How Inflammation of Tendons Can Cause Tendonitis

A tendon is a tough yet flexible band of fibrous tissue. The tendon is the structure in your body that connects a muscle to a bone. Tendons are very organized. The body creates very tightly packed fibers of collagen in parallel arrays that are flexible but very strong. The strength of tendons is important as these tight structures are required to resist the forces of very heavy loads.

A runner holding his Achilles tendon
Jan Otto / Getty Images

The skeletal muscles in your body are responsible for moving your joints, thus enabling you to walk, jump, lift, and move in many ways. When a muscle contracts, it pulls on a bone to cause this movement. The structure that transmits the force of the muscle contraction to the bone is called a tendon. In the case of the eyeball, tendons attach muscles to that structure rather than a bone, allowing the muscles to move your eye. There are about 4,000 tendons in your body.

Tendons vs. Ligaments

While both ligaments and tendons are made of fibrous connective tissue (collagen), ligaments attach bone to bone rather than muscle to bone. Ligaments hold structures together, such as in the joints.


Specific tendons are prone to developing tendonitis, a problem where the tendon becomes irritated and inflamed. This causes pain when you move the muscle or bone. Tendonitis can develop as an overuse injury from repetitive motion, or be caused by stress or injury to the muscle or joint.

Tendonitis often happens due to work activity or sports, but it can happen to anyone. You are at more risk of tendonitis as you get older. Tendonitis develops due to deficiencies in the blood supply to the tendon. Certain tendons with a "watershed zone" of blood supply are prone to developing tendonitis. These include:

  • Achilles tendon: This tendon attaches your calf muscle to your heel bone. If it is overstretched, it can tear completely or partially, often with a popping noise and sharp pain in the back of your ankle and leg. It may need surgical repair or respond to nonsurgical treatment.
  • Rotator cuff tendon: The rotator cuff tendons attach muscles to the shoulder joint. You can develop tendonitis due to an injury, repetitive lifting, or sports that engage your arms over your head.
  • Posterior tibial tendon: This tendon attaches the calf muscle to the bones inside the foot, holding up the arch and supporting the foot when you walk. It can be injured in a fall or it can have a repetitive use injury in high-impact sports such as basketball, tennis, or soccer.
  • Extensor carpi radialis brevis: This is inflammation of the tendon, often called "tennis elbow," that attaches your forearm muscles to your elbow. It happens due to many activities, including racquet sports such as tennis.
  • Patellar tendon: Common in sports that call for jumping, like basketball and volleyball, "jumper's knee" involves repeated stress on your patellar tendon, which connects the kneecap (patella) to the shinbone (tibia) and helps you extend your lower leg.

Symptoms of tendonitis include pain, tenderness, and mild swelling. Stopping the activity that results in the pain for a few days can help resolve minor cases, but if they persist you should see your healthcare provider. You may need to learn ways to prevent the recurrence by using proper techniques and alternative techniques.

1 Source
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  1. NIH News in Health. Protect your tendons. 2014.

By Jonathan Cluett, MD
Jonathan Cluett, MD, is board-certified in orthopedic surgery. He served as assistant team physician to Chivas USA (Major League Soccer) and the United States men's and women's national soccer teams.