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The Achilles tendon or heel cord, also known as the calcaneal tendon, is a
tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...
at the back of the lower
leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element ca ...
, and is the thickest in the human body. It serves to attach the
plantaris The plantaris is one of the superficial muscles of the superficial posterior compartment of the leg, one of the fascial compartments of the leg. It is composed of a thin muscle belly and a long thin tendon. While not as thick as the achilles te ...
,
gastrocnemius The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar ...
(calf) and
soleus muscle In humans and some other mammals, the soleus is a powerful muscle in the back part of the lower leg (the calf). It runs from just below the knee to the heel, and is involved in standing and walking. It is closely connected to the gastrocnemius mu ...
s to the calcaneus (heel) bone. These muscles, acting via the tendon, cause plantar flexion of the foot at the
ankle joint The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joi ...
, and (except the soleus)
flexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...
at the knee. Abnormalities of the Achilles tendon include inflammation ( Achilles tendinitis), degeneration, rupture, and becoming embedded with cholesterol deposits (
xanthoma A xanthoma (pl. xanthomas or xanthomata) (condition: xanthomatosis) is a deposition of yellowish cholesterol-rich material that can appear anywhere in the body in various disease states. They are cutaneous manifestations of lipidosis in which lip ...
s). The Achilles tendon was named in 1693 after the Greek hero
Achilles In Greek mythology, Achilles ( ) or Achilleus ( grc-gre, Ἀχιλλεύς) was a hero of the Trojan War, the greatest of all the Greek warriors, and the central character of Homer's '' Iliad''. He was the son of the Nereid Thetis and Pele ...
.


History

The oldest-known written record of the tendon being named for
Achilles In Greek mythology, Achilles ( ) or Achilleus ( grc-gre, Ἀχιλλεύς) was a hero of the Trojan War, the greatest of all the Greek warriors, and the central character of Homer's '' Iliad''. He was the son of the Nereid Thetis and Pele ...
is in 1693 by the Flemish/Dutch anatomist
Philip Verheyen Philip Verheyen (Verrebroek, April 23, 1648 – Leuven, January 28, 1710) was a Flemish surgeon, anatomist and author. As the third child of seven, Verheyen was born in Verrebroek, in modern Belgium (most likely in his parents' house, standing ...
. In his widely used text he described the tendon's location and said that it was commonly called "the cord of Achilles." The tendon has been described as early as the time of
Hippocrates Hippocrates of Kos (; grc-gre, Ἱπποκράτης ὁ Κῷος, Hippokrátēs ho Kôios; ), also known as Hippocrates II, was a Greek physician of the classical period who is considered one of the most outstanding figures in the history o ...
, who described it as the "" (Latin for "great tendon") and by subsequent anatomists prior to Verheyen as "" (Latin for "Hippocrates' string"). Verheyen referred to the mythological account of Achilles being held by the heel by his mother
Thetis Thetis (; grc-gre, Θέτις ), is a figure from Greek mythology with varying mythological roles. She mainly appears as a sea nymph, a goddess of water, or one of the 50 Nereids, daughters of the ancient sea god Nereus. When described as ...
when she dipped him in the River Styx as a baby to render his body invulnerable. As the heel by which she held him was not touched by the water, it was his one vulnerable spot (hence the expression " Achilles' heel") and he was eventually killed by a poison dart to the heel. The name thus also refers to the particularly disabling and painful effect of an injury to this tendon. The first closed rupture was described by Ambroise Pare in the sixteenth century. The Achilles tendon is also known as the "" (Latin for "calcaneal tendon"). Because eponyms (names relating to people) have no relationship to the subject matter, most anatomical eponyms also have scientifically descriptive terms. The term calcaneal comes from the Latin , meaning heel.


Structure

The Achilles tendon connects muscle to bone, like other
tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...
s, and is located at the back of the lower leg. The Achilles tendon connects the
gastrocnemius The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar ...
and
soleus In humans and some other mammals, the soleus is a powerful muscle in the back part of the lower leg (the calf). It runs from just below the knee to the heel, and is involved in standing and walking. It is closely connected to the gastrocnemius mu ...
muscles to the
calcaneal tuberosity In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. S ...
on the calcaneus (heel bone). The tendon begins near the middle of the calf, and receives muscle fibers on its inner surface, particularly from the soleus muscle, almost to its lower end. Gradually thinning below, it inserts into the middle part of the back of the calcaneus bone. The tendon spreads out somewhat at its lower end so that its narrowest part is about above its insertion. The tendon is covered by the fascia and skin, and stands out prominently behind the bone; the gap is filled up with
areolar Loose connective tissue, sometimes called areolar tissue, is a cellular connective tissue with thin and relatively sparse collagen fibers. Its ground substance occupies more volume than the fibers do. It has a viscous to gel-like consistenc ...
and
adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular ...
. A bursa lies between the tendon and the upper part of the calcaneus. It is about long. Along the side of the muscle, and superficial to it, is the
small saphenous vein The small saphenous vein (also short saphenous vein or lesser saphenous vein) is a relatively large superficial vein of the posterior leg. Structure The origin of the small saphenous vein, (SSV) is where the dorsal vein from the fifth digit (sma ...
. The
sural nerve The sural nerve ''(L4-S1)'' is generally considered a pure cutaneous nerve of the posterolateral leg to the lateral ankle. The sural nerve originates from a combination of either the sural communicating branch and medial sural cutaneous nerve, or ...
accompanies the small saphenous vein as it descends in the posterior leg, traveling inferolateral to it as it crosses the lateral border of the Achilles tendon. The tendon is the thickest tendon in the human body. It can receive a load stress 3.9 times body weight during walking and 7.7 times body weight when running. The blood supply to the Achilles tendon is poor, and mostly via a recurrent branch of the
posterior tibial artery The posterior tibial artery of the lower limb is an artery that carries blood to the posterior compartment of the leg and plantar surface of the foot. It branches from the popliteal artery via the tibial-fibular trunk. Structure The poster ...
, and some through arterial branches passing through surrounding muscles.


Function

Acting via the Achilles tendon, the gastrocnemius and soleus muscles cause plantar flexion of the foot at the
ankle The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joi ...
. This action brings the sole of the foot closer to the back of the leg. The gastrocnemius also flexes the leg at the knee. Both muscles are innervated by the
tibial nerve The tibial nerve is a branch of the sciatic nerve. The tibial nerve passes through the popliteal fossa to pass below the arch of soleus. Structure Popliteal fossa The tibial nerve is the larger terminal branch of the sciatic nerve with root val ...
. Because the fibres of the tendon spiral about 90 degrees, fibres from the gastrocnemius tend to attach to the outer part of the bone, whereas fibres from the soleus tend to attach closer to the midline. Vibration of the tendon without vision has a major impact on postural orientation. Vibration of the tendon causes movement backwards and the illusion of a forward body tilt in standing subjects. This is because vibrations stimulate
muscle spindle Muscle spindles are stretch receptors within the body of a skeletal muscle that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers. This information can be ...
s in the calf muscles. The muscle spindles alert the brain that the body is moving forward, so the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...
compensates by moving the body backwards.


Clinical significance


Inflammation

Inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...
of the Achilles tendon is called Achilles tendinitis. Achilles tendinosis is the soreness or stiffness of the tendon, particularly worse when exercising, and generally due to overuse. The most common symptoms are pain and swelling around the affected tendon. The pain is typically worse at the start of exercise and decreases thereafter. Stiffness of the ankle may also be present. Onset is generally gradual. It commonly occurs as a result of overuse such as running. Other risk factors include trauma, a lifestyle that includes little exercise, high-heel shoes,
rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are invol ...
, and medications of the
fluoroquinolone A quinolone antibiotic is a member of a large group of broad-spectrum bacteriocidals that share a bicyclic core structure related to the substance 4-quinolone. They are used in human and veterinary medicine to treat bacterial infections, as wel ...
or steroid class. Diagnosis is generally based on symptoms and examination. While
stretching Stretching is a form of physical exercise in which a specific muscle or tendon (or muscle group) is deliberately flexed or stretched in order to improve the muscle's felt elasticity and achieve comfortable muscle tone. The result is a feeling ...
and exercises to strengthen the back are often recommended for prevention, evidence to support these measures is poor. Treatment typically involves rest, ice, non-steroidal antiinflammatory agents (NSAIDs), and physical therapy. A heel lift or
orthotic Orthotics ( el, Ορθός, translit=ortho, lit=to straighten, to align) is a medical specialty that focuses on the design and application of orthoses, or braces. An is "an externally applied device used to influence the structural and functio ...
s may also be helpful. In those in who symptoms last more than six months despite other treatments, surgery may be considered. Achilles tendinitis is relatively common.


Degeneration

Achilles tendon degeneration (tendinosis) is typically investigated with either
MRI Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...
or ultrasound. In both cases, the tendon is thickened, may demonstrate surrounding inflammation by virtue of the presence of paratenonitis, retrocalcaneal or retro-achilles bursitis. Within the tendon, increased blood flow, tendon fibril disorganisation, and partial thickness tears may be identified. Achilles tendinosis frequently involves the mid portion of the tendon but may involve the insertion, which is then known as enthesopathy. Though enthesopathy may be seen in the context of advancing age, it is also associated with arthritis such as gout and the seronegative spondyloarthritides. Achilles tendinosis is a known risk factor for calf muscle tears.


Rupture

Achilles tendon rupture is when the Achilles tendon breaks. Symptoms include the sudden onset of sharp pain in the heel. A snapping sound may be heard as the tendon breaks and walking becomes difficult. Rupture typically occurs as a result of a sudden bending up of the foot when the calf muscle is engaged, direct trauma, or long-standing tendonitis. Other risk factors include the use of fluoroquinolones, a significant change in exercise,
rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are invol ...
, gout, or corticosteroid use. Diagnosis is typically based on symptoms and examination and supported by medical imaging. Achilles tendon rupture occurs in about 1 per 10,000 people per year. Males are more commonly affected than females. People in their 30s to 50s are most commonly affected. Prevention may include stretching before activity. Treatment may be by surgery or casting with the toes somewhat pointed down. Relatively rapid return to weight bearing (within 4 weeks) appears okay. The risk of re-rupture is about 25% with casting. If appropriate treatment does not occur within 4 weeks of the injury outcomes are not as good.


Xanthomas

Tendon xanthomas are cholesterol deposits that commonly develop in the Achilles tendon of people with lipid metabolism disorders such as familial hypercholesterolemia.


Neurological exam

The Achilles tendon is often tested as part of a neurological examination. In this examination, the tendon is hit with a
tendon hammer A reflex hammer is a medical instrument used by practitioners to test deep tendon reflexes. Testing for reflexes is an important part of the neurological physical examination in order to detect abnormalities in the central or peripheral nervous s ...
. This tests the S1 and S2 spinal nerves: a normal response is plantar flexion (downward movement) of the foot. Level or portion of tendon affected: * Paratendinopathy: The inflammation of a connective tissue sleeve which surrounds the tendon and protects it from friction, irritation, and repeated trauma * Insertional: Eminently overuse-injury which frequently occurs in running and jumping athletes. Patients affected by insertional Achilles tendinopathy complain of pain on the posterior aspect of the heel and may have morning stiffness, swelling with activity and tenderness at the tendon insertion level. If this condition becomes chronic, calcific deposits at the Achilles insertional level may be developed (due to microfractures and healing of the osteotendinous union) which can degenerate, if it persists over time, in the abnormal bony prominence on the posterior aspect of heel, condition known as Haglund deformity, which can be painful and difficult close-shoes fitting due to friction and irritation. * Mid-portion: Occurs approximately 2–7 cm proximal from the Achilles insertion into the calcaneus. Characterized by a combination of pain and swelling at this level. It has associated a remarkable impaired performance.


Other animals

The Achilles tendon is short or absent in great apes, but long in arboreal gibbons and humans. It provides elastic energy storage in hopping, walking, and running. Computer models suggest this energy storage Achilles tendon increases top running speed by >80% and reduces running costs by more than three-quarters. It has been suggested that the "absence of a well-developed Achilles tendon in the nonhuman African apes would preclude them from effective running, both at high speeds and over extended distances."


See also

* Heel lifts


References

{{Use dmy dates, date=April 2017 Human anatomy Tendons Lower limb anatomy Achilles