What is the difference between Achilles tendonitis and Achilles tendinopathy? Achilles tendinopathy is sometimes incorrectly called Achilles tendonitis. While the symptoms are nearly identical, they are not the same condition. Tendinopathy is caused by a breakdown of the collagen protein that makes up the tendon. Tendonitis, on the other hand, is caused by tendon inflammation. Learn more how physiotherapy can help Achilles Tendinopathy.