Inflammation of your bursa at the rear of the heel known as Retrocalcaneal Bursitis. Repetitive force or friction above the again on the heel triggers the bursa to swell resulting in heel pain and tenderness, swelling and ankle stiffness. Often connected to Achilles Tendonitis and Haglunds Deformity.   The First immobilisation https://www.theorthopaedicandpainpractice.com/the-definitive-guide-to-diagnosing-and-treating-ankle-pain-in-singapore/