Mallet Finger (or Mallet Thumb)
The injury you're describing at the distal interphalangeal (DIP) joint near the nail bed is called a "mallet finger" (or "mallet thumb" when it affects the thumb). This is a traumatic disruption of the extensor tendon at its insertion on the distal phalanx, resulting in inability to actively extend the fingertip 1, 2.
What Defines This Injury
A mallet finger occurs when the terminal extensor tendon is either:
- Ruptured from the bone (soft-tissue injury), or
- Avulsed with a bony fragment at the base of the distal phalanx (bony mallet) 3, 1
The mechanism is typically an axial load applied to a straight fingertip, followed by forced hyperflexion or hyperextension of the DIP joint 2. Common scenarios include:
- Sports injuries (ball striking the fingertip)
- Low-energy trauma (pulling up socks, making a bed)
- Crush injuries (finger caught in door) 1
Clinical Presentation
You'll see a characteristic flexion deformity at the DIP joint where:
- The fingertip droops and cannot be actively extended
- Passive extension is possible but cannot be maintained once released
- Pain and swelling localized to the DIP joint near the nail bed 1, 2
Why the Specific Name Matters
The term "mallet finger" is clinically important because it immediately conveys:
- The anatomic location: DIP joint/distal phalanx
- The functional deficit: Loss of active extension
- The treatment approach: Typically conservative with splinting 3, 2
Radiographs are always indicated to distinguish between soft-tissue mallet (tendon rupture alone) and bony mallet (fracture fragment), as this affects management decisions 3. Bony mallet injuries involving more than one-third of the articular surface, palmar displacement of the distal phalanx, or interfragmentary gap >3 mm typically require operative fixation 3.
Thumb vs Finger Distinction
When this injury affects the thumb specifically, it may be called "mallet thumb." Mallet fractures of the thumb behave differently than finger mallet injuries: they present sooner after injury, have less fragment displacement, less articular involvement, and notably never show subluxation (unlike 25% of finger mallet injuries) 4. This is clinically relevant because thumb mallet injuries generally have a more favorable prognosis.