It is now 10 years since the last technical review on preventative foot care was published
(1), which was followed by an American Diabetes Association (ADA) position statement
on preventive foot care in diabetes (2). Many studies have been published proposing
a range of tests that might usefully identify patients at risk of foot ulceration,
creating confusion among practitioners as to which screening tests should be adopted
in clinical practice. A task force was therefore assembled by the ADA to address and
concisely summarize recent literature in this area and then recommend what should
be included in the comprehensive foot exam for adult patients with diabetes. The committee
was cochaired by the immediate past and current chairs of the ADA Foot Care Interest
Group (A.J.M.B. and D.G.A.), with other panel members representing primary care, orthopedic
and vascular surgery, physical therapy, podiatric medicine and surgery, and the American
Association of Clinical Endocrinologists.
THE PATHWAY TO FOOT ULCERATION
The lifetime risk of a person with diabetes developing a foot ulcer may be as high
as 25%, whereas the annual incidence of foot ulcers is ∼2% (3–7). Up to 50% of older
patients with type 2 diabetes have one or more risk factors for foot ulceration (3,6).
A number of component causes, most importantly peripheral neuropathy, interact to
complete the causal pathway to foot ulceration (1,3–5). A list of the principal contributory
factors that might result in foot ulcer development is provided in Table 1.
The most common triad of causes that interact and ultimately result in ulceration
has been identified as neuropathy, deformity, and trauma (5). As identification of
those patients at risk of foot problems is the first step in preventing such complications,
this report will focus on key components of the foot exam.
COMPONENTS OF THE FOOT EXAM
History
While history is a pivotal component of risk assessment, a patient cannot be fully
assessed for risk factors for foot ulceration based on history alone; a careful foot
exam remains the key component of this process. Key components of the history include
previous foot ulceration or amputation. Other important assessments in the history
(Table 2) include neuropathic or peripheral vascular symptoms (7,8), impaired vision,
or renal replacement therapy. Lastly, tobacco use should be recorded, since cigarette
smoking is a risk factor not only for vascular disease but also for neuropathy.
General inspection
A careful inspection of the feet in a well-lit room should always be carried out after
the patient has removed shoes and socks. Because inappropriate footwear and foot deformities
are common contributory factors in the development of foot ulceration (1,5), the shoes
should be inspected and the question “Are these shoes appropriate for these feet?”
should be asked. Examples of inappropriate shoes include those that are excessively
worn or are too small for the person's feet (too narrow, too short, toe box too low),
resulting in rubbing, erythema, blister, or callus. Features that should be assessed
during foot inspection are outlined in Table 3 and are discussed below.
Dermatological assessment.
The dermatological assessment should initially include a global inspection, including
interdigitally, for the presence of ulceration or areas of abnormal erythema. The
presence of callus (particularly with hemorrhage), nail dystrophy, or paronychia should
be recorded (9), with any of these findings prompting referral to a specialist or
specialty clinic. Focal or global skin temperature differences between one foot and
the other may be predictive of either vascular disease or ulceration and could also
prompt referral for specialty foot care (10–13).
Musculoskeletal assessment.
The musculoskeletal assessment should include evaluation for any gross deformity (14).
Rigid deformities are defined as any contractures that cannot easily be manually reduced
and are most frequently found in the digits. Common forefoot deformities that are
known to increase plantar pressures and are associated with skin breakdown include
metatarsal phalangeal joint hyperextension with interphalangeal flexion (claw toe)
or distal phalangeal extension (hammer toe) (15–17). (Examples of these deformities
are shown in Fig. 1.)
An important and often overlooked or misdiagnosed condition is Charcot arthropathy.
This occurs in the neuropathic foot and most often affects the midfoot. This may present
as a unilateral red, hot, swollen, flat foot with profound deformity (18–20). A patient
with suspected Charcot arthropathy should be immediately referred to a specialist
for further assessment and care.
Neurological assessment
Peripheral neuropathy is the most common component cause in the pathway to diabetic
foot ulceration (1,4,5,7). The clinical exam recommended, however, is designed to
identify loss of protective sensation (LOPS) rather than early neuropathy. The diagnosis
and management of the latter were covered in a 2004 ADA technical review (7). The
clinical examination to identify LOPS is simple and requires no expensive equipment.
Five simple clinical tests (Table 3), each with evidence from well-conducted prospective
clinical cohort studies, are considered useful in the diagnosis of LOPS in the diabetic
foot (1–7). The task force agrees that any of the five tests listed could be used
by clinicians to identify LOPS, although ideally two of these should be regularly
performed during the screening exam—normally the 10-g monofilament and one other test.
One or more abnormal tests would suggest LOPS, while at least two normal tests (and
no abnormal test) would rule out LOPS. The last test listed, vibration assessment
using a biothesiometer or similar instrument, is widely used in the U.S.; however,
identification of the patient with LOPS can easily be carried out without this or
other expensive equipment.
10-g monofilaments.
Monofilaments, sometimes known as Semmes-Weinstein monofilaments, were originally
used to diagnose sensory loss in leprosy (21). Many prospective studies have confirmed
that loss of pressure sensation using the 10-g monofilament is highly predictive of
subsequent ulceration (3,21,22). Screening for sensory loss with the 10-g monofilament
is in widespread use across the world, and its efficacy in this regard has been confirmed
in a number of trials, including the recent Seattle Diabetic Foot Study (4,21,23,24).
Nylon monofilaments are constructed to buckle when a 10-g force is applied; loss of
the ability to detect this pressure at one or more anatomic sites on the plantar surface
of the foot has been associated with loss of large-fiber nerve function. It is recommended
that four sites (1st, 3rd, and 5th metatarsal heads and plantar surface of distal
hallux) be tested on each foot.
The technique for testing pressure perception with the 10-g monofilament is illustrated
in Fig. 2; patients should close their eyes while being tested. Caution is necessary
when selecting the brand of monofilament to use, as many commercially available monofilaments
have been shown to be inaccurate. Single-use disposable monofilaments or those shown
to be accurate by the Booth and Young (23) study are recommended. The sensation of
pressure using the buckling 10-g monofilament should first be demonstrated to the
patient on a proximal site (e.g., upper arm). The sites of the foot may then be examined
by asking the patient to respond “yes” or “no” when asked whether the monofilament
is being applied to the particular site; the patient should recognize the perception
of pressure as well as identify the correct site. Areas of callus should always be
avoided when testing for pressure perception.
128-Hz tuning forks.
The tuning fork is widely used in clinical practice and provides an easy and inexpensive
test of vibratory sensation. Vibratory sensation should be tested over the tip of
the great toe bilaterally. An abnormal response can be defined as when the patient
loses vibratory sensation and the examiner still perceives it while holding the fork
on the tip of the toe (3,4).
Pinprick sensation.
Similarly, the inability of a subject to perceive pinprick sensation has been associated
with an increased risk of ulceration (4). A disposable pin should be applied just
proximal to the toenail on the dorsal surface of the hallux, with just enough pressure
to deform the skin. Inability to perceive pinprick over either hallux would be regarded
as an abnormal test result.
Ankle reflexes.
Absence of ankle reflexes has also been associated with increased risk of foot ulceration
(4). Ankle reflexes can be tested with the patient either kneeling or resting on a
couch/table. The Achilles tendon should be stretched until the ankle is in a neutral
position before striking it with the tendon hammer. If a response is initially absent,
the patient can be asked to hook fingers together and pull, with the ankle reflexes
then retested with reinforcement. Total absence of ankle reflex either at rest or
upon reinforcement is regarded as an abnormal result.
Vibration perception threshold testing.
The biothesiometer (or neurothesiometer) is a simple handheld device that gives semiquantitative
assessment of vibration perception threshold (VPT). As for vibration using the 128-Hz
tuning fork, vibration perception using the biothesiometer is also tested over the
pulp of the hallux. With the patient lying supine, the stylus of the instrument is
placed over the dorsal hallux and the amplitude is increased until the patient can
detect the vibration; the resulting number is known as the VPT. This process should
initially be demonstrated on a proximal site, and then the mean of three readings
is taken over each hallux. A VPT >25 V is regarded as abnormal and has been shown
to be strongly predictive of subsequent foot ulceration (15,22).
Vascular assessment
Peripheral arterial disease (PAD) is a component cause in approximately one-third
of foot ulcers and is often a significant risk factor associated with recurrent wounds
(5,25). Therefore, the assessment of PAD is important in defining overall lower-extremity
risk status. Vascular examination should include palpation of the posterior tibial
and dorsalis pedis pulses (10,26), which should be characterized as either “present”
or “absent” (26).
Diabetic patients with signs or symptoms of vascular disease (Table 2) or absent pulses
on screening foot examination should undergo ankle brachial pressure index (ABI) pressure
testing and be considered for a possible referral to a vascular specialist. The ABI
is a simple and easily reproducible method of diagnosing vascular insufficiency in
the lower limbs. Blood pressure at the ankle (dorsalis pedis or posterior tibial arteries)
is measured using a standard Doppler ultrasonic probe. This technique is outlined
in Fig. 3. The ABI is obtained by dividing the ankle systolic pressure by the higher
of the two brachial systolic pressures (8). An ABI >0.9 is normal, <0.8 is associated
with claudication, and <0.4 is commonly associated with ischemic rest pain and tissue
necrosis.
The ADA Consensus Panel on PAD recommended measurement of ABI in diabetic patients
over 50 years of age and consideration of ABI measurement in younger patients with
multiple PAD risk factors, repeating normal tests every 5 years (8). ABI may therefore
be part of the annual comprehensive foot exam in these patient subgroups. ABI measurements
may be misleading in diabetes because the presence of medial calcinosis renders the
arteries incompressible and results in falsely elevated or supra-systolic ankle pressures.
In the presence of incompressible calf or ankle arteries (ABI >1.3), measurements
of digital arterial systolic pressure (toe pressure) or transcutaneous oxygen tension
may be performed.
Risk classification and referral/follow-up
Once the patient has been thoroughly assessed as described above, he or she should
be assigned to a foot risk category (Table 4). These categories are designed to direct
referral and subsequent therapy by the specialty clinician or team (17,20) and frequency
of follow-up by the generalist or specialist. Increased category is associated with
an increased risk for ulceration, hospitalization, and amputation (17). Patients in
risk category 0 generally do not need referral and should receive general foot care
education and undergo comprehensive foot examination annually. Patients in foot risk
category 1 may be managed by a generalist or specialist every 3–6 months. Consideration
should be given to an initial specialist referral to assess the need for specialized
treatment and follow-up. Those in categories 2 and 3 should be referred to a foot
care specialist or specialty clinic and seen every 1–3 months.
CONCLUSIONS
It cannot be overstated that the complications of the diabetic foot are common, complex,
and costly, mandating aggressive and proactive preventative assessments by generalists
and specialists. All patients with diabetes must have their feet evaluated at least
at yearly intervals for the presence of the predisposing factors for ulceration and
amputation (neuropathy, vascular disease, and deformities). This report summarizes
a simple protocol for doing so. If abnormalities are present, more frequent evaluation
of the diabetic foot is recommended depending on risk category, as described above
and in Table 4. It is through systematic examination and risk assessment, patient
education, and timely referral that we may further reduce the unnecessarily high prevalence
of lower-extremity morbidity in this population.