally fitted with a typical PTB prosthesis with cuff suspension. However, joints and a thigh corset were prescribed later when problems of suspension and stability arose. Fig. A depicts the stump deep in the socket (see reference line) and the placement of the prosthetic knee joints superior to the tibial plateaus. Fig. B (in flexed position) shows the stump being displaced in the socket due to the malalignment of joints.

    Remedy:

    1. The popliteal edge of the socket was built up to raise the stump to a more suitable position in the socket (see reference line, Fig. C ) .

    2. The joints and thigh corset were realigned (Fig. C ).

    Case Two - Shaw

    Problem:

    Fig. A reveals that the subpatella undercut is bringing pressure on the tibial tubercle (see arrow) and that the stump is not down in the socket.

    Remedy:

    Our prosthetic staff relieved the posterior brim of the socket to accommodate the hamstrings and reduced the popliteal edge to allow the stump to settle in a more suitable position in the socket. The subpatella undercut is no longer bringing pressure on the tibial tubercle (see arrow). Fig. B depicts good contact over the stump, except at the distal end.

  2. Diagnosis of Pressure Problems

    Case Three - Alexander

    Problem:

    The patient experienced excessive pressure on the (mid) anterior aspect of the stump. Inspection of the insert revealed unusual wear on the (mid) anterior aspect (Fig. A , see arrow). The child perspired profusely and the insert deteriorated rapidly.

    Remedy:

    The patient was fitted with a hard plastic PTB socket, with one 5-ply stump sock. Fig. B depicts the child wearing his new prosthesis. He now enjoys good contact and a satisfactory socket fit (see arrow) although there is some lack of contact at the anterior distal aspect of the stump.

    Case Four - Weaver

    Problem:

    The socket is too big (lack of total contact) with resulting uneven distribution of pressures (Fig. A ).

    Remedy:

    The patient has multiple scarring in the popliteal area of the stump. A new insert was prescribed and the popliteal area of the socket was built up to give adequate back pressure. However, the patient was unable to tolerate the popliteal build-up because of the tender scars. While at home, he cut down the posterior brim of the socket with his pocket knife. This impromptu effort by the young patient resulted in a satisfactory fit and an improved gait. The clinic team observed the X-rays shown in Fig. B and Fig. C and decided to permit the patient to wear the prosthesis in this condition. In subsequent visits to the clinic, it was found that no socket modifications were required.

  3. Relating the Inset-Outset of the Foot to Mediolateral Forces Acting on the Stump

    In fitting stumps four inches or less in length, particularly when the stump is in valgus, as many of them are in young children, we have frequently experienced problems of lateral distal stump pressure. Therefore, we have had to outset the foot more than is recommended for optimal alignment (see Diagram A 2). However, by checking the stump-socket relationship with X-rays, this outset can be minimized and better cosmesis achieved.

    For longer stumps where pressures are distributed over a larger area and present less of a problem, X-rays are utilized as an aid in securing optimal alignment.

    The antero-posterior forces at heel strike and push off cannot be evaluated appropriately by roentgenography but the lateral X-ray at total stance contributes pertinent information regarding the possible effects of antero-posterior forces operating during the shock of initial weight bearing.

In summary, this method has provided our clinic team with an inexpensive but highly useful means of understanding the stump-socket relationship and the possible effects of the forces acting on the stump in a PTB prosthesis. Antero-posterior and lateral X-rays of the stump in a Patellar-Tendon-Bearing Prosthesis in total stance phase have served as a helpful adjunct in the overall appraisal of fitting and alignment.

(The views of James W. Stanford, CP., of J. E. Hanger, Incorporated, and R. R. Rice, CP., of the Atlanta Artificial Limb Company, two of the prosthetists associated with our clinic team, are presented in the following sections of our report.)

Mr. Stanford's Remarks

The use of X-rays has been of valuable assistance in our fitting of PTB prostheses at the Atlanta Clinic. Before we began to use X-rays, we frequently encountered difficulty in determining precisely where weight was being borne in the socket. Powder or blue chalk could be used in an attempt to locate weight bearing areas but this is a rather indefinite arrangement because of sock displacement. It could only be assumed that the stump was in total contact with the socket when no complaints were received from the patient. The use of anteroposterior and lateral X-rays with the patient in stance phase eliminates doubt concerning the position of the stump in the socket.

With the aid of X-rays, we are able to see the position of the bony prominences and observe the outline of tissue along the wall of the socket. Guesswork is no longer involved when corrections in socket fit are necessary. The use of X-rays in the below-knee PTB prosthesis is now a standard procedure in our clinic. From the prosthetist' point of view, it is a definite aid in solving fitting problems.

Mr. Rice's Remarks

The routine practice of obtaining an X-ray of the below-knee stump in the PTB prosthesis under weight bearing conditions has been of major assistance to us in properly fitting this type of prosthesis.

The X-ray affords us a clear picture of the exact location of the stump in relation to the socket. It enables us to determine whether the suitable weight bearing areas of the stump, such as Patellar Tendon, Medial Condyle and Popliteal surfaces, are being utilized to the best advantage. In my estimation, this is the most important factor involved, comparable in importance to locating the ischium on the seat in an above-knee quadrilateral socket. The X-ray also provides us with a picture of the contact or lack of it between the distal end of the stump and the inner distal portion of the socket, and, of course, it aids us in planning future sockets for the amputee.

In the case of an ill-fitting socket, the X-ray shows us where the socket should be built up to obtain a closer stump-socket relationship. We have also found that it enables us to better determine the correct length of the prosthesis. This is very significant because improper seating of the stump in the socket may result in erroneous lengthening or shortening by the prosthetist unless, the socket fit is corrected first. The better fitted and aligned socket results in speedier gait training.

In my view, the X-ray of PTB prostheses could also be utilized in teaching the proper fabrication of sockets. In summary, I would state that the use of X-rays in fitting PTB prostheses is a definite assist to the experienced prosthetist and a must for the inexperienced.

Richard King is Clinic Chief, Georgia Juvenile Amputee Clinic, Crippled Children's Service, Georgia Department of Public Health, Atlanta, Georgia

References:
Murphy, Eugene F., Ph. D. and Wilson, A. Bennett, Jr., "Anatomical and Physiological Considerations in Below-Knee Prosthetics", Artificial Limbs, June, 1962, p. 4.
Radcliffe, Charles W., M. S., M. E., "The Biomechanics of Below-Knee Prostheses in Normal, Level, and Bipedal Walking", Artificial Limbs, June, 1962, Vol. 6, No. 2, pp. 16-24.