Transfemoral Amputation: Prosthetic Management

Mark David Muller CPO, MS, FAAOP

Neither Mark David Muller nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.

ABSTRACT

Clinicians have long strived to create optimal transfemoral prosthetic designs that will not only enhance the user’s ability to ambulate but also will be a functional element of the individual’s life. Although there have been many advancements in materials, socket designs, and components, there still is little research to help quantify how the individuals that use these prosthetics devices can best be served. It is helpful to explore clinical considerations and anticipated outcomes when creating transfemoral prosthetic devices. Prosthesis use is affected by many factors, including energy expenditure, body image, voluntary control within a transfemoral prosthetic system, socket fit and design, component selection, and alignment.

Introduction

Amputations at the transfemoral level account for approximately 19% of the approximately 1.6 million individuals in the United States who are currently living with an amputation.¹^,²^,³ Statistics from 2004 reported that 31% of all major amputations were performed at the transfemoral level,⁴^,⁵ with new evidence showing a decrease in the number of transfemoral amputations performed each year both nationally and internationally.² There also is evidence that individuals who have undergone amputation are living longer and will require prosthetics services throughout their lives.¹^,⁶ In 2015, certified prosthetic practitioners spent more than 25% of their time caring for patients with a transfemoral amputation.⁷

Those in the field of prosthetics have a long history of involvement with transfemoral prosthetic socket design and construction, with the first patents awarded in England in 1790 and the first US patent for a transfemoral artificial limb given in 1846.⁸^,⁹^,¹⁰^,¹¹^,¹² However, prosthetists still do not have universal clinical standards of practice for device creation, fit, suspension, and alignment. Throughout history, transfemoral design and fabrication techniques have been passed down from mentors to protégés, with no formal instructional courses available in the United States until 1949 when the University of California at Berkeley introduced a short course in transfemoral design of a suction socket. In the 1950s, several universities began formal education programs in prosthetics, with each school creating their own laboratory manuals and design iterations.¹³ The prevalent design at that time was the German transfemoral quadrilateral socket, which used skin suction suspension.¹⁴^,¹⁵ In the 1980s, the first ischial containment manual emerged and was quickly adapted by other institutions, although each institution implemented design iterations. As of 2021, there were 13 accredited institutions offering master level education for prosthetic and orthotic practitioners in the United States, with each institution offering differing theories and practical implementation of both traditional and digital fabrication techniques for transfemoral socket design, suspension, and clinical application.

One rationale for the differing designs may be the variability observed in the anatomy, size, and length of transfemoral residual limbs, as well as the level of voluntary control the individual possesses. It is accepted that no single design is appropriate for every individual with a transfemoral amputation. Accordingly, variations in the clinical applications of formalized training have led numerous practitioners to create unique styles and techniques.⁹^,¹⁰^,¹⁶^,¹⁷ These variations provide practitioners with the ability to adapt a transfemoral socket to best meet the needs and goals of an individual patient.

The common clinical goals and considerations that guide rehabilitation professionals through this patientspecific process are discussed along with an overview of current transfemoral socket designs and the implications of suspension, alignment, and biomechanical considerations in evaluating, fabricating, and fitting transfemoral prostheses.

Clinical Considerations and Anticipated Outcomes

Although prosthetic devices will never truly replace a missing limb, certain clinical considerations must be addressed,
irrespective of which socket or suspension design is chosen. The transfemoral prosthetic system must balance function, comfort, and appearance both dynamically and statically.⁸^,¹¹^,¹² To create the most appropriate plan, the treating team must consider energy expenditure, body image, the user’s level of voluntary control, and the fit of the prosthetic socket. In implementing the treatment plan, the team must determine socket construction and design, the degree and complexity of the suspension system, the appropriate components, alignment considerations, and outcome measures.

Energy Expenditure

Energy expenditure for a transfemoral amputee is of great concern. The effort required to ambulate with a prosthetic device at this level is dependent on the weight of the device, the quality of fit, the degree of suspension, the accuracy of alignment, and functional characteristics of the chosen components.¹⁷^,¹⁸^,¹⁹^,²⁰^,²¹ If any one of these factors is not properly addressed, the individual using a transfemoral prosthesis will exhibit higher levels of energy expenditure during ambulation than are necessary, increased loading on the sound limb, and increased spinal loading.¹⁹^,²¹ Increased energy expenditure is accompanied by an increase in the rate of oxygen consumption and an associated elevation in heart rate. An elevated heart rate can, in turn, lower the user’s self-selected walking speed and reduce gait efficiency.²² For elderly individuals with a transfemoral prosthesis, the physical burden of ambulating with a prosthetic device may exceed their abilities, leading to a lower rate of prosthetic use.²⁰^,²³ Knowing that ambulation with transfemoral prosthetic devices requires high levels of energy, practitioners must create treatment plans that meet the individual’s needs and goals with an acceptable burden level.

Fall Risk

Recent systematic review has confirmed an elevated fall risk among community ambulating users of transfemoral prostheses relative to transtibial prosthesis users.²⁴ This is significant as falling events can represent substantial medical expenses²⁵ and can limit future prosthetic mobility and activity levels. A growing body of evidence has suggested that this fall risk can be mitigated through the use of certain microprocessor knees.²⁶^,²⁷ Targeted exercise programs may also reduce fall risk in this population.²⁸

Body Image

Body image and appearance when using a transfemoral prosthesis are complex considerations and should be addressed within the treatment plan. Satisfaction with body image, psychosocial adjustment, lack of activity restriction, and satisfaction with the function of one’s prosthesis are positively associated with the cognitive performance of transfemoral amputees.²⁹ It is important to realize that appearance and self-image can be a cosmetic as well as a functional concern. An acceptable appearance and the ability of the user to integrate with peers play a large role in an individual’s positive adaptation to their altered body image and psychosocial adjustment.²⁹ Body image anxiety increases depression, reduces perceived quality of life, lowers self-esteem, reduces participation in physical activity, and lowers overall satisfaction.³⁰^,³¹ The prosthetist must create a device to maximize the confidence of the user through optimal fit, suspension, function, and alignment symmetry, as well as an acceptable energy expenditure.³² There is a growing trend toward user participation in aesthetic choices, including realistic silicone covers, water transfers, or 3D printed covers. These choices may help the user feel more involved with the creation of their prosthesis and thus increase device acceptance.²⁹

Effect of Voluntary Control

Functional ambulatory goals will be defined by the individual’s ability or potential to control the transfemoral prosthetic device. This is commonly known as the level of voluntary control.⁹^,¹⁰^,¹⁴^,³³ Because the user will not have direct musculoskeletal control of the prosthetic knee and foot, a determination of their potential voluntary control is an important consideration in determining the socket style, interface, suspension, and components used. Factors that determine the degree of voluntary control include residual limb length, positional awareness in space, active range of motion, muscle strength, and the ultimate ability to manipulate the limb in a controlled and deliberate manner. When voluntary control is limited, the rehabilitation team should design prosthetic systems that focus on prosthetic support and patient safety rather than function and performance. In contrast, enhanced voluntary control allows for the design of a more dynamic prosthesis. The degree of voluntary control also plays an integral role in component choice and alignment considerations.

Fit of the Prosthetic Socket

The ideal goal for any prosthetic device is for the user to feel that the device is part of their body. Irrespective of the socket design, materials used, or fabrication method, an optimal fit should be intimate to the contours of the residual limb and assist the user in controlling the prosthesis. Beyond these basic criteria, an optimal fit of a transfemoral prosthetic socket is poorly defined and has not been standardized. However, if users do not feel that they have control of the socket, they likely will not fully integrate their prosthetic device into their daily lives.³⁴

The Transfemoral Socket

Radcliffe¹⁴ suggested that the primary goals of a transfemoral prosthesis are to achieve comfort in weight bearing, provide a narrow base of support in standing and walking, and accomplish the swing phase of gait in a manner that is as close to normal as possible. The fit and orientation of the socket are paramount in achieving these goals. The socket must be donned in the correct orientation with respect to the user’s line of progression, must match the volume of the residual limb, and must create an environment of total contact without causing impingement or discomfort. Paramount is the ability of the socket to provide adequate stability in the sagittal, coronal, and transverse planes throughout the gait cycle.

Importance of Orientation

When donning the socket, the orientation of the socket must match the user’s residual limb and adjacent bony structures in a consistent rotational alignment. If the socket is malaligned, the device will cause undue pressure on the limb or the pelvis and compromise the rotational alignment of the distal prosthetic components. To properly integrate the limb within the socket, the individual should be instructed regarding socket orientation as it relates to their anatomy. This anatomic reference differs for the varying socket designs but must be addressed, especially in the initial and subsequent fittings of the device.

Importance of Total Contact Socket Fit

There are various techniques and outcome measures to assess whether the volume of the socket matches the volume of the residual limb.³⁵ Most clinical techniques rely on a combination of visual verification through a clear diagnostic interface and a determination of internal socket pressure through visual examination, tactile probes, or electronic pressure sensors.³⁶ Irrespective of the socket design, it is imperative that pressures are balanced and can be tolerated by the user.¹⁶^,³⁷ The prosthetist should ensure that all areas within the socket make contact because lack of contact with the residual limb may result in edema, socket migration, and compromised control of the prosthesis.

The tissues proximal to the trim lines must be free from impingement throughout gait and while seated. Tissue bulging over the proximal trim lines can lead to skin breakdown, edema, subdermal cysts, blisters, irritation, and discomfort.³⁸ Similarly, there must be adequate relief for the bony structures within the socket. Pressure on the ischial tuberosity, ascending pubic ramus, adductor longus tendon, greater trochanter, or distal femur can lead to socket rotation, pain, gait deviations, or rejection of the prosthetic device.³⁹

Socket Stability

Stability of the transfemoral prosthetic socket on the limb is vital to the control of the device. The prosthetist will make a clinical determination on the type of socket design based on the individual’s level of voluntary control and the stability required. Individuals with greater levels of voluntary control are less dependent on socket modification, component choice, and alignment accommodations to control unwanted socket displacement during ambulation. Excessive motion of the transfemoral prosthetic socket on the residual limb in the sagittal, coronal, and transverse planes can lead to increased energy expenditure, gait deviations, and dissatisfaction with the prosthesis.²³^,⁴⁰^,⁴¹

Sagittal Plane

The principles of prosthetic control in the sagittal plane are best considered in the early stance phase of the gait cycle. As the prosthetic foot contacts the floor, the ground reaction force quickly moves posterior to the mechanical knee joint center and creates an external knee flexion moment that will cause the prosthetic knee to buckle if it is not adequately controlled by the user. The ipsilateral hip extensor musculature of the individual must fire, pulling the residual femur and the prosthetic socket posteriorly to create a counterextension moment and stabilize the mechanical knee.⁴² Importantly, the residual femur must be adequately stabilized within the socket before the actions of the hip extensors can be translated through the prosthesis to act on the ground. In the absence of such femoral stabilization, the contractions of the hip extensor muscles are less effective, and the ability to control the prosthetic knee is compromised, causing the individual to compensate with a reduction in step length, a slower cadence, or an anterior shift in body weight. All of these compensatory actions increase energy expenditure.

Prosthetic control in the sagittal plane should also be considered in late stance. During this phase of the gait cycle, the individual must engage the hip flexors to drive the prosthetic socket anteriorly. This hip flexion action creates prosthetic knee flexion, thereby lifting the overall prosthesis off the ground to initiate the swing phase. Inadequate femoral stabilization may delay the execution of this action, resulting in a loss of control of the prosthetic knee and potential compromise of its function. The individual will likely display a shortened step length, reduced speed of ambulation, and a lack of confidence with the prosthetic device.³⁴^,³⁵

Coronal Plane

In the coronal plane, prosthetic control is critical in limiting the movement of the torso laterally over the prosthetic device during the single-limb support phase of the gait cycle. This compensatory lateral movement over the prosthesis is one of the most common prosthetic gait deviations seen in the user of a transfemoral prosthesis and has been at the root of controversy as to whether the socket design should contain the ischial tuberosity or not.⁴³^,⁴⁴^,⁴⁵ Unless a hip abduction contracture is present, the residual femur should be placed in an adducted position equal to the contralateral femur. This position ensures the efficient firing of the hip abductor muscles on the amputated side, which limits contralateral pelvic drop and associated lateral trunk bending. This is accomplished by fitting a flattened lateral socket wall that is countered by a sufficiently high medial socket wall aligned in the correct angle of femoral adduction.¹⁴^,³³^,⁴⁶

During the initial fitting of a transfemoral socket, the proximal coronal instability of the socket can be easily determined by performing the lateral and the medial displacement tests. For both of these assessments, the prosthesis user must be standing safely within parallel bars. To perform the lateral displacement test, the prosthetist places one hand on the proximal lateral brim of the transfemoral socket while the other hand is placed on the prosthesis user’s ipsilateral iliac crest. Gently but firmly, the prosthetist then pushes medially on the iliac crest while also pulling laterally on the proximal brim of the socket. If the socket displaces more than 0.5 inch (1.27 cm) from the residual limb during this static test, the socket may also displace laterally during single-limb stance in gait. This
lateral displacement often suggests coronal instability in the socket, and it can cause the individual to experience excessive proximal medial pressures on their residual limb. A compensatory lateral shift of the torso may be adopted to restore coronal stability and reduce these pressures (Figure 1).

The medial displacement test is performed with simultaneous medially directed compression of the proximolateral aspect of the socket and the greater trochanter of the contralateral limb. If the socket displaces more than 0.5 inch (1.27 cm) medially, it may suggest that either the mediolateral dimension of the transfemoral socket or its overall volume is too large. Alternatively, the prosthesis user may not possess enough voluntary control to resist the lateral forces created during single-limb support³³^,⁴⁶^,⁴⁷ (Figure 2).

FIGURE 1 Illustrations of the steps in the lateral displacement test. After donning, the socket is aligned with the line of progression and checked to ensure a total contact fit and a level pelvis. The prosthetist then can test for lateral displacement of the socket on the limb. A, One hand is used to grasp the proximal edge of the socket while the other hand is placed on the ipsilateral iliac crest to provide a counterforce and stabilization. B, The proximal socket is pulled laterally until displacement stops. C, The ideal amount of displacement is 0.5 inch (1.27 cm) measured from the skin to the socket wall. If the displacement is greater than 0.5 inch (1.27 cm), the transfemoral socket likely will be unstable in the coronal plane during single-limb support.

FIGURE 2 Illustrations of the steps in the medial displacement test. After donning, the socket is aligned with the line of progression and checked to ensure a total contact fit and a level pelvis. The prosthetist then can test for medial displacement of the socket on the limb. A, One hand is placed over the proximal lateral aspect of the socket and the other hand is placed over the greater trochanter on the contralateral side. B, Both hands are used for medial compression until socket displacement ceases. C, The ideal amount of displacement is 0.5 inch (1.27 cm) from the starting point. If the displacement is greater than 0.5 inch (1.27 cm), the transfemoral socket likely will be unstable for the user in the coronal plane during single-limb support.

Transverse Plane

Transverse stability, observed in the swing and early stance phases of gait, is also dependent on both the level of the individual’s voluntary control and the optimal fit of the transfemoral socket. During the evaluation of the residual limb, the strength of its subcutaneous tissue and musculature should be assessed to help determine if the individual can control the normal transverse plane motions of gait, including internal rotational motions during the swing phase and external rotations during early stance. If either the muscle or the underlying connective tissues are found to be inadequate, the individual will not be able to voluntarily control these forces, and the socket may rotate
on the limb. In such cases, either targeted socket modifications or external components are needed to aid in controlling transverse rotation.

If the individual has adequate voluntary control but still demonstrates whip-type gait deviations or excessive socket rotation, these problems may be caused by a suboptimal socket fit, with volumetric incongruences exerting the largest influence on rotational control. To reduce transverse rotation, socket fit must be optimized to match the individual’s limb volume or accommodations must be made for muscle contractions.

TABLE 1 Transfemoral Socket Construction

Primary Socket Construction
Construction	Example	Primary Indication	Major Advantages	Chief Limitations
Hard socket (integrated rigid inner socket and outer frame)		Mature limbs Firm limbs Situations that allow for reduced trim line height Minimal wall thickness	Simple design Durability Easy to clean Solid construction that will not alter over time	Comfort with rigid proximal trim lines Hard surface when sitting Adhered tissue, invaginations, or sensitive bony areas may not be accommodated
Removable flexible inner socket; rigid outer frame (flexible inner socket can be removed from outer frame)		Any limb shape Flexibility in design Dynamic muscle movement Relief areas for sensitive tissue Proximal soft-tissue support	Adjustable Allows for dynamic muscle movement and relief for sensitive tissue while maintaining a total contact fit Comfort in sitting Fenestrations can be created while retaining socket strength	Inner socket may change shape over time Durability
Emerging Socket Construction
Removable, flexible inner socket; rigid outer frame; dynamic panels (panels are adjustable to change compression on inner flexible socket)		Volume fluctuations Progressive pressure in specific areas User adjustability	Dynamically alters inner socket shape and compression felt on limb in specific areas Compression from panels is user adjustable	Lengthy fabrication process More maintenance
Flexible socket; embedded rigid frame (rigid frame is laminated between layers of flexible material)		Mature limbs High levels of voluntary control Dynamic muscle movement	Flexible interface Soft proximal brim Comfort in sitting Soft outer surface Rigid embedded frame supports socket with minimal surface area	Lengthy fabrication process Fragile Limited adjustability Heavier than other construction types