Achilles tendon bursitis is inflammation of the fluid-filled sac (bursa) located either between the skin of the back of the heel and the Achilles tendon (posterior Achilles tendon bursitis) or in front of the attachment of the Achilles tendon to the heel bone (anterior Achilles tendon bursitis, retrocalcaneal bursitis).
Posterior Achilles tendon bursitis occurs mainly in young women but can develop in men. Walking in a way that repeatedly presses the soft tissue behind the heel against the stiff back support of a shoe can cause or aggravate the bursitis. Shoes that taper sharply inward toward the posterior heel (such as high-heeled shoes) can cause irritating pressure that leads to the development of this bursitis. Any condition that puts extra strain on the Achilles tendon can cause anterior Achilles tendon bursitis. Injuries to the heel and diseases such as rheumatoid arthritis can also cause it.
When the bursa becomes inflamed after an injury, symptoms usually develop suddenly. When the bursa develops without an injury, symptoms may develop gradually. With both posterior and anterior Achilles tendon bursitis, symptoms usually include swelling and warmth at the back of the heel. A minimally red, swollen, tender spot develops on the back of the heel. When the inflamed bursa enlarges, it appears as a red lump under the skin of the heel and causes pain at and above the heel. If posterior Achilles tendon bursitis becomes chronic, the swelling may become hard, fluid-filled, and red or flesh-colored.
The diagnosis is based on the symptoms and an examination. For anterior Achilles tendon bursitis, doctors use x-rays to rule out a fracture of the heel bone or damage to the heel bone caused by rheumatoid arthritis or other inflammatory arthritis.
– Information taken from MerckManuals.com