Ruptured Achilles tendon. Sagittal (side view) magnetic resonance imaging (MRI) scan of a ruptured Achilles tendon. The tendon is dark blue line to the right of the ankle, the rupture is midway along its length. The Achilles tendon is the largest and strongest tendon in the human body, it connects the heel bone to the calf muscles. It can be injured during exercise, or by a trip or a fall, resulting in pain and swelling. Treatment is rest and physiotherapy, although in extreme cases surgery may be needed.