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# Achilles tendon

The Achilles tendon is the strongest tendon in the body; it joins the calf muscles to the heel bone and lets the foot push off.

Official name: Calcaneal tendon

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## What it is

The thick tendon at the back of the ankle. It joins the calf muscles (gastrocnemius and soleus) to the heel bone.

## What it does

Carries the pull of the calf to the heel, so you can point the foot, push off when walking, run and jump.

## Key points

- Ruptures and midportion tendinopathy cluster 2–6 cm above the insertion, the area with the poorest blood supply
- Thompson (Simmonds) test: squeezing the calf with the person prone fails to point the foot in a complete rupture
- It has a paratenon, not a true synovial sheath; its fibres spiral as they descend, so the soleus fibres end mostly medial
- Active plantarflexion can persist after a complete rupture (deep flexors and fibularis muscles), a classic reason it is missed

## Key facts

**Attaches**
Gastrocnemius and soleus (triceps surae) to middle of posterior surface of calcaneus

**Function**
Thickest, strongest tendon; plantarflexion for push-off; ankle jerk reflex (S1–S2)

**Tight in**
Ankle dorsiflexion with knee extended

## Relations

**Course**
Forms in mid-calf where the gastrocnemius and [soleus](https://durgical.com/en/anatomy/soleus-muscle/) tendons merge, narrows to its thinnest a few centimetres above the heel, then widens onto the [calcaneus](https://durgical.com/en/anatomy/calcaneus/)

**Superficial**
[Skin](https://durgical.com/en/anatomy/skin/) and [crural fascia](https://durgical.com/en/anatomy/crural-fascia/); the subcutaneous calcaneal bursa lies between it and the skin at the heel

**Deep**
Kager's fat pad, then the [flexor hallucis longus](https://durgical.com/en/anatomy/flexor-hallucis-longus/) and the deep posterior compartment; at the heel, the retrocalcaneal bursa between it and the posterosuperior calcaneus

**Medial**
[Plantaris tendon](https://durgical.com/en/anatomy/tendon-of-plantaris/), which runs along its medial edge and may insert separately on the calcaneus

**Lateral**
[Sural nerve](https://durgical.com/en/anatomy/sural-nerve/) and [small saphenous vein](https://durgical.com/en/anatomy/small-saphenous-vein/), which cross from its midline to its lateral side as they descend

## How to find it

Lying prone with the feet over the end of the bed, the tendon stands out as a thick cord behind the ankle. In a rupture, a gap is felt a few centimetres above the heel and the resting foot hangs more dorsiflexed than the other.

## Examination

- Thompson (Simmonds) test: prone, calf squeezed; no plantarflexion means a complete rupture
- Matles test: prone with both knees bent to 90°; the injured foot falls to neutral or dorsiflexion instead of resting slightly pointed
- Palpable gap along the tendon, best felt early before swelling fills it
- Arc sign: a thickening that moves with the tendon during ankle motion is in the tendon (tendinopathy); one that stays put is in the paratenon

## On imaging

Ultrasound is dynamic and measures the gap between the ends with the foot in plantarflexion; MRI shows tendinopathy and partial tears. A lateral X-ray may show loss of Kager's fat triangle in rupture, a Haglund prominence of the calcaneus or insertional calcification.

## Common problems

- Tendinopathy: pain, stiffness and thickening from overuse, either in the middle of the tendon or where it attaches to the heel.
- Rupture: a sudden tear, often during a push-off or jump. Many people feel as if they were kicked in the back of the ankle.
- Irritation of the bursa next to the tendon, sometimes with a bony bump on the back of the heel.

## How it is diagnosed

A physical exam, including squeezing the calf to see if the foot moves (Thompson test). Ultrasound or MRI shows thickening or a tear.

## Treatment

- Tendinopathy: rest from the painful activity, heel lifts and a physical therapy program of gradual strengthening.
- Rupture: a boot or cast with the foot pointed, then physical therapy; or surgery to repair the tendon. The choice depends on the person and the injury.
- Old or large tears: reconstruction, which may use a nearby tendon or a graft from the patient or a donor.

## Clinical notes

- Rupture risk rises with fluoroquinolone antibiotics, corticosteroids and pre-existing tendinopathy
- Insertional and midportion tendinopathy are different problems; insertional pain often comes with retrocalcaneal bursitis and a Haglund prominence
- Repair may be open or percutaneous; the sural nerve is at risk with lateral incisions and percutaneous sutures
- Thick, nodular Achilles tendons can be tendon xanthomas of familial hypercholesterolaemia

## Anatomical variants

- The plantaris tendon may be absent, join the Achilles tendon or insert separately on the calcaneus
- An accessory soleus muscle can appear as a soft-tissue mass in front of the tendon and cause exertional pain

## Related conditions

- [Familial hypercholesterolemia](https://durgical.com/en/conditions/familial-hypercholesterolemia/)
- [Achilles Tendinopathy](https://durgical.com/en/conditions/achilles-tendinopathy/)
- [Reactive arthritis](https://durgical.com/en/conditions/reactive-arthritis/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which muscles form the Achilles tendon, and where does it insert?

The gastrocnemius and soleus (triceps surae); it inserts on the middle of the posterior surface of the calcaneus.

## Where do Achilles tendon ruptures and midportion tendinopathy cluster, and why?

About 2–6 cm above the insertion, the area with the poorest blood supply.

## How is the Thompson (Simmonds) test done, and what result means a complete Achilles rupture?

With the person prone, the calf is squeezed; no plantarflexion of the foot means a complete rupture.

## Why is a complete Achilles tendon rupture often missed?

Active plantarflexion can persist through the deep flexors and fibularis muscles.

## Which nerve is at risk with lateral incisions and percutaneous Achilles repair?

The sural nerve, which crosses from the tendon's midline to its lateral side as it descends.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
tendo calcaneus TA2 2662

**Official Spanish (DeCS)**
Tendón calcáneo DeCS D000125

**English (TA2)**
Calcaneal tendon

**Also called**
Achilles' tendon · tendo Achillis

## Related

- [Heel bursae](https://durgical.com/en/anatomy/subtendinous-calcaneal-bursa/)
- [Calcaneus](https://durgical.com/en/anatomy/calcaneus/)
- [Plantaris tendon](https://durgical.com/en/anatomy/tendon-of-plantaris/)
- [Soleus tendon](https://durgical.com/en/anatomy/tendon-of-soleus/)
- [Sural nerves](https://durgical.com/en/anatomy/sural-nerve/)
- [Gastrocnemius (inner head)](https://durgical.com/en/anatomy/medial-head-of-gastrocnemius/)
- [Gastrocnemius (outer head)](https://durgical.com/en/anatomy/lateral-head-of-gastrocnemius/)
- [Soleus](https://durgical.com/en/anatomy/soleus-muscle/)

Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=134&filter=ths_termall&q=Tend%C3%B3n%20Calc%C3%A1neo); [Anatomy, Bony Pelvis and Lower Limb: Achilles Tendon](https://www.ncbi.nlm.nih.gov/books/NBK499917/).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/calcaneal-tendon/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/calcaneal-tendon/