A mallet finger injury is the most common closed tendon injury of the finger. The injury occurs most often in the workplace or during contact or ball-handling sports. It is most common in young to middle-aged males, which may reflect their higher rates of participation in such sports .
The diagnosis and management of mallet finger injuries will be reviewed here. Other finger injuries are discussed elsewhere. (See "Distal phalanx fractures" and "Flexor tendon injury of the distal interphalangeal joint (jersey finger)".)
Traumatic disruption of the terminal slip of the extensor tendon at the distal interphalangeal (DIP) joint is commonly referred to as a mallet finger (or less often as a baseball or drop finger) (figure 1). The terminal slip is responsible for extension of the DIP joint. A zone of relative avascularity just proximal to the extensor tendon insertion predisposes the tendon to injury at this site. A more detailed discussion of finger anatomy is found separately. (See "Finger and thumb anatomy".)
MECHANISM OF INJURY
Mallet finger occurs most commonly during collision sports, such as American football and rugby, or ball-handling sports, such as basketball and baseball. The injury is usually caused by a direct blow to the tip of the finger, such as when a ball strikes the fingertip or the fingertip strikes a rigid surface (figure 2). The axial load from the blow causes sudden, forceful flexion of the distal phalanx. This flexion damages the extensor tendon where it attaches to the proximal portion of the distal phalanx. Less frequently, a mallet finger may occur as part of finger injuries involving dorsal lacerations or crushing mechanisms.
With mallet finger injuries, the tendon may be partially torn, completely ruptured, or associated with an avulsion fracture of the distal phalanx. Unopposed flexion leads to a fixed flexion deformity (called extensor lag) at the DIP joint if the injury remains untreated (picture 1).