Central Slip Injury

Anatomy

The extensor mechanism of the proximal interphalangeal (PIP) joint is best described as a trifurcation of the extensor tendon (EDC) into the central slip, which attaches to the dorsal base of the middle phalanx, and the two lateral bands.¹

Injury to the central slip results in disruption of this extensor mechanism of the PIP joint and disruption of the normal movements of the distal interphalangeal (DIP) joint.¹

Illustration by Dr. Lisa Bryski

Classic presentation

The patient will present with PIP swelling and/or pain after forced hyperflexion, a laceration over the dorsum of the finger, or volar dislocation of the PIP joint.

The patient may have full range of motion immediately following the incident. However, in more severe cases, a full blown boutonniere deformity may be present.

Untreated, proximal migration of the disrupted central slip, and volar subluxation of the lateral bands leads to flexion deformity of the PIP joint and hyperextension at the DIP joint known as a Boutonniere Deformity.³

Diagnosis: Elson TEST

Tip: Provide patient with analgesia in the form of a ring block before performing the Elson Test. Be sure to check neurovascular status before administering local.

The Elson test reliably diagnoses loss of central slip function in the pre-boutonniere injury and in the passively correctable boutonniere deformity.⁴ The Elson test and modifications to this test which are shown in the video below.

With a central slip injury, force is distributed through the lateral bands. The lateral bands migrate volarly leading to extension through the DIPJ.

Clinical Pearl: It is normally impossible to extend the PIP joint without simultaneously extending the DIP joint. A positive Elson test is a hyper extended DIPJ with the PIPJ in flexion during active extension, while a negative Elson meaning a lax, flexed DIPJ while the PIPJ is flexed during active extension.

treatment

Splint PIP joint in extension with the DIP joint free. Referral to hand specialist. Extensor tendon lacerations may be repaired in the ED by a practitioner versed in their repair. However, the patient will still require splinting and referral as this injury requires regular followup ensuring the patient does not develop a boutonniere deformity. Patients may also be fitted for a custom made splint.

References

Skinner, S., & Isaacs, J. (2020). Extensor Tendon Injuries in the Athlete. Clinics in Sports Medicine, 39(2), 259-277.

2. Ostendorf, B., Iking-Konert, C., Cohnen, M., & Schneider, M. (2005). Finger joint swellings in a teenager: juvenile rheumatoid arthritis or a psychiatric disorder. Annals of the rheumatic diseases, 64(3), 501-502.

3. Lin, J. D., & Strauch, R. J. (2014). Closed soft tissue extensor mechanism injuries (mallet, boutonniere, and sagittal band). Journal of hand surgery, 39(5), 1005-1011.

4. Rubin, J., Bozentka, D. J., & Bora, F. W. (1996). Diagnosis of closed central slip injuries: a cadaveric analysis of non-invasive tests. Journal of hand surgery, 21(5), 614-616.

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