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Section 2: Upper Limb
Figure 6
consistency rubber silicone socket with an integrated shoulder saddle provides good suspension
and socket stability. B, The patient, who has quadriplegia, uses a hybrid myoelectric transhumeral
prosthesis with an integrated silicone shoulder saddle.
that feels firmly connected to the user.
This intimate fit will afford optimal
positioning control of the prosthesis
and minimize its perceived weight. In
both body-powered and electronically controlled systems, the socket is the
foundation of the prosthetic system; any
shortcomings will substantially affect
the successful use of the prosthesis. Ineffectual motion should be minimized
so that when the residual limb begins to
move, the prosthesis will move.
The materials used in the construction of a prosthesis are an important
consideration. For example, carbon fiber
and other composite materials provide a
strong and lightweight prosthesis.
Custom-made silicone sockets provide improved comfort for all levels of
upper-limb prostheses users compared
with previous construction materials.
These sockets are made of high consistency rubber (HCR) silicone, which
has several advantages over the rigid
and flexible plastics previously used
for socket construction.4 Because HCR
silicone is very flexible and elastic, it
facilitates greater range of motion as the
material bends and stretches with limb
movement (Figure 6). However, the
Clinical photographs of a patient wearing a shoulder saddle. A, A custom, high
tackiness of HCR silicone can complicate donning, and this should be taken
into consideration.
Patients with transradial amputations who use body-powered control
will often benefit from flexible hinges
because they allow the amputee to retain physiologic forearm rotation. When
self-suspension is desired, supracondylar sockets such as those typically
used for myoelectric control, and to a
lesser extent, for body-powered control,
are generally best donned by pushing
the residual limb into the socket. The
Northwestern University self-suspending socket5 offers particular advantages
for bilateral transradial fittings in which
supracondylar suspension is desired
because it tends to offer good range of
motion at the elbow and is easily donned
by pushing in. The Northwestern socket
can be modified with a cutout over the
olecranon, which reduces heat buildup
and improves appearance, especially
when the elbow is extended.6
Socket designs that require the limb
to be pulled in are generally avoided because of the obvious difficulties
presented by bilateral upper limb loss.
However, in rare instances when pulling
in is considered necessary, the use of a
nylon donning bag has proved an effective tool and can be used independently
by some patients.
The socket for a transhumeral prosthesis should provide for close coupling
of the residual limb and the prosthesis
to maximize prosthetic function. Because the ideal socket design should
cause little or no restriction of intact
joint motion, open shoulder designs are
preferred because they allow relatively free range of motion at the shoulder
joint, especially when sufficient residual
limb length remains.7 Another option
for transhumeral socket design is the
half-and-half socket.8 This socket uses
a flexible silicone proximal section that
is fitted over the shoulder region and is
fabricated as an integral part of a distal
inner flexible socket. The deltoid area
is cut out laterally, providing improved
flexibility and air circulation within the
socket. The rigid external frame of the
socket extends from the axilla level distally (Figure 6). Another option similar
to the half-and-half socket is the flexible
shoulder suspension system in which a
strip of spandex-backed neoprene (or
similar material) replaces the silicone
“saddle” and is attached to the “wings”
of the standard open shoulder socket.
1
In contrast, closed shoulder designs
are best used for short residual limbs
where insufficient leverage exists to use
the full range of physiologic shoulder
motion. The closed shoulder socket offers good stabilization of the prosthesis
on the user and a convenient and secure
anchor point for the lateral suspension
strap of the harness.
Designs for a shoulder disarticulation
interface require sufficient surface area
to effectively stabilize the prosthesis on
the amputee. Because of the length of
the lever arm of the prosthesis and the
weight of the components, there is a
strong tendency for rotation at the prosthesis-user interface, especially as the
terminal device is moved away from the
body. Therefore, the socket perimeter
Atlas of Amputations and Limb Deciencies, Fourth Edition © 2016 American Academy of Orthopaedic Surgeons
302
should extend sufficiently on the torso to resist these forces.9 A frame-type
socket allows for stabilization and heat
dissipation while minimizing weight. If
body-powered control is used, the frame
should capture as much body motion as
possible, particularly biscapular abduction. Any lost motion will reduce the
function of the prosthesis.
If the components are controlled
myoelectrically, the generation of
control signals may create incidental
shoulder motion that could displace the
socket and allow electrode movement.
In such cases, it may be advantageous
to allow the shoulder to move independently within the frame. The weight
of the prosthesis can serve to anchor the
frame to the user while allowing the use
of shoulder motion to activate various
electronic inputs.
Several shoulder disarticulation
frame designs are currently used. When
designing a frame for a particular individual, the prosthetist should consider
control sources, harness attachments,
and shoulder joint mounting as well as
design objectives. These design requirements will dictate the optimal frame geometry for a particular individual.
Harnessing
Conventional harnessing serves the
dual role of suspension and control of a
body-powered prosthesis. In designing
a harness system for the bilateral arm
amputee, it may be useful for the prosthetist to consider suspension and control separately. Harness requirements
are altered when electrically powered
components are used or when the socket
design provides suspension. Either or
both of these situations can lead to a
simpler harness design that can be worn
less tightly, potentially making the harness more comfortable.
In situations in which bilateral prostheses are harnessed together, each
prosthesis serves as the anchor point
for the other. When both prostheses rely
on the harness for control, inadvertent
Chapter 24: Bilateral Upper Limb Prostheses
Figure 7
shoulder level and transhumeral limb absence.
In some instances, the user may prefer to activate only the more dominant transhumeral
prosthesis. The passive shoulder level prosthesis then serves as an anchor for the control
harness.
Photograph of a patient with a
cable excursion (sometimes referred to
as cross-control) becomes a potential
problem. One solution to cross-control
is to provide a fully body-powered prosthesis on one side and a fully electrically
powered prosthesis on the other side so
that the control motions affect only the
intended device.
In some instances, a socket may
be fitted to provide an anchor for the
contralateral prosthesis (Figure 7). For
example, in the shoulder disarticulation/
transhumeral combination, the side of
the shoulder disarticulation might be
managed with a frame-type socket or
passive prosthesis to provide a firm
anchor for suspension and control of
the transhumeral prosthesis. These options can be shaped to provide aesthetic
shoulder symmetry.
The patient with a bilateral transradial amputation who uses body-powered control will generally be fitted
with a standard figure-of-8 harness,
which typically incorporates a ring at
Figure 8
a harness with a leather pad that is used to replace the cross point of the webbing harness.
This design spreads the load over a larger area
and helps position the control attachment
straps lower on the back.
Photograph of a p atient wearing
the cross point for free movement of
the straps, with flexible hinges and a
triceps pad. Compared with the unilateral figure-of-8 harness, the bilateral
version eliminates the axilla loop, which
frequently causes discomfort. This type
of harness is well tolerated by almost
all patients and is easy to don and doff
independently. At the transradial level, bilateral myoelectrically controlled
prostheses typically require no harness.
Similarly, a bilateral transhumeral
amputee wearing body-powered systems will usually be fitted with a figure-of-8 harness with or without a ring.
If cable excursion is limited, it is advisable to use a harness design without a
ring to limit any loss of motion that may
occur when the harness straps rotate
on the ring during use. Either a sewn
configuration or a leather pad may be
beneficial to direct the control attachment straps more inferiorly on the scapulae and increase the available excursion
(Figure 8). Alternatively, a cross-back
strap can be used to keep the control
attachment straps low on the scapulae.
This also can be accomplished with a
dual-ring type harness, with two rings
fixed to each other by a strap, one inferior to the other (Figure 9). Harness
configurations for mixed-level fittings
must use sound principles for prosthesis
stabilization, suspension, and control
(Figure 10).
© 2016 American Academy of Orthopaedic Surgeons Atlas of Amputations and Limb Deciencies, Fourth Edition
303
Section 2: Upper Limb
Components
Terminal Devices
The new bilateral upper limb amputee
will likely express a preference to be fitted with prosthetic hands because of the
assumption that available technology
can replace the function and appearance
of the physiologic hand. Unfortunately,
Figure 9
a bilateral transhumeral amputation wearing
a prosthesis with a double ring harness that
increases available excursion by positioning
the control attachment straps lower on the
scapulae.
Photograph of a patient with
most body-powered hands are mechanically inefficient and are not useful to the bilateral amputee. If hands
are desired, electrically powered hands
are generally indicated, although such
hands provide little or no proprioceptive
feedback.10 Advantages of electrically
powered prehensile devices are a high
grip force that can be sustained without
continued control input. Multifunctional hands offer a wider variety of grip
patterns and hand postures that some
bilateral prosthesis users have found
useful (Fig ure 11). Most bilateral amputees fitted with electrically powered
hands will also benefit from the use of
interchangeable electric hook prehensile
devices (Figure 12). This option allows
the amputee to choose which device is
best suited to accomplish specific tasks.
Cable-driven components, such as
the split hook, offer proprioception
through the cable and harness system
because component movement and
forces are reflected to and perceived by
the controlling body part.10 However,
electrically powered devices provide
prehension forces three to six times
greater than those experienced by users of typical voluntary-opening split
hook devices.
1
It is generally advisable to use two
different types of prehensile devices to
provide greater grasp versatility to the
bilateral upper limb amputee. A commonly used prehensile device combination is a canted approach hook on the
dominant side and a lyre-shaped hook
on the contralateral side. The canted
hook allows good visual feedback for
manipulating objects, whereas the lyreshaped hook provides better stability for
gripping large round objects. Another
successful terminal device combination
uses a canted hook on the dominant side
and an electrically powered prehensile
device on the nondominant side. This
combination, which has been particularly well accepted by the amputee with
a transhumeral/shoulder disarticulation,
provides the fine manipulation capabilities of a split hook and the superior gripping forces available with an electrically
powered prehensile device.
Figure 10
transhumeral prosthesis is entirely body powered and the shoulder disarticulation uses hybrid contro l with myoelectric control of the terminal device
and body-powered control of the elbow. Anteriorly, a single chest strap allows for independent donning and dong. B, A simple gure-of-8 ring
harness can be used for a transhumeral/transradial amputee when sucient excursion exists. C, If excursion is limited, it is advisable to use a harness
with a sewn cross point and a cross-back strap to maximize excursion.
Atlas of Amputations and Limb Deciencies, Fourth Edition © 2016 American Academy of Orthopaedic Surgeons
304
Photographs of various harness systems. A, A patient wearing a harness for a shoulder disarticulation/transhumeral amputation. The
Figure 11
bilateral transradial amputation wearing prostheses with multifunctional hands. A variety of
grip patter ns can be selected to accomp lish the
activities of daily living.
Photograph of a patient with a
Voluntary-opening hooks are primarily used because they maintain grip
without the need for continued cable
tension and are available in an array of
shapes, sizes, and specific patterns of
prehension. In contrast, voluntary-closing hooks have more limited use for the
bilateral amputee because of the limited
number of available designs and the requirement for either continuous cable
tension or a locking mechanism to maintain grasp. However, these hooks offer
both high grip strength and excellent
feedback regarding prehensile forces.
Task-specific terminal devices with
quick disconnect wrist components
should be considered for the bilateral
arm amputee. One innovative approach
uses a hands-free tool exchanger that allows for automatic release and exchange
of one device for another.
Wrists
Because wrist flexion is especially helpful in body-centered activities (such as
feeding, dressing, oral and facial hygiene, and toileting), it should be provided at least on the dominant side, if
Chapter 24: Bilateral Upper Limb Prostheses
Figure 12
devices is routine among bilateral prosthesis
users. Photograph of a patient using a myoelectric hand to rotate his electric hook. Mixing
terminal devices in this way provides the user
with the ability to manipulate a wider range of
objects.
The use of multiple terminal
not bilaterally. Similarly, wrist rotation
is essential for effective orientation of
the prehensile device.
If a cable-actuated prehensile device
is used, the range of wrist rotation will
be limited by the control cable that
crosses the joint. When an electric rotator is used in conjunction with an electric prehensile device, the elimination
of the control cable permits a rotation
range greater than 360°.1 Such continuous wrist rotation can be useful for
activities such as turning a water spigot.
It is generally beneficial to use
locking wrist components rather than
friction designs because bilateral amputees often find it necessary to apply
high forces through the prostheses to
accomplish various tasks. When friction
devices are used, it is often necessary to
adjust the friction to a very high setting,
which makes it difficult to reposition the
device when needed. Positive-locking
components become a rigid extension of
the body that can maintain position under high loads and can be repositioned
with ease when unlocked.
The four-function forearm setup is
a particularly useful body-powered
wrist system (Figure 13). This system
has been used successfully on transradial, transhumeral, and shoulder disarticulation prostheses.11 This system
has a common control cable to position
four different body-powered prosthetic
components—the split hook, the wrist
flexion unit, the wrist rotation unit, and
the elbow. The simplicity of the system
allows the same physiologic control
motion to be used to position each of
the four components, thus conserving
available control sources. However, the
control is sequential (only one device
can be positioned at a time). Therefore,
it is not possible to produce coordinated movements involving two or more
components. User feedback suggests
that the straightforward manner of
the control and the presence of proprioceptive feedback outweigh these
disadvantages.
1
Midforearm flexion offers a nonanthropomorphic solution to limited range
of motion that has been particularly useful for the patient with a short or very
short transradial amputation. By placing the flexion device more proximal in
the prosthesis, a greater arc of motion
is achieved at the terminal device. This
improves the ease of midline tasks. Because of the altered line of pull, a greater
amount of cable excursion is required to
activate the hook in the flexed position
(Figure 14).
Elbows
The selection of the most appropriate
prosthetic elbow should include careful
evaluation of weight, control options,
and compatibility with the other desired
components. Body-powered elbows are
lighter than electrically powered units,
but they provide considerably less live
lift. Electrically powered elbows have
greater lifting capacity but are heavier
and lack the proprioceptive feedback inherent in the cable control of body-powered elbows.
1
A spring lift assist or automatic forearm balance should be considered for
all body-powered elbow fittings. These
devices allow the prosthetist to optimize and balance the force/excursion
requirements of a particular system
© 2016 American Academy of Orthopaedic Surgeons Atlas of Amputations and Limb Deciencies, Fourth Edition
305
Section 2: Upper Limb
Figure 13
lock can be ac tuated by pulling against the k nee. When unlocked, the w rist is exed by pulling on the contro l cable and extended by an elastic tension
band. B, The wrist rotation feature is unlocked by depressing a lock lever against the torso. When unlocked, cable tension causes supination while
pronation is provided by an internally mounted coil spring.
Photographs of th e four-function forear m setup, which allows body- powered control of wrist exion and rotation. A, The wris t exion
elbow providing better positioning
control.
1
Elbow hinges are seldom indicated
for bilateral transradial amputees. A
rarely used but effective exception is
the appropriate application of step-up
hinges. The disadvantages of step-up
hinges include the increased force required to flex the elbow and, depending on the residual limb length, poor
forearm cosmesis when the elbow is
flexed. However, these disadvantages are sometimes outweighed by the
increased range of motion afforded
by this option. Also, a fair-lead cable
housing can be used with these hinges
to supplement elbow flexion forces if
there is sufficient physiologic elbow extension strength to stabilize the flexed
elbow during operation of the terminal device. This same approach can be
Figure 14
ion aords the necessary hook placement for midline activities for these patients.
Photograph of an amputee with limited elbow range of motion. Midforearm ex-
used for an individual who presents
with weak elbow flexion force using
standard single-pivot hinges if passive
with the abilities and needs of a particular user.
In patients with bilateral arm amputations who require two elbows, it
is sometimes beneficial to provide one
body-powered and one electrically
powered elbow. The two elbows complement each other, with the electrically powered device providing greater
live lift capacity and the body-powered
flexion range is available and there is
enough extension force to resist further
flexion during operation of the termi-
Atlas of Amputations and Limb Deciencies, Fourth Edition © 2016 American Academy of Orthopaedic Surgeons
306
Chapter 24: Bilateral Upper Limb Prostheses
Figure 15
to assist elbow exion if there is sucient extension force to stabilize the elbow during hook
operation.
Humeral Rotation
All internal locking elbow systems
routinely used in North America, both
body-powered and electrically powered,
are equipped with friction-moderated
humeral rotation. Friction control is
simple and does not require a control
source for operation. However, as with
the cited limitations of friction wrists,
friction control of humeral rotation may
compromise the usefulness of the prosthesis for certain tasks requiring high
force. Therefore, locking humeral rotation may be beneficial. Locking humeral
rotators may be used on body-powered
as well as electrically powered elbows.
Photograph of a man with a prosthesis with a fair-lead cable, which can be used
from a device that locks in position for
similar reasons as those described for
locking wrist and humeral components.
The LTI Locking Shoulder Joint (Liberating Technologies) provides a positive
locking feature for flexion and friction
for abduction control. The lock can be
operated by a cable nudge control or
with an electric actuator. The rigidity
of the locked shoulder joint allows the
amputee to use the prosthesis more effectively as an extension of the body to
transmit forces through the structure of
the complete prosthesis.1 In addition,
the terminal device allows overhead
1,12
operation (Figure 17).
The lock is operated by a control cable
that can be actuated through a control
harness in parallel with the elbow lock
or by a chin-actuated nudge control
(Figure 16).
Control Systems
Currently, the available control options
in upper limb prostheses can be divided
into two basic categories—body posi-
tion control and myoelectric control.
Shoulder Joints
The bilateral amputee who requires a
prosthetic shoulder joint will benefit
Body position control refers to the use
of intact body motions and the excur-
sion and/or forces produced by those
Figure 16
lows easy positioning of the terminal device
while providing a rigid limb as needed to resist
high forces. Photo graph of a man with a bilateral shoulder disarticulation who is demonstrating the ability to bring his terminal devices into
contact with each other; this allows bimanual
manipulation.
Figure 17
locking shoulder joint allows a patient with a
bilateral shoulder disarticulation to operate
the terminal device overhead. The terminal device is controlled by a linear transducer using
shoulder elevation, providing reliable variable
speed control.
Locking humeral rotation al-
Photograph showing that a
motions (Table 1). The most familiar of
these control options are cable-operated
systems, but body motions also are used
© 2016 American Academy of Orthopaedic Surgeons Atlas of Amputations and Limb Deciencies, Fourth Edition
307
Section 2: Upper Limb
to operate electric inputs such as switches, servos, transducers, and force sensitive resistors (Figure 18). Alternatively,
myoelectric control makes use of the
electric byproducts of voluntary muscle contractions. As such, myoelectric
control is generally independent of joint
position.
Tab le 1
Body Position Control
Sources
Primary Work Sources That Produce
Good Force and Excursion
Glenohumeral exion
Scapular/biscapular abduction
Control Sources for Mechanical Locks
and Electronic Inputs
Glenohumeral extension/abduction/
shoulder depression
Shoulder elevation
Chest expansion
Abdominal expansion
Chin nudge
Glenohumeral adduction
Other (any movable body part)
It is necessary to understand the relationship between the available control
sources and the types of components
that can be most effectively controlled.
Component selection should be based
on a careful analysis of which devices
and control options will best serve the
intended function of the particular user.
Of critical importance to the bilateral
amputee is the reliability of the control
system. A control source is reliable if
every control command results in the
desired component function. Equally
important, a component should function only as a result of an intentional
control command. When a control command fails to consistently produce the
desired result, the overall usefulness of
the prosthesis is greatly compromised.
Therefore, control systems that are too
complicated or that rely on a marginal control source are prone to failure.
Training on use of the prosthesis is often
essential in maximizing the reliability
of control. If training fails to produce
consistently reliable control function, an
alternative control method is indicated.
When controlling multiple components, control options can be further
categorized as either dedicated or sequential. Sequential control means
that two or more components will be
controlled from a common source; simultaneous control is not possible. Dedicated control assigns separate control
sources to each prosthetic component.
This method provides the user with immediate access to use of a component
and, in some instances, may support
the simultaneous control of two components for the production of coordinated
movements.
1,10
It is generally desirable
to devise a control scheme that provides
dedicated control whenever possible. At
higher amputation levels, this poses a
substantial challenge because of the increased number of prosthetic joints that
require control and the limited number
of available control sources. It is sometimes necessary to combine sequential
and dedicated control to provide the desired functions. In these cases, the component functions that may be combined
in simultaneous useful ways should be
Figure 18
putations, an d paraplegia. The us e of a single multifunct ional prosthesis provide s some independence i n self-feeding and simp le object manipulati on.
A, The wrist rotator, positioned at midforearm, is controlled by a chin-activated rocker switch. A wheelchair mounted bracket assists with internal
and external rotation of the humeral turntable. Wrist exion is achieved using a conventional exion wrist. B, An electric elbow is operated with a
pair of force-sensing resistors mounted anteriorly and posteriorly within the socket, and the terminal device is controlled using contralateral scapular
abduction and a harness pull switch. Coordinated simultaneous elbow exion and wrist rotation are possible and useful for self-feeding.
Atlas of Amputations and Limb Deciencies, Fourth Edition © 2016 American Academy of Orthopaedic Surgeons
308
Photographs of a single multifunctional prosthesis worn by a patient with bilateral shoulder disarticulations, bilateral transtibial am-
Chapter 24: Bilateral Upper Limb Prostheses
Figure 19
residual humerus provides excellent dedicated control of the electric terminal device using a pair
of force-sensitive resistors.
prioritized and assigned separate control sources (Figure 19).
It is often advisable to provide two or
more complete sets of prostheses with
different control and power sources to
enable the widest variety of functional capabilities and to provide a backup
when repairs are needed.
Photograph from a patient with bilateral humeral neck amputations. A mobile
prosthesis velocity, and joint force corresponds to prosthesis force.”
This type of control is referred to as
extended physiologic proprioception.
Although implementation of extended physiologic proprioception control
is possible with electronic compo-
13,16 -18
nents,
it requires fast, high-perfor-
mance components to produce optimal
Body-Powered Control
Cable actuation of body-powered prostheses provides users with a wealth
of proprioceptive feedback through
the physiologic joints harnessed to
the prosthetic components.13 Users of
these devices can readily perceive the
position and speed of movement of the
prosthetic components.1 Body-powered,
cable-operated control offers many of
the desirable characteristics of the theory of control proposed by Childress
based on the work of Simpson,
14,15
which
states: “The most natural and most subconscious control of a prosthesis can
be achieved through use of the body’s
own joints as control inputs in which
joint position corresponds (always in a
one-to-one relationship) to prosthesis
position, joint velocity corresponds to
results. Currently, such a system is not
commercially available.
Because of the inherent feedback
provided through the cable and harness
system, body-powered elbow control
is well accepted and quite functional
if adequate force and excursion exist.
Body-powered control of an elbow affords the greatest degree of graceful and
accurate positioning of the prehensile
device in space. Control can become
subconscious, as has been observed in
bilateral transhumeral amputees who
dynamically incorporate use of their
prostheses by gesturing with their limbs
and gracefully repositioning their elbows when speaking.
Cable efficiency is of critical importance to the success of a body-powered
fitting. Careful attention should be
devoted to producing the straightest line
of pull using materials that offer the least
amount of friction.
19
Myoelectric Control
In contrast to control methods that require body motions of more proximal
body segments, myoelectric control is a
more natural-appearing system because
the method of controlling the prosthesis is invisible.10 It also represents the
most physiologically natural method
of controlling an electric hand. This is
especially true for the transradial amputee because control is accomplished in
a physiologically natural fashion, with
myoelectric signals from the forearm
flexors closing the hand and signals
from the extensors opening the hand.
At this level, the harness can be eliminated, which allows for an improved
functional envelope because the position of the prosthesis and operation of
the terminal device are not confined by
straps. For more proximal amputation
levels, the flexor and extensor patterns
of more proximal muscles are associated with and well suited for the tasks
of grasping and releasing objects. The
transhumeral amputee would use the biceps to close the hand and the triceps to
open the hand because a flexion pattern
is closely associated with grasping and
an extensor pattern is associated with
releasing.10 Childress14 described this as
the principle of myoprehension, which
suggests that myoelectric control can be
somewhat naturally connected with the
control of prehension. An important disadvantage of this type of control is the
lack of direct feedback from the control
system to the user regarding the position, velocity, and force of the component controlled. Users of a myoelectric
control system must rely primarily on
visual feedback as they manipulate their
environment with the prosthesis.
10
Targeted muscle reinnervation (TMR)
surgery has been successful in increasing the number of useable myoelectric
control sites and directly associating
© 2016 American Academy of Orthopaedic Surgeons Atlas of Amputations and Limb Deciencies, Fourth Edition
309
Section 2: Upper Limb
them with more distal functions. With
TMR, remaining nerves in the arm are
transferred to residual chest or upper
arm muscles that are no longer biomechanically functional because of limb
loss. After reinnervation, these muscles
serve as biologic amplifiers of motor
commands from the transferred arm
nerves and provide physiologically appropriate electromyographic signals for
control of the elbow, wrist, and hand.20
Kuiken et al21 reported the success of
TMR surgery for improving ease of control and allowing simultaneous myoelectric control in an amputee with a
bilateral shoulder disarticulation.
Another promising technology for
prosthesis control is the use of pattern
recognition with or without TMR surgery. Pattern recognition uses multiple
electrodes placed around the residual
limb to record patterns of muscle activity that are then associated with corresponding prosthetic functions.22 Pattern
recognition control systems have the potential to provide more intuitive, direct
control of multiple functions without
the need for mode selection strategies.
Pattern recognition control systems have
recently become commercially available and training protocols have been
suggested.
23
Hybrid Control
The selected control arrangement should
impose the minimum amount of mental
stress on the user (that is, the control of
the prosthesis should not be so complicated that it becomes the primary object of the user’s attention).1 Faced with
the complexity of high-level bilateral
fittings, one seemingly small change in
the control strategy can cause a chain
reaction of control source interaction.1
Although hybrid components (electric
combined with body-powered) and hybrid input devices may provide the most
desirable results, these systems can be
technically demanding and require that
the prosthetist have a high degree of creativity and knowledge. In the experience
Figure 20
a bilateral transhumeral amputation using a
prototype prosthesis, which is a valuable tool
in the development of an optimal prosthesis.
The well-tted socket serves as the foundation
for the protot ype, and modular constru ction allows for trials of various prosthetic component
and control options.
Photograph of a patient with
of this chapter’s author, the benefits realized by the users of hybridized systems
far outweigh the technical difficulties
in producing these systems. The key
to optimal design of prostheses for the
bilateral amputee is in the details, and
each detail must be carefully considered
to achieve optimal results.
Prototype Prostheses
Given the large number of component
and control options available to the upper limb amputee, it is often advisable
to set up a clinical trial of the proposed
design using a prototype prosthesis. For
a patient with a higher level arm amputation, this process can be critical to the
outcome of prosthetic rehabilitation. The
availability of all component options and
the technical ability to mix and match
components from different manufacturers are critical to the success of this approach. The foundation of the prototype
prosthesis is a well-fitted interface for
evaluation. A prototype prosthesis may
be used for periods of time ranging from
a few hours for very straightforward fittings to several months for challenging
Figure 21
vide a simple and robust device to enhance the
function of a partial hand amputee with one or
more remaining movable digits. Photograph of
a patient with transradial/partial hand amputations. He nds his partial hand side most useful
for ne motor tasks primarily because of the
feedback provided by his sensate thumb.
An opposition post can pro-
cases in which several prosthetic options must be evaluated. The use of a
prototype prosthesis allows the amputee
and other concerned parties to evaluate
and validate the efficacy of any particular prosthetic component and control
configuration before completion of the
definitive prosthesis10 (Figure 20).
Fitting Consideration
by Level
Partial Hand
In patients with one or both limbs amputated at the partial hand level, the main
prosthetic considerations are to provide
effective prehension while limiting the
amount of sensate area that is covered
or encumbered by the device. Opposition posts (Figure 21), handihooks,
and myoelectric prostheses can be fitted at the partial hand level. Opposition
posts are particularly useful if a movable digit(s) remains. These devices are
simple, lightweight, and generally cover
the least amount of area. Body-powered
options include wrist-driven designs for
Atlas of Amputations and Limb Deciencies, Fourth Edition © 2016 American Academy of Orthopaedic Surgeons
310
Chapter 24: Bilateral Upper Limb Prostheses
activation of fingers when amputated at
or proximal to the metacarpophalangeal joints or finger-driven designs for
partial finger amputations (Figure 22).
The cable actuated handihook will provide grasp and release for amputees who
lack a movable digit(s) (Figure 23, A
and B). When fitted loosely, the user
can quickly doff the socket, leaving it
attached by the control system, while
objects are manipulated using their sensate residual hand. Powered fingers are
best suited for amputations at or proximal to the metacarpophalangeal joints.
Powered fingers may be controlled with
myoelectric signals or force sensing resistors and have been successfully fitted to bilateral partial hand amputees
(Figure 23, C). Wrist motion as well as
motion of any intact fingers should be
unrestricted by the prosthesis whenever
possible.
Transradial Level
Body-powered hooks and myoelectric
systems can be successfully fitted for
a patient with a bilateral transradial
amputation. Body-powered hooks offer fine manipulation and are robust
and lightweight (Figure 24, A). Myoelectric hands offer a good appearance
with acceptable manipulative abilities
(Figure 24, B). Myoelectric hooks of-
fer good, fine manipulation ability, and
because they have no cosmetic cover,
they are better suited to use for manual
labor than myoelectric hands. Myoelectric systems are unconstrained by the
need for a harness, increasing the work
envelope. Some users find both types of
prostheses useful and routinely switch
Figure 22
strating go od function with his l eft hand withou t a prosthesis (B). C, Right hand grasp was improved
with Partial M-Finger (Liberating Technologies) prostheses in which metacarpophalangeal exion
results in exion of the prosthetic ngers.
Photographs from a patient with bilateral partial nger amputations (A) demon-
between prostheses as required by the
type of activities pursued.
Sensation is of critical concern for
the transradial amputee. Exposed skin
can be desirable, especially at the longer
Figure 23
but was unable to hold objects securely because of the short length of the remnant digits. His right partial hand was tted with a body-powered
handihook–type prosthesis (B) and a powered nger prosthesis (C), allowing stable grasp of a wide variety of objects.
Clinical photographs from a patient with bilateral partial hand amputations. A, The patient relied on the sensation of his left hand
© 2016 American Academy of Orthopaedic Surgeons Atlas of Amputations and Limb Deciencies, Fourth Edition
311
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