CorpusHuman Anatomy
MuscularTendon

Calcaneal tendon

Tendo calcaneus

Also known as: Achilles tendon, tendo Achillis, heel cord

The thickest and strongest tendon in the body, formed by gastrocnemius and soleus. It inserts on the posterior calcaneus and transmits the force of plantarflexion.

Show on body map Muscles — Posterior View

Overview

Length≈15 cm
Watershed zone≈2–6 cm above the insertion
Peak load in runningseveral times body weight (est. up to ≈8–12×)

The calcaneal tendon begins about mid-calf where the aponeuroses of gastrocnemius and soleus fuse. It is roughly 15 cm long. As it descends it narrows, and it rotates ≈90°, so that soleus fibres end up inserting more medially and gastrocnemius fibres more laterally. It inserts on the middle third of the posterior surface of the calcaneus. A retrocalcaneal bursa lies between the tendon and the upper calcaneus, and a subcutaneous bursa lies behind it. The tendon has no synovial sheath. Instead it is wrapped in a vascular paratenon that allows it to glide.

It can withstand loads of several times body weight during running and jumping (estimated up to ≈8–12×), and it stores and returns elastic energy with each stride. Its blood supply is poorest in a watershed zone ≈2–6 cm above its insertion, the commonest site of tendinopathy and rupture.

Location

Posterior ankle, from mid-calf to the calcaneal tuberosity.

Parts & subdivisions

  1. Gastrocnemius contribution
    Superficial aponeurosis from the two gastrocnemius heads.
  2. Soleus contribution
    Deep part, forming the bulk of the tendon distally.
  3. Retrocalcaneal bursa
    Between the tendon and the superior calcaneal tuberosity. Inflamed in Haglund deformity.

Anatomy

Origin

Musculotendinous junctions of gastrocnemius and soleus (mid-calf).

Insertion

Middle third of the posterior surface of the calcaneus.

Innervation

Sensory: sural and tibial nerves. Reflex: S1 (ankle jerk).

Nerve roots

S1–S2

Arterial supply

Posterior tibial artery (proximal and distal parts) and fibular artery (mid-portion), via the paratenon. The mid-portion is a watershed area.

Relations

The sural nerve and small saphenous vein run along its lateral side. Plantaris lies on its medial side. Kager's fat pad lies in front of it.

Function

  • Transmits the force of the triceps surae to the calcaneus for plantarflexion
  • Stores and returns elastic energy in gait

Clinical significance

Achilles tendon rupture

Sudden pain, like "being kicked", during push-off, typically in middle-aged weekend athletes. It is also associated with fluoroquinolones and corticosteroids. Findings: a palpable gap, inability to stand on tiptoe, and a positive Thompson (Simmonds) test (no plantarflexion when the calf is squeezed). Treated with functional bracing in equinus or surgical repair.

Achilles tendinopathy

Mid-portion (2–6 cm above the insertion) or insertional pain and thickening from overload. First-line treatment is eccentric calf loading (heel-drop) exercises.

Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.