The Achilles tendon or heel cord, also known as the calcaneal tendon, is a tendon of the back of the leg, and 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, and (except soleus) flexion at the knee.
Abnormalities of the Achilles tendon include inflammation (Achilles tendinitis), degeneration, rupture, and becoming embedded with cholesterol deposits (xanthomas).
Video Achilles tendon
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 fleshy fibers on its inner surface, 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 4 centimetres (1.6 in) above its insertion.
The tendon is covered by the fascia and the integument, 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 the thickest and strongest tendon in the body. It is about 15 centimetres (6 in) long. Along the side of the muscle, and superficial to it, is the small saphenous vein. The tendon can receive a load stress 3.9 times body weight during walking and 7.7 times body weight when running.
Maps Achilles tendon
Function
Acting via the Achilles tendon, the gastrocnemius and soleus muscles cause plantar flexion of the foot at the ankle. 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.
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 compensates by moving the body backwards.
Clinical significance
Inflammation
Inflammation of the Achilles tendon is called Achilles tendinitis. Achilles tendinosis is the soreness or stiffness of the tendon, generally due to overuse.
Degeneration
Achilles tendon degeneration (tendinosis) is typically investigated with either MRI 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, however may involve the insertion where this is 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 spondyloarthitides. Achilles tendinosis is a known risk factor for calf muscle tears.
Rupture
Achilles tendon rupture is a partial or complete break in the tendon. Partial and full Achilles tendon ruptures are most likely to occur in sports requiring sudden eccentric stretching, such as sprinting. The area approximately two inches above the calcaneal attachment is most susceptible to these ruptures due to a zone of avascularity. They require immobilization or surgery.
Stretching the calf muscle, as well as calf-strengthening exercises are recommended to reduce the risk. Training intensity should be increased gradually. The most common Achilles tendon injuries occur when someone abruptly intensifies their training at an abnormal rate.
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.
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."
History
The oldest-known written record of the tendon being named for Achilles is in 1693 by the Flemish/Dutch anatomist Philip Verheyen. In his widely used text Corporis Humani Anatomia he described the tendon's location and said that it was commonly called "the cord of Achilles."
Verheyen referred to the mythological account of Achilles being held by the heel by his mother Thetis 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 Achilles tendon is also known as the 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 calcaneum, meaning heel.
See also
- Heel lifts
Additional images
References
External links
- Image sequence demonstrating Achilles tendinosis
Source of article : Wikipedia
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