These data indicate that despite advances in new pros-thetic components, health care pro-viders still face challenges in fitting patients with optimal prosthetic components and in rehabi
Trang 1Extremity Prostheses
Abstract
Prosthetic components for both transtibial and transfemoral amputations are available for patients of every level of ambulation Most current suspension systems, knees, foot/ankle assemblies, and shock absorbers use endoskeletal construction that emphasizes total contact and weight distribution between bony structures and soft tissues Different components offer varying benefits to energy expenditure, activity level, balance, and proprioception Less dynamic ambulators may use fixed-cadence knees and non–dynamic response feet; higher functioning walkers benefit from dynamic response feet and variable-cadence knees In addition, specific considerations must be kept in mind when fitting
a patient with peripheral vascular disease or diabetes
With the advent of new materi-als, designs, and technologic advances, the field of lower extrem-ity prostheses has expanded dramat-ically Prosthetic components have a significant impact on functional per-formance The choice of compo-nents varies depending on a patient’s functional level; this is especially true regarding the specific needs of patients with amputation secondary
to peripheral vascular disease or dia-betes These critical needs include protecting the sound limb, consider-ing abnormal and excessive forces
on the residual limb, and factoring in the metabolic costs of ambulation
Understanding lower extremity prosthetic componentry and how ap-plication varies is important Appli-cation is based on the level of ampu-tation in the context of the expected functional level of the user A classi-fication scale can assist in determin-ing appropriate components corre-sponding to each functional level
Etiology and Incidence
of Amputation
In the United States, lower extrem-ity amputation is not uncommon; approximately 110,000 people un-dergo some level of lower limb am-putation surgery each year.1Of those amputations, most are a result of disease (70%), followed by trauma (22%) and congenital etiology and tumor (4% each).1 Approximately 54,000 amputations secondary to di-abetes are performed annually in the United States.2 Further, more than half of all lower limb amputations occur in individuals with diabetes; below-knee or distal amputations are more common in this population than transfemoral amputations Be-tween 9% and 20% of patients with diabetes who have had an amputa-tion undergo a second amputaamputa-tion ipsilaterally or a new amputation contralaterally within 12 months of the first amputation.2Thirty percent
Karen Friel, PT, DHS
Dr Friel is Associate Professor and
Chair, Department of Physical Therapy,
New York Institute of Technology, Old
Westbury, NY.
Neither Dr Friel nor the department with
which she is affiliated has received
any-thing of value from or owns stock in a
commercial company or institution
re-lated directly or indirectly to the subject
of this article.
Reprint requests: Dr Friel, New York
Institute of Technology, Room 501,
Northern Boulevard, Old Westbury, NY
11568.
J Am Acad Orthop Surg
2005;13:326-335
Copyright 2005 by the American
Academy of Orthopaedic Surgeons.
Trang 2to 50% of patients with amputations
performed as a result of diabetes will
lose the contralateral limb within 3
to 5 years after the first
amputa-tion.1,2Therefore, preserving the
in-tact limb is of paramount
impor-tance and is a significant factor in
the prosthetic management of the
amputated limb These data indicate
that despite advances in new
pros-thetic components, health care
pro-viders still face challenges in fitting
patients with optimal prosthetic
components and in rehabilitating
them to a level of functional
inde-pendence
Although 85% of persons treated
with amputation for a poorly
vascu-larized lower limb are fitted with a
prosthesis, only 5% use the limb for
more than half of their waking
hours;3furthermore, within 5 years,
only 31% are still using the
prosthe-sis.4In addition, only 26% of patients
are walking outdoors 2 years after
amputation for an insufficently
vas-cularized or compromised limb.4
Fi-nally, the 5-year death rate for
pa-tients with amputation who are
fitted with a prosthesis is 48%,
whereas the rate is 90% for patients
not fitted with a prosthesis.4It is not
known whether these patients are ill
initially or whether a more sedentary lifestyle leads to their decline Fitting
a patient with prosthetic compo-nents that enhance ambulation and increase functional independence is therefore extremely important
Functional Classification Scale
A guideline useful in the selection
of prosthetic components is the K-rating scale of the US Department
of Health and Human Services’ Cen-ter for Medicare and Medicaid Ser-vices The K-rating scale classifies individuals with amputation into five functional categories Although primarily used for reimbursement considerations, the scale can provide
a context for the prescription of pros-thetic components, particularly prosthetic knees and feet For in-stance, a knee with a swing rate con-trol mechanism is appropriate for K-1 and K-2 levels, whereas a knee that permits a variable cadence swing rate mechanism would be ap-propriate for K-3 and K-4 levels5,6
(Table 1)
To assist clinicians in proper clas-sification, the Amputee Mobility Predictor has been developed to
determine functional ambulation ability following amputation This simple test, which objectively cate-gorizes patients into an appropriate K-level,8has proved to be reliable and valid It assesses sitting and standing balance, quality of ambulation, and ability to perform limited walking skills
Biomechanics of Gait Related to Amputation and Prosthetic Design
Walking is a highly efficient activity, with forces absorbed and dissipated throughout the gait cycle These forces include gravity, inertia, and muscular action Muscles transform potential energy into kinetic energy through viscoelastic elements and
by contracting both concentrically and eccentrically throughout the gait cycle After amputation, pa-tients lose many of the muscular forces that function during walking; they must rely instead on a variety
of bumpers, springs, and hydraulic/ pneumatic mechanisms in an at-tempt to simulate a normal gait pat-tern and enhance energy efficiency Many studies have investigated the energy expenditure and
metabol-The K-Classification System for Functional Ambulation 5,7
K Level
Description Nonambulator;
requires assist with transfers
Household ambulator
Limited community ambulation
Unlimited community ambulation
Exceeds basic use
Gait activity Nonambulance Fixed cadence;
level surfaces
Fixed cadence;
negotiates minor community barriers (eg, curbs, ramps, stairs)
Variable cadence;
negotiates environment freely;
has use beyond simple gait
Exhibits high-energy activity;
high-impact activity Recommended
feet
Not a pros-thesis candi-date
Non–dynamic response foot
Non–dynamic response foot
Dynamic response foot; energy-storing foot
Dynamic response foot;
energy-storing foot
Recommended
knees
Not a pros-thesis candi-date
Fixed-cadence swing rate
Fixed-cadence swing rate
Variable-cadence swing rate;
computer-assisted
Variable-cadence swing rate; computer-assisted
Table 1
Trang 3ic factors related to gait patterns
af-ter amputation Results of these
studies show that the cadence
fol-lowing amputation is slower (and
the metabolic output higher)
com-pared with the cadence of patients
without amputation.1,9These
differ-ences are related to factors such as
loss of kinetic energy, changes in
muscle symmetry, and loss of
coor-dination and balance in amputees,
not to mass of the prosthetic
compo-nents.9,10The weight of most
pros-theses is approximately equal to
30% of the weight of a normal
low-er limb.11Therefore, the weight of
various components should not be a
concern in prosthetic prescription;
rather, matching components to the
expected functional level of the user
should be paramount
During normal gait, the
muscu-loskeletal structures of the lower
ex-tremity help to attenuate impact
forces This is accomplished through
mechanisms that include knee
flex-ion from heel strike to midstance
during loading response, the plantar
fat pad at initial contact, foot
prona-tion during foot flat, and eccentric
loading of the muscles themselves
After amputation, however, many of
these mechanisms are lost, with the
prosthesis able to accommodate
only partially by using shock
absorb-ers and pylons
One study investigated the effect
of pylon material on ground reaction
forces during gait with a transtibial
prosthesis Results indicated that,
compared with prostheses with
py-lons made of aluminum, prostheses
with flexible pylons composed of
ny-lon had force patterns that more
closely mimic those of the
nonam-putated limbs Additionally, with
the flexible pylons, a smoother
tran-sition occurred between the braking
phase of gait at initial contact and
the propulsive phases of gait.12
Postema et al13suggested that the
degree of dorsiflexion allowed by the
prosthetic ankle at the end of stance
phase influences balance control
dur-ing gait They proposed that
creased dorsiflexion causes an in-crease in knee flexion torque, thus decreasing knee stability Conversely, decreasing the amount of available dorsiflexion decreases the flexor mo-ment to the knee, providing the user with added knee extension stability
at late stance Therefore, patients with balance difficulties may feel more secure with an ankle unit that allows for less dorsiflexion.11
Others have proposed, however, that mechanical stability (ie, balance control) differs from proprioceptive control.14 Although the more rigid foot may provide increased mechan-ical stability, active users interpret good balance as having a wider range
of balance options on uneven ter-rain, as can be accomplished with the more flexible design
Suspension
All of the various types of suspen-sion mechanisms are designed to hold the prosthesis securely onto the residual limb, prevent pistoning, and minimize breakdown
Traditional Suspension Systems
The supracondylar cuff was an ex-tremely popular means of suspen-sion for the transtibial prosthesis in the 1970s and 1980s However, this type of suspension should not be used for the individual with vascular compromise15 because, to hold the prosthesis on the patient, the cuff mechanism relies on constriction proximal to the knee.16 Although still used today, the supracondylar cuff is being replaced by more cos-metic, secure means of suspension
It is now most appropriate for the less active user and limited ambula-tor (K-1 level)
The suspension sleeve is another option for suspension of the transtib-ial prosthesis A sleeve made of neo-prene, latex, or elastomer materials
is fitted onto the upper aspect of the prosthesis The other end is rolled above the prosthesis onto the
pa-tient’s skin, adhering to the skin through negative pressure Sleeves are simple to use, inexpensive,
fair-ly cosmetic, and appropriate for any level of user The sleeve may be dif-ficult to don, however, for patients with hand weakness or poor dexter-ity, as is commonly seen in individ-uals with diabetes.15
The suprapatellar/supracondylar suspension system uses the bony structures of the knee to suspend the transtibial prosthesis The medial condyle of the femur and the supra-patellar aspect of the knee form bony locks against slippage of the prosthesis during the swing phase of gait and other activities when pis-toning may occur This suspension system may be used when there is
an exceedingly short residual limb or when additional knee stability is re-quired In some circumstances, aux-iliary suspension, such as a sleeve, may also be used with this design.16
Suspension around the waist can
be used both as the primary and the auxiliary means of suspension The Silesian belt and elastic suspension are composed of a strap or sleeve that attaches to the proximal end of the prosthesis and ascends to encircle the patient’s waist These straps may be composed of neoprene (called a total elastic suspension system) or of cotton.15 Neither of these methods helps to control the hip in the presence of instability
Contemporary Suspension Systems
The shuttle lock system, also known as the pin-and-lock system, continues to gain in popularity for both the transtibial and transfem-oral prostheses This system pro-vides cushioning, torque control, and shock absorption because the outer surface of the liner acts as an interface between the skin and the socket.17 This interface dissipates forces that would affect the skin in a total suction situation , which does not use a liner or interface between the residual limb and the socket
Trang 4The shuttle lock system uses a gel
or silicone liner with a locking pin on
the bottom, which is rolled onto the
skin The pin is then inserted into a
shuttle lock inside the socket (Fig 1)
This system helps to provide for a
total-contact fit, which minimizes
distal edema, distributes pressure
over the entire limb, and prevents
movement of the limb against the
socket The coefficient of friction
be-tween the stump-liner interface and
the liner-socket interface needs to be
high to minimize any movement
be-tween the surfaces The soft, flexible
gel liners can accomplish this.16,18In
fact, indications for these systems
in-clude patients whose skin is sensitive
to shear forces and uncontrolled
pis-toning in the socket.15Because of the
potential for skin breakdown and
sub-sequent infection, pistoning is a
threat to further loss of limb to an
amputee with vascular disease or
di-abetes Prosthetic socks can be added
to the shuttle lock system in the
event of limb girth fluctuations
The shuttle lock system is
appro-priate for all levels of users because
of the security afforded by this
sus-pension method as well as the
im-proved cosmesis and ease of
don-ning When the transfemoral
residual limb is long, there may be a
difference between the involved
limb and the sound limb in the knee
centers of rotation when the locking
hardware is placed inside the
pros-thesis.15The shuttle lock system is
an excellent alternative for users
who have difficulty donning the full
suction socket.19
Suction is a popular means of
sus-pension, particularly for the patient
with a transfemoral amputation It
provides for an intimate fit between
the limb and the socket, which
en-hances proprioception and muscular
control of the prosthesis.20Comfort
level is also enhanced because
auxil-iary suspension, such as a belt, waist
strap, or thigh corset, is not needed,
although an additional means of
sus-pension may be used when a higher
activity level requires it The socket
is held on through negative pressure and surface tension Because the pa-tient must stand to ensure that the limb is fully entered into the socket, patients with poor balance or prob-lems with manual dexterity may have difficulty donning this type of socket.15,19Total suction is not often used with the transtibial prosthesis because the bony characteristics of the lower limb make it difficult to obtain a tight seal
Prosthesis Construction
Traditional Construction
In the past, prostheses were fabri-cated in an exoskeletal fashion: the strength of the prosthesis derived from the solid outer walls Exoskel-etal prostheses were composed of a solid piece of wood or rigid polyure-thane covered with plastic laminate and fashioned into the shape of a leg
The components were embedded or built-in and thus were not inter-changeable.21 Unless an external frame was used, the entire prosthesis needed to be refabricated to change
componentry In addition, these prostheses were heavy and bulky Exoskeletal prostheses are not
usual-ly fabricated today unless a user spe-cifically requests such construction; some long-term prosthesis users have become accustomed to the exoskeletal design and opt not to change
Contemporary Construction
Today, most prostheses are of an endoskeletal design: components are located inside the prosthesis The strength of the prosthesis comes from the pylon—usually made of lightweight nylon, aluminum, or carbon/graphite—which is enclosed
in a cosmetic foam covering Bene-fits of the endoskeletal design are that components of a standardized design are completely interchange-able, the prosthesis is easily repaired, and the design is lighter and more cosmetic than the exoskeletal de-sign.21However, these prostheses are subject to external moisture and de-bris
Figure 1
A, Liner with attached pin for shuttle lock mechanism B, Shuttle lock mechanism in
clear check socket
Trang 5Transtibial Prostheses
The prosthetic socket has several
important functions It is designed
to accommodate the residual limb,
allow for weight bearing, distribute
forces, and provide total contact to
prevent distal pooling of fluid
with-in the residual limb The sockets are
custom-fitted and have specific areas
of weight bearing incorporated into
their design
Traditional Socket Design
Since the 1950s, the most
com-mon socket design has been patellar
tendon–bearing (PTB), still
consid-ered the standard today.16The design
is based on increasing
weight-bearing pressures in areas that are
pressure tolerant These areas
in-clude, but are not restricted to, the
patellar tendon, medial and lateral
tibial flares, and
gastrocnemius-soleus complex Conversely, the
socket is designed to decrease
pres-sures in areas that are
pressure-sensitive, such as the proximal and
distal fibula and the tibial crest
Contemporary Socket
Design
With the advent of new materials
and fabrication principles, an
in-creasingly common adjunct to the
PTB design is the use of hydrostatic
loading Hydrostatic loading
stabiliz-es the bony anatomy within the soft
tissues through the use of
compres-sion and elongation of the tissues
during casting for the socket The forces of weight bearing are distrib-uted through a greater surface area, thus decreasing pressures to any one area This technique is also known
as total-surface bearing; the force is evenly distributed throughout the entire limb.16This distribution may help to prevent breakdown of the skin and enhance comfort for the user
Foot/Ankle Assembly
Advances in the design of pros-thetic feet are occurring at a
dramat-ic rate, and new feet are introduced
to the market regularly Numerous factors must be considered when fit-ting a prosthetic foot (Table 2) The most notable factor related to the be-havior of the prosthetic foot is the presence or absence of a joint that al-lows for plantar flexion This factor
is significant because the ability to have both plantar flexion and dorsi-flexion range of motion forms the basis for the classification system of articulated and nonarticulated ankle designs.24Many of the newer designs have an integrated pylon/ankle/foot mechanism, which allows for both dorsiflexion and energy return to the user
It should be noted that there is no difference between the prosthetic feet used for transtibial prostheses and those used for transfemoral pros-theses The choice of foot depends
on the patient’s mobility, stability,
and functional use and control of the prosthesis
Non–Dynamic Response Feet
The solid ankle cushioned heel (SACH) foot (Sheck and Siress, Chi-cago, IL) (Fig 2) has been extremely popular since its inception in the 1950s and is very economical com-pared with other prosthetic feet The SACH foot uses compressible mate-rial in the heel to simulate plantar flexion at heelstrike It incorporates
a rigid, wooden keel that is unable to dorsiflex through the midstance phase of gait Because of this, during midstance, the center of mass on the prosthetic side is comparatively higher than on the nonamputated side This inequity leads to increased loads placed on the sound side during the weight acceptance phase of gait;25
instead of the normally smooth tran-sition provided by adequate dorsiflex-ion, the user tends to “fall onto” the sound side during weight transfer Studies have shown that ambulating with the SACH foot produces the greatest ground reaction forces on the sound side compared with both dy-namic response feet and other non– dynamic response feet.26,27 This means that the SACH foot is not op-timal at protecting the sound limb from excessive forces, which is a cern because of the high rate of con-tralateral amputation in the popula-tion with diabetes.2 However, the
Key Concepts for Foot Prescription
Ability to adequately absorb impact
forces
Ability to accommodate to uneven
terrain
Avoidance of the prosthesis being
too heavy distally22
Dynamic response of the foot (ie,
ability to return energy to the user
during push-off23)
Maintenance of proper balance
Table 2 Figure 2
Solid ankle cushioned heel (SACH) foot
Trang 6SACH foot is still appropriate for the
limited ambulator, the K-1 level user,
and the individual in the beginning
stages of rehabilitation One major
ad-vantage of using this type of
pros-thetic foot is that the rigid keel may
provide more balance than would a
dynamic response foot.6
Feet specifically designed for the
geriatric patient have keels
com-posed of flexible polypropylene This
design replicates a more pronated
position of the foot, with more of the
foot in contact with the ground This
factor provides for added stability
and a softer rollover, thus
minimiz-ing forces to the residual limb.5The
Dycor ADL uniaxial design (Dycor,
Missouri City, TX) is currently
cat-egorized for the K-2 level user
Dynamic Response Feet
Currently, the more responsive
prosthetic feet are generally reserved
for the more active ambulators
These feet are available in both
artic-ulated and nonarticartic-ulated designs
The dynamic response foot uses a
keel that deforms under pressure but
returns to its original shape when
the load is removed The keel acts as
a spring that on return to its original
shape returns energy to the user,
thereby assisting push-off The
flex-ibility of the keel allows for
dorsi-flexion.6The increased dorsiflexion
afforded by the dynamic response
foot allows for a longer midstance
time in the gait cycle Hafner et al28
noted that increased time spent in
midstance may increase the
percep-tion of stability, compared with the
rapid heel rise and toe-only support
in the non–dynamic response foot
Hafner et al28 compared patient
perception of energy-storing feet
ver-sus their perception of conventional
prosthetic feet using biomechanical
gait analysis Results indicated that,
despite advantages perceived by
us-ers when ambulating with a
dynam-ic response foot, supportive
biome-chanical data were inconsistent The
advantages that users reported when
ambulating at higher velocities with
a dynamic response foot were in-creased gait velocity, inin-creased sta-bility, increased ankle motion, de-creased shock at the hip and knee, and enhanced performance in “high activity” gait (ie, activities requiring increased ankle power and propul-sion).28
The impact that foot selection has
on forces taken through the sound limb also has been investigated Spe-cifically, the Flex-Foot (Össur, Aliso Viejo, CA) (Fig 3) was compared to SACH, Carbon Copy II (Ohio Willow Wood, Mt Sterling, OH), Seattle (Model and Instument Works, Seattle, WA), and Quantum (Hosmer Dor-rance Corp, Campbell, CA) feet The Flex-Foot notably reduced peak ver-tical ground reaction forces to the sound limb compared with the other feet In fact, the other feet on average increased peak forces to the sound limb 17% over normal values The authors therefore hypothesized that the increased dorsiflexion achieved with the Flex-Foot design allows for less of a fall onto the sound limb dur-ing the weight-acceptance phase of gait.26 All of the dynamic response feet are usually prescribed for the K-3
or K-4 level ambulator
Several shock absorbers are avail-able, many of them built into the an-kle mechanism of the foot/anan-kle as-sembly The Reflex Vertical Shock Pylon (VSP) (Össur), is a variation of the Flex-Foot, with the vertical shock absorber built into the ankle mech-anism.5Results of a study by Hsu et
al29indicated that the Reflex VSP al-lowed for improved energy cost and gait efficiency compared with the SACH foot or Flex-Foot Specifically addressing gait parameters, Miller and Childress30found that vertical compliance of the pylon caused little change in gait parameters during nor-mal speeds of walking With the Re-flex VSP system, greater changes were noted in ground reaction forces, vertical trunk displacement, and py-lon compression at faster walking and jogging speeds compared with normal walking speeds The most
re-cent version of this foot is called the Ceterus (Össur) (Fig 4)
Transfemoral Prostheses
The design principles for the trans-femoral socket are similar to those for the transtibial socket Currently, there are three primary designs The plugfit original sockets for transfem-oral prostheses were cylindrical and used the soft tissues of the thigh for weight bearing Today’s sockets, whether the traditional quadrilateral socket or more contemporary ischial containment or flexible sockets, all feature some level of shared weight bearing between the skeleton of the pelvis and the soft tissues of the thigh
Traditional Socket Design
Quadrilateral design sockets first appeared in the 1950s They are so named because each of the four walls of the socket has distinct features to apply forces and distrib-ute pressures Weight bearing is achieved primarily through the is-chial tuberosity and gluteal muscu-lature sitting atop a posterior shelf This socket provides for lateral sta-bilization of the femur to assist with pelvic stability.19
Figure 3
Flex-Foot, an integrated pylon/ankle/ foot
Trang 7Critics have suggested that use of
this socket results in skin irritation
in the ischium and pubis,
tender-ness over the anterior distal femur,
and discomfort from the anterior
wall when sitting, as well as poor
cosmesis and a tendency toward a
Trendelenburg-type gait.31This de-sign is rarely used today
Contemporary Socket Design
The ischial containment socket design, the current standard (Fig 5),
resulted from addressing some of the criticisms of the quadrilateral
sock-et Specifically, certain parameters regarding transfemoral socket fit in-corporate the design principles of the ischial containment socket devel-oped in 1987 by the International Society for Prosthetics and Orthot-ics19(Table 3) This design
emphasiz-es maintaining adequate femoral ad-duction for enhanced pelvic stability and improved gait Improved force distribution and stability are empha-sized by having more of the pelvis housed within the socket rather than sitting on top of the socket, as
in the quadrilateral design.20,31
The flexible above-knee socket (also known as the Icelandic, Scandi-navian, or New York socket), while still employing ischial containment principles, incorporates a flexible in-ner socket supported by a rigid
out-er frame with cut-out sections31(Fig 6) This design minimizes pressures within the socket of contracting muscles and soft tissues All of these socket designs can be used with any type of suspension
Knees
The variable that determines which knee is appropriate for each functional K-level is whether the knee allows for a fixed pendu-lum swing or a variable cadence of
Figure 5
Ischial containment socket Overhead view
Figure 4
Left, Reflex VSP with integrated shock absorption Right, Ceterus with integrated
shock absorption
Design Principles of the Transfemoral Socket19 Maintain normal femoral adduction and narrow-based gait
Enclose the ischial tuberosity and ramus within the socket to create a skeletal lock
Distribute forces along the shaft of the femur
Decrease emphasis on a narrow anterior-posterior diameter Provide total contact Use suction suspension when possible
Table 3
Trang 8swing A fixed-swing rate control
knee is appropriate for K-1 and K-2
level functional ambulators The
unlimited community ambulators,
K-3 and K-4 users, are capable of
us-ing a variable-cadence swus-ing
mech-anism (Table 1) This category of
prosthesis uses both hydraulic and
pneumatic mechanisms to control
the rate of swing.7
Fixed-Cadence Knee
Mechanisms
Conventionally damped
pros-thetic limbs use fixed resistance in
the knee unit to control the
pendu-lum action of the prosthesis This
rate of swing is set by the
prosthet-ist When the cadence of gait
changes, the user must compensate
for the fixed pendulum speed by
us-ing gait deviations to change the rate
of extension or by forcefully
throw-ing the limb forward to ensure that
the foot will be in the correct
loca-tion at heel strike.7 Many of these
knees have a stance lock control so
that the knee will not buckle during
stance This is useful for the patient
who has poor prosthetic control and
balance or for the K-1 and K-2 level
ambulator
Variable-Cadence Knee
Mechanisms
Variable-cadence knees use
pneu-matics or hydraulics to
accommo-date to the user’s walking speed The
range of velocities of swing rate set
into the unit is dependent on the
us-er’s typical level of functioning The
ambulator is free to change walking
speed within that range and still
avoid gait deviations
One option available to the user is
the addition of a stance flexion
com-ponent In normal gait, the stance
knee will flex approximately 15° to
18° as load is transferred onto the
weight-bearing leg This lowering of
the center of mass allows for a
de-creased load on the limb7as well as
a cushioned support with a gradual
weight transfer onto the sound limb.32
Given the propensity for contralateral
limb loss in patients with vascular disease or diabetes, decreasing the loads placed on the sound limb may help to prolong and protect the health
of that limb Stance flexion devices incorporate some degree of flexion during stance They have been devel-oped to decrease load as well as to add stability during gait by lowering the center of mass For the patient with potential proprioceptive difficulties, this could be advantageous for the safety and efficiency of gait In addi-tion, some degree of stance control is favorable for the more active person with a lower limb amputation when put into compromising situations for which additional stability may be necessary.7
A computer-assisted knee mech-anism uses a computer chip im-planted into the hydraulic knee unit
to accommodate to the walking speed of the user This allows for correction and control of the knee continuously throughout the gait cycle—up to 50 times per second with little or no thought required
by the prosthesis user—to ensure proper swing rate and stance con-trol.7 Hence, there is no need to compensate with gait deviations.33
Computer-assisted knees (eg, the C-leg [Otto Bock, Minneapolis, MN] and the Intelligent Knee [Endolite, Centerville, OH]) can assume part of the energy-absorbing functions of the quadriceps and hamstrings nor-mally seen during early and late swing phases of gait11 (Fig 7) Be-cause these knees allow for variable cadence, they would be appropriate only for the high activity−level user—K-3 or K-4 on the K-rating scale The expense of these knees is not warranted for the more limited ambulator who is unable to benefit from its advantages
Datta and Howitt34 compared user satisfaction and overall use when ambulating with a pneumatic swing phase–control knee versus a microprocessor-controlled intelli-gent knee Using a questionnaire for-mat, they found that most users pre-ferred the microprocessor-controlled knee unit In fact, 95% reported walking at different speeds to be “a lot easier” or “easier.” More than 81% said they could walk farther, and 59% found walking on slopes and hills “a lot easier.” An over-whelming 95% felt that walking was more nearly “normal.″34
Figure 6
Left, Flexible above-knee socket Right, Outer socket for flexible system.
Trang 9Studies addressing energy
expen-diture show that at gait velocities
>3.2 km/h, a decrease in energy
ex-penditure of approximately 10%
oc-curred when ambulating with a
mi-croprocessor knee compared with
ambulation using a conventional
knee prosthesis.33,35 A common
re-port of the elderly prosthesis user is
that the leg feels “heavy” or that the
prosthesis is too fatiguing to use A
knee that can markedly decrease
en-ergy expenditure may have
consider-able implications for the overall
ac-tivity level, health, and well-being of
the patient
Summary
Rapid advances in prosthesis
tech-nology have led to an expansion of
prosthetic options for individuals
with transtibial and transfemoral
amputations, regardless of cause of
the amputation These options may
be grouped into classes of
compo-nents, which can then be viewed in
the context of the needs of users with different functional levels Re-gardless of the functional level of the user, contemporary prostheses generally use endoskeletal con-struction, sockets that emphasize total contact, and weight distribu-tion between bony structures and soft tissues Such prostheses also use suspensions that minimize the use of constrictive belts and cuffs proximal to the level of amputation
For individuals expected to be household ambulators or limited community ambulators, tradi-tional, non–dynamic response pros-thetic feet and fixed-cadence knees may be appropriate For individuals who are expected to be unlimited community ambulators, or for those who will place high work or recre-ational demands on their prosthe-ses, contemporary dynamic re-sponse feet and variable-cadence knees should be prescribed
Specific considerations exist for persons with peripheral vascular dis-ease One primary concern is preser-vation of the intact limb, which can
be improved by components that help to lower the center of mass as well as ease weight transfer onto the sound limb Second, skin integrity is equally important and can be aided
by liners composed of gel, silicone,
or similar materials that serve to de-crease shear and dissipate friction forces The physician, therapist, prosthetist, and patient should all be actively engaged in the decision-making process
Acknowledgment
The author wishes to thank Eliza-beth Domholdt, PT, EdD, for her as-sistance with significant revisions of this manuscript
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