The structure of the foot can be confusing to
sort out, but a solid understanding of its structure and function
is important in order to correctly code the many orthopedic
procedures performed on the foot. This month we review the anatomy
of the foot and some common health problems associated with
the foot. Then we focus on the variety of corrective surgical
procedures performed for Hallux valgus (bunions), one
of the most common foot deformities, and some of the surgical
procedures coders should be familiar with.
Overview
of Structure and Function
Simply put, the structure of the foot enables its function.
The foot is a mobile, weight-bearing structure. The large
number of foot bones (26) is needed for flexibility and mobility.
The arrangement of bones produces three strong arches - two
longitudinal arches (medial and lateral) and one transverse
arch. Ligaments hold the foot bones together, and the
tendons of the foot muscles hold the bones in the arched position
while also allowing a certain amount of movement. The arches
assist in absorbing shock loads and balancing the body. The
medial longitudinal arch transmits the force of body weight
to the ground when standing and to the great toe when in motion,
creating a giant lever and putting spring in the gait.
The foot bones may be grouped as follows:
- Ankle: 7 tarsal bones: talus,
calcaneous, navicular, cuboid, medial cuneiform, intermediate
cuneiform, and lateral cuneiform
- Foot: 5 metatarsal bones
- Toes: 14 phalanges - Each great toe
has only two phalanges, one proximal and one distal. The
second through fifth toes each have three phalanges: proximal,
middle and distal.
In addition to the above bones, small, round, knobby protuberances
called sesamoid bones may be found on either side of
the plantar surface (undersurface) of the first metatarsal.
Sesamoid bones form in tendons subjected to compression. The
patella is one of the more familiar sesamoid bone.
Structural
Details
Our review of the foot’s structure begins at the ankle
joint. The ankle connects the tibia and fibula of the lower
leg to the foot. The short, thick tarsal bones are the seven
bones closest to the ankle. Only the uppermost tarsal, the
talus (which is also called the astralagus),
articulates with the tibia and fibula. The medial malleolus
of the tibia and the lateral malleolus of the fibula surround
the talus. During walking, the talus initially bears the
entire weight of the leg. About half the weight is then
transmitted to the heel bone, known as either the calcaneous or
the os calcis. The calcaneous is the largest and
strongest tarsal. The rest of the weight is distributed
to the other tarsal bones. Succeeding the tarsal bones
are the five parallel
metatarsals that form the front of the instep and
then fan out to form the ball of the foot. Each metatarsal
has a proximal base, a shaft, and a distal
head.
The metatarsals articulate proximally with the cuneiform
bones and the cuboid. Distally they articulate with the
proximal phalanges. The metatarsal of the great toe is thicker
than the others because it is designed to bear more weight.
Like the metatarsals, the phalanges of the second
through fifth toes consist of a proximal base, a shaft,
and a distal head. The hallux, or great toe,
has only two phalanges, proximal and distal. They are larger
and heavier than the others because of the need to support
more weight.
The longitudinal arch consists of tarsal and metatarsal
bones arranged to form an arch running from anterior to posterior.
The medial longitudinal arch begins at the calcaneous,
rises up the talus and then descends through the navicular,
the three cuneiforms, and the first, second and third metatarsals.
The keystone of this arch is the talus. The lateral longitudinal
arch also starts at the calcaneous, rises at the cuboid
and descends to the 4th and 5th metatarsals. The transverse
arch is made up of the calcaneous, navicular, cuboid,
and posterior parts of all five metatarsals.
Ankle Joint Structure
Many foot problems occur at the ankle joint as a result of
strain, sprain or fracture. There are actually two joints
in the ankle: one joint between the distal fibula, its lateral
malleolus, and the talus, and one between the medial malleolus
of the tibia and the talus. Both of these joints may be referred
to as talocrural joints. The components of the ankle
joints are:
- The articular capsule: surrounds the joint and
extends from the tibia and malleoli to the talus.
- Medial (deltoid) ligament: A strong, triangular
ligament extending from the medial malleolus of the tibia
to the navicular, calcaneous, and talus.
- Lateral ligament, consisting of three separate
parts:
- Anterior talofibular ligament, extending from
the anterior margin of the lateral malleolus of the fibula
to the talus;
- Posterior talofibular ligament, reaching from
the posterior margin of the lateral malleolus to the talus;
- Calcaneofibular ligament, extending from the
apex of the lateral malleolus to the talus.
Disease
and Injury
The feet are prone to many conditions that arise from constant
weight-bearing pressure as well as disease and injury. Let’s
take a look at some of the conditions that coders may encounter
in medical records.
Strains and Sprains
A strain is simple overstretching of a muscle. Sprains are
more severe injuries caused by wrenching or twisting of a
joint with partial rupture (tear) of its attachments. Sprains
may cause damage to blood vessels, ligaments, tendons, muscles,
or nerves. Swelling and ecchymosis around the joint are due
to damaged blood vessels. There is no misalignment of the
bony joint components in a sprain injury. The ankle is the
most often sprained joint in the body.
Conservative treatment for strains and sprains includes analgesics,
an anti-inflammatory drug, application of cold pack, elevation
of extremities, and immobilization of affected joints. Severe
tendon ruptures may require surgical repair.
Plantar Fasciitis and
Calcaneal Spur Syndrome
The plantar fascia is a dense fibrous sheet of tissue running
from the calcaneous to the metatarsals. It pulls on the heel
to raise the arch of the foot as it pushes off the ground.
It may become stretched or frayed with resultant swelling
and pain. A calcaneal spur is a bony exostosis on the medial
weight-bearing tuberosity of the calcaneous. The spur is the
result of excessive pulling and stretching of the calcaneal
periosteum by the plantar fascia. The spur is the result of
the fascial inflammation and not the cause of the foot pain.
Disorders associated with increased plantar fascial tension
include pes planus, more commonly known as flat feet, and
contracted heel cords.
Severe plantar fasciitis and calcaneal spur syndrome may
be treated surgically via an endoscopic plantar fasciotomy
(EPF). During this procedure, two small incisions are made
on either side of the calcaneous. A video endoscope is inserted
and a fasciotomy is performed near the heel to release the
tension. The calcaneal spur is not removed.
Ganglions
A ganglion is a fluid-filled swelling of the lining of a
joint or tendon. Ganglions may form in any part of the foot,
but usually they appear on the top of the foot or the ankle.
They may swell depending upon weather or activity, and they
are usually slow-growing. If a ganglion puts pressure on nearby
nerves it can cause tingling, numbness, or pain. Surgery involves
excision of the entire ganglion wall and surrounding tissue.
Morton’s Neuroma
Morton’s neuroma is a common foot ailment in which the
outer coating of a nerve in the foot becomes fibrous and thickened
from repeated irritation, resulting in formation of a tumor
composed of nerve cells. The neuroma is usually located on
the bottom of the foot at the head of a metatarsal bone. The
area between the third and fourth toes is most commonly affected,
followed by the area between the second and third toes. Morton’s
neuromas are treated by surgical excision.
Ingrown Nails
Nails that grow into the skin folds on either side of the
toe may become chronically infected and painful. They may
be treated either chemically or surgically. The chemical procedure
involves partial nail removal followed by a chemical such
as phenol to permanently kill the nail growth. In the surgical
procedure a wedge of the nail and the underlying nail bed
is removed and the nail growth cells are removed with a scalpel.
Hammertoe
A hammertoe is bent permanently downward due to buckling
of an interphalangeal joint. Joints at the end or middle of
the toe as well as the joint near the ball of the foot may
be affected. Hammertoes vary in severity and in the number
of joints involved and may be flexible or rigid depending
on the joint’s ability to move. Flexible hammertoes can
be manually straightened, but rigidity causes pain and joint
immobility. Surgical repairs for hammertoe include arthroplasties,
interphalangeal joint fusions, phalangectomies or filleting.
Hallux Abducto Valgus
Deformities (Bunions)
The hallux is the hardest working toe. Every time the foot
pushes off the ground, this toe supports most of the body's
weight. Because the great toe is so critical to movement,
any problem with it can make walking or standing painful.
A bunion (excess or misaligned bone in the joint) is one of
the most common great toe problems.
Although they may develop on the fifth toe, bunions usually
occur at the base of the great toe along its medial side.
The abnormal bony enlargement along the medial side of the
toe causes the toe to point out toward the little toe, thus
creating the hallux valgus deformity. Bunions may be caused
by incorrect foot mechanics, joint damage caused by arthritis,
or an injury. Some people are simply born with extra bone
near a toe joint. High heeled or poorly fitting shoes can
aggravate bunions.
A number of surgical procedures are available to correct
bunions. The difficulty for the coder lies in the terms used
to describe the specific surgical procedures. Generally bunion
surgeries are referred to by eponyms: McBride, Silver, Keller,
Mayo, etc. A coder needs to understand the components of these
procedures to code them correctly.
Silver
- This is the simplest bunion procedure in which
an incision is made on the medial side of the great toe and
the metatarsophalangeal (MTP) joint capsule is opened. The
bunion is exposed and excised with an osteotome. The surgeon
may refer to the procedure as shaving or excision of the medial
eminence. Closure of the joint capsule and skin completes
the Silver procedure.
McBride -
In addition to the elements of the Silver procedure, the
abductor tendon and transverse metatarsal ligament are cut
away from the base of the proximal phalanx. The joint capsule
is tightened to hold the toe in correct position. The sesamoid
bone may be released or excised.
Keller -
This procedure includes removal of the bunion and also partial
removal of the base of the proximal phalanx of the great toe.
A hemi-implant may be used with this procedure, or a wire
may be inserted to stabilize the repair.
Mayo - In
addition to the bunionectomy, part of the head of the first
metatarsal is excised in this procedure.
Keller-Mayo
- This combination procedure involves bunionectomy, partial
resection of the base of the proximal phalanx, and partial
resection of the first metatarsal head. A joint prosthesis,
such as a Swanson’s implant is usually inserted when
this procedure is performed.
Joplin -
In addition to bunionectomy, the MTP joint is fused in this
procedure. The extensor tendon of the great toe is then transplanted.
The tendon may be transferred to the head or neck of the first
metatarsal, or it may be grafted to the fifth toe to reduce
the spread between the first and fifth metatarsals.
Mitchell/Chevron/Austin
- This procedure involves removal of the bunion plus osteotomy
of the first metatarsal head or neck with realignment of the
metatarsal head and optional internal fixation.
Akin Phalanx Osteotomy
- This procedure involves removal of the bunion and osteotomy
of the proximal phalanx to correct the angular deformity of
the great toe.
Double Osteotomy
- Following removal of the bunion, osteotomies of the
base and neck of the first metatarsal or of the base
and head of the first metatarsal are performed.
To test your expertise in coding surgical procedures performed
on the foot, read the operative report on the Procedure
Coding Practice page and assign the appropriate
ICD-9-CM and CPT-4 procedure codes. Then compare your code
assignments to our coding suggestions that appear on the Coding
Recommendations page.
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