A distal phalanx avulsion fracture causing a mallet finger, or a terminal extensor mechanism injury (Figure 2).
Figure 2: Avulsion fracture of the proximal portion of the distal phalanx on the 3rd and 4th digit along with subluxation of the 4th distal phalanx at the DIP joint (green arrows). Author’s own images.
- 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].
The distal phalanx will typically be flexed with the patient unable to extend at the distal interphalangeal (DIP) joint actively. There is usually a normal appearance and function of the proximal interphalangeal (PIP) and metacarpophalangeal (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].
Figure 3: Extensor tendon deformities (Courtesy of Core EM).
The affected digit should be splinted in extension at the DIP joint, 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 joint 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 progressively increased extension tone across the PIP joint and migration of the extensor complex proximally, extension develops at the PIP and the DIP remains flexed (Figure 4) [3].
Figure 4: Mechanism of a swan neck deformity (Courtesy of Don’t Forget the Bubbles).
Resources & References:
Check out ALiEM’s Paucis Verbis cards to brush up on other can’t miss orthopedic injuries, and SplintER Series or EMrad for more cases. For further reading about myositis ossificans check out WikiSM.
- StatPearls. Mallet Finger. StatPearls. Published February 7, 2022. Accessed March 19, 2022.
- McDonald L. Finger injuries. Core EM. Published April 12, 2017. Accessed March 19, 2022.
- Lamaris GA, Matthew MK. The Diagnosis and Management of Mallet Finger Injuries. Hand (N Y). 2017;12(3):223-228. PMID: 28453357.
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