Chapter 20B - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles
Transfemoral Amputation: Prosthetic Management
C. Michael Schuch, C.P.O.
REVIEW OF TRANSFEMORAL BIOMECHANICS
The basic goals for fitting and aligning prostheses for transfemoral amputees seem simple enough: (1) comfort, (2) function, and (3) cosmesis; however, obtaining these goals is significantly more challenging than might be expected. This is because of the many and varied interrelationships between patient diagnosis, prognosis, medical history, residual and intact anatomy and kinesiology, and available prosthetic technology.
Analysis and Relevance of Residual-Limb Range of Motion
Careful measurement and evaluation of residual and intact anatomy and kinesiology are essential for correct socket design and initial socket alignment. The necessity for measurement of lengths, circumferences, and diameters is obvious enough. Perhaps more important and less understood is the need for accurate measurement and evaluation of the range of motion of the residual limb in both the sagittal and coronal planes.
Range of motion in the sagittal plane consists of flexion and extension of the residual femur. Especially important is the amputee's ability to extend the residual femur fully. The normal hip is capable of a maximum of 5 degrees of extension posterior to the vertical without anterior pelvic rotation or lordosis. The inability to fully extend the residual femur usually indicates a hip flexion contracture. Owing to the location of muscle insertion points, the flexors of the hip have a better mechanical advantage than the hip extensors do; thus a hip flexion contracture is not uncommon and is more prevalent in shorter residual limbs. This range of motion in the sagittal plane should be documented along with other necessary measurements.
Range of motion in the coronal plane consists of abduction and adduction of the residual femur. Especially important is the amputee's ability to adduct the residual femur fully, equivalent to the adduction of the femur on the sound side. Normal femoral adduction angles average about 6 degrees. The inability to fully adduct the residual femur usually indicates an abduction contracture. The adductors of the femur are at a mechanical disadvantage when compared with the abductors due to their location and the fact that the most effective adductors have been severed at amputation. Abduction contractures, like hip flexion contractures, are not uncommon and are more prevalent in shorter residual limbs. This range of motion in the coronal plane should also be documented.
The analysis and measurement of the ranges of motion of the femur in the sagittal and coronal planes are important in establishing the initial angular alignment of the socket for a transfemoral prosthesis. Proper planning and incorporation of these angular measurements into the socket and overall prosthesis design allow for certain biomechanical and alignment principles that are advantageous to the amputee during the various phases of gait. This will be demonstrated in the next sections on the biomechanics of transfemoral prosthetics.
Biomechanics of Knee Stability-Stance Phase of Gait
Knee stability in a transfemoral prosthesis refers to the ability of the prosthetic knee to remain extended and fully supportive of the amputee during the stance phase of walking. Knee instability is the buckling or unintended flexing of the prosthetic knee during the stance phase of walking. Obviously, instability can be quite dangerous by causing unexpected falls. Excessive knee stability is a condition in which the knee of the prosthesis is so stable and resistant to flexing that it is difficult for the amputee to initiate the knee flexion required to achieve toe-off and swing of the shank. Excessive energy expenditure and an unnatural swing phase of the gait cycle are the results. There is a very fine distinction between knee instability and excessive knee stability. The key to avoiding these two undesirable characteristics and achieving optimum knee stability is an understanding of the biomechanics of prosthetic knee function.
In biomechanical terms, there are two descriptions of knee stability or knee control: involuntary knee control and voluntary knee control (Fig 20B-1.).
Involuntary knee control implies that control is not subject to the will of the amputee but is automatic. The degree of involuntary control varies in complexity. One form of involuntary knee control is alignment stability in which the prosthesis viewed laterally is aligned so that the knee axis is posterior to the biomechanical weight line, which generally extends from the midpoint of the socket proximally to the midpoint of foot contact with the ground. With the weight line anterior to the prosthetic knee axis, increased weight bearing tends to force the knee into extension and locks it against the extension stop. Excessive knee stability, as described earlier, occurs when the prosthetic knee joint is located too far posterior to the biomechanical weight line. Other forms of involuntary knee control are mechanical and include locking knees, weight-activated stance-control knees, and certain hydraulic knee systems.
Voluntary knee control implies that control is directly subject to the will of the amputee and is achieved and maintained through active participation of the hip extensor muscles. These muscles include the gluteal muscles (primarily the gluteus maximus) and the hamstring muscle group. When these muscles can exert enough force and are consciously fired at the proper time by the amputee, knee stability is achieved in the stance phase of gait. For the stronger and more physically fit amputee, voluntary control provides for a smoother and more energy-efficient gait because it takes less effort to initiate swing-phase flexion than with an involuntary knee alignment. Better muscle tone and coordination are achieved as well. However, voluntary control is not always possible, especially when muscle weakness, hip flexion contractures, and fear, all common to the more elderly and otherwise debilitated amputee, are present. Additional factors that contribute to control of knee stability are initial socket flexion, the trochanter-knee-ankle (TKA) relationship, and ankle-foot dynamics.
Earlier, the need for analysis of the range of hip flexion and extension of the residual limb was discussed. The hip extensor muscles contribute to knee stability by pulling the prosthetic knee into extension or by maintaining existing knee extension. The hamstring muscles, which are transected by transfemoral amputation, are believed to function best when stretched just beyond their rest length. It is also known that the only intact hip extensor, the gluteus maximus, is not capable of exerting any significant force until the hip is flexed at least 15 degrees. To achieve some degree of stretching of the gluteus maximus, the prosthetic socket is designed and aligned in a position of "initial flexion." The amount of initial flexion increases as the amputees ability to extend his hip decreases. The only limiting factor is the length of the residual limb. For longer residual limbs, some cosmesis has to be sacrificed as initial flexion is increased. In addition to enhancing voluntary control of knee stability, initial socket flexion decreases the tendency of the amputee to use increased pelvic lordosis to compensate for weak hip extensors.
The TKA relationship is best understood as the socket-knee-ankle relationship. To review, the more anterior the socket is placed to the knee joint and ankle, the more stable the knee. In most cases, transfemoral prostheses are set up so that the socket is mounted on an adjustable alignment device that permits multidimensional freedom of movement of the socket with respect to the knee-shank and ankle-foot components. (Such an alignment device may later be transferred out of the finished prosthesis.) In this ideal situation, the anteroposterior (AP) setting of the socket is determined under dynamic conditions as the amputee's gait is analyzed carefully. The goal is to align the prosthesis so that the amputee uses the minimum amount of "alignment stability" or involuntary knee control necessary, thereby optimizing voluntary knee control for each individual patient. A critical balance between these two biomechanical conditions is required to achieve a safe, yet efficient gait.
Ankle-foot dynamics refers to the shock-absorbing and stabilizing abilities of this combined component system of the prosthesis. The most unstable phase of gait for a transfemoral amputee is at heel strike. At heel strike, a moment or torque is created that tends to rotate the shin forward and thus flex the knee, thereby creating an instant of potential knee instability (Fig 20B-2.). In normal human locomotion, smooth and uninterrupted plantar flexion serves to dampen the significant moment initiated at heel strike. In the transfemoral prosthesis, ankle-foot components that more closely replicate normal ankle-foot function contribute to knee stability. The goal is inherent stability throughout mid-stance followed by smooth, uninterrupted, gradually increasing flexion throughout the initial swing phase of gait.
Biomechanics of Pelvis and Trunk Stability-Stance Phase of Gait
In any discussion of gait of the transfemoral amputee, two specific goals are mediolateral pelvis-trunk stability and a narrow-based gait. These two goals are very much interrelated and are perhaps the most difficult and challenging of goals facing the prosthetist as well as the amputee.
In normal locomotion, the pelvis drops about 5 degrees toward the unsupported side during midstance, with such motion occurring around the hip joint of the weight-bearing limb. The hip abductors, primarily the gluteus medius, prevent any additional drop through eccentric contraction. This phenomenon is one of several "gait determinants" inherently designed to provide energy efficiency in normal locomotion. In normal locomotion, weight bearing occurs through the bones of the leg, and contraction of the gluteus medius is effective in controlling pelvic tilt at the hip joint of the stance leg. In the case of the transfemoral amputee, the femur does not terminate in a foot planted firmly on the ground. The residual femur, now a lever only 40% or less of the normal length of the lower limb, floats in a mass of muscle, tissue, and fluid. The residual femur tends to displace laterally in the mass of residual muscle and tissue rather than maintain horizontal stability of the pelvis and trunk. This lack of support and ineffective pelvic stabilization results initially in excessive pelvic tilt from the prosthetic support leg (positive Trendelenburg sign), with concurrent perineal or pubic ramus pressure and discomfort. The amputee will typically compensate by widening the base of his gait and using trunk sway over the wide-based point of support (compensatory Trendelenburg) rather than gluteus medius activity.
Effective pelvis-trunk stabilization and the resultant narrow-based gait can only be achieved in a transfemo-ral prosthesis by providing adequate lateral support to the femur. The femur must be maintained in a position as near as possible to normal adduction, thereby putting the gluteus medius and other abductor muscles in a position of stretch that allows them to function most effectively. This objective is accomplished through socket design and alignment, with particular attention to the medial and lateral walls of the socket(Fig 20B-3.). Generally, the medial wall is flat and vertical to help distribute stance-phase counterpressure forces; the lateral wall of the socket should be designed and aligned in a position of adduction that matches the "adduction angle" measurement obtained early in the residual-limb range-of-motion evaluation. Obviously, restriction of adduction, as when an abduction contracture is present, will significantly limit the ability to control pelvis and trunk stability.
Additional factors that affect the ability to maximize mediolateral pelvis and trunk stability are the length of the residual limb, proximomedial tissue density, and proper alignment of the prosthetic components below the socket. These factors are discussed below.
A longer residual limb provides a longer lever and larger surface area over which to distribute the inherent forces. Shown in Fig 20B-4. is a lever system: "W" (weight), "F" (fulcrum), "P" (proximal part of the femur), and "D" (distal part of the femur). The effective lever arms are "W-F" and "P-D," and resulting forces or moments depend on weight and lever length. For example, if the lever "W-F" has an effective length of 4 in. and the force or weight is 150 lb, the moment or torque around this lever system will be 600 in. lb. If the lever "P-D" is 10 in., only 60 lb of force need be exerted to equalize the moment or torque of 600 in.-lb and thus stabilize the pelvis and trunk. However, if the femur length as simulated by lever "P-D" is only 5 in. in length, 120 lb of force is required to equalize the 600 in.-lb of torque, thus subjecting our hypothetical femur to much greater levels of pressure. The more evenly that pressures can be distributed, the more tolerable they become. If the force is distributed over a smaller area, pressure concentration may cause discomfort, pain, or skin breakdown. For this reason, the shorter the residual limb, the more difficult the task of establishing and maintaining mediolateral pelvis and trunk stability. In these situations, the ideal gait is compromised for the first and foremost goal of comfort (Fig 20B-5.,A and B).
The biomechanical reaction to the contraction of the hip abductors and resultant femoral force against the lateral wall of the transfemoral socket is a laterally directed force or moment concentrated at the proximo-medial aspect of the transfemoral socket during mid-stance. When coupled with the normal and desirable gait determinant of lateral pelvic shift over the support limb, the forces generated at the perineum are significant. Firmer, denser, and more muscular residual limbs (which are often longer in length) are better able to tolerate this reaction force. Soft, fleshy (often shorter) residual limbs lacking muscle tone in the adductor region are very susceptible to tissue trauma and bruising and offer a less stable reaction point for support. In such cases, mediolateral pelvis-trunk stability will be compromised unless these reaction forces are directed against more stable anatomic features such as the skeletal anatomy in this area. The relatively recent advent of the ischial-ramal containment transfemoral socket design provides one solution to this problem.
Prosthetic alignment is a significant variable that contributes to trunk and pelvis stability. There has been considerable controversy over socket and foot relationships in the coronal plane as viewed from the sagittal plane. Foot placement in the coronal plane is best determined dynamically by using adjustable alignment devices within the prosthesis (Fig 20B-6.).
Biomechanics of Knee and Shank Control-Swing Phase of Gait
The requirements and goals of the swing phase of gait for the transfemoral amputee are normally easier to attain and are less demanding than those of the stance phase of gait. However, from the standpoint of energy consumption, significant deviations result in greater demand. Our discussion will focus on two aspects of the transfemoral prosthesis swing phase: swing-phase timing control and swing-phase tracking.
When the prosthesis is aligned with too much "alignment stability," excess energy and effort are required to initiate knee flexion. Overcoming such "alignment stability" takes effort and delays the initiation of swing phase. Vaulting, which is usually thought of as a deviation in response to a prosthesis that is too long, can also serve to subtly compensate for a delayed advancement of the prosthetic shank in midswing.
Swing-phase tracking refers to the smoothness of the pathways of the prosthetic limb during the swing phase of the gait cycle. Goals are to minimize vertical displacement of the prosthesis on the residual limb and to minimize deviations in the sagittal plane as the prosthetic limb advances during swing phase. Problems with vertical displacement are due to poor suspension and resulting piston action and/or inappropriate length of the prosthesis. Deviations in the sagittal plane include "whips" during the swing phase caused by improper socket shape or improper knee axis alignment, as well as circumduction, usually caused by excessive prosthesis length or poor alignment.
TRANSFEMORAL SOCKET DESIGNS: VARIATIONS AND INDICATIONS
Overview of Transfemoral Variants
The total-contact quadrilateral socket, which has both American and European variations, was the socket of choice from the 1960s until recently and remains the most commonly prescribed socket system even today, despite new designs and techniques.
By the early 1980s, innovative designs for transfemo-ral sockets began to emerge and were published under various acronyms. This socket design and philosophy has become known generically as the "ischial containment" socket. The origin is attributed to Ivan Long, with credit for furthering its development due John Sa-bolich, Thomas Guth, Daniel Shamp, and Christopher Hoyt. Techniques of molding and fabricating the socket remain similar in content and approach to those of the quadrilateral socket. Changes center around the position of the ischium with respect to the socket proper and related biomechanical and socket comfort enhancements.
Specific Transfemoral Socket Designs and Rationale
Hall described five important principles of socket design that were intended as objectives of the quadrilateral socket but apply equally well to any modern trans-femoral socket:
- The socket must be properly contoured and relieved for functioning muscles.
- Stabilizing pressure should be applied on the skeletal structures as much as possible and areas avoided where functioning muscles exist.
- Functioning muscles, where possible, should be stretched to slightly greater than rest length for maximum power.
- Properly applied pressure is well tolerated by neurovascular structures.
- Force is best tolerated if it is distributed over the largest available area.
Regardless of the fitting method employed, the socket for any amputee must provide the same overall functional characteristics, including comfortable weight bearing, stability in the stance phase of gait, a narrow-based gait, and as normal a swing phase as possible consistent with the residual function available to the amputee. These characteristics will provide the format for a description of transfemoral sockets.
The term quadrilateral refers to the appearance of the socket when viewed in the transverse plane (Fig 20B-7.) because there are four distinguishable sides or walls of the socket. The orientation of the four walls will vary according to the amputee's specific anatomy and the biomechanical requirements of the socket. According to Radcliffe, "the socket is truly more than just a cross-section shape at the ischial level, it is a three-dimensional receptacle for the stump with contours at every level which are justifiable on a sound biomechanical basis."
Weight bearing in the quadrilateral socket is achieved primarily through the ischium and the gluteal musculature. This combination of skeletal and muscular anatomy rests on the top of the posterior wall of the socket, which is formed into a wide seat that is parallel to the ground.
Countersupport, intended to maintain the position of the ischium and gluteals on this posterior seat, is provided by the medial third of the anterior wall of the socket, which is carefully fitted against Scarpa's triangle. The AP dimension of these respective walls is based on anatomic measurements. A common error is to create deep, exaggerated Scarpa's triangle contours. As the concepts of total contact and total surface bearing became better understood, anterior counterpressure was de-emphasized. Clinical experience with other socket designs has shown that enlarging this dimension of the socket often allows for additional comfort in the perineum with no loss of comfortable weight bearing. This suggests that tissue and muscle loading occurs as a supplementary weight-bearing mechanism. The concept of total surface bearing suggests that weight bearing be as evenly distributed over the entire surface area as possible, with the forces and loads being evenly shared by skeletal anatomy, muscle, soft tissue, and hydrostatic compression of residual limb fluids.
Incorporation of adduction into the quadrilateral socket depends on the range of motion available, generally a function of the length of the residual limb. The goal is to re-establish the normal adduction angle of the femur with respect to a level pelvis. The quadrilateral socket accomplishes this by contouring the lateral wall in the desired degree of adduction. The entire lateral wall is flattened along the shaft of the adducted femur with the exception of a laterally projected relief for the terminal aspect of the femur. Proximal to the greater trochanter, the lateral wall is contoured into and over the hip abductor muscle group to discourage abduction. As previously discussed, midstance firing of the hip abductor muscles leads to reaction forces occurring in the proximomedial aspect of the residual limb and socket. As a means of providing counterpressure and distributing these reaction forces, the contour of the medial wall of the socket is flat in the sagittal plane along the proximal 4 in. of the socket before reversing into a smooth flare directed away from the residual limb and toward the perineum. Careful attention to this proximomedial socket contour is absolutely essential for stance-phase comfort in the perineum.
The quadrilateral socket should be designed with "initial flexion" to improve the ability of the amputee to control knee stability at heel contact and to help in minimizing the development of lumbar lordosis at toe-off (Fig 20B-8.).
The achievement of normal swing phase is dependent upon several factors. Obviously, proper suspension enhanced by careful matching of residual-limb and socket contours aids in achieving a normal swing phase. Proper socket contours for actively functioning muscles (primarily the rectus femoris and gluteus maximus) also affect swing-phase tracking in the sagittal plane. The depth of the rectus femoris channel, in the transverse view, will vary depending on proximal circumference and muscular firmness of the residual limb, as well as femoral anteversion. The posteromedial wall angle varies from 5 to 11 degrees, depending on the muscular density of the proximoposterior aspect of the residual limb (Fig 20B-9.,A and B). If the AP dimension of the lateral half of the quadrilateral socket is too tight, as viewed transversely, then muscle activity in the swing phase of gait can lead to undesirable socket rotations about the residual limb that appear clinically as swing-phase "whips."
The distal end of the socket must match the contour of the distal end of the residual limb and provide adequate distal contact, or else edema and other skin problems will develop.
The concept of the "U.S. quadrilateral socket" was borrowed from Europe and refined through significant biomechanical analysis and research conducted in the United States. The original concept also continued to develop independently in Europe. During the decade of the 1980s, several European-style quadrilateral socket casting brims became available in the United States. When compared with the U.S. quadrilateral brims, the transitions from the four socket walls were smoother and less abrupt. The medioproximal wall was slightly lower and increased comfort in the perineum. In the transverse view, these European brims featured a larger AP dimension balanced by a smaller mediolat-eral dimension as compared with typical U.S. quadrilateral shapes. Although the biomechanical principles remained the same, these subtle changes began to influence U.S. quadrilateral techniques at about the time that the "ischial containment" socket initiated new concepts in transfemoral socket theory.
Ischial Containment Socket
The term "ischial containment" is rather self-descriptive. It describes several similar concepts in socket design in which the ischium (and in some cases the ischial ramus) are enclosed inside the socket.
Pritham has described objectives that would ideally be achieved in the ischial containment socket:
- Maintenance of normal femoral adduction and narrow-based gait during ambulation.
- Enclosure of the ischial tuberosity and ramus, to varying extents, in the socket medially and posteriorly so that forces involved in maintenance of mediolateral stability are borne by the bones of the pelvis medially and not just by the soft tissues distal to the pelvis, that is to say, creation of a "bony lock."
- Maximal effort to distribute forces along the shaft of the femur.
- A decreased emphasis on a narrow AP diameter between the adductor longus-Scarpa's triangle and ischium for the maintenance of ischial-gluteal weight bearing.
- Total contact.
- Utilization of suction socket suspension whenever possible.
The physical and functional characteristics of this socket will be described within the perspectives of comfortable weight bearing, stance-phase stability, and normal swing phase.
Weight bearing in the ischial containment socket is focused primarily through the medial aspect of the ischium and the ischial ramus. The socket encompasses both the ischial tuberosity and the ramus; the specific contour depends on the musculature, soft tissue, and skeletal structure of the amputee. As opposed to the quadrilateral socket, in which the proximal contours are affected primarily by muscular variation, proximal contours of the ischial containment socket are affected by differences in pelvic skeletal anatomy. Of particular importance are the variations in the position of the ischium with respect to the trochanter; in females, the is-chia are positioned more laterally, or closer to the trochanter, to allow for childbearing (Fig 20B-10.). The posterior brim of the socket is proximal to and tightly posterior to the ischium. Countersupport, intended to keep the ischium and ramus solidly against the medio-posterior aspect of the socket, is produced in three ways. First, the "skeletal mediolateral" dimension, the distance between the medial aspect of the ischium and the inferolateral edge of the trochanter, must be carefully designed into the socket. Second, countersupport occurs through the "distal mediolateral" dimension, a soft-tissue measurement that reflects the diameter of the residual limb 1 to 2 in. distal to the skeletal mediolateral dimension. The third form of counterpressure, most important in females because of their pelvic anatomy, is anterolateral counterpressure from the trochanter anteriorly to the tensor fasciae latae. Additional weight-bearing support is thought to be provided by the gluteal musculature and the lateral aspect of the femur distal to the trochanter, as well as from pressures distributed as evenly as possible over the entire surface of the residual limb. It should be noted that significantly more residual limb surface and volume is contained within the ischial containment socket as compared with the quadrilateral socket. Therefore, identical residual limbs have greater force distribution and hence lower pressures with an ischial containment design.
It has been hypothesized that the quadrilateral socket is displaced laterally during midstance and thus results in a shearing force on the perineal tissues. Secondarily, femoral abduction may occur and decrease the effectiveness of the gluteus medius. The solution provided by the ischial containment socket is to extend the medial brim of the socket upward until pressure is brought to bear against the ramus. The resulting "bony lock" between the ischium, trochanter, and laterodistal aspect of the femur provides a much more stable mechanism for acceptance of perineal biomechanical forces. Two clinical results are increased comfort in the groin and better control of the pelvis and trunk (Fig 20B-11.,A and B).
Stance stability may be enhanced by extensive contouring posterior to the femoral shaft; this allows more effective transmission of the movements of the femur to the prosthesis.
Swing-phase suspension is critical and is usually achieved by suction. As with the quadrilateral socket, proper contours allow for smooth swing-phase tracking. Rotational control is provided by the proxiomedial brim and its bony lock against the ischium, the shape and channels of the anterior wall, and the post-trochanteric contour of the lateral wall seen in transverse view(Fig 20B-12.,A and B). Socket rotation control for very fleshy residual limbs with poor muscle tone is best achieved with an ischial containment socket.
Flexible Transfemoral Sockets
In 1983 Kristinsson of Iceland introduced the concept of a flexible socket design. Taught in the United States under various acronyms such as ISNY (Icelandic-Swedish-New York) and SFS (Scandinavian Flexible Socket), these techniques have gained considerable favor during the past decade. The concept uses flexible thermoplastic vacuum-formed sockets supported in a rigid (or semirigid) fenestrated frame or socket retainer (Fig 20B-13.,A-D). The socket retainer may be either vacuum-formed or laminated plastic (Fig 20B-14.). Kristinsson describes a flexible socket as follows: "To label a socket as flexible I would say that you should be able to deform it by your hands, and the material should not be elastic enough to stretch under the loads it will be subjected to." Kristinsson additionally states:
When designing a flexible socket system the most critical aspect for the comfort of the wearer is how the frame is designed. It has to be capable of supporting the flexible socket, preventing permanent deformation, and the socket-frame combination has to be structurally strong and stable enough to counteract the reaction forces.
The advantages of flexible wall sockets as put forth by Pritham are as follows:
- Flexible walls
- Improved proprioception
- Conventional fitting techniques
- Minor volume changes readily accommodated
- Temperature reduction
- Enhanced suspension
Pritham proposes the following indications for use of a flexible socket:
- Mature residual limb (frequent socket changes not anticipated)
- Medium to long residual limb (where a significant portion of the wall will be left exposed and flexible)
- Suspension not a factor
The most recent form of flexible socket used in trans-femoral prostheses is in the form of a silicone roll-on socket (used to enhance suction suspension) coupled with a socket retainer.
Socket Indications-Current Trends
The question has been previously put forth: how is the clinician to choose among these competing philosophies? Some of the new socket designs have been associated with strident claims coupled with concurrent rebuttal of the quadrilateral design. To quote Pritham,
In the process considerable confusion has caused many of the issues involved to be obscured; and somehow or another, the perception that the new style sockets are different from quadrilateral style sockets and unaffected by the principles of above-knee prosthetics as explained by Radcliffe (1955, 1970, 1977) has crept into popular consciousness. Recently, however, some semblance of order has begun to emerge (Pritham, 1988; Schuch, 1988) and attention has come to be focused on the role of the ischium. It is the author's [Pritham's] contention that most if not all of the major factors influencing the shape of the newer sockets can be explained in terms of the principle of ischial containment. Further, it is the author's [Pritham's] belief that this principle is fully compatible with Radcliffe's biomechanical analysis of the function of the quadrilateral socket and that the varying socket configurations are not at odds but rather are separate but related entities in a continuum labeled above-knee sockets.
In a similar vein, Michael contends "that these new designs represent evolutionary rather than revolutionary advances." In reality, socket design indications can only be offered from shared clinical experience and workshops because there are no impartial field tests or objective scientific studies produced to date to provide substantial answers to this question. The conclusions of a panel of physicians, prosthetists, and engineers who participated in an international workshop on transfemoral fitting and alignment techniques follows:
- No specific contraindications were noted for any socket design.
- Some advocated not changing successful quadrilateral socket wearers.
- Quadrilateral sockets are most successful on long, firm residual limbs with firm adductor musculature.
- Ischial containment sockets are more successful than quadrilateral sockets on short, fleshy residual limbs.
- Ischial containment sockets are the better recommendation for high-activity sports participation.
- Lack of agreement existed on the best recommendation for the bilateral transfemoral amputee.
- Flexible wall sockets are not linked to any one philosophy of transfemoral socket design.
- Total flexible brims are essential to the success of "maximal" ischial-ramal containment sockets.
There are several additional factors to be considered to a lesser degree. One concern regarding the ischial containment technique is the difficulty some prosthetists have reported in efficiently obtaining a successful fit. Repeated test or trial sockets are the norm in this technique; in contrast, more than one initial test socket is rarely necessary with the quadrilateral technique. Two reported factors creating concern about flexible-socket techniques have been the tendency for the thin flexible thermoplastic to tear and the tendency of the thermoplastic to shrink when removed from the patient cast model and continue shrinking over time, thereby compromising socket fit. Both of these concerns are being reduced with experience and new materials. Thermoplastics are now being extruded for use in prosthetic socket construction that are specially designed to resist both tearing and shrinkage. As experience gained in both thermoplastics techniques and ischial containment fitting techniques is further disseminated, these concerns should cease to be a consideration. Indeed, it seems that the use of thermoplastics in prosthetic socket design is on the rise and offers some significant advantages over conventional laminated plastic socket techniques.
TRANSFEMORAL PROSTHETIC COMPONENTS: VARIATIONS, INDICATIONS, CONTRAINDICATIONS
As noted by Wilson,
The above-knee prosthesis consists of a minimum of four major parts: the socket, the knee system, the shank (or shin), and the foot-ankle system. If suction is not used to retain the leg in place, a suspension system is needed. A variety of designs for each of these components is available which can be combined to meet the individual needs of the amputee.
Two construction alternatives are available for trans-femoral prostheses (Fig 20B-15.,A and B). The traditional form of construction is the exoskeletal or "crustacean" design fabricated from wood or polyurethane foam covered with a reinforcing, plastic-laminated outer skin. In this design, the strength is obtained by the outer plastic lamination through which the weight load is transmitted. The cosmesis or leg shape is integral to the system because the thigh, shank, and ankle are custom-shaped to the individual amputee's contours and measurements before being covered with an outer plastic-laminated skin that is pigmented for appropriate color.
The endoskeletal form of prosthesis is constructed of an inner tube or pylon (of aluminum, titanium, and/or carbon fiber epoxy) through which the weight load is transmitted. The knee units are usually interchangeable, at least within the manufacturer's system. The cosmesis, considered by most to be superior to exoskeletal prostheses, is provided by an external soft foam cover shaped to the individual amputee's anatomy and measurements. The cosmetic covering may be additionally covered with skin-colored hosiery or custom-sprayed with one of the "skinlike" finishes available.
The increasing compatibility of components from all manufacturers greatly enhances prosthetic prescription options. Hybrid endoskeletal prostheses utilizing several different manufacturers' components are quite common, and in some cases, a mix of endoskeletal and exoskeletal components may be beneficial.
This topic has been previously discussed in detail in the transtibial chapter of this Atlas. However, there is one special consideration for the transfemoral amputee.
Since heel strike though midstance on the transfemoral prosthesis is the most difficult period for knee control, an ankle-foot combination that dampens the knee flexion torque moment generated at heel strike can be an important consideration. This is particularly true for the elderly or otherwise debilitated amputee.
Use of an ankle-foot combination that allows true plantar flexion within the ankle mechanism (single-axis foot, multiaxis foot, other ankle components), as opposed to simulated plantar flexion (solid-ankle feet), provides better absorption of shock and torque generated at heel strike, thereby decreasing potential knee instability. The more quickly the foot achieves foot flat, the greater the knee stability. Ankle-foot combinations with actual moving joints achieve foot flat more rapidly than do the solid-ankle feet that lack a moving joint and are therefore often preferred for the transfemoral amputee.
Prosthetic Knee Components
Prosthetic knees provide three functions: (1) support during stance phase, (2) smooth and controlled swing phase, and (3) unrestricted flexion for sitting, kneeling, stooping, and related activities. In most cases, the knee component systems described are available in both exoskeletal and endoskeletal formats.
This knee consists of a simple hinge mechanism. It is mechanically simple, and stance stability is dependent on alignment stability (involuntary control) and amputee muscle contraction (voluntary control). The simplicity of design and low maintenance of this knee mechanism leads to its popularity and frequent use. The primary disadvantage of this knee design is its lack of mechanical stability (Fig 20B-16.).
This knee mechanism usually consists of a four-bar linkage that provides more than one point of rotation. The design is mechanically complex and provides a changing instantaneous center of rotation between the prosthetic thigh and shank, depending on the relative amount of flexion or extension of these components(Fig 20B-17.). This results in the advantage of varying mechanical stability throughout the gait cycle, with enhanced stability during heel strike and decreased stability at toe-off, thus allowing for easier initiation of swing phase (Fig 20B-18.). Additional advantages of the poly-centric design are the inherent shortening of the shank during flexion, which improves foot clearance in swing phase, and the ability to rotate the shank under the knee during sitting, which enhances sitting cosmesis for very long residual limbs (Fig 20B-19.,A and B).
As noted by Mooney and Quigley,
Polycentric knees are generally used on three categories of amputees. The first is the knee disarticulation amputee, in whom the high instant center of rotation is advantageous, so that the polycentric knee will swing under the thigh when the amputee sits, allowing the appearance of equal thigh and shank lengths compared to the sound limb. Amputees with short above-knee amputations (femur length less than 50%) will benefit from this unit because they also can take advantage of the higher instant center of rotation and the increased zone of stability provided by the polycentric unit. The third group of amputees benefitting from the polycentric knee mechanism is those individuals with weak hip extensors.
The historical disadvantage of polycentric knees is the increased weight and bulk due to the numerous linkage mechanisms and greater amount of moving parts. This disadvantage has been reduced with the advent of newer materials such as carbon fiber, titanium, and aircraft aluminum. Currently there are lightweight polycentric knee components available in both children's and adult sizes (Fig 20B-20.,A and B).
Weight-activated Stance-control Knee
In this knee mechanism, when weight is applied, a braking mechanism mechanically prevents the knee from flexing or buckling. The amount of weight required to effectively engage the "brake" and prevent flexion can be adjusted depending on the amputee's weight, activity level, and stance-control needs. The "braking" mechanism is usually only effective to a maximum range of 15 to 20 degrees of flexion (Fig 20B-21.,A and B).
This knee design is generally used for weak or debilitated amputees who cannot rely on more complicated and demanding means of stance control. The primary disadvantage is increased maintenance. An additional disadvantage is delayed initiation of swing phase if the stance-control "brake" is set for a high degree of stance stability.
Manual Locking Knee
This knee unit automatically locks in extension but can be unlocked by voluntary action. Ambulation with the locking mechanism disengaged is also possible.
When locked, this knee is by far the most stable during stance. However, due to the lack of knee flexion during swing phase, increased energy expenditure and gait deviations often occur during ambulation with a locked knee.
A positive locking knee is generally indicated for weak, unstable, debilitated amputees, but may also be used by amputees in unstable situations such as uneven terrain when hiking or hunting or activities such as fishing while standing in a boat.
Knee swing is dampened by some form of mechanical friction, usually applied to the axis of rotation. The friction is adjusted to the patient's normal cadence so that the pendulum action of the shank will correspond to that of the opposite limb.
This is the most commonly used system for control of swing phase, primarily due to its simplicity and dependability. The one disadvantage is that the friction can be set for only one cadence and any variation in cadence by the amputee results in a prosthetic knee and shank that will not flex and extend with the same timing as the natural leg.
In the simplest form, an extension assist is a spring that is compressed during knee flexion in initial swing, uncoils during late swing, and propels the shank into full extension, thereby reducing the effort expended by the amputee. Extension assistance also prepares the prosthetic limb for initial stance support by ensuring full knee extension at terminal swing, before initial stance.
Pneumatic control of the swing of the prosthetic shank is provided by a pneumatic cylinder attached to the knee and housed within the upper shank. As described by Mooney and Quigley, this
Mechanism consists of a piston rod that is attached to the thigh section of the prosthesis behind the knee bolt. Knee flexion forces the piston down into the cylinder, which in turn forces air through a bypass channel at the bottom of the cylinder. The air travels upward within and around the sides of the cylinder, through a port at the top of the cylinder, and back into the central cylinder above the piston.
Resistance to knee swing velocity can be adjusted for the individual amputee by adjusting the opening size of the port at the top of the cylinder. An adjustment knob is turned clockwise or counterclockwise to either decrease or increase this port opening. Decreasing the opening provides greater restriction of the amount of air passing through the port and, therefore, greater swing-phase control. Setting this opening too small would make the swing too stiff, possibly preventing adequate knee flexion and speed during swing phase.
Pneumatic control is more responsive to varying walking speeds and is a more advanced form of swing control than friction is. Because air is compressible, it acts as an extension assist within the pneumatic unit. Some pneumatic units also have coil spring-type extension assists built into them.
Disadvantages of pneumatic units include increased necessity for maintenance, increased weight, and increased expense. However, they are simpler, lighter, and less expensive than hydraulic units.
The principles of hydraulic control are similar to those of pneumatic control, the difference being the medium: liquid is used rather than air. Hydraulic units also utilize a cylinder and piston rod arrangement as described earlier. The liquid provides resistance to motion depending on its viscosity and temperature. Silicone oil is used in most prosthetic hydraulic units because it minimizes viscosity changes with temperature, thus avoiding stiffness in cold weather and looseness in hot weather.
Hydraulic control achieves nearly normal knee action over a wide cadence range. The varying control is caused by the characteristics of hydraulic flow through ports or orifices where the resistance to flow increases with increasing cadence. The design provides normal heel rise and extension in the swing phase independent of walking speed. The programmed flow is obtained by a special pattern of internal ports, check valves, and needle valves to meet normal walking requirements. Independent adjustments of flexion and extension control are available on most hydraulic units and are easily adjusted by the prosthetist and, in some instances, the amputee.
The hydraulic knee mechanism is indicated for amputees who can take advantage of the cadence response function. Teen and adult males are commonly hydraulic users; however, there are active females who enjoy the benefits as well.
Disadvantages are the same as those of pneumatic units, but to a greater degree: need for increased maintenance, increased weight, and increased expense.
Two hydraulic systems that provide more than simply swing-phase control are worthy of special mention.
The "Hydra-Cadence" hydraulic system is an entire knee, shank, ankle, and foot system that is hydraulically linked at the knee and ankle. It allows free plantar flexion of the foot at heel strike and provides dorsiflexion of the foot after 20 degrees of knee flexion in swing for improved ground clearance during swing phase. The heel height of the foot is adjustable through the hydraulic mechanism of the ankle and allows for patient changes and adjustments. The knee and shank swing control is hydraulic. Although quite advanced in design and function, the Hydra-Cadence is quite heavy and expensive and has been associated with decreasing durability and reliability during recent years.
The "Mauch Swing-N-Stance" (S-N-S) is the most advanced system of hydraulic control and the only system that includes hydraulic stance-phase control. The hydraulic control of swing phase is fundamentally the same as that described earlier; there are separate adjustments for flexion (initial swing) and extension (terminal swing), and the range of adjustments is greater than in other hydraulic units.
Provision of stance-control options is what makes this system uniquely functional. The design provides a high resistance to knee flexion, unless the amputee generates a hyperextension moment about the knee that occurs naturally when rolling over the ball of the prosthetic foot after midstance. The hyperextension moment, which can only occur when the knee is safely extended, results in disengagement of the high flexion resistance and permits the knee to flex easily to begin the swing phase. As the knee nears maximum flexion and the speed of bending decreases to zero, the higher level of resistance is reinstated. Thus, if during extension of the shank the toe is stubbed, the high resistance to flexion is available to aid in stumble recovery. Release of the high flexion resistance can also be accomplished voluntarily by an amputee who is standing and wishes to sit down quickly. He simply extends his residual limb while maintaining the foot in contact with the floor, thus generating the hyperextension moment necessary to release the high flexion resistance. The amputee may also walk downstairs and downhill step over step in a weight-bearing manner by stepping on the prosthesis without hyperextending the knee. The yielding speed in weight bearing is easily adjustable to accommodate the amputee's weight and needs.
The unit may also be set to function without stance control for activities such as bicycling. An additional functional mode available is a setting that provides a lock against knee flexion. This is useful for situations requiring maximum knee stability such as rough terrain or standing and fishing from a pitching boat.
The S-N-S unit is the most reliable and durable of the hydraulic systems. This fact coupled with its significant variety of functional options makes it the most widely used hydraulic system. It too has the disadvantages of extra weight and additional expense (Fig 20B-22.).
There are three additional components available that provide additional and useful functions.
A torque-absorber component is designed to allow transverse rotations about the long axis of the prosthesis. Without such a component, these forces are transmitted as shear forces between the residual limb and the socket. This component is particularly useful for bilateral amputees and is especially indicated for any amputee participating in golf, tennis, and other sports and activities demanding rotational movements.
Knee-shank Rotation Components
Such components were initiated in the Orient where sitting cross-legged on the floor is a cultural requirement. By releasing a locking mechanism, the knee and shank are free to rotate. This can also facilitate entry/ exit to or from confined spaces such as an automobile.
Multiaxis Ankle Modules
These are modular, endoskeletal components that provide multiple degrees of motion within the ankle independent of the foot. Conventional multiaxial feet require the use of a specific ankle-foot combination. The multiaxis ankle modules are adaptable to a variety of feet. Although primarily intended for endoskeletal prostheses, they can also be incorporated into an exoskeletal prosthesis by creating a hybrid system. This type of ankle system smooths out the gait pattern and enhances knee stability in transfemoral prostheses.
Improper suspension results in poor gait, decreased safety, and increased skin problems. Secure and dependable suspension enhances proprioception and provides the feeling that the prosthesis is more a part of the wearer.
Suction suspension is usually accomplished by the use of an air expulsion valve at the distal end of the socket combined with a precisely fitted socket. Negative air pressure suspends the prosthesis during swing phase. The socket is sealed around the residual limb directly against the skin, without the use of prosthetic socks.
The prosthesis is donned by one of two methods. Most commonly, the amputee pulls his residual limb into the socket by applying a length of open-ended stockinette around his residual limb, putting the end of the stockinette through the valve hole at the distal end of the socket, and pulling the residual limb down into the socket. In the process of pulling the residual limb completely into the socket, the stockinette is gradually removed from the socket. This donning procedure requires some skill and effort. Balance problems, upper-limb deficiencies, strength deficiencies, heart problems, and other such conditions preclude this method of donning and have traditionally been considered contraindications for suction suspension.
An alternative and easier method of donning a suction socket is with the use of hand creams or lotions. Lotion is spread either on the residual limb or inside the socket, and the amputee pushes into the socket. After the limb is completely into the socket, the valve is applied and suction achieved. Within a short period of time the lotion is absorbed into the skin. This method of donning a suction socket has allowed its use by amputees who traditionally would have been excluded from consideration for this suspension.
Generally, suction suspension is indicated for amputees with smooth residual limb contours. Volume fluctuations such as weight gain or loss or fluid retention problems are contraindications for suction sockets. With the advent of ischial containment sockets, even very short amputation limbs can often be successfully fitted with suction as a primary suspension. Additional auxiliary belt suspension is generally prudent. Suction suspension can be used along with any of the other forms of suspension.
Suction suspension of transfemoral prostheses provides the best proprioception. The suspension is applied directly to the residual limb, as opposed to belts around the waist; the skin is in direct contact with the socket, and the movements of the limb are transmitted to the prosthesis without lost motion. Disadvantages include difficulty in obtaining such a precise fit with some amputees and occasional loss of suction in sitting or other positions. Other disadvantages include no medium for absorbing perspiration, skin shear, and the requirement of weight and volume stability. Partial suction suspension in which the above principles are utilized with a thin prosthetic sock or nylon sheath sometimes eliminates or reduces the disadvantages.
There are two types of soft suspension belts available, either as primary or auxiliary suspension. The traditional form of soft belt is the Silesian belt or bandage. As the category implies, it is a flexible, soft belt usually made of leather, cotton webbing, or Dacron materials. It is attached to a pivot point on the socket in the area of the greater trochanter and passes as a belt around the back and opposite iliac crest, where it achieves most of its suspension. Anteriorly, it attaches at either a single point or, in some cases, double attachment points (Fig 20B-23.,A). This belt provides a comfortable and positive form of suspension of the prosthesis and is simple to use. The disadvantages of the Silesian belt are hygiene, especially if it is not removable for washing, and the discomfort associated with constrictive waist belts.
A new and quite simple alternative soft belt is the TES (total elastic suspension) belt made of elastic neo-prene material lined with a smooth nylon material. This suspension belt fits around the proximal 8 in. of the prosthesis and then around the waist and fastens anteriorly with Velcro (Fig 20B-24.). It is quite comfortable and forgiving due to its elasticity. It provides very positive suspension and enhances rotational control of the prosthesis. Disadvantages include body heat retention and limited durability.
Hip Joint With Pelvic Band and Belt
Although this form of belt does provide suspension, there are simpler and less cumbersome alternatives if suspension alone is the goal. The hip joint with pelvic band and waist belt also provides rotational stability plus a significant degree of mediolateral pelvic stability. This is usually necessary in obese amputees or those with significant redundant tissue that is difficult to stabilize. For the patient with weak hip abductors, this suspension is particularly useful (Fig 20B-23.,B). Because most amputees object to the weight and bulk of this suspension, it is generally reserved for cases where rotational control or mediolateral stability is needed.
PRESCRIPTION CRITERIA: RELEVANT CASE PRESENTATIONS
When recommending transfemoral prosthetic components, two levels of criteria may be utilized. The first and most important level includes previous experience of the amputee, safety requirements, and functional requirements. Secondary considerations include the level of amputation, vocational and avocational needs, durability of components, weight of components, cosmesis, and cost.
Prosthetic components that previously have been satisfactory should not be changed without significant discussion with the amputee. The longer the amputee's experience with a specific system, design, component, etc., the less the likelihood of success in change.
Following are five case presentations, including one prosthetic recommendation, plus the rationale for each case. Clearly, other good recommendations are also possible. The intent is to exemplify several typical amputee cases as encountered in everyday prosthetic practice.
Case 1.-A 29-year-old woman presents with a long left transfemoral amputation at the supracondylar region of the femur. She has no other health problems, has normal range of motion and strength, and is athletically and socially active. Her preferred sports are tennis and racquetball. She is employed as an attorney's assistant.
Recommendation.-A quadrilateral suction socket is recommended with either a rigid laminated plastic socket or a thermoplastic flexible socket with semiflexi-ble socket retainer. An endoskeletal component system with soft-cover cosmesis, a four-bar polycentric knee with either pneumatic or hydraulic control, a torque absorber, and a dynamic-response foot are also suggested.
Rationale.-There are no contraindications for an ischial containment socket. However, quadrilateral sockets are usually quite successful in the young and muscular amputee with a long residual limb. Suction suspension is ideal for active amputees and is enhanced by a long, muscular residual limb. A flexible socket system is more forgiving for the active athlete and thus more comfortable. The cosmesis afforded by an endoskeletal prosthesis with soft cover meets the social and vocational needs of this amputee. The four-bar polycentric knee provides inherent stability during the critical stance phases of activity, is smooth in swing, and is compatible with long amputations that might not have room beneath for other knee components. Either pneumatic or hydraulic knee control is essential for active athletes with varying cadences, and the dynamic-response foot, designed for the active amputee, provides better propulsion and response during all activities.
Case 2.-A 78-year-old man presents with a right transfemoral amputation and a history of peripheral vascular disease secondary to diabetes mellitus. His left lower limb has vascular disease involvement and is weak and insensate. He has decreased strength and range of motion of the residual limb. He is plagued with failing eyesight as well. He is retired and interested in household ambulation.
Recommendation.-A semiflexible thermoplastic quadrilateral socket fit with thin prosthetic socks and the use of a soft suspension belt such as a neoprene TES belt is suggested. A lightweight endoskeletal component system of titanium or carbon graphite epoxy with a manual locking knee and either a lightweight solid-ankle, cushion-heel (SACH) foot or multiaxis foot and ankle is also advised.
Rationale.-Stability is a primary concern due to the combination of weakness and poor vision. Minimization of weight reduces effort involved in ambulation.
Case 3.-A 15-year-old boy presents with a right transfemoral amputation at the proximal third of the femur secondary to cancer 6 years ago. He is very healthy and active now and participates in junior varsity basketball and baseball, as well as being an avid hunter and fisherman. He is reportedly "growing like a weed."
Recommendation.-An ischial containment, flexible socket with a rigid socket retainer and suction suspension is recommended with the option of auxiliary suspension in the form of a soft TES belt that is removable when desired. An endoskeletal system with hydraulic knee control, preferably swing and stance control, is advised, along with a carbon graphite epoxy strut shank-ankle-foot (e.g., Flex-Foot) for maximum dynamic response. An endoskeletal-type torque absorber in the shank above the graphite shank-ankle-foot should be considered.
Rationale.-An ischial containment, suction socket is indicated by both the short residual femur and high activity level. The flexible socket enhances comfort and suspension. The optional auxiliary suspension provides confidence for high-demand activities. The endoskeletal construction readily accommodates linear growth, and the swing-and-stance (e.g., Mauch S-N-S) hydraulic knee control offers many options, including a knee-locking option when hunting and ambulating in rough terrain. The graphite epoxy shank-ankle-foot provides maximum possible dynamic response for demanding sports activities in addition to dependable durability, and the torque absorber reduces shear stresses to the residual limb.
Case 4.-A 24-year-old woman presents with a very short left transfemoral amputation caused by a motor vehicle accident 2 years ago. Her short residual limb is significantly scarred, has poor muscle tone, and lacks rotational stability. She is currently wearing her first prosthesis, which is a quadrilateral socket with a hip joint, pelvic band, and waist belt. It has a single-axis friction knee. She complains of inability to control the prosthesis and the knee. She also complains about the heavy feeling of the prosthesis. She is currently finishing college and is interested in dating and dancing. She has not been able to consider a more demanding activity level.
Recommendation.-An ischial containment, flexible thermoplastic suction socket with a semiflexible thermoplastic socket retainer is advised, as well as auxiliary suspension provided by a soft TES or Silesian belt. An endoskeletal system of ultralight components and soft-cover cosmesis is recommended, along with a weight-activated stance-control knee and a multiaxis ankle foot.
Rationale.-Although perhaps difficult to fit in this case, the suction suspension should be attempted to reduce the sensation of a heavy, clumsy prosthesis. An ischial containment socket will provide better mediolat-eral and rotational stability, both difficult to achieve given her femur length and poor muscle tone. The foot and knee mechanisms enhance stability while allowing active function.
Case 5.-A 38-year-old male presents with a muscular, midthigh, left transfemoral amputation. The cause of the amputation was a mine explosion in the Viet Nam War. He has worn several prostheses, all quadrilateral socket designs. He works as a framing carpenter and climbs ladders and scaffolding. Heat and perspiration are a problem; therefore he requests a socket fit with prosthetic socks. He is very strong and agile and needs to depend on his prosthesis for his work.
Recommendation.-A quadrilateral socket, thin cotton sock fit with a valve for partial suction is advised. Silesian belt suspension is preferred. An exoskeletal design, Mauch swing-and-stance hydraulic-control knee, and a simple, maintenance-free, conforming foot such as a solid-ankle flexible-endoskeleton (SAFE) foot should be considered.
Rationale.-The quadrilateral socket is familiar to this amputee and, when properly fitted, is quite adequate for a muscular, midthigh residual limb. The partial suction socket with a cotton sock provides a medium for absorption of perspiration and excellent and safe suspension when coupled with the Silesian belt. The exoskeletal construction is durable for vocational needs. The Mauch S-N-S hydraulic knee provides stability and safety options meeting vocational needs. The foot is simple and durable and conforms well to varying terrain.
SUMMARY AND CONCLUSION
During the decade of the 1980s, significant and controversial progress and change have taken place in transfemoral prosthetics. Clinical improvements and new materials and components will continue to be developed. The fundamental goals of comfort, function, and cosmesis are unchanged. Through the use of new materials, components, and designs, the transfemoral amputee can now achieve a higher activity level than was possible before.
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Chapter 20B - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles