Figure 1. Laceration overlying proximal interphalangeal (PIP) joint of right second digit. (Photograph by Daniel Ting and Jared Baylis)
A 34-year-old cabinet maker presents to your Emergency Department after accidentally getting his finger caught in a drawer. On examination, he has a superficial, clean laceration over the dorsal surface of the right second digit (Figure 1).
In a previous post, we discussed the approach to identifying, treating, and managing extensor tendon injuries of the hand. In it, we advocate for a high index of suspicion for extensor tendon injuries whenever a patient suffers a laceration to the dorsal aspect of the hand. However, lacerations over the PIP joint deserve special mention. In this article, we focus on the diagnosis of a specific type of extensor tendon laceration: the central slip injury.
Anatomy
As the extensor mechanism of the hand crosses over the PIP joint, it branches into 3 bands: the central slip and 2 lateral bands (Figure 2).1 The central slip attaches to the middle phalanx and the lateral bands attach to the distal phalanx. When it comes to our case, the 3 bands have significant implications on how we should proceed with examination.
Figure 2. Extensor mechanism over the finger. A) Intact central slip and lateral band mechanism. B) Disrupted central slip leading to a Boutonnière’s deformity. (Illustration by David Ting)
Physical Exam: Elson’s and Modified Elson’s Test
For injuries of overlying or near the PIP joint, suspect a central clip injury. These extensor tendons run superficially! In the acute setting, a central slip injury will often not result in an anatomically evident abnormality, unlike in a chronic injury which results in a Boutonnière deformity[Figure 2B].1 There is often some level of preservation of active PIP extension due to the intact lateral bands.2
To check for this extensor tendon injury, test extension strength against resistance.3 This can be done by the Elson’s4 and Modified Elson’s Tests [Figure 3].2,5 For both, interpretation of the results focuses on the DIP joint.
- Normal test: Results in active extension of the PIP joint and a floppy, flexed DIP joint.
- Abnormal test: Results in no active extension of the PIP joint and a slightly extended, taut DIP joint.
Elson’s Test
Read more in an earlier ALiEM Quick Clinical Tip on Elson’s Test.
Modified Elson’s Test
Figure 3. The modified Elson’s test. A) Uninjured fingers show a symmetric inability to straighten the distal interphalangeal joint when the middle interphalangeal joints are flush against each other. B) In a central slip injury, the distal interphalangeal joint is pathologically straightened, which is seen in the left hand in this example. (Illustration by David Ting)
One approach can be to use both these tests in conjunction to confirm injury.
Dr. Brian Lin’s excellent laceration repair website, as well as his segment on EM:RAP from January 2016, also contain videos and further discussion about the central slip.
Management
Compared to other extensor tendons, the central slip is thinner and may be more challenging to repair in the ED. Often, the best setting to manage these injuries is the operating room. Remember that for all extensor tendon injuries, extension splinting with referral to a hand surgeon within 1 week is an acceptable strategy. In a central slip injury, splinting and referral is generally the preferred management after general wound care and skin closure is performed. This is because specialized procedures such as suturing together of portions of the lateral bands to recreate the central slip may be required.6
Take-Home Points
- Missed central slip injuries can lead to a Boutonnière deformity and patient morbidity.
- Lacerations over the PIP joint demand testing for a central slip injury.
- A combination of the Elson’s and modified Elson’s tests evaluate the central slip.
- Central slip injuries should be splinted in extension and referred to a hand surgeon in 1 week for repair.
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