Experiences With Non-Standard Below-Knee Prostheses

Charles H. Epps, Jr., M.D. John Hile

Our efforts to provide prosthetic rehabilitation for a patient with congenital absence of most of both feet (apodia) led to the development of an artificial limb which borrowed features from both the patellar tendon-bearing (PTB) and the Syme prostheses. To date we have applied the basic design of this prosthesis to four cases and have achieved gratifying results. Three of the patients had similar congenital deficiencies (apodia), while the fourth case was amputated just proximal to the ankle joint as the result of burns to the foot complicated by infection. The distal stump was conical and covered largely by adherent scar tissue.

The length of the three congenital stumps was similar to that of a conventional Syme amputation, although a rudimentary os calcis was present. X-ray examination revealed that the os calcis had retracted proximally posterior to the tibia producing a prominence in that area. The result was a stump that was not as satisfactory for total end bearing as the classical Syme amputation. For this reason a limb which utilized both patellar tendon and partial end-bearing seemed indicated (Fig. 1 ).

The technical details of fabrication of the PTB and the modern Syme prostheses are well documented. Hence we will confine our presentation in this article to consideration of pertinent aspects of the "hybrid" prosthesis.


In these cases the cast is taken with the patient in a non-weight bearing position. The patient is seated with the knee flexed and a thin cast sock is applied snugly to extend well over the knee. Areas that are prominent or sensitive to pressure, bone spurs, adherent scar tissue, neuromas, the patella and patellar ligament, the tibial tubercle, the head of the fibula and the crest of the tibia are identified and marked with an indelible pencil. These markings will be transferred first to the negative mold and then to the positive model.

The actual plaster wrapping utilizes two layers of plaster splints running lengthwise beginning in front above the patella, passing down in front and around the distal stump, and back to the posterior crease of the knee. Circumferential wraps of plaster are then spiraled down and smoothed to form a thickness of approximately 1/8".

When the heel pad is normal and can be used for partial weight-bearing (Cases 1, 2 and 4), the end of the cast is flattened. This allows for expansion of the heel pad during weight bearing. However, if the end of the stump is scarred (Case 3), has a bone spur, or an irregular shape, the original shape of the end of the stump is maintained.

As the plaster begins to harden, the thumbs outline the patella tendon and compress the popliteal tissues in the manner prescribed for the PBT socket. This definition is maintained until the plaster hardens. A longitudinal cut is made along the posterior midline to permit removal of the cast.

The cast sock is turned down and the splint shell closed with a few additional spiral turns of plaster. The cast is then filled to the top with liquid plaster of Paris and a length of pipe is imbedded at the proximal end to provide an extension for handling the model.

The Plaster Model

When removed from the wrap cast, the male mold should be a fairly accurate representation of the stump. However, it should be modified by removal of plaster in the weight-bearing areas and the addition of skived leather patches in the areas to be relieved, in accordance with standard practice for the Patella Tendon-Bearing Prosthesis.1 Distally, the model should also be modified to take advantage of whatever weight-bearing potential is available.


The socket is laminated in the routine manner, utilizing polyvinyl (PVA) sleeves and a resin-catalyst mixture.

Two of our patients (Cases 1 and 3) had tapered stumps, and the cured sockets were removed from the model in standard PTB fashion. The other two (Cases 2 and 4) had bulbous stump and, after curing, a posterior panel was cut in the socket prior to removal from the model. The posterior panel is attached to the socket by the conventional tongue and slot method and secured by straps. A posterior cut-out does not present a problem to males, but is an unsatisfactory arrangement for females, especially from a cosmetic standpoint.

When the lamination is completed, the calf may be built up to improve the cosmetic attractiveness of the limb for the female patient.

Attaching the Foot and Alignment

While a commercial SACH Foot may be used in cases of this type, our prosthetic staff fabricated SACH-type feet for the four children fitted. The keel and neoprene crepe are hollowed to receive the bulbous end of the stump. The socket is usually placed forward on the foot, which is set in a small amount of dorsiflexion (5° to 7°), again in accordance with standard PTB practice. An effort is made to avoid inversion or eversion of the foot.

Initial or static alignment is achieved by having the patient don the socket and then placing the distal end into the recess in the SACH Foot. Any necessary adjustments in the socket-foot relationship are made, and the socl et is then bolted to the keel. The alignment is checked under walking conditions, and indicated adjustments are made prior to finishing the leg.

An alternate method, used in our first case, was to laminate the keel to the socket and build the SACH Foot around the keel. After the alignment was judged to be satisfactory, the foot was bonded to the socket and a smooth transition between foot and socket obtained by grinding. This method is more time-consuming, but produces a better cosmetic result.

The following four case histories are illustrative of our experiences with the nonstandard below-knee prosthesis:

Case One

Subject M.H., a female, was born on December 24, 1942. She was referred to us at the age of 16 years because she was experiencing difficulties with her prostheses.

Our examination revealed bilateral central hemimelia (T/ Partial Adactylia: 2, 3, 4) in the upper extremities (Fig. 2A ) and bilateral apodia with a vestigial os calcis present in each limb (Fig. 2B ). Her leather and plastic prostheses extended to about the mid-tibia level (Fig. 3 ). The cosmetic effect, which is quite important to a girl in this age group, was poor, and she wore thick bobby socks to conceal the prostheses. Moreover, proximal socket pressure had produced skin breakdown.

Combination prostheses, which utilized patellar tendon and distal weight-bearing, were then fabricated (Fig. 4 ). The appearance of the prostheses was markedly improved and she was able to wear nylon hose for the first time. It was also noteworthy that her skin irritation rapidly disappeared. The young lady completed business school and subsequently obtained employment as a parking lot cashier.

Case Two

Subject D.W., a male, was born on June 20, 1952. He was initially seen at our clinic at the age of two months with multiple congenital anomalies, which included: (1) right upper central hemimelia (T/ Partial Adactylia: 2, 3, 4); (2) right lower apodia with 45° internal tibial torsion; and (3) partial aphalangia of the left hand and foot (Fig. 5A and Fig. 5B ). The Moebius Syndrome was also included in the diagnosis.

At the age of one year, D.W. was fitted with a Syme-type prosthesis with a posterior panel. The SACH Foot was externally rotated on the socket to prevent toe-in. Since the initial fitting, he has had appropriate replacements to accommodate growth to his present age of 12 years, when he was fitted with a combination below-knee prosthesis. This prosthesis utilized end bearing and patellar tendon weight bearing, and had a posterior panel (Fig. 6A and Fig. 6B ). A skin irritation which had developed at the proximal socket of his old prosthesis cleared rapidly and did not recur. His gait was considered to be excellent.

Case Three

Subject T.T., a male, was born on April 3, 1961. At the age of two months, his left foot and lower leg were severely burned in a home fire. Subsequent infection made amputation proximal to the foot necessary (Fig. 7 ) .

T.T. was first seen in our clinic at the age of one year, at which time he was attempting to pull himself up in his crib. Since there was an extensive adherent scar over the lateral stump, which made pressure tolerance questionable, a combination below-knee prosthesis without a posterior panel was prescribed. The child was able to walk with assistance within two weeks of receiving the limb, and after four months, he walked independently. The scar tissue has held up well and does not present a problem. Fig. 8 depicts the prosthesis fitted recently.

Case Four

Subject J.H., a male, was born on October 8, 1961. He was first seen at our clinic at the age of one week with a lower left congenital partial adactylia (a rudimentary fifth metatarsal was present). The foot was in calcaneus position and the extremity was 1/2" short overall, measured from knee joint to heel pad. As the child grew, the calcaneus deformity progressed and the shortening was 1-1/4" at the age of 19 months.

After a high-top shoe with a filler proved to be unsatisfactory, the existing fifth metatarsal was resected and the anterior tibial tendon sectioned to bring the remaining foot into equinus. This procedure provided a more acceptable stump for fitting purposes.

Two weeks post-operatively, the child was ambulated in a plaster walking cast, which he used until his combination prosthesis with a panel was completed in eight weeks. After donning his permanent prosthesis, he was able to walk immediately with an excellent gait. At this writing, J.H. continues to wear the prosthesis without difficulty. His present fitting is depicted in Fig. 9A and Fig. 9B .


The prosthesis described in this report is non-standard in the sense that it is utilized for unconventional stumps, and its construction and weight bearing characteristics borrow from both the patellar tendon and Syme prostheses.

Four cases represent a very small series, of course, and preclude any sweeping conclusions. However, our experiences indicate that this prosthesis has a definite value for patients with apodia and may also be useful for amputees with long atypical below-knee stumps with poor skin which makes full weight-bearing impractical.

The child or adult with a conventional Syme stump who has poor distal pressure tolerance may also benefit from this fitting since the alternative of amputation at a higher level presents disadvantages, such as impairing the ability of the patient to go to the bathroom at night without donning a prosthesis - a distinct advantage in the unilateral, and essential to the bilateral, Syme amputee.

1 Radcliffe, C. W., and Foort, J., "The Patellar-Tendon-Bearing Below-Knee Prosthesis", Biomechanics Laboratory, University of California, 1961.

Charles Epps is Clinic Chief and John Hile is Clinic Prosthetist, Juvenile Amputee Clinic, Handicapped and Crippled Children's Service, District of Columbia General Hospital, Washington, D.C.