Myelodysplasia As A Complicating Factor In Lower-Extremity Prosthesis Fitting

Yoshio Setoguchi, M.D. Cameron B. Hall, M.D. Carl Sumida, C.P.& O

With current techniques, fitting a prosthesis for a conventional lower-extremity amputation, either acquired or congenital, usually presents no special problem for the prosthetics staff. There are, however, instances of apparently normal below-knee stumps where associated anomalies may pose unexpected hazards; for example, a cardiac problem, motor dysfunction, cerebral palsy, or skeletal defects such as kyphosis, scoliosis, or ankylosis. Another anomaly, uncommon but not rare, is spina bifida-the developmental failure of some portion of the spinal column, in which there may also be an involvement of the spinal cord itself, resulting in impairment of motor and/or sensory function. This impairment, termed myelomeningocele, often results in a dysplasia in which one or more areas of partial anesthesia are present.

The case described below is an example of the way in which an associated anomaly can create baffling complications in an apparently simple and straightforward case of prosthetic replacement. This patient came to the Child Amputee Prosthetics Project approximately one year ago, when she was 16 years of age. Multiple congenital deficiencies had been noted at birth: spina bifida with myelomeningocele, and clubfeet. By the age of eight years she had undergone 14 surgical procedures-primarily tendon transplants to correct the foot anomalies. Because of the sensory loss resulting from myelomeningocele, recurrent slow-healing ulcers occurred on the left lower extremity, and a left below-knee amputation was performed at the age of 13 years.

When the girl arrived at this Project she was wearing her second below-knee prosthesis-a patellar-tendon-bearing type with waistband suspension and insert liner. Physical examination revealed a 2 by 2 cm ulcer over the lateral aspect of the tibial tubercle, with moderate induration around the site of ulceration. The remainder of the stump was quite clear, except for a slight discoloration in the popliteal area. The stump was of normal size and conformation, with excellent knee musculature and no significant ligamentous instability. Some sensory deficit was noted, but did not appear to be marked, and she had excellent proprioception as well as true sensory patterns. No X-rays accompanied her medical records, and it was assumed that the skeletal structure of the remaining portion of the limb was normal.

Because of gait deviations, she was given instruction in stretching exercises for her tight right lateral abdominal muscles, plus strengthening exercises for the abdominal and trunk musculature.

Her first CAPP prosthesis was a patellar-tendon-bearing type with a hard socket and patellar cuff suspension (Fig. 1 Fig. 2 ). The fit and function appeared to be most satisfactory, although a slight redness was noted on the distal-anterior part of the tibia.

However, within four months the patient had developed a large abrasion on the distal-anterior area of the stump (Fig. 3 ). When she returned to the Project she was placed on a program of stump bandaging, with sterile dressing, and prosthesis use was discontinued. The area of ulceration diminished, and there was obvious healing. Sensory testing revealed the ulceration to be in an area of analgesia (illustrating one of the problems likely to be encountered in the treatment of a partially anesthetic stump).

A new socket was made, but within approximately one month of wear, the girl began to have considerable edema problems, with mild blistering at the distal stump. Examination revealed considerable pressure on the lateral aspect of the popliteal area, and it appeared that this pressure might be presenting some resistance to venous return.

At this point X-rays were taken (Fig. 4 and 5 Fig. 6 and 7 Fig. 8 ). They revealed a marked superior migration of the patella, an abnormal posterior tibial flare, and a pronounced valgus of the fibula. All of these factors served to complicate the already-existing vascular problem. The true complexity of the fitting problem was revealed when it was discovered that the axial alignment of the femur and the tibia, which ordinarily allows the transverse location of the patellar shelf and the popliteal depression (counterforce to the patellar shelf) to be placed in essentially the horizontal plane, was quite altered in this case.

The normal individual has a relatively short patellar tendon, the mid-portion of which establishes the level of the patellar shelf, this level ordinarily corresponding to the height of the medial-tibial plateau. However, in the myelodys plastic patient the tendon and ligamentous structures may be relaxed. This difference in tendon structure was the first abnormality discovered in this case: the patellar tendon (or the distance from the inferior pole of the patella to the tibial tubercle) was pathologically lengthened. Location of the patellar shelf at the mid-portion of this patellar tendon placed it at a considerably higher level than that ordinarily found. Following normal fitting technique (in which the patellar shelf and popliteal concavity are at approximately the same levels), the posterior indentation was placed too high, resulting in abnormal pressure on the popliteal vascular structures. (See Diagram 1 and Fig. 9 and 10 , which illustrate the position of the patient's stump in her old prosthesis.)

The external rotation and deformity of the tibia were such that although the patellar shelf could be aligned on the coronal plane, the popliteal indentation and hence the socket had to be aligned on an anterolateral-posteromedial axis (Fig. 11 ).

The X-rays had given us clues as to means for providing support and stabilization without compromising the already dangerous vascular problem. The position of the patellar shelf was improved, and we attempted to relocate the popliteal depression beneath the tibial condylar flare by preflexing the socket about 45 degrees (Diagram 2 ). However, the patient could not tolerate the pressures created by this amount of flexion, so it was necessary to relieve them by grinding out the distal-anterior socket. This change reduced the amount of flexion and raised the posterior counterpressure somewhat, but still has resulted in a relatively horizontal alignment of the anteroposterior diameter between the patellar shelf and the femoral condyle, and brought the popliteal concavity beneath the posterior condyle (Diagram 3 ). In this new socket, the medial and lateral flares extend up over the condyles (Fig. 12 ), and following cast relief over the prominent distal tibia and terminal fibula, the fit and function appear to be excellent (Fig. 13 and 14 ). The patient's gait is much improved, and she is able to perform all desired activities.

The series of X-rays of the patient wearing her two prostheses reveal clearly the position of the tibial and fibular elements.

At the time of writing, there has been only a one-month follow-up on this patient's newest prosthesis; however, the prognosis is most encouraging.

The case described is the only one of its kind we have encountered. The staff of the Child Amputee Prosthetics Project would be most interested to learn if any other clinics have encountered the same problem and, if so, what solutions they have found. For us the experience with this patient has particularly underscored two points:

  1. The necessity of prefitting X-rays, and the value of postfitting socket X-rays, especially when anomalous conditions are involved.

  2. The excellent results that can be achieved even when deviations from "standard" fitting techniques must be introduced.

Yoshio Setoguchi, M.D., Cameron B. Hall, M.D., and Carl Sumida, C.P.& O are associated with the Child Amputee Prosthetics Project University of California Los Angeles, California