What causes the finger not to straighten with a mallet finger?
A mallet finger is an injury to the extensor tendon on the back of the finger. The extensor tendon is the tendon used to straighten the finger. The tendon has several attachments on the back of the finger, including one just beyond the last knuckle that allows this last finger joint to extend (straighten). When the tendon is injured, there is nothing to pull that last knuckle straight, and therefore, the joint stays bent.
What are the symptoms of a mallet finger?
A mallet finger is an obvious injury, if you know what you're looking for: the last joint of the finger will be bent down, and while the joint can be straightened with assistance, you will be unable to fully straighten the tip of the finger on your own.
The pain associated with a mallet finger can be significant at the time of the injury but is usually minimal within a short time. Most people with a mallet finger are tender at the site of the injury, just behind the base of the fingernail. Due to minimal pain, many mallet fingers go undiagnosed for weeks or longer, because people are unaware of the significance of their injury.
What is the treatment of a mallet finger?
Most often, a mallet finger can be treated with a simple splint. A Stack splint is the easiest type of splint to use for this injury. The difficult part is if the splint is removed and the finger tip is allowed to bend, the treatment must be restarted from the beginning. Since a Stack splint is usually worn for 6 to 8 weeks, this can be a significant challenge!
There are some situations that may require additional treatment. Most mallet fingers are injury to the tendon itself, but in some cases, the tendon may pull off a small fragment of bone from the finger bone. If the fragment is large enough, it may require surgical treatment to prevent joint problems from developing.
Surgical treatment may also be needed in situations where the injury is left untreated for more than 4 to 6 weeks. In these patients, a surgical correction of the tendon injury may be required. If a mallet finger is left untreated, the deformity of the finger can worsen. Patients who leave a mallet finger untreated may develop a deformity of the finger joints called a "swan neck deformity."
Bendre, AA, et al. "Mallet Finger" J. Am. Acad. Ortho. Surg., September 2005; 13: 336 - 344.