553

Lower Limb Prosthetics

Chapter 20

LOWER LIMB PROSTHETICS

SUSAN KAPP, MEd, CPO, LPO*; and JOSEPH A. MILLER, MS, CP, CPT†

INTRODUCTION

ROLE OF THE PROSTHETIST 

OVERVIEW OF COMPONENTS

SYME PROSTHESIS

TRANSTIBIAL PROSTHESIS

KNEE DISARTICULATION

TRANSFEMORAL PROSTHESIS

HIP DISARTICULATION AND TRANSPELVIC AMPUTATION

COMORBIDITIES AFFECTING THE REHABILITATION PRESCRIPTION

THE PROSTHETIC REHABILITATIVE PROCESS

ACTIVE -DUTY MILITARY, LOWER LIMB PROSTHETIC PROTOCOLS

SUMMARY

*Associate Professor and Director, Prosthetic and Orthotic Program, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines 

Boulevard, Suite V5.400, Dallas, Texas 75390

†Captain, Medical Service Corps, US Army; Chief Prosthetic and Orthotic Service, Integrated Department of Orthopaedics and Rehabilitation, Walter 

Reed Army Medical Center, 6900 Georgia Avenue, NW, Building 2, RM3H, Washington, DC 20307, and the National Naval Medical Center, 8901 

Rockville Pike, Bethesda, Maryland 20889; formerly, Deputy Chief, Prosthetic and Sensory Aids Service, Department of Veterans Affairs, Central Office, 

50 Irving Street, NW, Washington, DC 20422
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Care of the Combat Amputee

INTRODUCTION

volunteers) who provide comprehensive services 

throughout the service members’ rehabilitation.

The goals of providing lower extremity prosthetics 

devices are to allow the service member to achieve 

basic ambulation, to progress to a variety of advanced 

activities (eg, running, skiing), and, if warranted, to 

perform warrior tasks required to meet return-to-duty 

standards. These goals are best accomplished by using 

the comprehensive team approach to rehabilitation 

and prescribing multiple prosthetic limbs that include 

the use of technically advanced prosthetic devices. 

Use of advanced prosthetic limb components in this 

population is associated with successful rehabilitation 

outcomes. Experience has revealed that this group consistently outperforms the most advanced systems. 

The purpose of this chapter is to identify the role 

of the prosthetist as a member of the comprehensive 

rehabilitation team, provide an overview of prosthetic 

components used at MTFs, and present the treatment 

protocol.

Lower extremity amputation is the most common 

level of amputation in both civilian and military 

populations. These two groups, although outwardly 

similar, have vastly differing etiologies that lead to 

amputation and have dramatically different rehabilitation and prosthetic concerns that exist throughout their 

lifetimes. A service member with lower extremity amputation will rely on a variety of prosthetic devices and 

components to maximize rehabilitation and integration 

to independence. The proper prescription, fitting, and 

training of lower extremity prosthetic devices are critical to successful usage and reintegration.

Military medical treatment facility (MTF) personnel, who specialize in amputee care, have designed 

programs based on a multidisciplinary team approach. 

The team is comprised of both medical professionals 

(surgeons, physiatrists, prosthetists, physical therapists, occupational therapists, nurses, physician assistants, psychiatrists, and physiologists) and nonmedical 

specialists (case managers, benefits counselors, and 

ROLE OF THE PROSTHETIST

Ideally, the rehabilitation team works in unison and 

complements each other’s roles. Prescription formulation usually occurs during an interdisciplinary specialized clinic and is centered on the service member’s 

needs and desires for prosthetic rehabilitation. Each 

member of the clinical team plays an important role. 

However, during prosthetic limb prescription formulation, the prosthetist takes center stage. The increasing 

complexity involved in prosthetics technology and the 

development of unique materials, computer programs, 

and fabrication techniques/applicability require the 

specialized knowledge of the prosthetist. The American Board for Certification in Orthotics, Prosthetics 

& Pedorthics (ABC) and the Board for Orthotic/

Prosthetic Certification (BOC) provide benchmark 

certification levels for competency in the field. There 

are several pathways to certification, and it is important for each MTF to ensure that its prosthetists are 

appropriately certified. ABC, formed in 1946, requires 

that prosthetic education be obtained from institutions 

accredited by the Commission on Accreditation of Allied Health Education Programs and that prosthetists 

successfully complete a 1-year residency requirement 

per discipline (prosthetics and orthotics), as well as 

take subsequent board examinations. BOC requires 2 

years of education, training, and/or work experience 

and 2 years of experience in providing direct patient 

care services.

Nearly all of the clinical specialties that comprise 

this interdisciplinary team are uniformed service 

members bridging both officer and enlisted ranks. 

The military occupational specialty classification for 

orthotist (originally code 42C) was eliminated in the 

mid-1990s. However, because of the global war on 

terror and the ensuing combat operations in Iraq and 

Afghanistan, the need for military prosthetists and orthotists is on the rise. To fill this gap, civilian orthotists 

and prosthetists have been employed at MTFs either 

through service contracts with companies or through 

hiring individual prosthetists as government service 

employees. It is important that prosthetists have a 

clear position within the military organizational system. This position has typically been classifed under 

the Department of Orthopaedics and Rehabilitation. In addition, it has not been uncommon for the 

Department of Defense to request that prosthetists 

help provide strategic and operational knowledge of 

prosthetic programs to allied governments, which has 

called into question the need for uniformed military 

prosthetists. 

For example, during Operation Iraqi Freedom (specifically from January 2006 to June 2006), a five-man 

team of rehabilitation providers from the US Armed 

Forces Amputee Patient Care Program worked with 

Iraqi prosthetic and rehabilitation specialists to educate them on best practices in caring for patients with 

limb loss and complex trauma. The team instructed, 

assisted, and supervised Iraqi clinicians in the deliv-
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Lower Limb Prosthetics

ery of prosthetic and rehabilitation services to 124 

patients (totaling more than 350 patient clinical visits). 

The clinic that they developed was transferred to the 

Iraqi Veterans Agency (in Baghdad, Iraq) and is now 

considered the premier prosthetics and rehabilitation 

clinic in Iraq. 

The prosthetic mission was to educate Iraqi providers on state-of-the-art prosthetic care, with emphasis 

on enhancing provider clinical decision-making skills, 

improving tradecraft and bench skills, and enhancing the use of available technology. The primary goal 

was to shift Iraqi practice patterns from those of a 

semiskilled worker model to a more professional paradigm. Typically, Iraqi prosthetists are locally trained 

by the International Committee of the Red Cross or 

by nongovernmental organizations with support 

from the Iraqi Ministry of Health. Practitioners are 

often characterized as technicians working in “limb 

factories,” as opposed to the Western model of an allied health professional performing clinical services. 

The assistance team trained local Iraqi prosthetists 

how to adopt an internationally recognized role as allied health providers in a community of rehabilitation 

science experts. Clinically, this required a change in 

paradigm from fabricating, fitting, and delivering fairto-adequate lower extremity prosthetic limbs to one of 

consistently producing reliable and comfortable prosthetic arms and legs in a reasonable and timely manner while optimizing the use of available technology 

[eg, computer-aided design (CAD)/computer-aided 

manufacturing (CAM) systems]. Additionally, their 

Iraqi counterparts were instructed in how to refine 

their clinical evaluation skills, clinical documentation 

techniques, and prosthetic fabrication abilities. On 

completion of formal training, the Iraqi prosthetic 

providers returned to full-time direct patient care. 

The art and science of prosthetic care and rehabilitation of persons with limb loss and polytrauma by 

necessity accelerates during times of war. Clinicians 

have a strong moral imperative to share with our allies 

the lessons learned in caring for seriously wounded 

service members. Thus, the outcome of this mission 

was to demonstrate the importance of appropriate 

technology, emphasize a multidisciplinary approach to 

care, and describe the standard of care in a subsegment 

of the Iraqi population of war wounded.

OVERVIEW OF COMPONENTS

Prosthetic Feet

Function

Prosthetic feet are classified according to function 

and features. An understanding of prosthetic foot function and design will assist clinicians in selecting feet 

best suited to a patient’s activities. The prosthetic foot 

is the interface between the patient and the ground, 

and ideally would emulate the anatomical foot perfectly. Achieving this, however, is difficult. Prosthetic 

feet range from simple to complex as they attempt to 

mimic anatomical function. Anatomical articulation 

at the ankle and midfoot greatly affects gait efficiency 

and smoothness. It can increase knee stability, and a 

multiaxial foot can increase the base of support by 

accommodating uneven terrain. Prosthetic joint simulation can be accomplished by true articulation of the 

prosthetic foot, as well as compression of the foot itself. 

Related to joint movement is shock absorption, another 

critical feature that the prosthetic foot must emulate. 

The foot must dampen the impact at loading response 

during gait. This is necessary to diminish forces transmitted to the residual limb. An example of this is the 

compressible heel of the foot. At loading response, the 

heel of the prosthetic foot compresses, emulating the 

eccentric contraction of the dorsiflexors. This is referred 

to as simulated or relative plantar flexion. Another less 

functional, yet important, feature of prosthetic feet is 

appearance. This is more important to some individuals than others. If the patient intends to wear sandals, 

it is obvious that the cosmetic appearance of the foot 

must be good. With the exception of specialty feet 

designed for running or other activity, all feet have a 

cosmetic foot shell as a minimum. This shell protects 

the internal components from unnecessary wear and 

tear. The overall design of the prosthetic foot, its ability 

to articulate, and its material composition can have a 

significant effect on the foot’s ability to emulate anatomical function. Generally, the greater the ability and 

activity of the patient, the more features the patient 

may be able to take advantage of during use.

Dynamic Response

The dynamic response foot has a deformable springtype keel that provides a lively, responsive feel while 

the patient is walking. As the keel deforms under 

loading, it absorbs shock and then quickly returns to 

its original position once the load is removed. This type 

of design is often referred to as an energy storage and 

return (ESAR) design.1 Suggested benefits of ESAR feet 

include the following: increased self-selected walking 

velocity, increased stride length, decreased sound side 

weight acceptance force, and increased prosthetic side 

propulsive force.2,3 The spring-like keels are fabricated 
556

Care of the Combat Amputee

from carbon fiber, Delrin (E. I. du Pont de Nemours 

and Company, Wilmington, Del), or other materials. 

They deform as body weight is applied (Figure 20-1). 

Designs vary in configuration. Most have a forefoot 

keel and a hind foot keel that function as springs 

and deform primarily in the sagittal plane. The hind 

foot keel that projects posteriorly (a heel spring) 

deforms at loading response and simulates plantar 

flexion. From late midstance to toe off, the forefoot 

keel deforms under the increased load. As the patient 

begins to push off, the spring resists this motion while 

it yields slightly. As the load is being removed from 

the foot, the toe spring pushes back against the patient until it returns to its original shape. This yields 

a livelier feel for the patient. Some carbon keels are 

split longitudinally, which allows the toe spring to 

scissor slightly, thus simulating inversion and eversion. Dynamic response feet are designed to yield 

upon load application. Keel thickness and strength 

are based on the patient’s weight and activity level. 

If either one increases, it is possible that the keel may 

fracture. A decrease in activity or weight may make 

the keel seem too rigid. Therefore, it is crucial that 

body weight and activity level be accurately assessed 

when selecting a dynamic response foot, given that 

keels are designed with a relatively narrow tolerance. With many carbon dynamic response feet, the 

keel continues to the distal socket that acts as both 

the foot and shank of the prosthesis. This increased 

carbon strut length provides more stored energy than 

those that terminate at the ankle. Patient height and 

residual limb length often will determine which style 

of foot can be used. Dynamic response feet provide 

excellent stability. The composition may vary, but, in 

general, these feet are typically lightweight, durable, 

and covered with a cosmetic foot shell.

Dynamic Response With Vertical, Shock-Absorbing 

Pylons

Vertical, shock-absorbing pylons help to dampen the 

axial loading of the prosthesis and thereby decrease 

the shock transmitted to the residual limb.4 Several 

designs are available; some are integrated into the foot 

using a side carbon strut (Figure 20-2) that supports 

Figure 20-1. Renegade Prosthetic Foot (Freedom Innovations, 

Irvine, Calif).

Photograph: Used with permission from Freedom Innovations.

Figure 20-2. Re-Flex VSP prosthetic foot (Ossur Americas, 

Aliso Viejo, Calif).

Photograph: Courtesy of Ossur Americas, www.ossur.com.
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Lower Limb Prosthetics

the patient’s weight and bows outwardly on weight 

bearing as the piston slides freely into and out of the 

cylinder. Other designs provide the user with the ability to adjust the resistance to vertical load by changing 

the psi in the unit (Figure 20-3), whereas other designs 

are separate components added to the standard pylon. 

These feet are available in standard and low profile 

heights to accommodate most limb lengths. Their 

ability to provide shock absorption can increase the patient’s comfort significantly when stepping off a curb, 

going down stairs, or performing other high-impact 

activities. These feet are designed with a split keel and 

also offer simulated inversion and eversion.

Articulated. Commonly used articulated feet are 

multiaxis in the sagittal, coronal, and transverse planes. 

Articulating dynamic response feet possess the advantages of the multiaxis foot in terms of terrain accommodation and the liveliness of the dynamic response 

foot. These feet are intended to provide accommodation with the ground without sacrificing their ability 

to provide dynamic response. They articulate through 

either a joint or a deformable wedge. If the prosthetic 

foot has an actual joint axis about which it articulates 

(Figure 20-4), it is referred to as a true articulation. 

Almost any prosthetic foot with an axis of rotation 

will require regular maintenance to lubricate the joint, 

which prevents wear and tear. Compressible bumpers 

are available with varying firmness (or durometer), 

allowing the prosthetist to adjust the plantar flexion 

resistance to accommodate the patient. Some designs 

also allow for dorsiflexion bumper exchange so that 

resistance to dorsiflexion may be adjusted until the 

foot hits the anterior stop.

Another method of providing articulation without 

moving parts, such as an axis, is to use an elastic bond 

of some sort between two dynamic response keels to 

provide ground conformance (Figure 20-5). A strap 

on the posterior aspect of the foot prevents excessive 

Figure 20-3. Ceterus prosthetic foot (Ossur Americas, Aliso 

Viejo, Calif). 

Photograph: Used with permission from Ossur Americas, 

www.ossur.com.

Figure 20-4. TruStep prosthetic foot (College Park Industries, 

Fraser, Mich).

Photograph: Courtesy of College Park Industries.

Figure 20-5. Talux prosthetic foot (Ossur Americas, Aliso 

Viejo, Calif).

Photograph: Courtesy of Ossur Americas, www.ossur.com.
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Care of the Combat Amputee

elongation of the posterior section of the elastic bonding material as the patient rolls over onto the toe of the 

foot. Other dynamic response feet use a thick elastomeric material between carbon fiber keel plates. In 

this case, the bottommost keel readily accommodates 

to uneven terrain, while the more proximal keel may 

provide the typical energy-storing function. These 

types of feet are referred to as simulated articulation, 

because there is no true articulation (Figure 20-6).

Increased knee stability on the prosthetic side can 

be achieved by an articulated ankle. The knee flexion 

moment is reduced as the foot plantar flexes at loading 

response. The articulation can also increase knee stability as the patient walks down an incline. Plantar flexion 

resistance in the foot can be adjusted to accommodate 

the patient with compressible bumpers or wedges and 

through prosthetic alignment.

Additional Features

Heel Height Adjustability. Prosthetic feet are usually manufactured with a contour on the plantar surface. This is intended to match the patient’s preferred 

heel height. Heel height is defined as the net difference 

between the thickness of the shoe sole at the ball of the 

foot (eg, ÷ inch) and the thickness of the heel at the 

posterior aspect of the shoe (eg, 1 inch). In this instance, 

the net difference is 3⁄4 of an inch; a prosthetic foot with 

a 3⁄4-inch heel rise would be appropriate. When placed 

in the shoe, the proper orientation of the prosthetic foot 

aligns the proximal surface of the foot horizontally, 

parallel to the floor. Feet are available that permit patients to adjust the foot’s dorsiflexion/plantar flexion 

position, providing them with the freedom to wear 

shoes of varying heel heights.

Inversion/Eversion. Many carbon keels are split 

longitudinally (Figure 20-7), which allows the forefoot keel to scissor slightly, simulating inversion and 

eversion as the foot traverses uneven terrain. This 

increased ground conformance provides greater stability. Another way to accomplish inversion and eversion 

is with an articulated foot, which provides coronal 

plane motion about the joint and is dampened by stiff 

rubber bumpers.

Microprocessor Ankle/Foot. One foot incorporates 

microprocessor-controlled and motor-powered dorsiflexion and plantar flexion during the swing phase. 

It is designed to make navigation of inclines, stair 

ascent and descent, and sitting onto or rising from a 

chair easier. A combination of sensors acts together 

to replace the mechanoreceptor function and provide 

artificial proprioception via gait pattern recognition 

algorithms (Figure 20-8). It is especially useful when 

there is a range of motion limitation of the contralateral 

knee and/or ankle.

Knee Units

Axis

Single Axis. In addition to their other features, 

prosthetic knees can be categorized as single axis or 

polycentric. The single axis knee is a simple, lowmaintenance hinge design generally lightweight and 

Figure 20-6. Axtion prosthetic foot (Otto Bock HealthCare, 

Minneapolis, Minn).

Photograph: Courtesy of Otto Bock HealthCare.

Figure 20-7. Vari-Flex prosthetic foot (Ossur Americas, Aliso 

Viejo, Calif).

Photograph: Courtesy of Ossur Americas, www.ossur.com.
559

Lower Limb Prosthetics

low profile. Prosthetic knee stability with a single axis 

knee relies heavily on alignment of the knee in relation 

to the socket and foot, and on the volitional control 

of the patient. The single axis design is coupled with 

constant friction, fluid, and microprocessor or powered stride control features. It is used for any level of 

patient ability.

Polycentric. The polycentric design is more complex 

and yields multiple centers of rotation, much like the 

anatomical knee. Prosthetic polycentric knees simulate 

the rocking and gliding motions of the anatomical knee 

either by curved-bearing surfaces or by linkages. Location of the axis changes as the prosthetic knee moves 

through its available range of motion. This is referred to 

as an instantaneous center of rotation (ICR) and results 

in an inherently stable knee. The way that the ground 

reaction forces move about the ICR makes this design 

more stable early in stance when the patient needs it 

most. In addition, the polycentric design shortens the 

shank during the swing phase, thus helping the foot 

clear the ground. Because of reorientation of the linkages during flexion of the polycentric knee, the shin 

segment translates posteriorly, and the segment rotates 

differently than it would if it acted about a single axis. 

This action results in a relative dorsiflexion of the foot 

as the knee flexes, which in turn creates increased 

toe clearance. The polycentric design also provides 

a more cosmetic appearance while sitting for those 

patients with long transfemoral amputations or knee 

disarticulations. The knee is designed so the shin folds 

back behind the socket at 90 degrees of flexion. This 

design minimizes the length discrepancy between 

the knees while sitting. The polycentric design is also 

ideal for patients with short residual limbs because the 

linkages place the axis of rotation proximal (closer to 

the workforce of the hip), requiring less hip extensor 

action, and the linkages also place the axis of rotation 

posterior to the weight line.5

Cadence Control

Constant Friction. Prosthetic knee joints should 

provide stability during stance and smooth, controlled 

knee extension during the swing phase. The most basic 

knee joint operates via a feature termed constant friction. A constant friction, single axis knee has a feature 

that provides continuous pressure/friction around the 

knee axis to control the velocity at which the shank 

and foot can swing to prevent excessive heel rise during flexion and terminal impact at full extension. The 

resistance to swing is adjustable, but not self-adjusting 

as velocity changes. For patients who do not alter the 

speed of their cadence, a constant friction knee is indicated because of its simplicity, durability, and ease of 

use. However, most individuals walk at varying speeds 

and will require a more gait-responsive knee.

Pneumatic/Hydraulic/Magnetorheologic. A fluid 

(or hydraulically)-controlled knee provides frictional 

resistance about the knee axis that will increase proportionally with speed. There are two basic types of 

fluid-controlled knees: (1) hydraulic or (2) pneumatic. 

Fluids include liquids, vapors, and gases. The major 

difference with fluids in prosthetic knees is that air 

is more easily compressible, and hydraulic fluids 

are not. Oil or air is forced through a small orifice 

or tube. Adjustment screws allow the size of the orifice to be changed to control the rate in which fluid 

flows through these ports. This permits fine-tuning 

of swing-phase resistance to individual needs. If air 

is used, the air under compression within the pneumatic cylinder also acts as an extension assist. The 

ability of air to compress gives pneumatic knees a 

springier feel to the patient. One knee functions with 

a magnetorheologic fluid (Figure 20-9). This fluid 

contains metallic particles that respond to an electrical charge affecting the viscosity of the fluid. Instead 

of flowing through valve-controlled ports, the fluid 

acts on the knee axis to provide braking friction by 

becoming more or less viscous. Here, too, sensors 

Figure 20-8. PROPRIO FOOT (Ossur Americas, Aliso Viejo, 

Calif).

Photograph: Courtesy of Ossur Americas, www.ossur.com.
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Care of the Combat Amputee

send knee angle, velocity, and force data to the knee’s 

microprocessor, which in turn adjusts a magnetic field 

around the fluid.

Microprocessor Knee

Microprocessor knees (Figure 20-10) are a class of 

knees that sense the conditions acting on the knee joint 

and can quickly make internal adjustments to safely 

meet those conditions. Joint angles and forces on the 

pylon are measured via sensors and are then sent to 

the microprocessor for rapid adjustment. Valves open 

or close electronically to increase or decrease fluid 

flow through the knee’s internal ports, or the viscosity 

of the magnetorheologic fluid changes to vary resistance to knee flexion or extension. The advantage that 

microprocessor knees have over mechanical knees is 

that rapid input from the microprocessor makes them 

significantly more responsive to the patient’s activity, 

whether walking, running, descending stairs, or stumbling.6

 These knees allow for manipulation of the computer program to vary the stability and safety of the 

knee as the patient progresses through rehabilitation. 

Stumble recovery is a significant feature of these knees.

Motorized Knee

Building on microprocessor technology, the motorized knee (Figure 20-11) provides flexion and extension 

to an externally powered motor-driven knee. The knee 

replaces lost muscle function. It is therefore possible for 

the user to climb stairs step by step, ascend inclines, 

and walk longer distances on level ground. Sensors 

are positioned on the sound side, which accurately 

measure motion, load, and position. This information 

is transmitted to the knee via Bluetooth technology, 

where the microprocessor analyzes the data and determines the response of the knee to the activity and 

the amount of power or force needed from the knee to 

generate the appropriate knee flexion or extension. 

Additional Knee Features

Stance Flexion. Controlled prosthetic knee flexion 

under weight bearing is referred to as stance flexion. 

As the patient transfers weight onto the prosthesis 

in the early stance phase, the knee gradually yields 

to approximately 15 degrees, thereby cushioning the 

impact of weight bearing to the wearer. Stance flexion 

is adjustable and may be completely eliminated if the 

patient finds it disconcerting and fears that the knee 

may buckle, or it can be adjusted to allow up to 15 

degrees of flexion. Although it requires some getting 

used to, this can be a very smooth knee mechanism for 

the patient to ambulate on because the stance flexion 

absorbs some of the shock transmitted to the socket 

during loading response.

Geometric Lock. The geometric lock feature, also 

Figure 20-9. RHEO KNEE (Ossur Americas, Aliso Viejo, 

Calif).

Photograph: Courtesy of Ossur Americas, www.ossur.com.
561

Lower Limb Prosthetics

referred to as a mechanical stance phase lock, locks 

the knee on full extension (initial contact) and does 

not release it until the weight line passes over the 

forefoot and hyperextension of the knee unit occurs. 

This clever geometric design is engineered into a 

polycentric knee and provides excellent stability. The 

geometric lock can be convenient because it provides 

reliable stance control.

User-Activated Lock. A manual lock is available 

on some constant friction and fluid knees. For those 

activities requiring maximum stability, this mechanism 

is ideal. Prolonged standing (ie, at a workbench) is one 

such example, as is traversing exceptionally rugged 

terrain. The patient simply flips a lever to engage the 

locking feature. A patient with bilateral amputations 

may occasionally need the stability of a locked knee. 

Ambulation with a locked knee compromises normal 

gait mechanics and should be carefully considered 

before being used for the purpose of daily ambulation. Locked knees are intended for activities beyond 

normal ambulation. Whereas mechanical knees are 

locked at full extension, one microprocessor knee can 

be adjusted through programming to lock the knee at 

any degree of knee flexion.

Other Components

Torsion

The rotation/torsion that occurs about the limb 

during gait can result in shear pressures if too much 

torsion is translated onto the limb.7 Gel liners, feet with 

integrated ankles, and torsion adaptors can absorb 

Figure 20-10. C-Leg (Otto Bock HealthCare, Minneapolis, 

Minn).

Photograph: Used with permission from Otto Bock HealthCare.

Figure 20-11. POWER KNEE (Ossur Americas, Aliso Viejo, 

Calif).

Photograph: Courtesy of Ossur Americas, www.ossur.com.
562

Care of the Combat Amputee

some of this torsion to decrease the rotational shear 

preventing skin abrasions and reducing stress on the 

knee joint. The torsion adaptor should be placed as 

proximal on the transtibial or transfemoral prosthesis 

as possible to minimize the perceived weight of the 

prosthesis by the patient. This feature is particularly 

helpful with activities that include a lot of pivotal 

movements (eg, golfing) in which patients experience 

a greater level of comfort. Axial motion occurs in the 

adaptor instead of between the socket and the skin. 

Some torsion adaptors have independent internal and 

external rotation adjustments.

Combined Torsion and Vertical Shock

Independent torsion and shock-absorbing units 

are available and can be paired with any foot. Interchangeable elastomer rods or adjustable springs 

provide dampening of vertical and rotational forces, 

thus reducing the strain on joints and soft tissues. Both 

torsion absorption and vertical shock dampening are 

inherent to some prosthetic feet (Figure 20-12).

Positional Rotators

A positional rotator (Figure 20-13) permits the patient to rotate the flexed knee and shank of the prosthesis out of the way for ease of movement. It enables 

patients to sit cross-legged and swing the prosthesis 

away from the pedals while driving. This is an added 

convenience for patients with transfemoral or higher 

level amputations. Designed for non–weight-bearing 

activities only, the rotation is activated by pressing a 

button, and snaps back into place. Changing shoes 

and socks while wearing the prosthesis also becomes 

a much easier task.

Quick Release Couplings

Knees and feet can be easily interchanged by the 

patient under a well-fitting socket. A quick release 

coupler is available when varying activities necessitate such a change. Examples include the following: 

exchanging a microprocessor knee for a water-resistant 

knee and foot or temporarily removing components 

below the socket to maneuver about tight spaces. 

Figure 20-13. Positional Locking Rotator (Otto Bock Healthcare, Minneapolis, Minn).

Photograph: Used with permission from Otto Bock HealthCare.

Figure 20-12. Delta Twist Shock Absorber (Otto Bock HealthCare, Minneapolis, Minn).

Photograph: Courtesy of Otto Bock HealthCare.
563

Lower Limb Prosthetics

Socket Interfaces

Gel Liners

Cushioning and shear-reducing properties of gel 

liners make them ideal for all patients at any level of 

amputation. In addition, their compressive properties 

make them ideal as a shrinker during the early phase 

of rehabilitation. Gel liners can be used as a means of 

suspension, given their friction properties against the 

skin that prevents distal migration of the liner (Figure 

20-14). They can be used for comfort in conjunction 

with any type of suspension. Patients exhibiting scar 

tissue will particularly benefit from the gel. Not only 

is shear greatly reduced, but also some liners slowly 

diffuse a medical-grade mineral oil or other emollient 

onto the skin. This aids in scar management by keeping 

the scar tissue soft and supple. Protection from socket 

pressures and shear has historically been treated with 

custom-made soft liners of high-density foams or with 

a combination of leather and silicone. Additionally, 

lack of protective sensation is another condition commonly managed with gel liners. Gel liners are available 

in 3-mm, 6-mm, and 9-mm thicknesses, with the latter 

being the most protective. They are available with or 

without fabric covering. Choosing a liner with a matrix 

embedded within the gel minimizes vertical displacement. The liners are available off the shelf in many 

sizes, durometers, and thicknesses. They are made 

of silicone, urethane, mineral oil, or a thermoplastic 

elastomer. Custom liners can be designed for atypical 

limb contours with varying durometers. Some liners 

are manufactured with a unique distal fabric weave to 

minimize elongation, and most are thinner posteriorly 

or rippled, thus facilitating comfortable knee flexion. 

Although the liners are relatively durable, they are 

not puncture-resistant or tear-resistant. Proper caution 

must be exercised to minimize damage. Longevity of 

the liners is very much dependent on the activity level 

of the patient and the care given to the liner. Heavy 

duty use, improper donning, lack of routine cleansing, 

or careless storage can shorten the life of a liner. Worn 

liners may abrade the skin and should be replaced. 

Given direct contact with the skin and the sealed environment, it is imperative that the liners be cleansed 

daily. They are designed to be hypoallergenic, and 

the occurrence of dermatitis or other skin irritations is 

rare. If a skin reaction does occur, it can be dealt with 

by switching to a gel liner made of another material 

and/or consulting with a physician. If the problem 

persists, a physician should be notified. Applying the 

liner correctly requires some degree of dexterity and 

cognitive function. Donning is achieved by turning 

the liner inside out, placing the end firmly against the 

limb, and rolling the liner up the limb. The inherent 

frictional (suspension) properties of the liners preclude 

them from being pulled on like a sock. Prosthetic socks 

can be worn over the liner to accommodate limb volume fluctuation.

Prosthetic Socks

Prosthetic socks are the interface materials between the residual limb and the socket. Even with 

the use of a gel liner, socks are still required to 

adjust the fit of the prosthesis. Generally, socks are 

Figure 20-14. Original Alpha Liner (or gel liner; Ohio Willow Wood, Mt. Sterling, Ohio).

Photograph: Used with permission from Ohio Willow Wood.
564

Care of the Combat Amputee

provided in one-ply, three-ply, and five-ply thicknesses, and are combined to the desired thickness. 

They cushion the limb and wick away moisture 

when worn against the skin. In suction or vacuum 

suspension prostheses, they are necessary to wick 

air out of the system. Socks are knitted with wool, 

cotton, or any number of synthetic fibers. Some 

synthetic blends offer stretch, increased wicking 

ability of moisture away from the skin, and ease of 

care. When using a hard socket, oftentimes placing 

a prosthetic nylon sheath directly over the skin, 

followed by thicker prosthetic socks, reduces shear 

and increases comfort. As the patient’s limb volume 

changes throughout the day, the addition or reduction of a few plies will maintain a comfortable fit. 

Temperature, activity, weight change, and diet all 

have an effect on socket fit.

Prosthetic socks for fit adjustment are placed over 

the liner and do not affect the function of the pin. 

A hole is required in the distal end of the sock to 

allow the pin to pass through to the locking mechanism. Sock ply can be adjusted without affecting pin 

suspension. Patients should always be reminded to 

pull up the sock completely onto the liner and not 

allow any sock material to remain over the area of 

the pin. If the fabric is pulled into the locking mechanism along with the pin, it may jam and prevent 

the disengagement of the pin. This action prevents 

removal of the prosthesis. If this happens, it may 

be necessary to dismantle the locking mechanism 

to free the pin.

Hard Sockets

Transtibial hard socket designs have the advantage 

of simplicity, less bulk, durability, and easy cleanability. The classic description indicates that only a sock 

interface is present. The popularity of gel liners makes 

the hard socket with socks only a less prescribed option. However, patients who choose not to wear a gel 

liner and who desire the low maintenance and simple 

socket style can use the hard socket with a sock interface. Because the socket is not as forgiving as one 

with a gel liner, a well-fitting socket is crucial, and the 

patient must be diligent in sock management to remain 

comfortable. Scar tissue and sharp bony prominences 

are contraindications for this socket style.

Transfemoral Flexible Inner Liner With Rigid Frame

The rigid frame provides socket stability, and the inner 

flexible socket provides comfort proximally in the transfemoral socket and also space for muscle expansion in 

both the transtibial and transfemoral sockets via specifically placed frame cutouts. If designed with large frame 

cutouts, the flexible inner socket might even provide 

added proprioceptive feedback through the socket wall 

when in contact with, for example, a chair edge while 

sitting. Postfabrication adjustments of socket contours 

are also more easily accomplished when there is a flexible inner liner. In the instance of heterotopic ossification, 

flexible inner liners can be removed, heat-expanded to 

provide relief, and placed back into the rigid frame.

SYME PROSTHESIS

Socket Design and Suspension

Although the Syme amputation is considered end 

bearing, the socket design and trimlines remain similar 

to that of the transtibial socket. The high socket trimline 

provides the same loading characteristics as that of the 

transtibial socket. This trimline also reduces the likelihood of edge pressure along the tibial crest during late 

stance. The prosthesis should spread the load over the 

entire limb. The Syme prosthesis generally resists axial 

rotation because of the elliptical contour at the level 

of the malleoli. Shock absorption is limited because 

of length constraints because no vertical shock units 

can be incorporated into the prosthesis. The calcaneal 

heel pad, however, provides padding and protects the 

distal limb.

Commonly used suspension designs are window 

designs placed medially, cut to the smallest size necessary to allow the malleoli to pass through, and are of 

tubular construction with no opening to weaken the 

design. The latter offers the greatest socket strength 

against compressive forces during gait and is therefore 

most desirable. The medial window design is most appropriate when the distal limb width is much greater 

than the width just proximal to the bulbous end. This 

commonly occurs when the flares of the malleoli are 

left intact and prominent. The tubular-styled prosthesis 

is donned by applying a thin pad placed just proximal 

to the widest part of the distal limb. Once the limb is 

seated firmly into the prosthesis, it is wedged into the 

socket. Secure suspension is achieved via pad thickness and sock ply. Occasionally, this pad may also be 

incorporated into a full polyethylene closed-cell foam 

liner. If the malleoli have been completely tapered and 

no flare at the distal limb exists, then the prosthesis 

cannot be self-suspended. In this case, a gel liner, outer 

sleeve, and one-way expulsion valve can be used to 

provide suction suspension.
565

Lower Limb Prosthetics

Foot Options

The Syme amputation retains the talus and calcaneus, resulting in limited clearance between the limb 

and floor. Most prosthetic feet are too tall to fit under 

a Syme prosthesis without creating a limb length discrepancy. Low profile feet specifically designed for use 

with the Syme amputation are available. Many are of a 

carbon plate design. Bolted directly to the distal socket, 

they can also be affixed with epoxies or other adhesives. 

Syme Biomechanics and Socket Strength

At loading response, the patient will feel pressure 

on the posterior proximal and anterior distal residual 

limb. At late-stance phase, the pressures occur in exactly the opposite locations: the anterior proximal and 

posterior distal residual limb. Pressures are greatest 

on the residual limb during this late-stance phase as 

the patient pushes off to propel forward. To decrease 

forces on the residual limb at this time, the foot can be 

slightly dorsiflexed or moved more posterior. This is 

also the rationale for keeping the socket trimline to the 

level of the patellar ligament, thereby preventing edge 

pressure along the tibial crest. Similarly, increasing 

toe-out to functionally reduce the toe lever will lower 

anterior proximal pressure on the limb. Increased toeout can provide additional lateral stability.

The greatest forces on the socket occur in the sagittal plane. The anterior distal aspect of the socket is 

subject to high compressive loads during late stance 

and should be strengthened to prevent socket failure. 

This is most important when using a socket with a 

medial window. Extra layers of carbon fiber or fiberglass should be incorporated into the laminated socket 

in this area. Decreasing the anterior lever (toe lever) 

during alignment reduces the compressive loads on 

the anterior distal socket.

TRANSTIBIAL PROSTHESIS

Socket Design

Patellar Tendon Bearing

The patellar tendon-bearing (PTB)8 socket consists 

of a laminated or thermoplastic socket that provides 

an intimate, total contact fit over the entire surface of 

the residual limb. The anterior wall of the socket extends proximally to encapsulate the distal third of the 

patella. Just below the patella, located at the middle 

of the patellar ligament, is an inward contour or bar 

that (via other biomechanical forces) converts the 

patellar tendon (ligament) of the residual limb into a 

weight-bearing surface. PTB is a misnomer, however, 

because the patellar tendon is not the only weightbearing surface used by the PTB socket. The medial 

and lateral walls extend proximally to about the level 

of the adductor tubercle of the femur. Together, they 

serve to control mediolateral/rotary forces applied to 

the residual limb. The medial wall is modified with an 

undercut in the area of the medial flare of the tibia, a 

pressure-tolerant surface and primary weight-bearing 

area. The lateral wall provides relief for the head of 

the fibula and the cut end of the fibula. This wall 

applies pressure along the fibular shaft to enhance 

medial-lateral stability. In addition, the lateral wall 

acts as a counter pressure to the medial wall. The 

posterior wall is slightly higher than the patellar bar 

and is designed to apply an anteriorly directed force 

to maintain the patellar tendon on the bar. The posterior wall is flared proximally to allow comfortable 

knee flexion and is contoured to prevent pressure on 

the hamstring tendons. The total contact fit provides 

relief over nonpressure-tolerant areas and supports 

the body’s weight over the pressure-tolerant areas of 

the limb. Total contact is necessary to prevent limb 

edema, but does not imply equal pressures throughout 

the socket. PTB socket design is appropriate for nearly 

all transtibial amputations, but is seen less often with 

introduction of the total surface-bearing socket. The 

PTB prosthesis is designed to maintain the residual 

limb in slight initial flexion (from 5 degrees to 10 degrees) to convert the patellar bar to a more horizontal 

supporting force. However, because the patellar bar is 

not completely horizontal, the residual limb still has 

a tendency to slide down posteriorly. This tendency 

must be counteracted by the posterior wall that is 

contoured to maintain the patellar tendon’s position 

on the patellar bar.

Total Surface Bearing

The total surface-bearing (TSB) socket design is 

commonly used when a gel liner is prescribed. The 

gel dissipates pressures throughout the socket and 

relieves bony prominences. Different from the PTB 

socket, pressure is intended for global distribution over 

the entire limb, as opposed to pressure-tolerant areas 

only. Bone and other sensitive regions are cushioned 

by the gel liner. Socket contours are smooth and without any obvious reliefs or undercuts lowering peak 

pressures.9 Similar to the PTB socket, this design also 
566

Care of the Combat Amputee

provides a total contact fit for comfort. The TSB socket 

significantly differs from PTB concepts in modification technique. In the PTB socket, plaster is removed 

over the patellar tendon, lateral pretibial group, the 

medial flare, and the popliteal region. Areas of plaster 

addition are the tibial tubercle, along the tibial crest, 

and the proximal and distal fibulae. TSB modification 

does not require buildups. The gel material dissipates 

pressures throughout the socket and relieves bony 

prominences. Patients with fragile soft tissues, burns, 

skin grafts, scarring, or bony residual limbs can benefit 

significantly from the extra protection offered by the 

gel liner and TSB design.10,11

Suspension

Suspension Sleeves

Suspension sleeves (Figure 20-15) are available in 

neoprene, gel, or a breathable elasticized fabric. A neoprene suspension sleeve provides simple, low profile, 

relatively effective suspension. Its ease of application 

makes it an ideal option as an auxiliary form of suspension for periods of increased activity. The sleeve is 

fitted to the proximal third of the prosthesis and onto 

the midthigh several inches past the prosthetic socks. 

A small puncture or tear in the neoprene or gel sleeve 

can significantly impact its effectiveness because it 

provides suspension through a snug fit, resulting in 

friction and negative pressure. Activities such as kneeling or other heavy duty use may easily cut through 

a sleeve, thus hindering the ability to provide partial 

suction. On occasion, a patient may be allergic to the 

material. Because sleeves fit snuggly onto the thigh, 

the patient must have the strength and dexterity for 

proper application. If this is not the case, a more suitable suspension option should be sought. Heat buildup 

and perspiration are also concerns. Patients with upper 

extremity involvement may find the sleeve difficult to 

pull up onto the thigh. Sleeves do not provide sagittal 

or coronal stability.

Supracondylar/Supracondylar Suprapatellar Design

The supracondylar socket design affords the patient 

two primary benefits: (1) its high trimlines offer inherent suspension, and (2) it provides some control to a 

mildly unstable knee joint. The medial wall encompasses the femoral condyle and contours closely to the 

femur to purchase just past the level of the adductor 

tubercle, therefore creating a reduced proximal mediolateral dimension. This tight proximal configuration 

suspends the prosthesis over the femoral condyles. It is 

indicated primarily for individuals with short residual 

limbs to provide increased medial-lateral stability. It is 

Figure 20-15. Neoprene suspension sleeve (Southern Prosthetic Supply, Alpharetta, Ga).

Photograph: Used with permission from Southern Prosthetic 

Supply.
567

Lower Limb Prosthetics

contraindicated when knee instability requires more 

support. When a high anterior trimline—just past the 

proximal aspect of the patella—is added, then the 

socket becomes a supracondylar suprapatellar design. 

This area is referred to as the quadriceps bar. Encompassing the patella provides additional suspension, a 

kinesthetic reminder to limit knee extension, and prevents the medial and lateral brims from spreading.

Mechanical Lock Mechanisms

Mechanical locks are a positive locking system for 

suspension of the prosthesis. They are coupled with 

gel liners. The gel liner is rolled directly onto the skin 

and provides suspension through the mechanical 

lock. A variety of locks are available, some providing 

an audible clicking sound (ratchet style) that lets the 

patient know that the pin is engaged. Another lock 

style incorporates a clutch mechanism that allows the 

patient to manually draw the limb even deeper into 

the socket by turning a knob to eliminate any vertical 

displacement. A lanyard system is available when 

pin engagement is difficult because of mobile distal 

tissue or when a low profile lock is required to avoid 

making the prosthesis too long and creating a length 

discrepancy (Figure 20-16). Lock mechanisms can be 

very secure and less cumbersome forms of suspension, 

avoiding straps, belts, etc. To remove the prosthesis, a 

release pin is depressed that disengages the lock. 

Suction

Suction suspension can be created by using a gel 

liner without the locking pin and by adding an airtight outer sealing sleeve. A one-way expulsion valve 

located at the distal socket removes air from the socket, 

thus creating a negative vacuum environment. With 

such a system, the patient can enjoy the benefits of suction suspension, minimal vertical displacement, and 

increased proprioception. Maintenance of an airtight 

seal is important for the system to function properly.

Sealing Liners

Similar to suction suspension with a knee sleeve, 

sealing liners have the added benefit of eliminating the knee sleeve by providing a hypobaric seal 

(Figure 20-17) between the liner and the socket. The 

seal is pressed against the socket wall, and suction is 

maintained below the level of the sealing ring. A thin 

sheath is worn below the seal to wick air out through 

a one-way, push-button release expulsion valve. Knee 

flexion is unrestricted because no additional sleeve is 

required. These liners are available prefabricated or can 

be customized to place the seal at any desired level.

Vacuum Assisted

Suction can be enhanced with a vacuum. The hypobaric environment is achieved and maintained via a 

telescoping mechanical vacuum pump (Figure 20-18)

or an electric pump. With each step, air is actively 

drawn out of the socket, maintaining a consistent and 

Figure 20-16. Lanyard-style suspension (KISS Technologies 

LLC, Baltimore, Md).

Photograph: Used with permission from KISS Technologies 

LLC.

Figure 20-17. Iceross Transfemoral Seal-In Liner with DermoSil (Ossur Americas, Aliso Viejo, Calif).

Photograph: Courtesy of Ossur Americas, www.ossur.com.
568

Care of the Combat Amputee

comfortable level of vacuum. Additionally, the mechanical pump acts as a vertical shock absorber. The 

system consists of a gel liner covered by a sheath with 

a sealing sleeve placed over the prosthesis and rolled 

onto the thigh to create a sealed chamber. A tube exits 

the socket distally and routes into the vacuum pump. 

As with other suction systems, patients typically report 

increased proprioception.

Transtibial Biomechanics and Alignment 

(Endoskeletal Systems)

Biomechanics

The biomechanics of socket fit, alignment, foot function, and suspension are interrelated and highly dependent on each other. Socket biomechanics has already 

been partially covered in the section on socket design. 

To complete the discussion, dynamic forces and their 

relationship to the socket should also be explained. 

By placing the foot just medial (12 mm) to the socket 

midline, the medial flare and the shaft of the fibula 

are loaded during single limb support. These are both 

excellent, weight-tolerant areas, and foot placement 

is fine-tuned during dynamic alignment to maximize 

these regions of the limb. Contours to the pretibial region and the medial aspect of the tibia protect the distal 

end and crest of the tibia during loading response. At 

this time, the quadriceps are active, and distal tibial 

pressures can occur. Foot selection can alter gait and 

pressures within the socket. Articulated feet, feet with 

firm hind foot keels, or feet with shorter internal keels 

all have a different effect on a patient’s comfort and 

gait efficiency. Inadequate suspension will result in a 

prosthesis that appears too long and will alter swing 

phase gait. The patient may vault on the sound side 

to clear the prosthesis. Shear within the socket may 

cause skin breakdown.

Prosthetic alignment refers to the fixed spatial relationship between the prosthetic socket and foot. With 

appropriate attachments, it is possible to reposition the 

foot in all planes. The foot can be moved in a linear 

fashion anteriorly or posteriorly and medially or laterally in relation to the socket. Prosthetic foot inversion 

or eversion and foot dorsiflexion or plantar flexion 

(socket flexion and extension) are also possible. All of 

these adjustments directly affect pressures within the 

socket as the patient ambulates. 

Overall length of the prosthesis is determined by 

the length of the pylon used. Length of a transtibial 

prosthesis is correct when the medial tibial plateau 

of the residual limb is maintained at the same height 

as the medial tibial plateau on the sound side (as the 

patient stands with weight borne equally on both feet). 

The most convenient indication of correct height is 

through a comparison of the iliac crests (or the anterior 

superior iliac spines). If they are not the same level, 

then the height of the prosthesis should be corrected. 

This is a general rule, of course, and may not apply if 

the patient has scoliosis, pelvic obliquity, or congenital 

leg length discrepancy. Such cases must be taken individually, and often the best indicator of correct height 

Figure 20-18. Harmony mechanical vacuum pump (Otto 

Bock HealthCare, Minneapolis, Minn).

Photograph: Used with permission from Otto Bock 

HealthCare.
569

Lower Limb Prosthetics

is through gait analysis and patient comfort.

Proper foot rotation is important both cosmetically 

and functionally. Toe-out refers to the angle between 

the line of progression and the medial border of the 

prosthetic foot. A transtibial prosthesis is initially 

aligned with the medial border of the foot parallel to 

the line of progression. This position may need to be 

altered during static and dynamic alignment so that 

foot rotation on the prosthesis visibly matches that of 

the sound limb. In addition to appearance, foot rotation 

affects prosthetic function. How this occurs may be 

understood if the keel of the foot is viewed as a lever 

arm. During the stance phase, the tendency of the body 

to fall over the foot is resisted by the counter force of 

this lever arm. Therefore, rotation of the foot directly 

affects the length and direction of force exerted by the 

lever arm. The net effect of externally rotating the foot 

is to increase stability by widening the base of support. 

There is a cosmetic trade-off, of course, because the 

toe-out attitude of the prosthesis will not match that 

of the contralateral limb. Although it is rarely necessary to alter toe-out in this way, an awareness of the 

biomechanical effects of foot rotation is important.

Socket flexion was briefly discussed in the section 

on PTB design. To reiterate, pressures on the residual 

limb can be greatly influenced by the inclination of the 

supporting surfaces in contact with the limb. For example, if a prosthesis was fabricated with the patient’s 

residual limb in 90 degrees of flexion, the shaft of the 

tibia would be horizontal in relation to the supporting 

surface of the socket, and the vertical force exerted by 

the socket would be equal to the weight of the body. 

The socket is placed in 5 degrees to 10 degrees of initial 

flexion to increase its supporting surface.

Alignment

Prosthetic alignment will change as the patient’s 

range of motion, muscle strength, and balance improves, and as the patient gains confidence and becomes more physically comfortable in the prosthesis. 

Intervention by physical therapy is crucial during 

this early period to aid the patient in developing appropriate gait habits. Prosthetic alignment during 

early fitting, just after amputation, can be significantly 

different on the same patient one year later when the 

limb is well healed and the patient returns to highlevel activity. As confidence and ability increase and 

limb contours change, the socket and/or foot will be 

replaced, resulting in a need for prosthetic alignment 

change. Initial static and dynamic alignment goals 

consider the patient’s level of ability, limb length, stage 

of healing, range of motion, and muscle strength. Use 

of instrumented gait evaluation has also been beneficial in optimizing prosthetic alignment. The goals in 

each plane during the first fitting/alignment visit are 

as follows:

Coronal

	 •	 Iliac crests are at the same level. Patient’s gait

is smooth and symmetrical with no excessive 

trunk lean to either side.

	 •	 Foot is inset loading the proximal-medial

and distal-lateral aspects of the residual limb 

and encouraging an energy-efficient, narrowbased gait.

	 •	 Socket adduction or abduction matches the

residual limb, resulting in a vertical pylon or 

a foot that is flat on the floor at midstance. On 

average, sockets are in 5 degrees of adduction, 

but some patients may actually require an 

abducted socket.

	 •	 There is less than 6 mm of socket displacement

during the swing phase. 

Sagittal

	 •	 No forced knee flexion or extension when

standing. Shoe has even contact with floor 

and is bearing weight evenly.

	 •	 Presence of a smooth, energy-efficient gait

pattern—including controlled knee flexion 

after initial contact-loading response—smooth 

rollover with no recurvatum tendency, or 

early dropoff at late stance.

	 •	 As previously described, an attitude of initial

flexion increases the weight-bearing capacity of all load-tolerant areas. In addition to 

improving the weight-bearing characteristics, appropriate socket flexion also allows 

a smooth gait pattern by placing the quadriceps muscles on stretch. Because the knee is 

maintained in slight flexion, the quadriceps 

have a mechanical advantage to control the 

prosthesis. The constant attitude of knee 

flexion also lessens the possibility of hyperextension of the knee during midstance and 

terminal stance.

Transverse

	 •	 The degree of toe-out on the prosthesis should

approximate that of the sound limb. The 

degree of toe-out should not decrease the 

patient’s stance phase stability.
570

Care of the Combat Amputee

KNEE DISARTICULATION

Although the anatomical knee joint has been lost, 

the patient with a knee disarticulation amputation 

will be somewhat more functional than those with a 

higher level transfemoral amputation. The intact femur 

provides a long lever arm with good muscle control 

and strength because muscle insertions are not compromised. The asymmetrical shape of the distal end 

prevents socket rotation about the limb and provides a 

broad, partial weight-bearing surface. Another benefit 

of the knee disarticulation is that outward flaring of 

the femoral condyles can often be used to suspend the 

prosthesis. Control of the prosthetic knee is analogous 

to transfemoral principles. However, the full-length 

lever-arm, retention of thigh muscles, and center of 

rotation close to the knee center all enable the patient 

with a knee disarticulation amputation to have better 

control of the knee joint. The stable femur minimizes 

lateral socket shift and allows for abbreviated socket 

trimlines, resulting in increased comfort and range of 

motion. It is unlikely that hip flexion or hip abduction contractures will exist because the musculature 

remains balanced across the hip. When the prosthesis 

is removed, it is still possible for the patient to kneel 

because the residual limb can commonly withstand 

end bearing.

Socket Design

Socket design for knee disarticulation is often 

dictated by the degree to which distal weight bearing can be tolerated by the patient, as well as size 

of the femoral condyles in relationship to the thigh. 

Although knee disarticulation amputation is able to 

tolerate partial or full end bearing, the socket should 

provide total contact over the entire thigh to dissipate 

pressures over the greatest amount of surface area as 

possible. Ischial containment socket concepts remain 

the same, but trimlines and dimensions can be less 

aggressive than those of the transfemoral prosthetic 

design, even to the point of totally eliminating ischial 

containment. The proximal brim of the socket will 

be near round, terminating just distal to the ischium 

and pubic ramus to prevent impingement (similar to 

the old plug-fit transfemoral socket). Weight bearing 

will be distributed over the entire surface area of the 

residual limb contained in the socket, as well as over 

the distal end. Sockets are either thermoplastic or 

laminated and can include a gel liner or a flexible inner liner with a rigid outer frame. In weight bearing, 

a thin, firm, resilient pad provides the patient with 

a distal end pad to increase comfort under the bony 

condyles. During the early stance phase, the patient 

stabilizes the prosthetic knee in much the same way as 

a person with a transfemoral amputation: by actively 

contracting the hip extensors. Therefore, the rotary 

forces occurring in the sagittal plane during this gait 

phase will be greatest over the anterior proximal aspect of the thigh and over the distal posterior end of 

the residual limb. Consequently, the proximal anterior 

brim of the socket should provide even, comfortable, 

counter pressure, and the distal posterior socket should 

provide total contact and comfortable loading. During 

midstance, the socket will rotate about the distal end 

of the knee disarticulation, thus generating counter 

pressure against the proximal tissues of the thigh. 

Although the long residual limb provides a greater 

surface area to disperse these forces, the direction of 

socket rotation concentrates pressures around the distal femur laterally and the proximal thigh medially. In 

light of these forces, socket design for this level should 

facilitate comfortable distal loading, the proximal brim 

should stabilize laterally, and the medial-proximal 

brim should flare generously to minimize tissue rolls 

and avoid painful pressure.

Suspension

The spared femoral condyles offer similar suspension options as the malleoli do in the Syme prosthesis. 

Supracondylar suspension is obtained with either a 

pad placed over the flares of the condyles to wedge 

the limb into the socket or a medial cutout in the distal 

socket that allows the widest points of the condyles to 

pass. The cutout is closed to hold the socket in place. 

A removable medial plate is locked in place over the 

opening with Velcro (Velcro USA, Inc, Manchester, NH) 

straps after the prosthesis is donned to securely hold 

the residual limb in place. A disadvantage of this design is that the opening weakens the structural strength 

of the socket, and care in fabrication to reinforce this 

area is necessary. This suspension method works well 

when the femoral condyles are prominent, but suspension can be compromised by excessive redundant soft 

tissue or postoperative edema. In such cases, some 

form of auxiliary suspension is needed. The medial 

window design is simple and easy to don. The pad or 

partial sleeve suspension design results in a strong, 

continuous socket and eliminates circumferential 

straps about the distal aspect of the socket. It consists 

of a split cylindrical pad that the patient slips over the 

lower femur proximal to the condyles, converting the 

residual limb to a cylindrical shape. Prosthetic socks 

are used to hold the pad in place. The patient then 

pushes into the socket until it is firmly seated. Com-
571

Lower Limb Prosthetics

pression of the pad and friction suspend the prosthesis. 

Because this method does not require a complete liner, 

no additional bulk is added around the bulbous distal 

end. Both designs require a socket interface, such as a 

gel liner, socks, or both. Suspension during swing is 

maintained by ensuring a tight fit via added sock plies 

or by increasing the thickness of the suspension pad. 

If the distal residual limb contours are captured well 

enough, this can provide suspension and rotational 

control because the rounded brim cannot be relied on 

to prevent rotation.

Knee Selection Considerations

The full length of the femur poses a challenge in that 

virtually any prosthetic knee joint will result in a lower 

knee center on the prosthetic side. Historically, outside 

knee joints were incorporated to minimize knee center 

discrepancy, but their many disadvantages—most 

importantly lack of swing phase control—make them 

rarely used today. The knees of choice at this level are 

those of the polycentric design, and some knees are designed specifically for the knee disarticulation amputation. They decrease the overall prosthetic length of the 

thigh section, while decreasing the length of the shin 

section. In addition, some knees incorporate a linkage 

that, when flexed to 90 degrees, translates posteriorly 

under the socket, thereby reducing the thigh section 

length. As the linkage folds up underneath the prosthetic socket during sitting, the foot will often rise off 

the floor. The thigh segment will still appear somewhat 

longer when compared with the sound side. These are 

common issues, and the patient should be made aware 

of them during the fitting process. The polycentric 

design also reduces the length of the shank section 

during swing, thus facilitating toe clearance.12

TRANSFEMORAL PROSTHESIS

Socket Design

Ischial Containment

In 1955, Radcliffe13 described the biomechanics 

affecting lateral stabilization of the femur and pelvis 

in the transfemoral prosthesis. These principles are 

summarized as follows:

	 •	 During single limb support on the prosthetic

side, the weight of the amputee’s body, acting 

through the center of gravity, causes the pelvis 

to dip toward the sound side.

	 •	 Because of this tendency for the pelvis to

rotate toward the sound side, the pelvis can 

be described as a lever with a fulcrum, or supporting point, located lateral of the ischium.

	 •	 The tendency forthe pelvis to dip orrotate toward the sound side is resisted by contraction 

of the hip abductor (gluteus medius), which 

exerts a counteracting moment to the pelvic 

lever.

	 •	 For the gluteus medius to have maximum

effectiveness, it should be maintained at its 

normal resting length.

	 •	 This can be achieved if the femur is kept in a

normal position of adduction.

	 •	 For the person with a transfemoral amputation, the lateral wall of the socket must be 

shaped to maintain the femur in adduction 

because contraction of the gluteus medius 

causes the femur to stabilize against the lateral wall. Pressures thus generated must be 

distributed evenly, and excess pressure over 

the distal lateral end of the femoral shaft must 

be avoided.

	 •	 As a result of these forces acting against the

lateral shaft of the femur, counter pressure 

is generated by the medial wall against the 

proximal medial tissues of the limb.

These principles have not changed, although the 

ongoing challenge of managing them has produced a 

gradual evolution toward ischial containment socket 

designs and changing theories of prosthetic alignment.

One of the primary goals of the ischial containment 

socket is to provide medial-lateral stability by controlling the lateral shift of the femur during stance. This is 

accomplished by the narrow medial-lateral design and 

closely fitting socket that encases the medial aspect of 

the ischial tuberosity and ramus.14 Per its name, the 

ischial containment socket has the ischium within 

the socket itself. The socket is just wide enough at the 

level of the ischial tuberosity to allow the ischium to 

drop down inside the socket. The portion of the socket 

that extends proximally along the medial aspect of the 

ischial tuberosity and the ischial ramus is called the 

medial containment wall. This wall is angled to match 

the ischial ramus angle and does not follow the line 

of progression. Because the medial containment wall 

extends above the ischium, it will not allow the socket 

to migrate laterally. A tight dimension spanning the 

area just below the trochanter and at the medial aspect 

of the ischium maintains the bony structures snugly 

against the medial containment wall. In the transverse 

plane, the ischial containment socket tends to follow 
572

Care of the Combat Amputee

the anatomical shape of the proximal thigh.

It has been proposed that the ischial containment 

socket can provide a bony lock via a three-point force 

system and increase femoral stabilization in the socket 

during weight bearing. It is also believed that this 

three-point force system provides additional means 

for holding the femur in adduction. In 1989, a study 

by Gottschalk et al15 demonstrated that socket design 

is not necessarily a primary determinant of femoral 

adduction. This work showed that there was no significant difference in femoral adduction in the socket 

when comparing quadrilateral or ischial containment 

designs. The postsurgical length of the adductor 

musculature had a much greater bearing on proper 

femoral adduction.

When the socket trimlines in the perineum are aggressively high to capture the ischium and posterior 

aspect of the ramus, using a flexible inner liner with 

a rigid frame is recommended. The frame needs only 

to support or control the bony structures, thus leaving 

the flexible plastic to contain the anterior ramus and 

soft tissues. The added feature of the frame cutouts 

provides comfort, room for expanding musculature, 

and some proprioceptive feedback.

Ischial Containment Variants 

Once the concept of ischial containment was established, there have been varied iterations of this 

design. Some sockets accentuate and clearly define the 

functioning muscle bellies, allowing space for muscle 

contraction. Others lower the posterior aspect of the 

socket for sitting comfort. This minimizes gluteal support, but renders a better cosmetic result. Each of these 

designs follows the basic ischial containment principles 

with additional specific goals. Furthermore, each prosthetist will custom design any socket a bit differently, 

given the many contours and trimlines possible with 

the transfemoral socket.

Quadrilateral

If the ischial containment design is not successful, 

then the more historical quadrilateral socket may be 

considered. Quadrilateral refers to the four-sided 

shape of the socket when viewed transversely. As Radcliffe13 states: “The four walls of the socket are designed 

to apply pressures and counter pressures to facilitate 

comfortable load bearing through soft tissue and underlying structures.” The ischial tuberosity and gluteal 

musculature are used as primary weight-bearing 

structures and are supported by a posterior shelf. The 

ischium is maintained on the shelf or seat by the counter force of an inward contour (Scarpa’s bulge) in the 

anteromedial socket located over the femoral triangle. 

Although the femoral triangle contains the femoral 

artery, vein, and nerve, years of clinical trials have 

demonstrated that correctly distributed pressure over 

these structures is well tolerated. A convex contour in 

the proximal anterolateral socket accommodates the 

bulk and the contraction of the quadriceps muscle 

group. The quadrilateral socket may be suspended in 

a number of ways, including use of suction, a Silesian 

belt, or a hip joint with a pelvic belt. 

Suspension

Suction by Skin Contact

A suction socket offers intrinsic suspension and 

is held in place by a combination of negative air 

pressure, surface tension between the socket and 

the patient’s skin, and muscular contraction against 

the socket walls. For the socket walls to be in direct 

contact with the patient’s skin, no socks are worn. A 

valve, usually located at the distal-medial aspect of 

the socket, allows air to escape from the socket during 

weight bearing while preventing air entrance during 

the swing phase. The patient generally dons a suction 

socket by removing the valve, applying a donning 

sleeve over the residual limb, and feeding the loose 

end of the material through the valve hole. The material breaks the surface tension between the socket and 

the patient’s skin, allowing the patient to pull the limb 

comfortably into the socket. By using the donning 

sleeve to help pull skin and soft tissue into the socket, 

the patient can usually minimize problems caused by 

tissue overhanging the socket brim. Patients with a 

long, muscular limb may choose to push directly into 

the socket with a small amount of skin lubricant. Either 

way, it is critical that no distal air pockets remain. If 

there is lack of total contact distally in a suction socket, 

the high negative pressures created in the air space 

can result in circulatory congestion and edema. There 

are many advantages to selecting suction suspension. 

The most apparent advantage is elimination of belts 

and liners. Thus, the patient enjoys an unencumbered, 

lightweight, and relatively simple-to-apply suspension. The socket is a total contact fit that minimizes 

the possibility of edema. Suction is a solid form of 

suspension because once the skin is drawn down into 

the socket, the residual limb is effectively trapped in 

the socket, thereby minimizing vertical displacement. 

Because the socket is firmly attached to the patient’s 

residual limb, and rotational control is provided by 

the brim design, patients usually report that they have 

much better control of the prosthesis when using this 

form of suspension, especially during the swing phase. 
573

Lower Limb Prosthetics

One noted contraindication to a suction socket is that 

limb volume must remain stable to maintain a negative pressure environment. It is common for a patient’s 

residual limb to change volume over time, especially 

within the first year postsurgery. Even the residual 

limb of a longtime wearer can decrease in volume over 

the course of the day. Slight fluctuations are normal 

and generally not problematic, but those seen just after 

surgery make this suspension option inappropriate. 

If the patient presents with scarring, which extends 

across the proximal tissues of the residual limb, it is 

possible that those scars will break the air seal around 

the proximal socket and allow air to enter. As a result, 

suction is not maintained. Donning the suction socket 

requires strength and balance. If the patient does not 

possess sufficient ability and endurance, or has upper 

extremity involvement, another suspension mechanism must be used.

Sealing Liners

Suction is the suspension of choice because it 

eliminates belts and buckles. To address some of the 

aforementioned contraindications, a sealing liner as 

presented in the transtibial section is a good choice. A 

gel liner with a hypobaric seal is rolled onto the limb 

and then pushed into the socket. The seal is pressed 

against the socket wall, and suction is maintained below the level of the sealing ring. A thin sheath is worn 

below the level of the ring to wick air out through a 

one-way, push-button release expulsion valve.

Locking Gel Liners

When the two previous suspensions cannot be used, 

gel locking liners may be considered. The locks can 

incorporate pins, lanyards, or buckles. The goals of the 

gel locking liner for the transfemoral design are similar 

to that of the transtibial socket, with a primary goal to 

suspend the prosthesis and distribute pressure over the 

entire surface of the residual limb. As in the transtibial 

prosthesis, the silicone or gel type liner can provide a 

significant amount of protection for the residual limb. 

Locking liners can be applied to virtually any length of 

transfemoral residual limb. If a locking liner is planned 

for a long transfemoral or knee disarticulation amputation level, then a lanyard-type suspension may be 

required. This does not require the use of a long locking 

mechanism and keeps the prosthetic knee center at or 

just slightly below the anatomical knee. 

The most common advantage for the gel locking 

liner is an added measure of protection for the residual limb. The use of a liner can provide reduced 

shear on the residual limb and thus increased protection for fragile tissues. The liner can accommodate 

varying circumferences of the residual limb, thus 

ensuring total contact in the socket. As a result, the 

patient is much less likely to experience the failure 

of suspension because of suction loss. As an added 

benefit, donning the locking liner can be much easier 

than the skin suction socket because the patient is not 

required to lean over and pull into the socket. Typically, this locking liner suspension only requires that 

the patient engage the pin or pull up on a lanyard 

while stepping into the socket. Another significant 

advantage for the transfemoral patient, who tends to 

experience volumetric changes of the residual limb, 

is that the patient can apply prosthetic socks over the 

locking liner. The socks must have a hole at the distal 

end, which allows the pin to pass through and engage 

into the locking mechanism of the distal socket. As the 

patient’s residual limb volume decreases, the sock ply 

can be increased accordingly and vice versa.

Silesian Belt

The Silesian belt is a simple, low-profile, belt-type 

suspension mechanism. Indication for its use is primarily the need for rotational control of the prosthesis. 

The Silesian belt can be used as an auxiliary to suction suspension and, the in the case of an individual 

with weak adductors, can even assist the adductor 

muscles during swing phase. The belt sits firmly over 

the sound side ilium and may not be as effective with 

the obese patient. Scarring about the pelvis can also 

prevent its use because the belt creates friction in this 

area. If the patient presents with severe mediolateral 

instability, the hip joint and belt are better choices. The 

Silesian belt can be easily used with prosthetic socks 

to suspend the prosthesis while also accommodating 

residual limb volume fluctuation. The Silesian bandage 

is an excellent auxiliary suspension for a suction socket 

fitting for shorter levels. Support of the belt helps to 

prevent the socket from slipping off when the patient 

is seated. It also provides additional security during 

any activity.

Elastic Belt

An elastic suspension belt is fabricated of Neoprene 

(or polychloroprene; DuPont Performance Elastomers 

LLC, Wilmington, Del) or similar elastic material. 

Typically, this kind of belt is fastened anteriorly by 

Velcro (Velcro USA, Inc, Manchester, NH). Because 

the belt is made of elastic material, it is not ideal as a 

primary suspensor. The belt can allow rotation and 

elongation of the prosthesis. Because of its simplicity, 

however, it is not uncommon for an elastic belt to be 
574

Care of the Combat Amputee

used as an intermediate form of suspension or as an 

auxiliary suspension (along with suction). If the patient 

is involved in high-level activities, there might be a 

concern, on occasion, of losing suction. For those highlevel activities, the patient may choose to temporarily 

apply a belt to the prosthesis in the event that suction 

suspension is lost. With its simple Velcro closure, it is 

very easy to don.

Hip Joint and Pelvic Band

Whereas the Silesian belt is generally considered 

an auxiliary suspension, the pelvic belt is a primary 

suspension. This system includes a hip joint attached 

to the proximal lateral socket, a metal or plastic pelvic 

band contoured to the patient’s pelvis just below the 

iliac crest, and a leather belt that encircles the patient’s 

pelvis. The hip joint and pelvic band are typically 

considered a suspension means of last resort. Accurate 

placement is critical to proper function. If any other 

suspension can be successfully used, it should be explored first. A short transfemoral residual limb may be 

too short or may not generate enough abductor force 

during single limb support on the prosthetic side to 

provide a level pelvis. The added leverage offered by 

the hip joint and extension up to the pelvic band can 

usually provide adequate medial-lateral stability to the 

hip. This suspension system is very simple to use. If 

the patient can use an ordinary belt, then usually this 

form of suspension can be adequately donned, thus 

allowing the amputee to wear socks so that volumetric 

changes can be easily accommodated. The hip joint 

and pelvic band are obviously bulky and heavy. This 

can restrict hip range of motion and make sitting less 

comfortable. 

Transfemoral Biomechanics and Alignment 

(Endoskeletal Systems)

The smooth and safe function of a transfemoral 

prosthesis is dependent on the relation between socket, 

suspension, knee, and foot. The socket is positioned in 

all planes for optimum function. Generally, 5 degrees of 

socket flexion will place the hip extensors at a mechanical advantage, ready to resist a knee flexion moment 

at heel contact. If a hip flexion contracture is present, 

additional socket flexion will be necessary. A flexion 

contracture of up to 25 degrees may be accommodated 

by prosthetic alignment. Anything beyond 25 degrees 

will cause excessive lumbar lordosis, leading to possible low back pain. Knee stability is determined by 

volitional control, the mechanics of the knee itself, and, 

most importantly, alignment. The knee is positioned 

at or just behind a line connecting the trochanter and 

ankle (also known as the TA line). Moving the knee 

fore or aft, even a few millimeters, can have significant impact on the overall safety of the prosthesis. In 

the coronal plane, the adduction angle of the sound 

side is matched, unless there is a limitation at the hip 

preventing full adduction. The posterior brim of the 

socket is divided into thirds, and the foot is placed under the medial third mark. This provides good lateral 

loading of the femoral shaft during stance. A shorter 

limb or weak hip abductors might require that the foot 

be placed a bit more laterally under the midsocket to 

reduce the forces along the lateral aspect of the socket. 

In the transverse plane, the medial containment wall is 

rotated to follow the angle of the ramus. The prosthetic 

knee is set into 5 degrees of external rotation to the line 

of progression, and the foot is positioned to match the 

patient’s sound side foot rotation. Alignment of prosthetic components can be refined by gait lab analysis 

using center of mass instead of the TA line.

Alignment

As described in the section on transtibial prostheses, 

the prosthetic alignment will change as the patient 

progresses through the first year postsurgery, especially during early therapy treatment. Improvements 

in strength, balance, comfort, and confidence will 

periodically make reassessment of alignment necessary. Much attention is given to knee stability. Not 

only does moving the knee in relation to the ground 

reaction line affect stability, but also internal knee 

adjustments to resistance can reduce the likelihood 

of unexpected knee collapse and yield a smooth and 

efficient gait pattern.

Initial static and dynamic alignment goals take into 

consideration the patient’s level of ability, limb length, 

stage of healing, range of motion, and muscle strength. 

The goals in each plane during the first fitting/alignment visit are as follows:

Coronal

	 •	 Iliac crests are at the same level.

	 •	 Patient’s gait is smooth and symmetrical with

no excessive trunk lean to either side.

	 •	 Foot is inset-loading the lateral femur during stance, encouraging a narrow-based and 

energy-efficient gait.

	 •	 The foot/shoe has even contact with the floor

and is bearing weight evenly.

	 •	 The socket is well suspended and does not

drop away from the residual limb. 
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Lower Limb Prosthetics

	 •	 There is no vaulting on the sound side.

	 •	 There is no abducted or circumducted gait.

Sagittal

	 •	 The prosthetic knee is stable at initial contact/

loading response.

	 •	 During terminal stance, the footrolls without

dropping off or causing pelvic rise.

	 •	 The plantar flexion bumper of the articulated

foot is firm and does not allow foot slap.

	 •	 Heel rise is not excessive.

	 •	 There is no terminal impact.

	 •	 Steps are equal.

	 •	 Lumbar lordosis is not excessive.

Transverse

	 •	 The degree of toe-out on the prosthesis should

approximate that of the sound limb. The 

degree of toe-out should not decrease the 

patient’s stance phase stability.

	 •	 There is no medial or lateral whip at terminal

stance.

	 •	 There is no rotation of foot at initial contact/

loading response.

HIP DISARTICULATION AND TRANSPELVIC AMPUTATION

These levels of amputation are almost always 

treated with the lighter weight endoskeletal prosthesis, given their lightweight properties, ease of 

fabrication, and postfabrication adjustability. Knee 

components, feet, and alignment are selected to enhance stability and ease of use. Energy required to 

ambulate with these prostheses is 200% times greater 

than normal.16

Hip Disarticulation Socket Design

Originally developed as the Canadian hip disarticulation prosthesis, this prosthesis incorporates both the 

sound and affected side iliac crest contours into the 

socket design. The socket is intended to bear weight 

on the ischium; however, this weight is shared along 

the anterior torso and the posterior gluteal muscle area 

by sloped anterior and posterior walls lifting the torso 

off the ischium to some degree. Primary suspension 

is provided over the affected side ilium. The contralateral ilium provides only minimal support during 

swing phase. Trimlines extend proximally above the 

ilium, and socket contours accentuate the narrower 

waist groove. During swing phase, the weight of 

the prosthesis is borne here. One socket feature that 

facilitates donning and doffing the prosthesis is a flexible lamination located about the posterior midline. 

Flexibility at this location allows the patient to spread 

the rigid, supporting socket open and wrap it around 

the pelvis. Because of the asymmetric contours of the 

pelvis and the intimate socket fit, rotational stability 

of the socket is good. 

A two-piece socket design was developed at the 

University of California, Los Angeles.17 By splitting 

the socket into two parts and fastening them together 

with a crisscrossing strap design posteriorly, this 

design can provide support and suspension during 

stance, as well as swing phase. During midstance, as 

the weight is borne into the socket, the strap system 

draws the inferior aspect of the sound side portion of 

the socket medially. This holds the patient firmly into 

the prosthetic socket while easing up on the iliac crest. 

During swing phase, the prosthesis attempts to move 

inferiorly on the patient’s pelvis. The contralateral 

portion of the socket provides increased pressure over 

the iliac crest, increasing swing phase stability of the 

socket on the patient. This floating sound side design 

is more comfortable for the patient and is easier to 

fabricate for the prosthetist.

Transpelvic Socket Design

Transpelvic amputation is completed at the junction 

of the sacrum and ilium. The primary consideration 

with the transpelvic socket design is that the patient’s 

weight is borne against the socket wall through soft tissues alone. The transpelvic socket extends to the body 

midline and encompasses the lower rib cage bilaterally, 

with the abdomen and the pelvis on the sound side. 

The socket may extend superiorly as high as the tenth 

rib. Inferiorly, the socket must clear the sound side 

limb and genitalia. On the sound side, the trimlines 

are brought inferior just proximal to the trochanter. 

In general, by encompassing more of the rib cage, the 

stability of the socket on the lower trunk is improved. 

There is generally less rotation of the pelvis and the 

socket because no ischial tuberosity exists that forms 

a fulcrum, as in the case of hip disarticulation. Raising the trimlines also increases the available surface 

area over which weight can be borne. The concave 

contour of the socket matches the convex contour of 

the residual limb. The socket wall generates forces oriented obliquely upward on soft tissue and the sound 

side pelvis.
576

Care of the Combat Amputee

Hip and Knee Joint Considerations

There are numerous endoskeletal components 

available to be used in the hip disarticulation prosthesis. Hip joints are single axis requiring an extension 

stop and extension assist. Single axis or polycentric 

knee units can be incorporated into the prosthetic 

design. A polycentric knee with a mechanical stance 

phase lock with extension aid in reaching full knee 

extension is a good choice for this prosthesis. The 

polycentric feature shortens the shank during swing 

phase, making it easier to clear the ground. In the 

polycentric design, the knee joint center resides more 

proximally than a single axis design. This provides 

the patient with an added biomechanical advantage 

in both initiating and resisting flexion because of 

the proximity of the instantaneous center of rotation to the anatomical hip joint center. Also ideal is 

a microprocessor knee. Both designs offer excellent 

stance phase stability. Careful consideration of overall prosthetic weight versus function and stability is 

necessary for optimal outcome.

Hip Disarticulation/Transpelvic Biomechanics 

and Alignment

The hip joint is placed far anterior on the socket 

relative to the normal hip joint location. The knee 

axis also falls considerably posterior to the anatomical knee. A combination of these two joint positions creates a significant knee extension moment. 

The knee hyperextends until an extension stop is 

contacted. This particular alignment provides an 

extremely secure knee, making it difficult for the 

knee to buckle inadvertently. If the center of gravity 

remains within boundaries formed by vertical reference lines placed at both the hip and knee centers, 

the hip and knee joints will remain stable. If the patient’s center of gravity falls behind the posterior line 

located at the knee joint, this creates a knee flexion 

moment and causes the knee to buckle. If the center 

of gravity falls anterior to the hip joint, this creates 

a hip flexion moment and causes the socket to flex 

at the hip joint.

Alignment

A line projected through the hip joint axis and the 

knee joint axis should intersect with the ground approximately 1ö inches posterior to the heel. The theoretical 

weight line begins at the point in the socket 1 inch 

anterior to the ischial tuberosity. It extends vertically to 

the ground passing ö inch anterior to the knee center 

and intersects with the ground at approximately 7/16 of 

an inch anterior to the center of the prosthetic foot. In 

proper coronal plane alignment, one proposed method 

places the hip joint 10 mm lateral to the lateral ÷ mark. 

In the transverse plane, the hip joint should be externally 

rotated 5 degrees to 10 degrees for a more anatomical 

swing phase action of the thigh and shank. The length 

of the prosthesis should be approximately ö inch shorter 

than the sound side to provide adequate clearance of 

the toe during gait.

Gait

The gait pattern for these individuals to properly 

ambulate requires that the patient use atypical motions to generate appropriate forces to advance the 

prosthetic limb. These forces include vaulting on the 

sound side, hip hiking on the prosthetic side during 

swing, and posterior tilting of the pelvis at late stance 

on the prosthetic side to initiate hip and knee flexion. 

As patients become more proficient, these motions are 

minimized, but nevertheless are present during gait. 

The gait of these individuals requires a great deal of 

energy expenditure to facilitate balance and advance 

the prosthetic limb. The energy costs can be twice that 

of normal human gait. Comfort is another issue for 

these individuals. Whether sitting, standing, or ambulating, it is important that socket contours and trimlines 

provide the greatest comfort to the patient. 

COMORBIDITIES AFFECTING THE REHABILITATION PRESCRIPTION

Multiple Limb Loss

Bilateral lower extremity amputations require 

special consideration related to prosthetic design and 

alignment. Socket design remains the same; however, 

accommodative gel liners are recommended because 

the patient is not able to shift weight to a sound side 

foot. This is particularly important for the more bony 

transtibial amputation. Torsion adaptors reduce anatomical knee and hip joint torque and shear at the 

skin/socket interface. Any additional components 

placed as close to the sockets as possible reduce the 

perceived weight of the prostheses. Constructing the 

prosthesis as light in weight as possible helps the 

patient keep energy costs down. An alignment that 

moves the feet slightly more lateral or increasing 

toe-out gives a wider base of support. This decreases 

the coronal plane forces placed on the limb during 
577

Lower Limb Prosthetics

weight bearing. A wider base also results in additional stability. Foot selection can influence prosthetic 

knee stability and ground conformance. For bilateral 

transfemoral patients, articulated feet—or those with 

a softer heel or hind foot keel—move the weight 

line anterior to the knee joint more quickly, stabilizing the knee in early stance. Regardless of the level 

of amputations, identical foot components should 

be used for consistent gait mechanics. The use of 

stubby prostheses, sockets without knees, keeps the 

patient’s center of gravity low to ground and helps 

the patient gain balance, strength, and confidence 

early on. Incremental height increases and the addition of knees, added one at a time if necessary, bring 

the patient to, or near to, preinjury height. If only one 

knee at a time is added, leaving the other side with 

a straight pylon, then the longer limb or the limb 

with better muscle control is fitted with a knee first. 

Progress requires commitment by the patient and an 

intense physical therapy regimen. To facilitate good 

posture and a well-placed base of support, feet may 

be articulated and perhaps mounted backward. Foot 

blocks with rocker design are also common. Knees 

for the bilateral transfemoral patient should offer 

good stability. Polycentric design, fluid control, and 

microprocessor control all offer stability and can be 

aligned for maximal safety. The polycentric knee 

shortens through swing phase, a useful feature, when 

the opposite limb is a transtibial amputation. Marking 

liners, socks, valves, etc, as right and left is helpful 

when donning.

When upper limb amputations are also present, the 

most pressing issue is one of independent donning. 

Donning devices can be designed for individual needs, 

and easy suspension options (eg, gel liners with locking pins or sealing liners) can be used.

Bone

Heterotopic ossification is a concern for amputations resulting from blast injuries.18 Socket modifications, a soft gel interface, and/or socket replacement 

help to manage and accommodate the changing limb 

contours. External fixators on the amputated side or the 

contralateral limb do not preclude prosthetic fitting. 

The prosthetic management goal is to get the patient 

ambulatory quickly. Sockets can be modified to distribute weight away from the fixator, and/or cutouts can 

be made around the device. Prosthetic knees offering 

maximum stability will provide safer ambulation.

Soft Tissue 

Shrapnel fragments, foreign bodies, and other detritus may migrate until they are just under the skin 

surface. Often they are expelled. This process requires 

close monitoring and ongoing socket modification. 

Neuromas are treated prosthetically in much the same 

way because they are painful and limit prosthetic 

use.

Skin

Grafted skin or excessive scar tissue can be a challenge, and a comfortable fitting socket can be difficult 

to achieve. Liners made of softer rather than firmer 

gel protect fragile skin. Alignment intended to reduce 

forces on the limb is also helpful. Pain as a result of 

fragments in the soft tissue and under the skin may 

be managed with soft gel liners as well. Occasionally, 

shrapnel can work its way through the skin.

Joint Function and Condition

Limited range of motion, contractures, and/or loss 

of muscle function require alignments and component selections that accommodate these situations. 

Fall prevention and socket comfort are the foremost 

considerations. If alignment alone does not produce 

the desired results, then components providing either 

additional range of motion (eg, articulated feet) or 

knee components with added stance control can be 

selected. 

Blindness

Donning is a consideration when the patient is 

blind. Tactile markers on the prosthesis and its components help the patient to orient the gel liner, socks, 

or belt for proper donning. Ratcheted locking pins 

emit audible clicks as they engage into a shuttle lock 

confirming positive suspension.

THE PROSTHETIC REHABILITATIVE PROCESS

The prosthetic phases (preprosthetic, initial prosthetic, basic prosthetic, and advanced prosthetic) mirror the timelines set by the Physical Therapy Service 

for treatment protocols for amputees. 

Phase I: Preprosthetic (Weeks 1–4)

Care typically includes prosthetic plan formulation, 

patient education, wound management, and volume 
578

Care of the Combat Amputee

control through the use of shrinker socks, silicone or 

equal liners, or elastic wraps.

Phase II: Initial Prosthetic (Weeks 2–10)

Care typically includes the provision of a prosthetic 

limb with multiple replacement sockets as warranted. 

The use of early postoperative prosthesis (EPOP) is 

common at military MTFs. EPOPs comprise customdesigned sockets fabricated from ThermoLyn PETG 

(Otto Bock HealthCare, Minneapolis, Minn) material attached to advanced prosthetic components. 

The components may consist of a C-Leg (Otto Bock 

HealthCare, Minneapolis, Minn) microprocessor knee 

unit for knee disarticulation level and higher, and a 

dynamic response or stored energy foot. EPOP sockets 

are replaced at an extraordinary rate. Standard practice is to maintain an appropriately fitting socket at 

all times. As service members progress through the 

rehabilitation process, their limbs undergo changes 

in size and shape. These changes are atypical when 

compared with the geriatric dysvacular amputee, 

in which shape and size reductions are typically 

uniform. For the service member who has sustained 

a blast injury, limb size and shape reduction are not 

uniform, in particular for those with heterotopic ossification.

CAD/CAM is an excellent tool to use in an acute 

care setting for a variety of reasons. It does not replace 

the skill and experience of the prosthetist; rather, it 

enhances prosthetic services by decreasing delivery 

times and increasing efficiency. It provides a way to 

objectively document limb morphology and volume 

and to track limb change. Residual limb shape capture 

is accomplished by noncontact scanners, digitized 

passive casts, measurements, or photos dependent 

on the particular CAD system used. The software to 

manipulate the shapes is intuitive and relatively easy 

to use. Output is to a milling machine for fabrication 

of a positive model. Standard fabrication procedures 

of the prosthetic socket are followed at that point.

Use of microprocessor knee units as first-fit systems 

are not uniform at all military MTFs. Safety is paramount, and the facilities rely on a team approach for 

prescription rationale of such devices. In general, all 

of the military MTFs are prescribing microprocessor 

units for those with bilateral lower extremity amputation and/or those with lower and upper extremity 

amputations. 

Phase III: Basic Prosthetic (Weeks 11–20)

Care includes continued socket replacements, also 

the introduction of dynamic response or stored energy 

prosthetic feet as indicated. Progression to more dynamic feet should coincide with the patient’s progress 

in physical therapy. Sockets may be fabricated from 

definitive materials (eg, carbon graphite and acrylic 

resin) as indicated.

Phase IV: Advanced Prosthetic (Months 3–6)

Care includes the design and delivery of specialty 

prostheses to include, but are not limited to, sport use 

prostheses. These prosthetic limbs should be fabricated 

from definitive materials.

ACTIVE DUTY MILITARY, LOWER LIMB PROSTHETIC PROTOCOLS

Recommendations for Daily Use Prosthesis

1. Sockets 

a. ThermoLyn or its equal until ready for 

definitive socket. 

b. Definitive socket materials (eg, carbon 

graphite and acrylic or epoxy resin) 

prior to high-level sporting/recreational 

activities.

c. Definitive socket for transfemoral amputees: flexible socket with rigid frame.

d. Hip disarticulation: start with socket; add 

custom liner/suspension system, depending on individual limbs; consider using 

three-dimensional modeling to help guide 

design as indicated, especially with secondary problems (eg, heterotopic ossification).

2. Suspension

a. Suction suspension for all amputees 

unless meets criteria for pin lock or lanyard.

b. Pin lock or lanyard for amputees with anticipated large-volume changes or when 

suction is contraindicated.

c. Auxiliary suspension added as needed 

for higher level activities.

3. Feet

 In general, limit three different feet for each 

amputee during the first year. Integrate gait 

lab to augment clinical decisions.

a. Transtibial

i. Use soft, multiaxial, easy, rollover, and 

shock-absorbing properties to promote early weight bearing and weight 
579

Lower Limb Prosthetics

shifting (eg, Talux [Ossur Americas, 

Aliso Viejo, Calif] or TruStep [College 

Park Industries, Fraser, Mich]).

ii. Progress to a higher energy returning 

foot, such as Ceterus (Ossur Americas, 

Aliso Viejo, Calif), Renegade (Freedom 

Innovations, Irvine, Calif), Re-Flex 

VSP (Ossur Americas, Aliso Viejo, Calif), Modular III (Ossur Americas, Aliso Viejo, Calif), or low-profile equivalents. Can have a second, high-energy 

returning foot if properties of new 

foot are different from existing foot.

iii. Consider microprocessor foot or other 

advanced power prosthesis, depending on individual goals and activity 

levels after they have mastered above 

feet for a minimum of 3 months or as 

otherwise decided by the rehabilitation team. 

b. Transfemoral

 Same as transtibial level.

4. Specialty Prosthetic Limbs

 Lower extremity amputees may also receive 

a water/swimming leg and running leg.

a. The water leg may be used for bathing, as 

well as for other water activities. Modifications to be used for swimming may 

be added if the amputee expresses such 

interest.

b. Running-specific legs will be prescribed 

when clinically appropriate for amputees 

who express the desire and motivation to 

return to more frequent and longer distance running than that accommodated 

through the use of the dynamic response 

foot. The primary goal will be to help the 

service member return to Army physical fitness standards. Providers must be 

aware that conditions such as osteoporosis, nerve injury, fractures, etc, might 

be contraindicated to aggressive running 

with a running specialty leg. Use of a 

dual-energy X-ray absorptiometry scan 

(or DEXA scan) is warranted to determine 

osteopenia. Furthermore, appropriate 

training with an experienced therapist is 

essential to successful and safe running on 

a running specialty leg. All running legs 

will be fabricated with a definite socket. 

Guidance is to start with a distance foot 

(eg, FlexRun [Ossur Americas, Aliso Viejo, 

Calif] or Cheetah [Ossur Americas, Aliso 

Viejo, Calif]) and progress to a sprint foot 

if the patient demonstrates proficiency.

5. Knees

 One microprocessor; need to have gait assessment first with the C-Leg, then gait analysis 

after 4 weeks of training with the RHEO KNEE 

(Ossur Americas, Aliso Viejo, Calif) and/or the 

POWER KNEE (Ossur Americas, Aliso Viejo, 

Calif).

SUMMARY

This chapter focused on the prosthetist as a member of a comprehensive, clinical rehabilitation team 

at military MTFs. Also reviewed were the unique role 

of prosthetists during combat deployments, as well 

as the lower limb prosthetic technology provided to 

combat-injured service members who sustained an 

amputation. The prosthetist is an integral part of the 

multidisciplinary rehabilitation team, often working 

in unison with other team members, yet also taking 

center stage during formulation of the prosthetic 

limb prescription. During the global war on terror, 

prosthetists played a unique role in worldwide deployments. They provided strategic and operational 

knowledge to allied governments in the areas of 

prosthetic clinical education, clinical evaluation, 

and prosthetic fabrication techniques. The increasing complexity involved in prosthetics technology 

and the development of unique materials, computer 

programs, and fabrication techniques applicability 

require the specialized knowledge of the prosthetist. 

This chapter provided an overview of lower limb 

prosthetic technologies, ranging from classification 

of prosthetic feet, knee units, socket design, socket 

interfaces, and components to how these technologies 

related to the amputation levels of the lower limb. 

The prosthetic rehabilitation process used at military 

MTFs and the comorbidities affecting the rehabilitation prescription were also examined.

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