The mallet finger injury is caused by forced flexion on the tip of the finger while the DIP joint is extended.  This is the most common hand tendon injury in athletes.  The classic mechanism is being struck on the extended finger tip by a softball, volleyball, or basketball.  Other mechanisms are tucking in a bedspread or pushing off a sock. It can affect any finger, even the thumb, but the middle finger is the most common site. 

     Physical exam typically reveals pain and swelling over the involved DIP joint with inability to actively extend the DIP.  Passive extension is possible.  The DIP joint assumes an abnormally flexed position at rest, but this may be subtle.   This injury may have only minimal pain so patients may not present immediately.