The Anatomy of Tendons

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Tendons are strong, flexible tissue bands connecting muscles to bones. When you tighten your muscles, tendons shorten and pull on your bones to move your joints. They are prone to injuries like inflammation (swelling) from overuse, strains from overstretching, and tears.

This article discusses the anatomy of tendons, including where they are in the body and common injuries that affect these structures.

Man stretching before a run

Natastic / Getty Images


Tendons are structures located at each end of a muscle. One end of the tendon attaches to your muscle while the other connects to a membrane over your bone, called the periosteum. These structures are flexible but not elastic, and may tear if you stretch them too far.


Tendons are a type of dense, regular connective tissue. They are primarily made of strands of protein called collagen. These strands run parallel to each other to allow your tendons to effectively and efficiently transmit the force produced by your muscles to move your bones.

Tendons are composed of cells called fibroblasts and an extracellular matrix (a supportive network of proteins and molecules).

Fibroblasts fuse to form bundles of fibers. Groups of fiber bundles form fascicles, and groups of fascicles form your tendons. The tendons' extracellular matrix is comprised of water, collagen, and other proteins.

Some tendons in the body are covered by sheaths that contain synovial fluid, which is like a slippery tunnel that protects your tendons. You can find sheaths where your tendons would otherwise rub on your bones if they weren't protected.


In some areas of the body, muscles attach directly to your bones. However, most of your moveable joints have tendons, including:

  • Shoulders
  • Elbows
  • Wrists
  • Fingers
  • Hips
  • Knees
  • Ankles
  • Toes

Tendons can also be found in smaller joints of the body, such as your jaw.

Function of Tendons

Tendons attach muscles to bone. The movement produced by these structures depends on the alignment of the fibers in the muscle they are attached to. Examples include:

  • Flexion: bending a joint
  • Extension: straightening a joint
  • Abduction: moving your arm or leg out to the side
  • Adduction: bringing your arm or leg next to your body
  • Internal rotation: rotating your limb toward your body
  • External rotation: rotating your limb away from your body
  • Dorsiflexion: pulling your foot upward
  • Plantarflexion: pointing your foot downward
  • Pronation: rotating your forearm palm-down
  • Supination: rotating your forearm palm-up

Types of Tendon Injuries

Tendon injuries are common—particularly in athletes and people who perform repetitive movements with their joints.

There are different types of tendon injuries:

  • Tendonitis: This condition typically occurs from repetitive movement, lifting something heavy, or performing a sudden movement. It causes inflammation of the tendon, along with micro-tearing of the tendon fibers. Symptoms include pain, swelling, and difficulty moving the affected joint.
  • Tendinopathy: This causes collagen breakdown in your tendon. It develops over time from the overuse of your tendons. Something as simple as repetitive use of a computer mouse can lead to tendinopathy. Symptoms include pain and eventually weakness.
  • Tendon tears: Tendons that are stretched too far can tear. Long-term use of certain medications such as corticosteriods can also make your tendons weak and more prone to tearing. These injuries are often classified as mild, moderate, or severe, based on how much of the tendon is affected.

When to Seek Medical Attention

If your tendon pain isn't getting better with home remedies, or if the pain is interfering with your daily activities, see your healthcare provider. If you have an injury that makes you unable to move your joint, seek urgent medical attention—you could have a torn tendon. Early treatment is key for the best outcome after this injury.

Common Tendon Injuries

Some tendons are more prone to injuries than others. Commonly injured tendons include the Achilles tendon, tibialis posterior, patellar tendons, forearm extensors, and the rotator cuff.

Achilles Tendon

The Achilles tendon is the largest and strongest tendon in the body. This thick tendon is located at the back of each ankle and attaches to the muscles that perform plantarflexion (pointing your foot down toward the ground). This movement occurs with every step you take throughout the day. It also helps you stand up on your toes and jump.

Achilles tendinitis often occurs with activities such as running—particularly if you do too much, too fast. It can also occur from tight calf muscles or from bone spurs that rub the tendon as you move.

Achilles tendon ruptures (tears) are another common injury that typically occurs during sports activities. Surgery is usually required to repair the tendon, followed by physical therapy to regain range of motion and strength.

Tibialis Posterior Tendon

The tibialis posterior (or posterior tibial) tendon runs along the inside of your lower leg and under the arch of your foot. This tendon supports your arch while you walk.

Tibialis posterior tendon conditions can occur from injuries, such as a fall, or from overuse. Tendinitis or tears in this tendon can cause your arch to collapse. These injuries cause pain, swelling, and difficulty bearing weight on your foot.

Treatment for tibialis posterior injuries can include physical therapy, orthotics (shoe inserts) to support your arch, and rarely even surgery.

Patellar Tendon

The patellar tendon runs from the bottom of your patella (kneecap) to the top of your tibia (shinbone).

Patellar tendinitis can occur from sports activities that include a lot of running and jumping. This condition is sometimes called "jumper's knee." Symptoms include pain at the front of your knee and eventually weakness.

The patellar tendon can also tear. This high-force injury occurs from trauma, such as a fall or landing from a jump. Tendon tears can cause an audible "pop" or tearing sound. You'll also have severe pain, swelling, and difficulty straightening your knee.

Patellar tendon injuries are treated with physical therapy, and sometimes a brace that holds your knee in a straight position while your tendon heals. If your patellar tendon tears completely, you'll need surgery to repair it.

After surgery, you won't be able to put pressure on your leg for several weeks. Physical therapy is also key for regaining function after this surgery. Full recovery takes six to 12 months.

Forearm Extensor Tendon

The forearm extensor muscles bend your wrist backward. They share a tendon that attaches to the outside of your elbow.

The forearm extensor tendon is prone to overuse injury—a condition called lateral epicondylitis or "tennis elbow." Microtears and inflammation develop as the tendon rubs on bone during repetitive activities such as playing racket sports, painting, hammering, or using a computer mouse.

Lateral epicondylitis is usually treated conservatively with rest from aggravating activities, nonsteroidal anti-inflammatory drugs (NSAIDs), counterforce bracing (a strap placed a few inches below the tendon), and physical therapy. It can also be treated with steroid injection or platelet-rich plasma injection.

Very rarely, surgery is required to repair damaged tissue with tennis elbow.

Rotator Cuff Tendons

The rotator cuff is a group of four muscles that helps move and stabilize your shoulder joints. These muscles include the supraspinatus, infraspinatus, teres minor, and subscapularis.

Rotator cuff tendons are prone to tendinitis, as well as tears. These injuries often develop over time from overuse activities, as tendons "fray" and become inflamed.

Rotator cuff tendinitis is often treated with NSAIDs, rest from aggravating activities, steroid injections, and physical therapy. Tears are treated based on the extent of the injury.

Rotator cuff tears are classified as "partial" or "full-thickness." Partial tears affect part of the tendon, while full-thickness tears mean that the tendon is torn completely.

Small tears in the rotator cuff tendons can be treated conservatively. However, larger or complete tears often require surgery. After surgery, your arm is immobilized for several weeks, and then physical therapy is started to help you regain range of motion and strength. Full recovery from rotator cuff surgery often takes six to nine months.


Tendons are made of connective tissue that attaches muscles to bone. These structures can be found on muscles located around the moveable joints in your body. Tendons are prone to injury, including tendinitis and tendon tears. Treatment for these injuries include rest, anti-inflammatory medications, physical therapy, and sometimes surgery.

A Word From Verywell

Chances are, you haven't given a whole lot of thought to your tendons—that is, until they hurt. If you suspect that you have a tendon injury, talk to your healthcare provider. Early intervention can prevent more serious injuries from developing.

13 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Aubrey Bailey, PT, DPT, CHT
Aubrey Bailey is a physical therapist and professor of anatomy and physiology with over a decade of experience providing in-person and online education for medical personnel and the general public, specializing in the areas of orthopedic injury, neurologic diseases, developmental disorders, and healthy living.