Achilles tendonitis, also sometimes called Achilles tendinitis, is a painful and often debilitating inflammation of the Achilles tendon (heel cord). The Achilles tendon is the largest and strongest tendon in the body. It is located in the back of the lower leg, attaches to the heel bone (calcaneus), and connects the leg muscles to the foot.

The Achilles tendon gives us the ability to rise up on our toes, facilitating the act of walking, and Achilles tendonitis can make walking almost impossible.

There are three stages of tendon inflammation:

Peritenonitis is characterized by localized pain during or following activity. As this condition progresses, pain often develops earlier on during activity, with decreased activity, or while at rest.

Tendinosis is a degenerative condition that usually does not produce symptoms (i.e., is asymptomatic). It may cause swelling or a hard knot of tissue (nodule) on the back of the leg.

Peritenonitis with tendinosis results in pain and swelling with activity. As this condition progresses, partial or complete tendon rupture may occur.