Achilles tendon injuries can be caused by the following:
Tendonitis might be due to overuse or damage to the area. It can cause pain down the back of your leg and around your heel. You might notice that parts of your tendon are getting thicker and hardening because of tendonitis. This will get worse if you don't treat it. There are two main types of tendonitis:
Noninsertional Achilles tendonitis. Small tears in the middle fibers of your tendon start to break it down. This causes pain and swelling. This type of tendonitis usually affects active, younger adults.
Insertional Achilles tendonitis. This damage occurs in the spot where your tendon meets your heel bone. Bone spurs (extra bone growth) often form with this type. This type of tendonitis can happen at any age, even in people who are not active.
The tears in your tendon fibers can cause a complete or partial break (or tear) in your tendon. You might hear a “pop” that seems to come from the back of your heel or calf. This may be a tendon rupture, which needs immediate medical attention.