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Critical Factors in Electrically
Powered Upper-Extremity Prosthetics |
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Reprinted with permission - American
Academy of Orthotists & Prosthetists, JPO, Vol. 14, Num.
1, pp. 36-38 |
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| Essential in the formation
and execution of successful prosthetic rehabilitation
is the knowledge of design theory. Design theory takes
into consideration volume containment, suspension, comfort,
range of motion, component considerations, stabilization,
anatomical contouring, and cosmesis. This knowledge
allows the team to select the appropriate interface
design, componentry, and control schemes that best suit
the patient's level of amputation, skin, tissue, musculature
condition, range of motion, learning ability and desire,
and vocational and avocational goals. 1 Although knowledge
of design theory in itself does not guarantee successful
prosthetic rehabilitation, a lack of knowledge can often
overshadow the contributions of the rehabilitation team.
At the center of the rehabilitation team is the patient
and insuring his involvement and "buy in"
is also critical to a successful outcome. |
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2 One should view the patient as the
hub of the wheel, whereas the physician, nurse, case manager, therapist,
psychologist, prosthetist, and reimbursement agency form the spokes
of the wheel. The purpose of this paper is to detail a protocol to
address the critical factors that should be considered when an electrically
powered upper-extremity prosthesis is prescribed. |
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METHODS |
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Begin with the patient evaluation phase,
which should include an introduction to the patient and a description
of the purpose of the evaluation and resulting formation of the rehabilitation
plan. Discussing the patient's goals, concerns, and observations should
follow, taking into account vocational, avocational, and family considerations.
Throughout the evaluation process, the team should focus on listening
and observing the patient because the patient's psychological condition
and expectations factor heavily into the resulting rehabilitation
plan. A thorough physical evaluation should include observation of
skin condition, tissue condition, skeletal anatomy, |
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muscle strength, range of motion,
EMG testing, and contralateral side involvement ( Figure 1 ). Education
of the patient as to the prosthetic options available, their advantages
and disadvantages, is time well spent, as many patients fit with electrically
powered prostheses that elect not to utilize their prostheses long
term can be traced back to unrealistic expectations of function, comfort,
and fit. Once the above has been accomplished, a strategy that includes
interface design, primary and secondary control schemes, suspension,
and cosmesis can be formulated by combining data collected throughout
the evaluation with knowledge of design theory. This strategy will
dictate componentry selection and interface design. Interface design
criteria include residual limb length, skeletal protuberances, range
of motion sensitive regions ( Figure 2 ), electrode placement, suction
interfaces, "pull in" versus "push in," self-donning
versus assisted donning, and vocational and avocational requirements. |
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The diagnostic phase begins with obtaining a plaster
impression of the patient's residual limb, taking careful attention
to prepare the patient both physically and psychologically for the
procedure. Consideration to interface material, donning and doffing,
and suspension should occur before modification as they will dictate
modification requirements. Once a clear diagnostic interface has been
fabricated, the analysis is divided into two components: static and
dynamic. During the static diagnostic analysis, auxiliary suspension
should be included if dictated by the initial strategy. This is |
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an important factor because interface
to skin contact can often change once auxiliary suspension is incorporated.
Several modifications to the interface and auxiliary suspension maybe
required to obtain a static, total contact, comfortable interface.
Once an acceptable static interface has been achieved, the dynamic
diagnostic analysis follows insuring maximum range of motion with
minimal skin to interface contact loss. |
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Primary control inputs/schemes, which in most instances
involve terminal device and elbow control, are now reevaluated to
insure that the final interface design allows for optimal function.
Several primary control schemes to consider are myoelectric, force-sensing
resistors, servo, and switch. If myoelectric control is selected as
the primary control scheme, site identification should take into consideration
EMG signal level, EMG separation, and skin condition ( Figure 3 ).
Marking an area on the skin surface that has acceptable EMG signal
strength and separation and then donning the interface and transferring
this site provides the best results. Once electrodes are mounted into
the diagnostic interface, an EMG analyzer should be attached to insure
that the tissue-containment strategy of the interface does not adversely
affect EMG signal strength and separation both in static and dynamic
conditions. |
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After optimal electrode sites are determined, a diagnostic frame with
componentry attached should be fabricated and aligned to maximize
the patient's functional envelope and cosmetically resemble the contralateral
limb ( Figure 4 ). Now that the interface is under load, reevaluation
of the interface should take into account donning/doffing effort,
contralateral limb involvement, comfort, range of motion, stabilization,
electrode site contact, suspension, alignment, and cosmesis. For higher
levels of deficiency, secondary control options should be considered
at this time. Secondary control options may include remote on/off,
wrist rotator, mode selector, elbow lock/unlock, sensory feedback
activation/deactivation, humeral lock/unlock, and shoulder lock/unlock.
After determining the type and amount of secondary control options,
secondary control inputs can be selected. Secondary control inputs
are defined as inputs that can be isolated from primary control inputs/schemes
and, therefore, similar options exist (myoelectric, force-sensing
resistor, servo, and switch). The most efficient manner of selecting
secondary control inputs is through an analysis of functional range
of motion without activation of primary controls. Once an activation
movement can be isolated, installation of the secondary input followed
by verification of control isolation can occur to insure that the
patient can easily activate the desired function ( Figure 5 ). |
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Prefabrication issues that must be determined are
inner-socket material, frame material and shape, component orientation,
and measurement information (linear, circumferential, and special
functional or cosmetic considerations). Analysis of fit, comfort,
function, and cosmesis are important considerations during system
delivery. Initial prosthetic training includes basic operations instruction
and care and maintenance. Initial system optimization should occur
during this phase. Evaluation of the patient's function, comfort,
and cosmesis should be included in the post delivery evaluation plan
and communicated to the rehabilitation team to insure efficient transition.
Therapeutic intervention is essential and can be divided into three
phases: preprosthetic, interim-prosthetic, and postprosthetic rehabilitation.
Preprosthetic rehabilitation can |
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include wound healing, range of motion,
scar tissue manipulation, and adaptation training. Interim-prosthetic
rehabilitation can include EMG site selection, enhancement, and separation.
Postprosthetic rehabilitation can include controls training, simple
task training, advanced activities of daily living tasks, and vocational
training. Identification of an experienced therapist at onset will
have a dramatic effect on maximizing the patient's rehabilitation
potential. |
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CONCLUSION
Due to the finite number of candidates for electrically powered prosthetic
intervention and the limited number of experienced practitioners in
this discipline, a prosthetic rehabilitation plan addressing these
specific critical factors and executed by a knowledgeable and cohesive
team will improve the function and long-term success of patients fit
with an electrically powered prosthesis.
References:
References1.Heger, H, Millstein, S, Hunter,
GA. Electrically powered prostheses for the adult with an upper
limb amputation. J Bone Joint Surg. 1985;67B:278-281.
Meier RH. Evaluation and planning for acquired upper limb amputee
rehabilitation. In: Meier RH, Atkins DJ, eds. Comprehensive Management
of the Upper Limb Amputee. New York, Springer-Verlag; 1989:16
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