Definition
Synonyms: Tendo calcaneus (lat.) The structure known as the Achilles tendon is the attachment tendon of the three-headed muscle (Musculus triceps surae) of the lower leg. It is the thickest and strongest tendon in the human body.
Anatomy of the Achilles tendon
The Achilles tendon is the thickest and strongest tendon in the human body. A tendon is the part of a muscle that connects the muscle to the bone and consists of connective tissue. The Achilles tendon measures about 20 centimetres in length, is surrounded by a tendon sheath and consists of several tendon bundles, which in turn are made up of connective tissue fibres.
The musculus triceps surae consists – as the name suggests – of 3 muscle heads. Two of them belong to the calf muscle (Musculus gastrocnemius), one of them belongs to the plaice muscle (Musculus soleus). All three muscle heads unite in their course to form an Achilles tendon, with which they attach to the heel bone (calcaneus).
The Achilles tendon is attached to the entire width of the bony prominence located here, the calcaneus tuber. Over the upper part of this bone projection the Achilles tendon pulls away, in order to set then a piece further down at the bone. So that the tendon does not lie directly against the bone in this area, there is a bursa (bursa tendinis calcanei) between the Achilles tendon and the bone.
A bursa is a small fluid-filled bag that serves to reduce the pressure and friction between the tendon, muscle and bone. The Achilles tendon is widest at the base of the bone and tapers upwards. The narrowest point is about 4cm above the bone base, after which it runs wider and wider in the three-headed calf muscle.
This is composed of two individual muscles: a two-headed calf muscle (Musculus gastrocnemius), which originates on both sides of the thigh bone (femur) in the hollow of the knee, and a single-headed plaice muscle (Musculus soleus). The plaice muscle has its origin at the back of the tibia and at the fibula. The Achilles tendon transmits the force of this large three-headed calf muscle.
This enables above all the powerful bending of the foot towards the sole of the foot (plantar flexion) and the lifting of the inner edge of the foot while simultaneously lowering the outer edge of the foot (supination). The Achilles tendon runs at a certain distance from the lower leg bone, embedded between the superficial and the deep leaf of the so-called lower leg fascia of an enveloping layer of connective tissue. Also enclosed by these two fascia leaves is a fatty body (Corpus adiposum subachilleum), which fills the space between the Achilles tendon and the lower leg bone.
The skin above the Achilles tendon is relatively thin and easily slidable, so the Achilles tendon itself is easy to feel from the outside. The branches of the posterior tibial artery (Arteria tibialis posterior) and the calf artery (Arteria fibularis) supply the Achilles tendon with blood. The innervation of the three-headed calf muscle and the Achilles tendon is carried out via the tibial nerve (nervus tibialis), which originates from the sciatic nerve (nervus ischiadicus).
