Tendons are tissues that connect muscles to bone. When muscles contract, tendons pull on bones. This is what causes some parts of the body to move. The muscles that move the fingers and thumb (the flexor muscles) are located in the forearm, above the wrist. Long tendons extend from the flexor muscles through the wrist and attach to the small bones of the fingers and thumb.

Tendons are stretched tightly as they connect the muscle to the bone. If the tendon tears, the end of the tendon that is released pulls back toward the area to which it remains attached. A tear (rupture) or cut of the tendon anywhere along its route, at the wrist, in the palm of the hand, or along the finger, may make it impossible to bend one or more fingers.

Each finger has two flexor tendons; the thumb has one tendon. The tendons run along the palm side of the fingers. They are very close to the surface of the skin, particularly where the skin folds as the finger bends.

One tendon attaches to the last bone of the finger and bends the tip. This is the longer tendon and is called the flexor digitorum profundus, or FDP.

The other tendon bends the middle joint of the finger. It is the shorter tendon and is called the flexor digitorum sublimis, or FDS.

Most often the flexor tendons are damaged by a cut. Because the nerves to the fingers are also very close to the tendons, a cut may damage them as well. This will result in numbness on one or both sides of the finger.

Athletic injuries are also common, usually in football, wrestling, or rugby. One player grabs another's jersey, and a finger (usually the ring finger) gets caught and pulled. This type of injury is so common, it even has a name: "jersey finger."

Tendons can also be stretched (strained) or ruptured. This can happen during sports like rock climbing.

In rheumatoid arthritis, flexor tendons may rupture without warning or injury (spontaneously). One may simply notice that the finger no longer bends, but cannot recall what may have caused that to happen.

• An inability to bend one or more joints of the finger.
• Pain when the finger is bent.
• An open injury, such as a cut, on the palm side of the hand, particularly in the joint area where the skin folds as the finger bends.
• Mild swelling over the joint closest to the fingertip.
• Tenderness along the finger on the palm side of the hand.

It is important to see a physician whenever the fingers are injured. This is especially true if the finger is jammed and the fingertip cannot be bent or straightened. With an injury of the FDS tendon, it may still be possible to bend the finger, but not completely. Bending the finger will be painful.

The doctor will test the fingers by asking the patient to bend and straighten the fingers. Sometimes he or she may apply resistance in order to test the strength of the fingers. The doctor may test the feeling and blood flow to the fingers to see whether any nerves or blood vessels were injured. An X-ray may be needed to learn whether there is any damage to the bone. If the wound is open, a tetanus shot or antibiotics may be needed to avoid infection.