Achilles Tendonitis is a painful inflammation of the Achilles tendon at the back (posterior aspect) of the heel and ankle. The Achilles tendon is the largest and most frequently injured tendon in the human body. Often, a bone spur develops in the area where the Achilles tendon inserts/attaches into the heel bone (calcaneus). An ultrasound or an MRI may reveal a tear in the tendon. Removal of the bone spur and repair of the Achilles tendon alleviates the discomfort and allows returning to normal activity.