Imaging description

Mallet (or baseball) finger is used to describe traumatic avulsion of the extensor tendon from the dorsal base of the distal phalanx or a traumatic avulsion fracture of bone from the dorsal base of the distal phalanx. This traumatic avulsion is caused by sudden flexion at the distal interphalangeal (DIP) joint while the finger is extended. If the injury is confined to the soft tissues, then radiographic images will demonstrate soft tissue swelling and fullness centered about the DIP joint of the involved digit. If the mallet finger involves an avulsion fracture, then this is best seen on the lateral radiographic view of the digit. The avulsion fragment is seen to arise from the dorsal base of the distal phalanx (Figure 40.1). Advanced imaging is usually not indicated.

Importance

A mallet finger injury must be identified, as it needs to be treated early to prevent proximal migration and retraction of the extensor mechanism of the digit. After retraction of the tendon occurs, it becomes more difficult to treat mallet finger and requires surgical intervention. Untreated mallet finger will lead to increasing imbalanced extensor tone at the proximal interphalangeal joint relative to the DIP joint. This imbalance will cause development of a biomechanically debilitating swan neck deformity of the involved digit. Both the mallet finger injury confined to the soft tissues and the mallet finger injury with a non-displaced small avulsion fracture fragment (< 50% of the articular surface) are treated with a simple splint for several weeks. A displaced fracture or a large fracture requires reduction and fixation by a surgeon.