The Achilles tendon or heel cord, also known as the calcaneal tendon, is a

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

at the back of the lower leg, and is the thickest in the human body. It serves to attach the plantaris, gastrocnemius (calf) and soleus muscles to the calcaneus (heel) bone. These muscles, acting via the tendon, cause plantar flexion of the foot at the ankle joint, and (except the soleus)

flexion Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

at the knee. Abnormalities of the Achilles tendon include inflammation ( Achilles tendinitis), degeneration, rupture, and becoming embedded with cholesterol deposits ( xanthomas). The Achilles tendon was named in 1693 after the Greek hero

Achilles In Greek mythology, Achilles ( ) or Achilleus () was a hero of the Trojan War who was known as being the greatest of all the Greek warriors. The central character in Homer's ''Iliad'', he was the son of the Nereids, Nereid Thetis and Peleus, ...

History

The oldest-known written record of the tendon being named after

is in 1693 by the Flemish/Dutch anatomist Philip Verheyen. 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 (; ; ), also known as Hippocrates II, was a Greek physician and philosopher of the Classical Greece, classical period who is considered one of the most outstanding figures in the history of medicine. He is traditionally referr ...

, 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 ( , or ; ) is a figure from Greek mythology with varying mythological roles. She mainly appears as a sea nymph, a goddess of water, and one of the 50 Nereids, daughters of the ancient sea god Nereus. When described as a Nereid in Cl ...

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 An Achilles' heel (or Achilles heel) is a weakness despite overall strength, which can lead to downfall. While the mythological origin refers to a physical vulnerability, idiomatic references to other attributes or qualities that can lead to do ...

") 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 tendons, and is located at the back of the lower leg. The Achilles tendon connects the gastrocnemius and soleus muscles to the calcaneal tuberosity 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 and adipose tissue. 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

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, ...

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, 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, 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 joint. The ...

. 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. 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 spindles 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, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

compensates by moving the body backwards.

Clinical significance

Inflammation

Inflammation Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin ''calor'', '' ...

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 sharp achy 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 Running is a method of terrestrial locomotion by which humans and other animals move quickly on foot. Running is a gait with an aerial phase in which all feet are above the ground (though there are exceptions). This is in contrast to walkin ...

. 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 synovial joint, joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and h ...

, and medications of the fluoroquinolone or

steroid A steroid is an organic compound with four fused compound, fused rings (designated A, B, C, and D) arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes t ...

class. Diagnosis is generally based on symptoms and examination. While stretching 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 Physical therapy (PT), also known as physiotherapy, is a healthcare profession, as well as the care provided by physical therapists who promote, maintain, or restore health through patient education, physical intervention, disease preventio ...

. A heel lift or orthotics may also be helpful. In those in whose 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 or

ultrasound Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...

. 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 Gout ( ) is a form of inflammatory arthritis characterized by recurrent attacks of pain in a red, tender, hot, and Joint effusion, swollen joint, caused by the deposition of needle-like crystals of uric acid known as monosodium urate crysta ...

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,

, or

corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are invo ...

use. Diagnosis is typically based on symptoms and examination and supported by

medical imaging Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to revea ...

. 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 Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or ...

with the toes somewhat pointed down. Relatively rapid return to weight bearing (within 4 weeks) appears acceptable. The risk of re-rupture is about 25% with casting. If appropriate treatment does not occur within 4 weeks of the injury outcomes suffer.

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. 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 75%. 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."

References

External links

* {{Use dmy dates, date=April 2017 Human anatomy Tendons Lower limb anatomy Achilles Words and phrases derived from Greek mythology