Mallet finger is an injury to the thin tendon that straightens the end joint of a finger or thumb. Although it is also known as “baseball finger,” this injury can happen to anyone when an unyielding object (like a ball) strikes the tip of a finger or thumb and forces it to bend further than it is intended to go. As a result, you are not able to straighten the tip of your finger or thumb on your own.
Tendons are tissues that connect muscles to bone. The muscles that move the fingers and thumb are located in the forearm. Long tendons extend from these muscles through the wrist and attach to the small bones of the fingers and thumb.
The extensor tendons on the top of the hand straighten the fingers. The flexor tendons on the palm side of the hand bend the fingers.
In a mallet injury, when an object hits the tip of the finger or thumb, the force of the blow tears the extensor tendon. Occasionally, a minor force such as tucking in a bed sheet will cause a mallet finger.
The injury may rupture the tendon or pull the tendon away from the place where it attaches to the finger bone (distal phalanx). In some cases, a small piece of bone is pulled away along with the tendon. This is called an avulsion injury.
The long, ring, and small fingers of the dominant hand are most likely to be injured.
The finger is usually painful, swollen, and bruised. The fingertip will droop noticeably and will straighten only if you push it up with your other hand.
It is very important to seek immediate attention if there is blood beneath the nail or if the nail is detached. This may be a sign of a cut in the nail bed, or that the finger bone is broken and the wound penetrates down to the bone (open fracture). These types of injuries put you at risk for infection.
To relieve pain and reduce swelling, apply ice to your finger immediately and keep your hand elevated above your heart.
A mallet finger injury requires medical treatment to ensure the finger regains as much function as possible. Most doctors recommend seeking treatment within a week of injury. However, there have been cases in which treatment was delayed for as long as a month after injury and full healing was still achieved.
After discussing your medical history and symptoms, your doctor will examine your finger or thumb. During the examination, your doctor will hold the affected finger and ask you to straighten it on your own. This is called the mallet finger test.
Your doctor will most likely order x-rays of the injury. If a fragment of the distal phalanx was pulled away when the tendon ruptured, or if there is a larger fracture of the bone, it will appear in an x-ray. An x-ray will also show whether the injury pulled the bones of the joint out of alignment.