COMMON
FOOT INFECTIONS
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| COMMON INFECTIONS OF FOOT |
The foot exists in an environment that unfortunately can be conducive to infection. Primarily, the use of shoes constricts the foot and produces a warm, moist environment that encourages bacterial growth. Foot infections can occur in all individuals. But, the diabetic patient is particularly susceptible to foot infection owing to the loss of protective sensation. Even trivial trauma either from a poorly fitting shoe or from bare-foot walking can result in violation of the skin and lead to severe infection. Poor blood supply and diminished immune function further compromise the diabetic patient’s ability to fight foot infection. Common locations for foot infections include the paronychial (nail) area and the deep spaces of the foot.
PARONYCHIAL INFECTION
Onychocryptosis is the formal
name for the common condition referred to as ingrown toenail. The great toe is
most frequently affected. Both medial or lateral sides of the nail may be
involved. Three patterns of ingrown toenail can be observed. In the first,
incorrect nail trim- ming technique results in a fishhook-shaped spur that digs
into the lateral nail groove. In the second type, the nail develops an inward
curvature of the lateral margin that also produces impingement with the tissue
of the nail groove. In the last type, hypertrophy of the paronychial tissue
at the margin of the nail produces the impingement. Wearing tight shoes that
pinch the lateral skin fold between the shoe and the underlying toenail often
precipitates or aggravates the problem. In each of these instances, the
resulting impingement produces inflammation where the nail meets the nail fold.
This inflammation can then lead to secondary infection.
Ingrown toenail is best
prevented with proper toenail-trimming technique. The toenail should be allowed
to grow beyond the lateral skin fold and should be cut straight across, not
rounded at the corners. The risk of ingrown toenail is minimized by making sure
that the square edge of the nail extends just slightly beyond the skin fold and
by wearing well-fitting shoes. An inflamed, ingrown nail is treated initially
with removal of all compressive shoes and stockings and warm soaks in Epsom
salts and water. Oral antibiotics can be started if significant erythema
consistent with cellulitis develops along the affected border of the toe. If
the inflammation or infection fails to resolve with these measures,
particularly if purulence persists beneath the paronychial fold, then surgical
treatment may be required. The most common surgical treatment involves a
hemi-resection of the nail plate. This is usually performed under digital
block. An elevator is used to lift the lateral nail margin from underneath the
hypertrophied paronychium. A scissors then makes a longitudinal cut in the nail
plate and the lateral quarter of the nail plate is removed. After partial
excision of the toenail and the surrounding granulation tissue, the patient may
be given oral antibiotics and encouraged to soak the toe twice a day in warm
water. The excised area heals by secondary intention.
FUNGAL INFECTION OF TOENAIL
Chronic fungal infection of the
nail is called onychomycosis. The fungal infection causes the toenail to become
hypertrophic, deformed, yellow, and friable. Once established, a fungal infection
is extremely difficult to eradicate.
Conservative treatment includes
simple trimming of the toenail to maintain an essentially normal shape and
appearance. When the toenail becomes severely deformed and thickened, it may
cause painful pressure on the adjacent skin. Occasionally, pressure from large,
deformed nails creates a secondary, low-grade cellulitis around the periphery
of the nail. Removal of the toenail may be necessary to decrease the pain and
inflammation.
Under a digital block, the
surgeon may elevate the toenail from its bed and remove it entirely. Necrotic
debris that has accumulated beneath the nail is then debrided. Performed in
isolation, nail removal provides only temporary relief of mechanical symptoms
because when the nail regrows, the fungus is still present and the nail
deformity recurs. Administering antifungal topical medications after nail removal can
significantly improve the success rate. Currently, the most effective means of
definitively treating this infection involves the use of powerful oral
antifungal antibiotics.
PUNCTURE WOUND
Puncture wound of the foot
remains one of the most common presenting injuries seen in hospital emergency
departments and one of the most common causes of serious infection in the foot.
The penetrating object frequently carries pathogens with it when it breaks the
skin and deposits these organisms deep into the foot. Once the object is
removed, the skin may close over the top, preventing drainage. This creates an
ideal environment for abscess formation. Although shoes provide some
protection to the foot, sharp objects such as nails can pierce the sole of the
shoe and penetrate the foot. Although tetanus, which is caused by Clostridium
tetani, is a theoretical complication of a puncture wound, such an
infection is exceedingly rare because of widespread effective immunization. On
the other hand, penetration of the sole of the foot may seed the foot with
other aggressive bacteria that can produce serious local infection.
Gram-positive cocci such as Staphylococcus and Streptococcus species
remain common causes of foot infection after puncture wounds, but a large
number of infections are due to gram-negative organisms, particularly Pseudomonas
aeruginosa. It is believed that Pseudomonas thrives within shoes and
is delivered into the foot when the puncturing object penetrates both the shoe
and the foot. Gram-negative infections can be quite aggressive, particularly if
the puncture wound extends to bone, and can result in not only deep abscess
formation but also bone infection known as osteomyelitis.
It is critical to take
aggressive steps to prevent infection after puncture wound of the foot.
Adequate anesthesia is required, often employing a tibial nerve or ankle block.
The puncture wound is opened up widely to allow for removal of any foreign
bodies or debris and to allow ample irrigation. The tract must be spread to the
depth of the penetration. Once adequate debridement and irrigation has been
performed, it is critical to leave the wound open to allow for drainage. This
greatly decreases the risk of subsequent infection. The wound heals
secondarily, usually in 1 to 2 weeks.
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| DEEP INFECTIONS OF FOOT |
DEEP INFECTION
A neglected or improperly
treated puncture wound may lead to a serious deep space abscess in the foot. An
abscess is a focal collection of purulent material in a defined closed space.
The foot possesses five distinct deep fascial compartments in which infection
may occur (see Plate 5-45). These compartments include the superficial
posterior, plantar, central, posterior dorsal, and dorsal spaces. The central
plantar space in particular is frequently involved when a deep foot abscess
develops. Symptoms frequently include diffuse swell-ing, pain, and erythema of
the foot, particularly along the instep. If untreated, deep space infection of the
foot can extend along the flexor tendons to involve the deep fascial
compartment of the leg.
Antibiotics alone are
insufficient to treat a deep space infection. Once an abscess has developed in
one of the closed spaces of the foot, it must be treated with surgical incision
and drainage. The central space of the plantar aspect of the foot is best
approached through a medial foot incision, which reflects the abductor hallucis
muscle plantarly and allows both access to the central space and visualization
of the critical neurovascular structures coursing to the toes. Alternatively,
if the infection appears to be more dorsal, a dorsomedial and dorsolateral
incision can be used to decompress the abscess. All necrotic and infected
tissue must be debrided and the wound thoroughly irrigated and left open.
Severe infection may require repeat surgical debridement. Wounds are usually
allowed to heal by secondary intention, which may be facilitated by negative pressure
wound dressings.
Tissue specimens are obtained
for culture, and broad-spectrum antibiotics are administered. Appropriate
antibiotics are administered when cultures identify the specific organisms
involved. The infection is often polymicrobial.
