Mallet finger describes a type of injury where there is disruption of the extensor mechanism of the finger at the distal interphalangeal joint (DIP). It is the most prevalent finger tendon injury in sport. The term includes both bony avulsion injury and tendinous injury without avulsion.
It is characterised by an inability to extend the finger at the distal interphalangeal (DIP) joint. There is slight flexion at this joint, which is where the term "mallet" comes from -- the finger position resembles a mallet (for example, a piano key mallet).
The injury classically occurs sports where the DIP undergoes sudden flexion (extended finger is struck at the tip by an object, e.g. baseball or basketball) or a crush injury (slamming a door towards the distal interphalangeal joint) in the extensor direction.
If there is a bony avulsion, a plain film will classically show a triangular avulsion fragment at the insertion of the common extensor tendon on the dorsal aspect of the distal phalanx at the DIP joint.
A high proportion of mallet finger injuries will present as isolated tendon injuries with any associated avulsions fractures known as a "mallet fracture" 5.
The findings on ultrasound include 6
- loss of real-time movement of the tendon
- complete or partial extensor tendon tears
- fluid in the region of the extensor tendon insertion
- avulsion fracture
- untreated mallet fingers may progress to a swan neck deformity that will require surgical intervention 3-4
- development of secondary osteoarthritic changes 4
Treatment and prognosis
Mallet injuries are predominantly conservatively treated via a splint maintaining the DIP joint in fixed hyperextension. It is uncommon for any mallet finger injuries to require surgical intervention 5.
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Wrist and hand fractures
- wrist and hand fractures (Amsterdam wrist rules)
- distal radial fracture (Frykman classification)
- distal ulna fractures
- fracture dislocations of the radius and ulna
- carpal fractures
- metacarpal fractures
- phalanx fractures