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The Achilles tendon, or the heel cord, also known as the calcaneal tendon, is a tendon at the back of the lower leg, and is the thickest in the human body.[1][2][3] 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 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.[4]
The oldest known record of the tendon being named after Achilles was written in 1693 by the Flemish 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."[5][6] The tendon has been described as early as the time of Hippocrates, who described it as the "tendo magnus" (Latin for "great tendon") and by subsequent anatomists prior to Verheyen as "chorda Hippocratis" (Latin for "Hippocrates' string").[6]
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.[6] The first closed rupture was described by Ambroise Pare in the sixteenth century.[6]
The Achilles tendon is also known as the "tendo calcaneus" (Latin for "calcaneal tendon").[6] 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.
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).[7] 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 4 cm (1.6 in) above its insertion.[8]
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 (Achilles bursa) lies between the tendon and the upper part of the calcaneus. It is about 15 centimetres (6 in) long.
Along the side of the muscle, and superficial to it, is the small saphenous vein. The sural 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.[9] The tendon is the thickest tendon in the human body.[8] It can receive a load stress 3.9 times body weight during walking and 7.7 times body weight when running.[10]
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.[8]
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.[11] 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.[8]
Vibration of the tendon without vision has a major impact on postural orientation.[12] Vibration of the tendon causes movement backwards and the illusion of a forward body tilt in standing subjects.[13] 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.
Inflammation 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.[14] The most common symptoms are sharp achy pain and swelling around the affected tendon.[15][16][17] The pain is typically worse at the start of exercise and decreases thereafter.[18] Stiffness of the ankle may also be present.[14] Onset is generally gradual.[15]
It commonly occurs as a result of overuse such as running.[14][18] Other risk factors include trauma, a lifestyle that includes little exercise, high-heel shoes, rheumatoid arthritis, and medications of the fluoroquinolone or steroid class.[15] Diagnosis is generally based on symptoms and examination.[18]
While stretching and exercises to strengthen the back are often recommended for prevention, evidence to support these measures is poor.[19][20][21] Treatment typically involves rest, ice, non-steroidal antiinflammatory agents (NSAIDs), and physical therapy.[14][15] A heel lift or orthotics may also be helpful.[14][18] In those in whose symptoms last more than six months despite other treatments, surgery may be considered.[14] Achilles tendinitis is relatively common.[14]
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 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.[22]
Achilles tendon rupture is when the Achilles tendon breaks.[23] Symptoms include the sudden onset of sharp pain in the heel.[15] A snapping sound may be heard as the tendon breaks and walking becomes difficult.[24]
断裂は通常、ふくらはぎの筋肉が使われているときに足が急に曲がったり、直接的な外傷を受けたり、長期間の腱炎の結果として起こります。[24][23] その他の危険因子には、フルオロキノロンの使用、運動の大幅な変化、関節リウマチ、痛風、またはコルチコステロイドの使用が含まれます。[ 25 ] [ 23 ]診断は通常、症状と診察に基づいて行われ、医用画像によって裏付けられます。[ 23 ]アキレス腱断裂は、年間約1万人に1人の割合で発生します。[ 23 ]男性は女性よりも罹患しやすいです。[ 25 ] 30代から50代の人が最も罹患しやすいです。[ 23 ]
予防策としては、運動前にストレッチを行うことが挙げられる。[ 24 ]治療は、手術またはギプス固定で、つま先をやや下向きにしておく。 [ 26 ] [ 23 ]比較的早期の荷重復帰（4週間以内）は許容範囲内と思われる。[ 26 ] [ 27 ]ギプス固定による再断裂のリスクは約25%である。[ 23 ]受傷後4週間以内に適切な治療が行われない場合、予後が悪化する。[ 28 ]
腱黄色腫は、家族性高コレステロール血症などの脂質代謝障害のある人のアキレス腱によく発生するコレステロール沈着物である。[ 29 ]
アキレス腱は神経学的検査の一環として検査されることが多い。この検査では、腱を腱ハンマーで叩く。これによりS1およびS2脊髄神経が検査される。正常な反応は足底屈（下方への動き）である。[ 30 ]
腱のどのレベルまたは部分が影響を受けているか: [ 31 ]
The Achilles tendon is short or absent in great apes, but long in arboreal gibbons and humans.[35] It provides elastic energy storage in hopping,[36] walking, and running.[35] Computer models suggest this energy storage Achilles tendon increases top running speed by >80% and reduces running costs by more than 75%.[35] 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."[35]
Vocatum passim chorda Achillis, & ab Hippocrate tendo magnus. (Appendix, caput XII. De musculis pedii et antipedii, p. 269)
Media related to Achilles tendon at Wikimedia Commons