Posterior Achilles tendon bursitis presents as a painful red lump over the back of the heel. So how is this caused? Let’s take a look! Posterior Achilles bursitis is most commonly seen in young women, but can also occur in men. As the heel tends to move in an inversion position throughout the stride cycle, excessive pressure is placed on the soft tissue between the outer posterior side of the heel bone and the top of the shoe (forming a hard callus on the heel). This side of the heel bone becomes elevated and easily palpable and is often mistaken for an exophytic bone wart. In the early stages, only a small, mild, hardened and painful erythema is seen over the posterior aspect of the heel, where patients often apply adhesive tape to relieve shoe pressure. As the inflamed bursa enlarges, a painful red lump appears on the Achilles tendon. Depending on the type of shoe the patient is wearing, the swelling sometimes extends to both sides of the Achilles tendon. In chronic cases, the bursa forms permanent fibrosis.