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Elson Test

Exams and Signs

Historical Overview

  • A test developed by Boyes was traditionally used to evaluate the integrity of the central slip of the extensor tendon at the proximal interphalangeal (PIP) joint after injury, but it only became positive at a later stage.1
  • Elson proposed a new test in 1986 for detecting ruptures of the central slip that became positive immediately after injury.2

Description

  • The Elson test determines whether the central slip is still intact after injury by having the patient attempt to extend the PIP joint while the finger is comfortably flexed.2

Pathophysiology

  • Lacerations and other injuries at the PIP joint may involve the underlying central slip of the extensor tendon.2,3
    • Volar dislocation of the PIP joint can also lead to a central slip rupture.4
  • If a central slip injury is undetected and left untreated, it will typically lead to the development of a Boutonnière deformity, which is characterized by flexion of the PIP joint and extension of the distal interphalangeal (DIP) joint. The injury may be overlooked initially as the finger will retain some active extension and the Boutonnière deformity subsequently develops over the following days and weeks.3,4

Instructions2

  1. Obtain an accurate and complete patient history with a description of the injury.
  2. Have the patient flex the injured finger over the edge of a table comfortably with the PIP joint at 90°.
  3. Apply resistance to the middle phalanx.
  4. Ask the patient to attempt to gently extent the PIP joint. 

Variations

  • Schreuders described a modification of the Elson test that involves the patient pushing the middle phalanx of the injured finger against the non-injured finger on the opposite hand with each PIP joint at 90°. Asymmetric movement is easily observed by comparing the two sides simultaneously.3
    • Additional stability may be gained while performing this modified test by using the thumb tips pushed against one another to support the fingers.
    • The modification also has the advantage of simultaneous comparison with the contralateral digit without a need to test the resistance.
    • Ultimately, this direct comparison with the uninjured side allows clinicians to be more confident when interpreting test results.3,4

Related Signs and Tests

  • Evaluation of DIP flexion with the PIP held in extension (Boyes test)1
  • Evaluation of active PIP extension (Carducci test)5
  • Central slip tenodesis test5

Diagnostic Performance Characteristics

  • The biomechanical basis of the Elson test is that, in the case of a central slip lesion, it is possible to actively extend the DIP joint because the lateral bands now move independently of the central slip. The central slip is no longer attached to the middle phalanx, so pulling on the extensor tendon produces no traction on the middle phalanx, only via the lateral bands on the distal phalanx.
    • Normally, excursion of the central slip and lateral bands are interdependent, which has been called the “checkrein” effect. The central slip “checkreins” the proximal excursion of the extensor mechanism and, therefore has no extension effect on the distal phalanx.
    • In central slip lesions, the movements of the lateral bands are no longer restricted and will be able to extend the DIP joint in all positions of the PIP joint.4
  • Rigidity at the DIP joint during PIP extension indicate a complete central slip rupture, as the test cannot detect partial ruptures.2

Additional Information

Definition of Positive Result
  • A positive result occurs with weakness in extension of the PIP and rigidity in the DIP joint.
Definition of Negative Result
  • A negative result occurs when PIP joint extension is strong and the DIP joint remains floppy.
Comments and Pearls
  • Few individuals can flex the IP joints independently because both flexor profundus and flexor superficialis act on the checkreins afforded by the extensor hood with its three uncompliant components.2
  • The Elson test has been found to be the most reliable of four tests for diagnosing central slip injury and function.5
  • The Elson test has been found to have two disadvantages:
    1. Estimation of the amount of extension (range of motion and strength) is difficult to interpret in only one injured finger
    2. The inter-individual differences of finger joint mobility can also influence the extensor tendon excursion and, therefore, the DIP joint range of motion4
Diagnoses Associated with Exams and Signs
References
  1. Boyes, JH. Bunnel's surgery of the hand, 5th Ed. Philadelphia, JB Lippincott, 1970, pp 393.
  2. Elson, RA. Rupture of the central slip of the extensor hood of the finger. A test for early diagnosis. J Bone Joint Surg Br1986;68(2):229-31. PMID: 3958008
  3. Venus, MR, and Little C. Injury Extra2010;41(11):128–129.
  4. Schreuders, TA, Soeters JN, Hovius SE, and Stam H. A Modification Of Elson's Test For The Diagnosis Of An Acute Extensor Central Slip Injury. The British Journal of Hand Surgery 2006;11(4):111-112.
  5. Rubin, J, Bozentka, DJ, and Bora, FW. Diagnosis of closed central slip injuries. A cadaveric analysis of non-invasive tests J Hand Surg Br1996;21(5):614-6. PMID: 9230945
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