Diagnosing the central slip injury

2017-03-11T00:19:16+00:00
Extensor Tendon Laceration Finger 6 sm

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.

central slip anatomy boutonniere

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.

  1. Normal test: Results in active extension of the PIP joint and a floppy, flexed DIP joint.
  2. 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

 

modified Elson's test diagram

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.
1.
Harrison B, Hilliard M. Emergency department evaluation and treatment of hand injuries. Emerg Med Clin North Am. 1999;17(4):793-822, v. [PubMed]
2.
Venus M, Little C. The modified Elson’s test in open central slip injury. Injury Extra. 2010;41(11):128-129.
3.
Calabro J, Hoidal C, Susini L. Extensor tendon repair in the emergency department. J Emerg Med. 1986;4(3):217-225. [PubMed]
4.
Rubin J, Bozentka D, Bora F. Diagnosis of closed central slip injuries. A cadaveric analysis of non-invasive tests. J Hand Surg Br. 1996;21(5):614-616. [PubMed]
5.
Vermaak P, Devaraj V. Don’t slip up! A modified technique for assessing central slip injuries. J Hand Surg Eur Vol. 2012;37(9):893-895. [PubMed]
6.
Rockwell W, Butler P, Byrne B. Extensor tendon: anatomy, injury, and reconstruction. Plast Reconstr Surg. 2000;106(7):1592-603; quiz 1604, 1673. [PubMed]

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.

Brian Lin, MD
UCSF Assistant Professor of Emergency Medicine, Kaiser Permanente Hospital, San Francisco, CA; Founder and author, LacerationRepair.com

Daniel Ting, MD

Daniel Ting, MD

National medical education editor, CanadiEM
Emergency Medicine Resident
University of British Columbia
Jared Baylis, MD

Jared Baylis, MD

Emergency Medicine Resident
University of British Columbia
  • Glenn Paetow

    Fantastic post! Any pearls when trying to make this diagnosis in a pediatric patient? I’m thinking about a recent case I had of a 1-year-old who had a dorsal laceration after a door was closed on their pinky.

    • Brian Lin, MD, FACEP

      Yes, both tests (Elson’s and its modification) require patient cooperation, so wouldn’t be useful on a 1 year old. Your saving grace here is that these pediatric injuries generally find a way to heal themselves incredibly well. But, when you are concerned, splinting in extension is always your safest option.

  • katxox

    My left little finger PIP joint was dislocated toward the palm. Put back in by ER doc, ortho doc follow up instructed me to buddy tape it to the ring finger to “keep the pinky moving”. He didn’t want to splint to prevent it from getting stiff. After 6 weeks, I stopped buddy taping. The pinky finger is now frozen at about a 45° angle. The injury is now 12 weeks old. New ortho doc says central slip. The PIP will flex but not extend. The DIP will flex but not not hyper-extend. X-ray shows minimal PIP, MCP joint space. Thoughts on whether I have a central slip tear or complete rupture?