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What is an Achilles tendon injury?

An Achilles tendon injury is an injury that happens to the largest tendon in the human body: the fibrous tissue that connects the two large muscles in the back of your calf with your heel bone. These muscles (the gastrocnemius and the soleus) create the power needed to push off with your foot or rise up on your toes.  

Although your Achilles tendon can withstand forces of 1,000 pounds or more, it is the tendon most frequently injured by professional athletes and weekend athletes alike, according to the American Academy of Orthopaedic Surgeons (AAOS). An Achilles tendon injury can range from a mild case of tendinitis (inflammation and swelling) to a more serious rupture or tear that requires repair surgery. The AAOS reports that an acute Achilles tendon rupture affects an estimated 5.5 to 9.9 of every 100,000 people in North America each year. 

Depending on which part of your Achilles tendon is inflamed, you could be experiencing:

  • Noninsertional Achilles tendinitis—Fibers in the middle portion of the tendon begin to break down, causing tiny tears, swelling and thickening. Younger, active people are more often affected by this problem.
  • Insertional Achilles tendinitis—This type of tendinitis involves the lower portion of the heel where the tendon attaches (inserts) to the heel bone.
  • Additional complications of both types, including painful bone spurs (extra bone growth) and the calcification or hardening of the damaged tendon fibers.

Treatment options for Achilles tendon injuries range from nonsurgical approaches like rest, exercise, anti-inflammatory medications and a leg cast to repair surgery. The type of treatment depends on the cause and symptoms of the injury.

Symptoms

Symptoms of Achilles tendinitis can come on gradually or suddenly. According to the American Orthopaedic Foot and Ankle Society, you may feel one or more of these common symptoms:

  • Mild pain after exercise or running that gradually worsens
  • A sense of sluggishness in your leg
  • Episodes of diffuse or localized pain along your tendon that can sometimes be severe, often while running or a few hours after you've run     
  • Tenderness along your Achilles tendon in the morning
  • Stiffness that generally diminishes as your tendon warms up with use
  • Some swelling or pain in the back of your heel where the tendon attaches to the heel bone
  • Pain along the tendon or back of the heel that worsens with activity
  • Severe pain the day after exercising
  • Thickening of the tendon
  • Bone spur (extra growth of bone that can add to the pain of tendonitis)
  • Swelling that is present all the time and gets worse throughout the day with activity

If you have experienced a sudden "pop" in the back of your calf or heel, you may have ruptured (torn) your Achilles tendon, a more serious condition than Achilles tendinitis—see your doctor immediately.

Causes

Achilles tendinitis results from repetitive stress to your Achilles tendon, especially when you push your body to do too much, too soon. Other factors can make it more likely for you to develop Achilles tendinitis, including:

  • Sudden increase in your exercise activity; for example, increasing the distance you run every day by a few miles without giving your body a chance to adjust to the new distance
  • Not stretching enough before exercise
  • Wearing high heels, which increases the stress on the Achilles tendon
  • Flat feet, also known as fallen arches or overpronation, which can stretch the muscles and tendons
  • Tight calf muscles and tendons, often caused by suddenly starting an ambitious exercise program
  • Bone spur, which is the growth of extra bone where the Achilles tendon attaches to the heel bone, just enough to rub against the tendon and cause pain
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