Haglund’s deformity is a bony enlargement on the back of the heel. The soft tissue near the Achilles tendon becomes irritated when the bony enlargement rubs against shoes. This often leads to painful bursitis, which is an inflammation of the bursa (A fluid-filled sac between the tendon and bone).
Haglund’s deformity can occur in one or both feet. The symptoms include: a noticeable bump on the back of the heel; pain in the area where the Achilles tendon attaches to the heel; swelling in the back of the heel; and redness near the inflamed tissue.
Haglund’s Deformity, Foot Health Facts, https://www.foothealthfacts.org/conditions/haglund%E2%80%99s-deformity