What is your diagnosis?

A distal phalanx avulsion fracture causing a mallet finger, or a terminal extensor mechanism injury.

• Pearl: Mallet fingers can be either isolated extensor tendon injuries or bony injuries with an avulsion of the proximal dorsal portion of the distal phalanx [1].

What are the key exam findings?

The distal phalanx will typically be flexed with the patient unable to actively extend at the distal interphalangeal (DIP) joint. There is typically a normal appearance and function of the proximal interphalangeal (PIP)  and meatcarpo-phalangeal (MCP) joints in the weeks to months after the initial injury. 

• Pearl: It is important to isolate each interphalangeal joint when testing extension and flexion

• Pearl: Mallet finger should not be confused with other common traumatic finger deformities such as a boutonniere deformity (central slip deformity) or a swan-neck deformity (untreated mallet finger) [2]. 

Image 2: Courtesy of Core EM

What kind of forces cause these injuries?

A mallet finger injury is typically caused by forced flexion at the DIP against resistance. This most commonly occurs in sports when an object such as a ball strikes the tip of a finger forcing it into flexion at the DIP [3]. 

What is your management in the ED? Do I need to consult Orthopedics?

The affected digit should be splinted in extension at the DIP, ideally with a stack splint or figure of 8 splint, for 6-8 weeks [1]. Orthopedics does not need to be consulted in the ED but urgent follow-up should be arranged, especially if there are bony avulsions, to evaluate the need for surgical repair. 

• Pearl: Management is typically non-operative with the DIP splinted in extension AT ALL TIMES FOR 6-8 WEEKS. If the finger is allowed to flex at the DIP joint even briefly, the clock is reset and an additional 6-8 weeks of extension will be required [3].
  
  
• Pearl: Relative indications for surgical repair include an avulsion fracture involving >30% articular surface or volar subluxation of the distal phalanx [3].
  
  
• Pearl: If a mallet finger isn’t treated appropriately, it is likely to develop into a swan-neck deformity. Due to progressive increased extension tone across the PIP and migration of the extensor complex proximally, extension develops at the PIP and the DIP remains flexed, see image 3 [3].

Image 3: Courtesy of Don’t Forget the Bubbles