A 36-year-old carpenter is working on a new home and is temporarily distracted. He misses a nail with his hammer and hits his distal phalanx, which was hanging over the end of a board. He presents to you after the event.
Your examination reveals erythema and swelling of the distal interphalangeal (DIP) joint. You obtain an x-ray (see Figure).
Figure.
The skin and nail are intact.
Which of the following statements is correct?
Answers:
- The central extensor slip may be ruptured.
- If it is not properly treated, this may result in a boutonniere deformity.
- Optimal management is surgical.
- This represents a zone 3 injury with possible concomitant flexor superficialis tendon injury.
Many select option #4, however the correct answer is #3.
Why This Question Is Often Missed
– Learners confuse zone 1 mallet injuries (distal extensor tendon avulsion) with zone 3 central slip lesions that cause boutonnière deformity.
– The presence of a small dorsal bony fragment on X‑ray may be misinterpreted as a tuft fracture rather than a bony mallet requiring articular management.
What the Distractors Indicate
| Option | What It Tests / Implies | Why It’s Wrong Here |
|---|---|---|
| The central extensor slip may be ruptured. | Knowledge of zone 3 injuries | This is a zone 1 injury at the DIP, not a central slip lesion. |
| If not properly treated, this may result in a boutonnière deformity. | Consequence of untreated central slip injury | Boutonnière deformity follows zone 3 tears, not mallet lesions. |
| Optimal management is surgical. | Recognition of bony mallet finger indications | — |
| This represents a zone 3 injury with possible concomitant flexor superficialis tendon injury. | Confusion between extensor and flexor zones | Flexor tendons lie volar; this is an extensor avulsion (zone 1). |
High-Yield Pearl
Bony mallet injuries involving > 1/3 of the articular surface or with DIP subluxation require surgical fixation; soft‑tissue mallets are splinted.
Core Learning Objectives
- Identify and classify extensor tendon injuries by zone, distinguishing mallet (zone 1) from boutonnière (zone 3).
- Apply management principles: differentiate when to use continuous extension splinting versus surgical fixation in mallet finger injuries.
The “Test Trick” at Play
This item leverages distractors that reference different extensor tendon zones and outcomes (e.g., boutonnière), hoping you’ll overthink the bony fragment on X‑ray and misapply central slip or flexor tendon logic rather than recognizing a classic zone 1 bony mallet.
Additional Practice Questions and Remediation
Question 1
A baseball player jams his finger while sliding head‑first into base. He has a prominent bony fragment off the dorsal aspect of the distal phalanx on X‑ray, involving about 40% of the articular surface, with slight DIP subluxation. Skin intact. Treatment should be:
A. Splint DIP in extension for 6 weeks
B. Closed reduction and K‑wire extension block fixation
C. Buddy‑tape to adjacent finger and early motion
D. Surgical central slip repair
Question 2
A hairdresser experiences minor trauma to the fingertip. X‑ray shows a tiny avulsion fragment off the extensor tendon insertion, < 2 mm, with no articular involvement or subluxation. Best management:
A. Surgical pinning
B. Splint DIP in slight flexion
C. DIP extension splinting continuously for 6 weeks
D. Immediate active motion in a protective splint
Question 3
A cyclist’s finger pain follows a direct blow. X‑ray reveals a volar lip fracture of the middle phalanx with DIP hyperextension, but intact extensor tendon. Next step:
A. Mallet finger splint
B. Volar plate splint in slight flexion
C. Buddy‑tape to adjacent finger
D. Central slip reconstruction
Mini Case Discussion Prompt
Compare the rehabilitation protocols and expected outcomes between soft‑tissue mallet and bony mallet injuries: when might surgical referral improve long‑term function versus splint-only management?
This question appears in Med-Challenger Emergency Medicine Review with CME
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