A
Achilles tendon A thick, strong band of connec-
tive tissue at the back of the heel that joins the
gastrocnemius and soleus muscles of the calf (back
of the lower leg) to the calcaneus (heel BONE). The
Achilles TENDONmakes possible extension of the
foot, a necessary element of walking, running,
and jumping. A sharp tap to the Achilles tendon
with a REFLEXmallet causes the foot to jerk down-
ward; this is the Achilles tendon reflex. Motor
NEURONdiseases such as AMYOTROPHIC LATERAL SCLE-
ROSIS (ALS) and post-polio syndrome produce
abnormal Achilles tendon reflex responses.
Injury to the Achilles tendon affects the ability
to move the foot down. The Achilles tendon is
vulnerable to damage during running and jump-
ing, and especially “plant and twist” kinds of
movements, common in numerous sports such as
baseball, basketball, tennis, soccer, football, and
running. The tendon may become inflamed (TEN-
DONITIS) or tear (rupture).
For further discussion of the Achilles tendon
within the context of musculoskeletal structure
and function, please see the overview section “The
Musculoskeletal System.”
See also ACHILLES TENDON INJURY; LIGAMENT;
POLIOMYELITIS.
Achilles tendon injury Traumatic damage to the
ACHILLES TENDON, the broad band of connective tis-
sue that joins the calf muscles to the heel of the
foot. The most common Achilles TENDONinjury is
INFLAMMATION, called Achilles TENDONITIS, tends to
develop somewhat gradually as an overuse injury.
A tear in the Achilles tendon, called a rupture,
generally happens suddenly during an athletic
activity or event. Extended running, especially
uphill or in shoes with flat heels (such as racing
flats), and jumping are activities that place the
Achilles tendon at risk for injury.
Achilles tendonitis causes PAINand tenderness
to touch at the base of the calf muscles on the
back of the leg. The inflamed area may appear
swollen. Though the pain may restrict the ability
to use the foot and ankle, the mechanical func-
tions of the Achilles tendon remain intact, and the
person can perform the movements necessary to
walk. Achilles tendonitis may follow a competitive
event that places high stress on the legs, such as a
race, or may develop during a new training regi-
men.
An Achilles rupture occurs suddenly during
movement that stresses the Achilles tendon, such
as running. The Achilles tendon is especially vul-
nerable to quick movements that place extreme
stress on it, such as a “plant and twist” maneuver
in sports such as tennis, soccer, basketball, soccer,
and football. Runners may tear the Achilles ten-
don when starting from blocks or when accelerat-
ing for the finish. The injury causes a popping
sensation, followed by pain and an inability to
move the ankle and foot very well. When the tear
is complete, severing the Achilles tendon, the per-
son cannot point the foot downward to perform
the basic movements of walking. Pain is most
often at the back of the heel.
The ability to move the foot is generally the dis-
tinguishing factor between Achilles tendonitis and
Achilles tendon rupture. The doctor’s examination
includes testing the Achilles tendon reflex, prob-
ing for areas of sensitivity (palpable divot), and
watching the person move the feet with the legs
dangling (seated on an examination table) and
when walking. Diagnostic imaging procedures
such as MAGNETIC RESONANCE IMAGING (MRI) and297