Neurological Aspects of Prosthetic/Orthotic
Practice
John H. Bowker, MD
ABSTRACT
Many patients referred for orthotic or
prosthetic services will have associated
neurologic deficits. These must be recognized by the practitioner prior to the
design and fitting of an orthosis or
prosthesis to avoid costly and potentially harmful errors in design and application. Commonly seen deficits are loss
of protective sensation, impaired proprioception and spasticity. Any one
of these may be associated with fixed
soft tissue or bony deformity. A working knowledge of sensory and motor
examination, combined with careful
history-taking, will greatly enhance
the clinical skills of the prosthetist/orthotist in this challenging aspect of practice.
Introduction
A wide variety of disorders as well as
trauma may result in neurological
problems requiring prosthetic and orthotic services. Sensory and/or motor
loss may exist alone or be complicated
by spasticity or deformity, profoundly
affecting the orthotic solution for
something as seemingly simple as foot
dorsiflexion paralysis.
The experienced prosthetist/orthotist realizes patients with virtually any
type of disease or injury require careful
evaluation for associated primary or
secondary neurological aspects of their
condition. When a detailed examination is performed prior to the design
and fitting of an orthosis or prosthesis,
costly and potentially harmful errors
in design and application can be avoided(1).
Clinical Examination
When evaluating sensory function, patient history is extremely important.
Patients with a sudden onset of sensory
loss are usually aware of the loss unless
a head injury or cerebrovascular accident occurred. Gradual loss related to
peripheral neuropathy, as in diabetes,
may be minimized or even denied by
the patient. Those patients who have
experienced congenital sensory loss,
as in the case of spina bifida, have never experienced normal sensation (Figure 1)
.
From a prosthetic/orthotic perspective, it is of utmost importance to determine if the body segment encompassed by a device has at least "protective" sensation, that is the ability to
feel excessive pressures that will eventually lead to skin destruction. A simple and inexpensive test kit is available
to determine if a part has normal, protective or absent sensation.
A simplified Semmes-Weinstein filament set' contains three filaments that
specifically detect these particular sensation thresholds. In this concise test,
each filament tip-starting with the
thinnest-is applied in turn to the skin.
Increasing pressure is applied until the
patient can sense its presence. (The patient's eyes should be closed.)
In cases of limb paralysis, it is important to distinguish between flaccid and
spastic types. Flaccid paralysis results
from damage to lower motor neurons
as in poliomyelitis, lumbosacral nerve
trauma, spina bifida, isolated peripheral nerve injury or diabetes mellitus.
Flaccid limbs, in the absence of contracture, are easily supported by orthoses in weightbearing postures. Many
of these patients' limbs are also insensate, with the exception of those patients whose conditions affect only the
motor cells of the anterior horn of the
spinal cord, such as poliomyelitis or
Guillain-Barre syndrome.
Spastic paralysis, in contrast, results
from spinal cord injury, traumatic
brain injury, cerebrovascular accident,
multiple sclerosis or cerebral palsy, all
of which involve damage to upper motor neurons of the brain and/or spinal
cord. The resulting increased tone can
sometimes be reduced without significant sedation with the use of antispastic
drugs such as baclofen. The limiting
factor in bracing spastic limbs remains,
of course, the severity of reflexive muscle tone.
For example, in the equinovarus gait
of the hemiplegic, if the foot becomes
plantigrade during midstance, the spasticity is considered mild and an anklefoot orthosis (AFO) with moderately
anterior trimlines will suffice to hold
the foot plantigrade throughout the
gait cycle.
If the foot remains in equinovarus
throughout the gait cycle, an AFO may
not be able to maintain a fully plantigrade position. When an AFO is indicated, it is essential the heel remains
seated properly in the brace and shoe.
If it does not, the patient's gait will be
unsafe since the unstable foot and functional leg length discrepancy will make
falls likely. If a patient with marked
spasticity is otherwise a good candidate
for ambulation, consider percutaneous
fractional lengthening of the Achilles
tendon coupled with a split anterior tibial tendon transfer (SPLATT) procedure (2). Such surgical intervention
will make effective orthotic fitting feasible.
The presence of proprioception, or
the ability to sense limb motion and
weightbearing, will help determine if a
patient will become a functional walker. Inability to sense floor contact and
joint position will make safe ambulation difficult, if not impossible, even if
other types of sensation are present.
In addition to severe spastic equinovarus, another condition in which bracing should be approached with caution
is deformity secondary to neuropathic
(Charcot) foot and ankle joints. Loss
of sensory function plays a major role
in the disintegration of bony structure
and increases the risks of skin necrosis.
If treated early, prolonged casting of
neuropathic foot fractures and fracture-dislocations followed by long-term circumferential bracing will usually result in a foot that can be fitted with
a custom-made or in-depth shoe with
custom-molded insert. Seen late, a severe and fixed deformity will likely not
be amenable to casting or an orthosis.
In fact, if "corrective" forces are orthotically applied in the face of rigid deformity, skin breakdown is to be expected. Charcot changes following simple
ankle fractures sometimes result in severe, irreducible deformity (see Figure 2a
and Figure 2b
). Surgical correction in
carefully selected cases has been successful.
Lack of protective sensation obviously requires precise fitting and appropriate cushioning of shoes (see Figure 3
) as well as orthoses and prosthetic
sockets (see Figure 4a
and Figure 4b
). Areas of
skin pressure, blistering or abrasion by
shear forces can be produced by loosely fitting shoes or by "pistoning" in
loose prosthetic sockets, especially at
the Syme or transtibial levels.
Conclusion
Patients with a wide variety of neurological deficits resulting from trauma
or disease will see the orthotist or prosthetist for definitive management. A
working knowledge of sensory and motor examination will assist greatly in
the proper design and fitting of an orthosis or prosthesis and help avoid costly
and potentially harmful errors in design and application.
John H. Bowker, MD, is professor and associate chairman of the department of orthopaedics and rehabilitation at the University of Miami School of Medicine, and director of ampputee and diabetic foot services at Jackson Memorial Medical Center, Miami, Fla.
References:
- Hoppenfield S. Orthopaedic neurology:
a diagnostic guide to neurologic levels 1977;
JB Lippincott Co., Philadelphia. Pa.
- Waters RL, Perry J, Garland D. Surgical
correction of gait abnormalities following
stroke. Clinical Orthopaedics and Related
Research 1978; 131:54-63.
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