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.
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.
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.
Read more in an earlier ALiEM Quick Clinical Tip on Elson’s Test.
Modified Elson’s Test
One approach can be to use both these tests in conjunction to confirm injury.
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
- 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.
Expert Peer Review by Dr. Brian Lin
Another nice article by Drs. Ting and Baylis, highlighting an anatomical idiosyncracy of the extensor tendon mechanism.
Elson\'s test has long been considered the gold standard for diagnosis of central slip injury, so knowledge of what it is and when to apply it is crucial. Keep in mind, central slip avulsion can also occur with closed injuries to the finger from blunt trauma, so there won\'t always be a laceration overlying the PIP (which would be your usual prompt).
I find Elson\'s test easy to understand in the minutes after I read about it or watch a refresher video on youtube. However, since the occasion to consider it is relatively infrequent, I don\'t usually have it ready-to-go as I examine a patient in real-time. This is why I like to use the modified Elson\'s test (a simple test of symmetry-- easy to perform, easy to remember) as a screening test. When positive, I will then go on to perform Elson\'s test for more diagnostic certainty.
This is not an injury we want to miss! Delayed recognition can lead to difficult-to-reverse or even irreparable deformity. Make sure to have familiarity with these important examination tools.