Clinical Management
of the Neuropathic Limb
Nancy Elftman, CO
Introduction
As medical research provides methods of extending the life of patients with previously
fatal diseases, we in the medical community
are seeing a rise in chronic complications.
Complications are increasing at an alarming
rate and are involving orthotists and prosthetists in the team management and assessment process.
An appropriate approach to this complex
subject would be to clarify the condition we
will be managing. Repeated articles refer to
these patients as dysvascular rather than as
neuropathic requiring orthotic intervention.
Emphasis should be placed on neuropathy
(insensitivity) because patients must be accommodated and pressure areas relieved of
potential and/or present breakdown. Dysvascular patients (see Figure la
and Figure 1b
) may
be neuropathic (see Figure 2a
and Figure 2b
) as
well, but they do not depend on orthotic!
prosthetic intervention to improve their condition or long-term medical outcome. Dysvascular patients require immediate attention from vascular specialists (to improve
condition) or surgery to remove or debride
tissue.
Historically, the neuropathic foot was
treated after foot ulceration appeared. We
now address neuropathy in an attempt to
prevent ulceration and ensuing complications, including amputations.
Neuropathy
Many conditions can leave patients with neuropathy in their limbs. Some diseases that
can result in neuropathy are:
- diabetes
- cancer
- Hansen's
- guillian barre
- influenza
- hepatitis
- lupus
- periarteritis
- nerve damage and entrapment
- spina bifida
- syringomelia
- tabes dorsalis (pseudo-Charcot)
- syphilis and
- multiple sclerosis
Toxins and syndromes also can cause insensitivity in the limbs. Toxins include alcohol,
arsenic, lead, gold, steroids, sulfonamides,
penicillin, prolonged INH use and uremia.
Syndromes include Charcot Marie Tooth,
Refsum's, Dejerine Sotta's and Riley Day.
In addition, HIV/ARC/AIDS medications
may also result in neuropathy.
Some of these conditions are complicated
further by dysvascularity. When arteries are
calcified, they provide poor healing potential. Antibiotics (oral or IV) cannot perform
optimally in an extremity they cannot reach.
Dysvascularity makes an injury or infection
in the neuropathic limb a serious medical
condition often leading to amputation or debridement.
The insensitive (neuropathic) foot is not
much weaker than the normal foot-it is just
poorly protected since it lacks pain reflex.
Patients lose all sense of identity with the
insensitive part. Subconsciously these patients don't have feet. While definitions of
neuropathy differ with the diagnosing profession, patients are tested to determine the
level of sensation loss and to "map out" the
area involved. A common and widely recognized tool is the Semmes Wienstein monofilament (von Frey) set. This is a set of three
brush-quality nylon monofilaments (38mm
long) that are calibrated to measure the
amount of bending force for each monofilament diameter.
The three sizes are 4.17, which applies one
gram of force for a normal sensation; 5.07,
which applies 10 grams of force to indicate a
level of protective sensation; and 6.10, which
applies 75 grams of force and determines if a
limb is completely insensate. When patients
cannot respond to the 5.07 or 6.10 size, they
are considered neuropathic because they
cannot feel pain and high pressures before
damage occurs. No person who is comfortably ambulating with plantar ulcerations can
feel 10 grams of force.
Types of Neuropathy
Peripheral neuropathy is a lack of sensation
that is symmetrical and equal from the spine
down the extremities. Patients with peripheral neuropathy will show equal mapping in
their feet with the insensitivity beginning in
the toes and continuing proximally. If the
pattern extends up the calf, the patient's fingertips and hands should be tested. True peripheral neuropathy will eventually involve
all four extremities and can be checked by
measurement from L5/S1 down the leg compared to the measurement of C7 down the
arm. The points where the patient is insensitive should be approximately the same (see
Figure 3
and Figure 4
).
Other neuropathic conditions. When the
pattern of sensation does not follow the criteria for peripheral neuropathy, other underlying conditions exist. The neuropathy
could be caused by single nerve damage or
entrapment (following a dermatome pattern). Vascular disease can cause neuropathy, but the patient would have an uneven
pattern or have only one extremity involved.
Why are we concerned about neuropathy?
Because patients will not compensate for
high plantar pressures by changing their gait
pattern, will not suffer pain or discomfort, or
even limp when damage occurs. When we
can provide an optimum environment for the
foot, equalize pressures and educate patients, they can continue ambulation without
damaging their extremities.
Diabetes and Peripheral Neuropathy
For most practitioners, diabetics display the
highest incidence of neuropathic limb complications. This group has a high incidence of
peripheral neuropathy as well as dysvascularity to complicate the healing process.
Diabetes is the third leading cause of
death in the United States. An estimated 14
million people have the disease (half undiagnosed), and each year about 700,000 new
cases develop-many diagnosed when treated for complications. The medical community estimates that $21.5 million is spent annually on diabetic complications.
The diabetic neuropathy process can begin regardless of the patient's history of control although patients with a history of compliancy and good control in their disease may
have fewer or less severe complications.
Neuropathy begins with nerve damage and
motor loss in the feet (claw toes). Patients
will suffer sensory loss in their hands, leaving
them unable to feel physical changes in their
feet. Several complications can occur. Retinopathy causes patients to be unable to see
changes in foot conditions. Autonomic neuropathy can impede senses, including smell,
as a warning of infection. A third, very destructive complication in the neuropathic
limb is Charcot joint, which destroys joint
structure and can lead to deformity.
Ulceration
Four types of stress can cause destruction of
tissue in the neuropathic limb.
lschemic necrosis is usually seen on the
lateral side of the fifth metatarsal head due
to a tight shoe. A very low level of pressure
(2 to 3 psi) over a long period of time causes
death of tissue.
Mechanical destruction occurs when direct
injury caused by a high pressure inflicts immediate damage to tissue. This may also be
caused by heat or chemicals that damage the
skin.
Inflammatory destruction occurs with repetitive moderate pressures (40 + psi). Inflammation gradually develops and weakens
the tissue, leading to callous and ulcers.
Osteomyelitis (and other sepsis) destruction is the result of moderate force in the
presence of infection. Infection is spread as
forces are applied.
The highest incidence of ulceration occurs
at sites of previous ulceration. A newly
healed ulcer is covered by thin skin that is
likely to tear. In completely healed ulcer areas, some scar tissue may adhere to underlying structures (see Figure 5
).
The Wagner Scale is used to grade ulcerations.
- Grade 0 ulcers have skin intact.
- Grade 1 is a superficial ulcer.
- Grade 2 is a deeper ulcer to tendon or
bone.
- Grade 3 ulcers contain an abscess or osteomyelitis.
- Grade 4 has gangrene on the forefoot.
- Grade 5 has gangrene over a major portion of the foot.
O&Ps are consulted in grade 0 and 1 conditions but may be called in for special cases
of higher grades when the patient refuses or
is not a candidate for other medical intervention.
Figure 6
shows a typical Grade 1 ulceration that will usually become a Grade 0
after excessive stress to the area is redistributed. Figure 7
is commonly seen after bony
destruction has recalcified, leaving a bony
deformity that is subject to high levels of
stress. This deformity must be accommodated with footwear to reduce high pressures. Figure 8
reveals a Grade 2 ulceration
with overlying callous buildup due to a hallux valgus condition that was not accommodated with footwear and an insert. Figure 9
shows a Grade 3 ulcer that is infected and
draining due to repetitive stress. This is a
common occurrence when one toe is removed, and excessive forces are transferred
to adjacent areas. This patient is neuropathic
and ambulates without a limp or any sign of
discomfort. Grade 4 feet can be found in
limbs suffering previous dysvascular lesions
as in Figure la
and Figure lb
.
With regular follow-up and intervention,
grade 1 and 2 ulcerations have a high probability of becoming Grade 0. Grade 3, 4 and 5
ulcers require extensive medical attention
before orthotists and prosthetists can be involved in treatment.
Clinical Evaluation
Clinical evaluation involves a visual and
physical examination, monofilament testing
and temperature recording. These processes
provide subjective and objective criteria to
be used for O&P design as well as in follow-up evaluation.
The visual and physical examination begins before the patient is taken to the exam
area. As you greet the patient, note injuries
to the hands (burns, etc.) indicating a high
level of peripheral neuropathy, especially atrophy of the thenar eminence. Note the patient's gait. Neuropathic patients will not
limp if they have ulcers because they are
unaware of a problem. Diabetes creates a tri-neuropathy with loss of sensory, motor and
autonomic nerves. Other losses include knee
and foot reflexes and hot/cold sensation. If
the patient has motor neuropathy, he or she
may have a drop foot or other weakness.
Note assistive devices, and visual and other
impairments.
The patient will remove shoes and socks.
Never take the patient's word for the condition of his or her feet. You must personally
examine the patient's feet at every appointment.
With the feet exposed, note skin discoloration, texture, keratin buildup and other abnormalities. Claw toes result from loss of
intrinsic control, allowing the PIP and DIP
joints to pull into abnormal alignment. Toes
may be normal, moderately clawed or severely clawed. Feel the foot and calf for severe temperature differences and loss of hair
growth (indication of vascular impairment).
This exam process will usually indicate the
level of neuropathic advancement. Figure 10
shows the physical exam where range of motion is evaluated, especially that of the great
toe, which must have extension range to obtain low pressures during gait and toe clearance. Hallux rigidus deformities are usually
due to the fibrosis of a healed first metatarsal
head ulceration. The rigid great toe will require a full shank in the shoe and a rocker
bottom.
Note areas of callous (high stress) and
skeletal alignment. Previous injuries and deformities lead to high pressure areas. Fat
pads tend to migrate distally, leaving metatarsal heads without padding. Unusual areas
of callous and ulceration may be due to
wedged shoes or inserts. These patients cannot be corrected, only accommodated.
To determine the amount of sensation the
patient retains, use the Semmes Wienstein
monofilaments. The monofilament should
first be shown to the patient and tested on his
or her upper arm so the patient will know
what to expect. Begin the test with the 4.17
monofilament indicating normal sensation.
If the patient cannot detect sensation, continue to 5.07 and 6.10.
To use the monofilament, hold the handle
so the monofilament is perpendicular to the
skin surface. Touch the end to the skin, deflect (bend) the monofilament and remove.
Note when the patient responds and the size
of monofilament he can feel. Map the area
that has no sensation. Never apply the
monofilament to callous, ulcer site, scar or
necrotic tissue-only to good skin closest to
desired site (see Figure 11
). Readings will
not be accurate from areas of damaged tissue.
Temperature readings will be taken at 10
locations on the foot (see Figure 12
). Temperature rise is an inflammatory response to
trauma. These locations are selected because of incidence of ulcerations (see Figure
5
), including the arch, dorsal surface and
alternating toes. Temperatures can be taken
with a thermocouple unit, which is expensive
and must contact the skin or with an infrared
unit, which costs more but is a valuable scanning tool.
Recording temperature provides an objective means of determining areas of high
stress before ulceration occurs. The foot
must be exposed to room temperature for
five to 10 minutes to allow normal tissue to
cool and differentiate elevated tissues. A difference in 3 degrees F between adjacent areas indicates a highly stressed area. A decrease in
temperature in previously highly stressed areas indicates that the insert relief has been
successful in redistributing pressure.
Evaluation
With the evaluation and measurements compiled, the information form can be completed. Temperatures should be recorded in corresponding circles, noting areas of high
stress. Remember that temperatures normally increase as measurements are taken
proximally (closer to the heart). Note ulcer
grade using Wagner Scale. Figure 13a
is a
standard evaluation form; Figure 13b
shows
a completed form, noting problem areas and
deformities. The categories on the form are
used to define insert requirements, ulcer and
deformity history, and resulting follow-up.
When following the categories A, B, C, D,
E across the form, note important differences in the patient evaluation that will require varied treatment and follow-up schedules. Category A patients may or may not
feel the 4.17 (1 g) monofilament, but they do
have protective sensation because they detect the 5.07 (10 g). These patients will
change gait or remove footwear in response
to pain and discomfort. They can be scheduled for annual follow-up and require a well-fitted shoe with cushion for comfort and
shock absorption.
Category B, C and D patients are similar
only because these patients do not feel the
5.07 (10 g) monofilament and do not have
protective sensation. These patients have
neuropathy and do not retain enough nerve
signals to protect their feet from damage due
to mechanical stresses.
The Category B patient is seen every six
months and requires accommodative molded inserts. These patients have no history of
ulcer or deformity.
Category C patients require the same protocol as B except follow-up is increased to
every four months. These patients have a
deformity that may require periodic inspection and insert modification.
Category D patients will increase follow-up appointments to every three months because of a history of ulceration. Previous ulcers will require special care or re-ulceration
is likely.
The insensate foot - Category B - is common in diabetics. These patients cannot feel
the 6.10 (75 g) monofilament - a force so
high that many patients come in with foreign
objects embedded in their feet. When patients cannot feel forces of this magnitude,
they must be seen every two months regardless of ulcer or deformity history.
Complications of Neuropathic Feet
The goal of orthotic design is to provide accommodative (molded) cushion inserts for
the foot that will distribute pressures, reduce
high stress areas and provide shock absorption. A common problem occurs when a calloused area is not debrided on a regular basis
to reduce pressure. Figure 14
shows a common area of callous (high stress).
When debrided and exposed (see Figure
15
), there is a sinus tract (see Figure 16
) that,
if not treated, continues to migrate under the
skin with the mechanical stress of weight-bearing. This can lead to infection of bone
and serious complications.
Another problem is the neuropathic foot
cannot detect proper shoe size or shape to
thereby prevent high pressures. Patients will
select a shoe that is one to two sizes too small
because they feel it is a good fit. They do not
have the sensory feedback to properly select
shoes so they must be told what size shoes to
buy. The length must be 1/2- to 3/4-inch beyond the longest toe. When it is not, the toe
suffers ulceration (see Figure 17
and Figure 18
).
The shoe must be a soft leather, void of
stitching or contours at toes and deep
enough to accommodate an insert under the
full foot.
When the nail and dorsal area of the great
toe show stress, there is usually a problem
with great toe extension (thrusting upward)
during gait, and a higher toe box is required
(see Figure 19
). Lesions as in Figure 20
are
commonly from a shoe with a narrow or
pointed toe.
The neuropathic foot must be accommodated to reduce risk of ulceration. Common
deformities include hypertrophic nails, claw
toes and deformities (see Figure 21
, Figure 22
and
Figure 23
). Figure 24
shows a common ulcer site due
to great toe pronation and requires that the
insert be high on the medial side of the great
toe.
Autonomic Neuropathy
An added complication with diabetes is
autonomic neuropathy. Sweat and oil are no
longer produced and secreted into skin layers. The elasticity is lost, and keratin builds
up, hardens, cracks and allows entry of bacteria (see Figure 25
). Feet that sweat rarely
ulcerate. Skin tears with joint flexion and
extension because sweat and oils no longer
keep the skin elastic and pliable.
The skin tends to suffer many dermatological conditions (see Figure 26
) and reactions.
The patient must be taught to moisturize
skin after bathing to retain moisture. Also,
patients must not use tape on dry, fragile
skin. When a Band-Aid or tape is removed,
an open lesion can be created, providing an
entry for infection (see Figure 27
).
Vascular Conditions
The neuropathic limb often exhibits vascular
conditions that require control of excess edema. Discuss with the prescribing physician
the stocking to be applied to the limb.
Venous stasis is a complication-due to
high pressures in the capillary system-that
produces open lesions. Venous stasis ulcers
(see Figure 28
) are difficult to treat and manage with pressure-gradiated stockings. Patients with a neuropathic limb cannot continually walk on a stocking seam or opening
on the plantar surface without skin breakdown. Be aware that the highest compression in medical gradiated stockings (standard or custom) is at the ankle. Make sure
you are not applying excessive force here.
Further complications can arise with zippers
or seams over bony prominences (especially
malleoli). Obtain stocking with the compression beginning at the metatarsal heads, equal
pressure to the ankle and then graduated
proximally with minimal seams (see Figure
29
).
Patient Education
Patient compliancy depends on education.
Patients must be taught to inspect their feet
daily for fungal (nails) problems, callous,
redness, swelling, heat and maceration between toes. Socks must not be mended, have
thick seams or holes. Shoes must be inspected for wear and foreign objects.
Neuropathy can cause a "cold" sensation
that is disturbing to patients. Burns can be
prevented by warming feet with socks instead of hot water bottles or heating pads.
An excellent way to improve compliancy
is to trace the perimeters of ulcerations onto
transparent film (exposed X-ray) and let patients evaluate their own healing rate between follow-up appointments. Patients may
be discouraged that callous areas decrease
slowly. The repeated temperature readings
will be an objective method of successfully
reducing stress to the area. Callouses retain a
three- to four-month memory and continue
to replenish for a short time even though
weight reduction is sufficient for long-term
management. Patients can control callous
production by following their daily bath with
five strokes over the callous area with a pumice stone.
Conclusion
While neuropathy exists in many disease
processes, we are concerned with the growing number of diabetics requiring management of chronic disease-related complications. These patients must be evaluated and
followed before ulceration occurs. When
breakdown begins in one diabetic foot, the
contralateral side is commonly involved
within 18 to 36 months so prophylactic measures are especially important.
There are many considerations in the neuropathic limb, and it is hoped this method of
clinical evaluation with treatment and follow-up will assist the orthotist's and prosthetist's involvement in a complicated disease
process.
Nancy Elftman is a certified orthotist at Rancho
Los Amigos Medical Center, Downey, Calif., and
provides services to the Ortho-Diabetes Service.
She is also actively involved with the American
Diabetes Association.
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