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The concept of constructing a below-knee prosthesis with side joints and a thigh lacer was set forth by the Dutch surgeon Verduin in (Fig. 1) and followed universally until the advent of the patellar-tendon-bearing prosthesis in the late 's. Although other innovations such as contact over the distal end of the stump, suction suspension, and "muley" sockets were introduced from time to time, they were never widely used, possibly because principles governing their use were not set forth in a systematic manner.
In , the predecessor of CPRD, the Advisory Committee on Artificial Limbs, encouraged the University of California at Berkeley to study the problems of the below-knee amputee and to improve the then current management practices. As a result, some of the leading prosthetists in this country were invited to Berkeley later in for the express purpose of examining in detail the prosthetics practices for BK amputees and rationales for those practices. An analysis of the findings of that conference led to the development of the patellar-tendon-bearing prosthesis, known now as the PTB prosthesis.
The original version of the PTB prosthesis was a plastic laminate socket which was formed over a modified plaster-of-Paris model of the stump, and which contained a soft inner liner that contacted the entire surface of the stump. The major weight was borne by the medial flares of the tibia and the patellar tendon. No knee joints or thigh corsets were used, suspension being effected by a fabric strap around the thigh just above the femoral condyles (Fig. 2).
The PTB concept was offered in formal education programs in this country and gradually gained acceptance, so that by slightly more than half of the below-knee prostheses provided in the United States were of that type. The concept also has been accepted widely in other countries, and the PTB now is generally considered to be the standard prosthesis for below-knee amputations.
In recent years, research groups and individual prosthetists have introduced improvements to the basic concept. This article describes the advanced practices in the management of the below-knee amputee that have been developed since the introduction of the PTB prosthesis.
The original PTB socket design called for a lining of leather or Naugahyde backed by sponge rubber. Perspiration caused problems in many instances, however, because Naugahyde does not "breathe" and leather deteriorates rapidly in the presence of sweat. This problem prompted some prosthetists to eliminate the liner, and the "hard" PTB socket has become increasingly popular.
The suspension strap for the PTB prosthesis, as designed originally, was usually satisfactory, but there were enough dissatisfied amputees to prompt a number of prosthetists to seek improved suspension methods. In addition to developing different strap designs (Fig. 3) , several groups experimented with new configurations for the proximal border of the socket. The research team at Nancy, France, introduced the "prothese tibiale a emboitage supracondylien," popularly known as the PTS, in which the proximal border extends above the patella and the femoral condyles (Fig. 4), thus holding the socket on the stump. This concept was introduced into the United States by Nitschke and Marschall and the PTS prosthesis is being used at an increasing rate in the United States. The technique may be used with or without a liner. Hamontree , in reporting his experiences with 94 cases, noted that, although he believed that the majority of the patients could have been satisfied with the original version of the PTB, a certain percentage could have been successfully fitted only with the PTS version.
Another attempt to improve upon the strap type of suspension resulted in the KBM (Kondylen Bettung Munster) prosthesis , in which a small wedge is inserted between the proximal area of the socket and the area of the stump along the medial condyles of the femur (Fig. 5). Developed at the University of Munster, this concept was introduced into the United States by Fillauer and is now known as the supracondylar-wedge suspension system. The wedge system may be used with or without a socket liner, but generally no liner is used.
In an effort to develop a socket that would permit the stump to bear the optimum amount of the weight load over its distal end, Wilson and his associates designed and developed the "air-cushion socket" (Fig. 6), which reduces the magnitude of the vertical components of weight-bearing forces at other points on the stump.
The air-cushion PTB consists of an elastic inner sleeve (stockinet impregnated with silicone rubber) suspended from the level of the tibial tubercle in a rigid outer shell that is closed distally. Stump support is provided by the tension of the sleeve itself and by the compression of the air in the chamber between the inner sleeve and outer cap.
Trials in the United States, Denmark, and Yugoslavia have shown that the air-cushion version of the PTB is particularly useful for patients with very sensitive stumps. In fact, there appear to be few, if any, contraindications to the use of the air-cushion socket, the only disadvantages being that slightly more time is required to fabricate the socket and that few modifications can be made after it has been fabricated.
In seeking ways to alleviate the problems caused by perspiration, the U. S. Army Medical Biomechanical Research Laboratory developed a porous plastic laminate. Conventional epoxy resins and filler materials are used in the fabrication, but special care must be taken in controlling the proportions of the ingredients and in curing. The first porous laminates developed by AMBRL were satisfactory for upper-extremity sockets, but they were not strong enough for routine use in lower-extremity sockets. Subsequently, the technicians developed a fabrication technique using epoxy resins that overcame the major shortcomings of the earlier laminates. New York University, after studying 20 children and young adults, reported that the porous-laminate socket appeared to be a "significant and worthwhile addition" to below-knee prosthetics specifically and to limb prosthetics generally. There were fewer problems with perspiration, and skin eruptions were ameliorated. In addition, the prostheses with porous-laminate sockets weighed less. When perspiration was a major problem, the two disadvantages cited-slightly increased fabrication time and greater difficulty in maintaining socket cleanliness-were far outweighed by the advantages.
Because most of the innovations to the original PTB design are not mutually exclusive, it was possible to develop a chart showing the combinations of features that can be used to devise a below-knee prosthesis that best meets the needs of the individual patient (Fig. 7).
The method for obtaining a model of the stump for fabrication of the PTB socket, as described in the original manuals, consisted of wrapping the stump with plaster-of-Paris bandages, shaping the wrap with the fingers, and subsequently modifying the male mold produced from the female cast, or wrap. Any number of attempts have been made to devise a procedure that would require less skill. One such method that has been accepted by many prosthetists is the sling-casting, or suspension-casting, technique developed by Hampton (Fig. 8).
In the suspension-casting technique, the stump is wrapped while it is held in a vertical position that simulates weight-bearing during standing. Felt patches to provide relief for sensitive areas of the stump can be applied directly to the stump, and a minimum amount of modification is necessary, although the need for modification is not eliminated entirely.
Research workers and clinicians have been searching for years for a material that will enable the prosthetist to form a socket directly over the stump, thereby eliminating the need for plaster wraps and male molds. Experience with a synthetic rubber, Polysar* X-414, has shown that this material definitely has a place in the fabrication of sockets. Temporary, or provisional, below-knee prostheses consisting of a synthetic-balata socket and pylon-type components are proving to be useful. Because it becomes pliable at temperatures easily tolerated by the skin, synthetic balata can be applied directly over the stump. Extruded tubing of various diameters with walls 1/4-in. thick is available. A piece of tubing slightly smaller in diameter than the stump is heated in water to about 160 deg F, then forced over the stump, which has been padded in appropriate areas (Fig. 9). To give proper shape to the socket, a length of pressure-sensitive tape, 1 in. wide, is wrapped over the outside, and final forming is carried out manually. To provide total contact, the distal end is filled with "foam-in-place" silicone. The socket is easily mounted on a pylon unit for use as a temporary prosthesis, or a more permanent one if desired. The prosthesis can be given a natural appearance by applying and shaping semirigid blocks of Koroseal "Spongex"* (Fig. 10). Contours of the socket can be changed at any time by heating the area with a heat gun and reshaping it manually.*
During the past decade, the advantages of fitting a prosthesis as soon after amputation as possible have been demonstrated repeatedly. Goldner and his associates demonstrated that "early" fitting-that is, providing the patient with a temporary prosthesis as soon as the wound has healed rather than waiting for a maximum amount of shrinkage to take place-could drastically reduce time and costs of rehabilitation. Even more dramatic results have been obtained by fitting artificial limbs immediately after surgery, especially with below-knee amputees (Fig. 11).
The technique of immediate postsurgical fitting was originated in France by Berlemont, was carried further by Weiss in Poland, and, after a considerable experimentation period in the United States, is now being taught routinely in the prosthetics education programs in this country. The technique consists of applying a rigid dressing over the stump and attaching an adjustable pylon and foot. Standing and ambulation is begun as soon as the patient's condition permits. For young, otherwise healthy patients, some ambulation can begin on the day following amputation.
Usually the rigid dressing is left in place until the wound has healed and the sutures can be removed-about 10-14 days postoperatively. A second rigid dressing is provided for another 10- to 14-day period, at which time a "permanent," or definitive, limb can be provided. The advantages of immediate postsurgical fitting include reduction of edema, less pain, shorter periods of hospitalization and therapy, and fewer contractures. The technique has become standard practice in many centers with trained teams.
To make early fitting and immediate postsurgical fitting easier, a number of adjustable pylons have been developed. Those currently available are shown in Fig. 12. Some of their characteristics are given in Table 1. These units are strong enough and light enough for extended usage with or without some sort of cosmetic cover. A number of approaches to cosmetic treatment such as the use of Spongex, mentioned above, have been offered, but none have been accepted widely by prosthetists. Work on this problem is continuing.
At the December "Symposium on Below-Knee Prosthetics", sponsored by the Committee on Prosthetics Research and Development, a number of suggestions for improving prosthetics education and practice were offered.
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Because most of the recent improvements to the design of the below-knee socket, especially in suspension techniques, have been accomplished by practicing prosthetists, there is little need for the research centers to devote their time to developing additional improvements. On the other hand, there is very little knowledge about the basic principles underlying optimum fitting of prostheses. Therefore, the research centers should be encouraged to obtain basic information about the effects of pressure and shear forces on tissues, and to more clearly indicate the biomechanical forces required in the various phases of walking. Following that work, methods by which those principles could be put into practice should be developed, including the use of hydrostatic sockets and other methods that might provide automatic adjustment.
As a result of these suggestions, a pilot course in advanced below-knee prosthetics practices was held at Northwestern University (see "News and Notes") on August 4-13, , for prosthetist instructors from the University of California at Los Angeles, New York University, and Northwestern University. The University Council on Prosthetics Education is now developing a curriculum for short-term postgraduate courses in below-knee prosthetics. The advanced techniques will also be offered in regular courses in below-knee prosthetics.
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Currently four types of basically designed prostheses are used for SA.
The Canadian design or posterior door design, also used for Chopart’s amputation is the commonly used prosthesis for individuals with large or bulbous residual limbs. Disadvantages of this prosthesis is heavier in weight when considered as a cosmetic option.
Medial door design (Figure 6) is a commonly used prostheis. It has great suspension due to intimate construction nature of the socket. It consists of an expandable door made up of an elastic sleeve which improves cosmesis and helps in donning and doffing process.
An expandable inner liner which is enclosed within the rigid outer shell. It has a hidden-panel expandable wall which is used for small distal ends.
Preparatory prosthesis which consists of a removable foam liner (Figure 7) that interfaces with the external socket. This allows or has the ability to modify accordingly further allowing for atrophy during maturation process by using the patellar tendon to assist by unloading the limb. It is lightweight and easily adjustable hence considered as the one with great cosmesis. Proximal region at the level of patella tendon or below can be trimmed as the amputee progresses with limb maturation.
A modified Jones compression dressing is used postoperatively to control edema and to help shape the stump [7].
The gait cycle which consists of two stages will also be termed as walking cycle. Initial contact is the first step in the starting point and the end point in every gait cycle. A single gait cycle has two phases. The stance phase and the swing phase. The stance phase is the initial step in which the foot contact starts followed by other steps in the ground. The stance phases contribute about 60% of the gait cycle and the swing phase contributes about 40% of the gait cycle. The swing denotes the single leg support in which the foot is off the ground.
The pattern of gait in subjects with prosthesis will present an altered gait pattern. Here the foot contact on the ground and the weight distribution on the foot is the key factor to be noted. The foot contact will occur on the heel in such a way the walking cycle will be as natural as possible. In this situation the sole of the foot will contact the ground and the weight is transmitted to the foot. Thus, the selection of foot component and the knee joint must be proper. This is because this will have an influence on the subject’s gait when he turns on to the next phase [9].
During swing phase, the knee function is so important so that the mobility on the knee joint performing both flexion and extension facilitating the foot transition from plantar flexion to dorsiflexion i.e toe elevation. This will prevent the subject from stumbling and subsequent fall.
The residual limb must be placed on the socket which provides rigid and stable attachment to the limb. This aids control over the subject’s limb during walking. The prosthesis socket can be divided into 3 parts. The top region of the socket is known as seating face. The central part of the socket is the primary control area. The function of the central part is to ensure correct movement and restrain it in the PA direction during walking. The last part is the distal socket end. This part will transfer only 10% of the subject weight to avoid abnormal weight transfer and this will cause subsequent damage to the soft tissues. The socket must be able to transfer the load thereby it ensures good stability of the subject’s gait with better control [10].
During standing, there will be a stretching of gluteus medius muscle. This will maintain the pelvis in a balanced position. For a subject with lower limb amputation this pelvis position is taken care by the prosthetic socket. In a transverse oval socket of transfemoral prosthesis, the pressure on the distal femur end increases and the body is excessively bending aside to reduce the pressure. It is a non-physiological load transfer, as the load is transferred through the tuberosity of the ischium which reduces the arm of the exerted force and the overturning moments are increased.
If there is any problem in procedure of construction and principles in aligning the prosthesis, there will be an abnormal deviation that may develop during gait. This gait deviations uses more energy expenditure during walking. Once this is practiced as a routine, may result in over use of certain muscle groups which also causes muscle imbalance.
In most cases, the improper construction of the transfemoral prosthesis and transtibial prosthesis includes
On circumduction, the foot swings outward which increases resistance to knee flexion with prosthesis. Here the prosthesis knee flexion has been limited for a reason. Thus, the subject has developed the avoidance mechanism.
The lateral flexion of the spine, the subject presents a leaning gait with the shoulder depressed towards the affected side. This is due to prosthetic foot is outset greater than 25mm, incorrect prosthesis length, insufficient adduction or amputee sensitivity.
Excessive heel raise, where the heel of the prosthetic foot comes up too far and too quickly. This is due to prosthetic knee flexion resistance is inadequate for the patient.
Drop off during the late stance, the subject presents excessive knee flexion. This is due to softness of the keel of the prosthetic foot. Also, the toe lever of the foot is too short of the heel height of the shoe is too high.
Foot slap, this occurs along with rapid and abnormal plantar flexion movement immediately after heel contact. This is due to insufficient resistance to plantar flexion on the prosthetic foot.
Thus, if there is an improper prosthetic fitting, there will be pain and altered muscle activity during execution of the normal daily activities. This pain may cause lateral asymmetry of the body which is due to incorrect length of the prosthesis or incorrect selection of the prosthetic component. This wrong construction can lead to abnormal force transmission, overloading the various muscles involved and also damage to the soft tissues which may affect the integration of the stump function.
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