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Paradoxical Extension

Exams and Signs

Historical Overview

  • Paradoxical extension in the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints is sometimes referred to as the “lumbrical plus finger.” The lumbrical muscles, which control extension and flexion of the interphalangeal (IP) joints, pull on lateral bands, leading to DIP and PIP extension of the affected finger(s).1
  • Because they are thin and elongated, the lumbrical muscles are named after the Latin word “lumbricus,” meaning earthworm.2

Description

  • Paradoxical extension of the PIP joint may occur while the patient is trying to flex the DIP joint. The lumbrical muscle becomes taut before the flexor digitorum profundus (FDP) to that finger becomes taut, leading to PIP extension.3
  • This sort of extension may be called the “extensor habitus” phenomenon and often requires surgical intervention.4

Pathophysiology

  • Paradoxical extension occurs when there is a severance of the FDP tendon, an avulsion of the FDP, an over-long flexor tendon graft, or an amputation through the middle phalanx.1
  • Paradoxical extension can also be caused by an IP injury or a DIP amputation.

Instructions

  1. Record the patient’s history, including any sports-related injuries. Ask the patient to rate how much pain s/he usually experiences in the affected finger on a scale from 1 to 10.
  2. Ask the patient to attempt to flex the DIP joint of the affected finger.
  3. Observe whether the PIP joint of that finger actually flexes or extends.
  4. Examine the contralateral hand for comparison.

Variations

  • Consider the total active motion (TAM) values. TAM is the sum of the angles produced by the metacarpophalangeal (MP), PIP and DIP joints in maximum active flexion. There is no universal TAM value, so it is essential to consider both hands of the patient.5

Related Signs and Tests

  • Electromyographic (EMG) examination of the lumbrical muscles4

Diagnostic Performance Characteristics

  • To improve reliability, use ROM tests and an EMG examination.4

Additional Information

Presentation Photos and Related Diagrams
Lumbrical Plus Finger with Paradoxical Extension
  • Lumbrical Plus Finger : Patient presents for simple index laceration who had serious injury to III,IV&V several years ago that required tendon graft (IV). Note old incisions (arrows). Now patient complains ring straightens when he tries to flex it.
    Lumbrical Plus Finger : Patient presents for simple index laceration who had serious injury to III,IV&V several years ago that required tendon graft (IV). Note old incisions (arrows). Now patient complains ring straightens when he tries to flex it.
  • Lumbrical Plus Finger : Patient presents for simple index laceration who had serious injury to III,IV&V several years ago that required tendon graft (IV). Now patient complains ring straightens when he tries to flex it.
    Lumbrical Plus Finger : Patient presents for simple index laceration who had serious injury to III,IV&V several years ago that required tendon graft (IV). Now patient complains ring straightens when he tries to flex it.
Definition of Positive Result
  • A positive result occurs when the DIP or PIP joint extends while the patient is trying to flex the fingers.  
Definition of Negative Result
  • A negative result occurs when the DIP and PIP joints flex when the patient tries to flex the fingers. 
Comments and Pearls
  • Surgical options for paradoxical extension include lumbrical release and replacement of an appropriate length tendon graft.2 
Diagnoses Associated with Exams and Signs
Videos
Lumbrical Plus Finger with Paradoxical Extension vs Long Flexor Tendon Graft vs Both: Patient had serious injury to III,IV&V several years ago that required tendon graft (IV). Now patient complains ring straightens when he tries to flex it.
References
  1. Parkes A. The “Lumbrical Plus” Finger. J Bone Joint Surg Br 1971;53B(2):236-9. PMID: 5578219
  2. Wang K, McGlinn EP, Chung KC. A biomechanical and evolutionary perspective on the function of the lumbrical muscle. J Hand Surg Am 2014;39(1):149-55. PMID: 24369943
  3. Scanlan MW, Ehrlich RV, Strauch RJ. Partially retained small finger flexor digitorum profundus function despite complete tendon loss in the forearm. J Hand Surg Am 2004;29(4):591-4. PMID: 15249081
  4. Kajiwara T, Onogi K, Shimizu H. Contribution of lumbrical muscle activity to the paradoxical extension phenomenon induced by injuries to the finger flexor tendons. Keio J Med 1999;48(4):175-8. PMID: 10638140
  5. Kleinert HE, Verdan C. Report of the Committee on Tendon Injuries. J Hand Surg Am 1983;8(5):794-8. PMID: 6630960
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