Why Won't My Finger Straighten Out?

Symptoms and Treatment for a Mallet Fracture

Mallet finger
(c) Melanie Martinez

A coworker tried to put on a pair of gloves that was too small for him and once he took the gloves off, he couldn't straighten his finger all the way. A reader shared a picture of a bent finger from getting it caught in a door. If your finger is bent at the last joint and won't straighten all the way out, do you know if it's a big deal?

Mallet Fractures

In most cases, the reason a finger won't straighten out is because the tendon that does the work is stretched or torn.

Sometimes, when a finger won't straighten, it's because the bone where the tendon is attached has broken off (avulsion fracture).

A finger that won't straighten out is called a mallet finger or a mallet fracture.

Tendons are like cables attached to muscles on one end and bones on the other. When muscles contract, they pull the tendon and move the bone. It's very similar to the way hand brakes work on a bicycle or the way flight controls work on an airplane.

Fingers are special because many of the muscles that move them are pretty far away, on the forearm. Some of the tendons for the fingers run past the wrist all the way to the tips. There are tendons on the palm side of each finger to make it close and tendons on the back side (dorsal) of each finger to extend it (make it straighten). If you tear or stretch the tendons on the dorsal side of the fingers, they won't properly straighten out.

The bones of your fingers are called phalanges and there are three for each finger (two for each thumb). The one at the tip has only one tendon to pull it out straight. If that tendon is damaged, it won't straighten all the way (the tip will stay bent—see the picture above).

There are three ways the tendon can be damaged:

  • Stretched out. The tendon is still attached but now it's too long.
  • Torn or cut. The tendon is torn or it has been cut and now it can't pull like it's supposed to.
  • Avulsion fracture. The tend is all there and not necessarily stretched out, but the bone where it's supposed to be attached (called the insertion point) is broken. This always reminds me of a picture falling down because the hook it was on ripped out of the wall.

Mallet Finger Treatment

First aid for a mallet finger is similar to any other type of fracture. It needs to be rested and immobilized in the proper position. Initial treatment (right when it happens) should cover the usual basics (RICE):

  1. Protect it from further injury
  2. Ice it to reduce swelling
  3. Elevate it to reduce swelling

If you injure your finger and it won't straighten out, you should see a doctor. This isn't something that needs to go to the emergency room, unless you see blood under the fingernail or the fingernail is coming off. Blood under the nail or damage to it could indicate a severe cut or severe fracture under there.

Assuming it simply won't straighten out, make an appointment with your doctor within the next three days. If it happens at a weekend football game, you can wait until Monday, for example.

Kids especially need to see a doctor if they get a mallet fracture. In kids, the part of the bone that controls growth could be affected, which might result in a deformed finger if not treated appropriately.

Continue to ice the finger a few times a day until you can get to the doctor. The doctor will likely give you a special finger splint that keeps your finger straight. If the tendon is just stretched, keeping it straight will allow it to heal. If it's torn or if the bone is fractured, your doctor may recommend surgery in order for the injury to heal correctly.


AAOS. "Mallet Finger (Baseball Finger)" Last reviewed Oct 2007.

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