Achilles Tendon

tendo calcaneus

The Achilles tendon is the largest and strongest tendon in the body, formed by the convergence of the gastrocnemius and soleus tendons, inserting onto the middle third of the posterior calcaneal surface. It transmits the powerful plantarflexion force of the triceps surae and bears loads of 6-8 times body weight during running. The tendon spirals 90 degrees as it descends, with gastrocnemius fibres rotating to insert laterally and soleus medially.

Region: Lower Leg

Clinical Relevance

Clinical Notes

The Achilles tendon has a watershed zone of poor vascularity 2-6 cm proximal to its calcaneal insertion — the most common site for both degenerative tendinopathy and spontaneous rupture. Achilles tendinopathy presents with morning stiffness, activity-related pain, and midportion tenderness on the Royal London Hospital test. Treatment follows the Alfredson eccentric loading protocol. Acute rupture produces a palpable gap, positive Thompson (Simmonds) test, and inability to single-leg heel raise. Conservative management in a functional boot competes with surgical repair for outcomes. Chronic rupture requires reconstruction with FHL transfer or V-Y tendon advancement.

Pathology

Common Injuries & Conditions

Achilles Tendinopathy

Degenerative mid-portion changes from overloading, producing morning stiffness and activity-related pain — managed with progressive loading over 12+ weeks.

Achilles Tendon Rupture

Complete failure 2–6 cm proximal to insertion producing a pop, inability to plantarflex against gravity, and positive Thompson test.