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Review Question - QID 218189

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QID 218189 (Type "218189" in App Search)
A 32-year-old orthopedic surgery resident was playing flag football on his day off. When he attempted to catch a pass, the distal aspect of his right middle finger got jammed, causing it to hyperflex. After the play, he noted he was no longer able to extend his distal interphalangeal joint (DIP). He was placed into a DIP extension splint and was compliant with wear for eight weeks. Now, at the end of his treatment, he can actively extend the DIP joint but has a 7-degree extensor lag at the DIP. Which of the following is true of his expected outcome?

There will be no negative effects on function

83%

278/335

He will have difficulty using the finger to perform activities requiring significant dexterity

5%

17/335

He will go on to develop post-traumatic arthritis in the DIP joint

1%

3/335

He will go on to develop a boutonniere deformity

4%

12/335

He will go on to develop a swan neck deformity

7%

22/335

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A healed mallet finger with 7 degrees of residual extensor lag has not been shown to have any negative functional effects.

A mallet finger is a deformity that is caused by injury/disruption to the terminal extensor tendon of a digit. It is usually due to a direct trauma to the distal aspect of the finger and a hyperflexion mechanism. It may be accompanied by other bony or soft tissue injuries. In isolation, mallet fingers are normally treated with extension splinting of the DIP joint for 6-8 weeks. It is imperative that patients maintain the splint in place in order for the tendon to heal. Healing with <10 degrees of extensor lag has been shown to demonstrate no negative functional effect. In cases of chronic, untreated mallet fingers, a swan neck deformity may form due to an imbalance of the extensor mechanism and compensatory hyperextension at the PIP joint.

Cheung et al. reviewed the treatment of mallet fingers, noting that most are caused by a forceful blow to the tip of the finger with sudden hyperflexion. They point out that most can be treated in an extension splint but the type and duration of splinting remain a topic of debate. Surgery may be indicated in cases of open injury, avulsion fracture with >1/3 of the articular surface involved, or with failed treatment.

Alla et al. published a current concepts article on mallet fingers. They discuss the mechanism of injury as well as the mechanics of the finger after injury, noting that loss of extensor continuity leads to an imbalance of force distribution between the PIP and DIP joints. Untreated, this imbalance can lead to a swan neck deformity due to DIP flexion and compensatory PIP hyperextension.

Incorrect Answers:
Answer 2: With extensor lag <10 degrees, there is thought to be no functional deficit.
Answer 3: Rupture of the extensor digitorum tendon and development of a mallet finger would not be a direct cause of arthritis at the DIP joint, despite the fact it can make the DIP joint painful and stiff.
Answers 4 & 5: Mallet fingers can be a cause of swan neck deformity if left unmanaged but given that this patient was treated appropriately without significant extensor lag, it is unlikely.

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