Haglund's Deformity (Back of Heel Bump)
Haglund's deformity is a bony bump where your Achilles tendon attaches at the back of your heel bone. Also known as a "pump bump," it is usually caused by shoes repetitively rubbing against your heel. Because of its prominence, the bump is subject to constant friction, causing redness, pain, swelling, and callouses.
Source: Verywell Health
