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Lumbrical Plus Finger

Exams and Signs

Historical Overview

  • Paradoxical extensor phenomenon of the finger was first described and given the term “lumbrical-plus" finger by Parkes in 1970.1,2
  • In his original paper on lumbrical plus finger, Parkes also described a clinical test that could be used to determine if the condition is present.1

Description

  • The lumbrical plus finger test is a clinical examination tool that evaluates the function of the fingers’ interphalangeal (IP) joints and determines if the patient has lumbrical plus finger based on whether the finger unintentionally extends during flexion.1,2

Pathophysiology

  • Lumbrical plus finger, which is also known as lumbrical plus syndrome and lumbrical tightness, typically results from flexor digitorum profundus (FDP) tendon disruption distal to the origin of the lumbricals.1,3
  • This disruption of the FDP tendon may be a consequence of FDP transection, FDP avulsion, excessively long flexor tendon grafts, amputation through the middle phalanx shaft, or distal interphalangeal (DIP) joint amputation.1,2
    • Repetitive trauma to the ulnar side of the palm has also been identified as a cause.2
    • In any of these cases, strong active flexion causes the affected digit to exhibit paradoxical extension of the IP joints, or of the proximal interphalangeal (PIP) joint in the case of a middle phalanx amputation.4
  • The injury mechanism of lumbrical plus finger is a contraction of the FDP that is transmitted through the lumbrical muscle to the expansion hood of the extensor and lateral band, which is usually attributed to flexor tendon injuries. The phenomenon arises when the FDP distal to the lumbrical muscle is either functionally too long or is absent.2,3
  • Lumbrical plus finger most commonly affects the long finger.2

Instructions1

  1. Obtain an accurate and complete patient history that includes an injury description if applicable.
  2. Have the patient place their hand in a relaxed supine position.
  3. The affected finger should be capable of full, passive flexion with ease.
  4. Ask the patient to form a grip with all fingers.
  5. Observe whether the affected finger extends with attempted flexion.

Variations

  • While the classical clinical manifestation of lumbrical plus finger is paradoxical IP joint extension that primarily affects the DIP joint, other authors have reported increased metacarpophalangeal (MP) flexion as an additional clinical sign of this condition.4

Related Signs and Tests

  • Electrical stimulation of the lumbricals

Additional Information

Presentation Photos and Related Diagrams
Lumbrical Plus Finger
  • Lumbrical Plus Finger: Patient presents for simple index laceration who had serious injury to III,IV&V several years ago that require tendon don graft (IV). Note old incisions (arrows). Now patient complains ring straightens while he tries to flex the ring finger.
    Lumbrical Plus Finger: Patient presents for simple index laceration who had serious injury to III,IV&V several years ago that require tendon don graft (IV). Note old incisions (arrows). Now patient complains ring straightens while he tries to flex the ring finger.
  • 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 there is unintended, paradoxical extension of the affected digit during active flexion of the fingers.1
Definition of Negative Result
  • A negative result occurs when there is normal flexion of all fingers.
Comments and Pearls
  • It’s important that hand surgeons recognize the importance of identifying lumbrical plus finger and treating it appropriately, as doing so can lead to dramatic functional improvements.1
Videos
Lumbrical Plus Finger 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;53(2):236-9.PMID: 5578219
  2. Abe, Y and Tominaga, Y. Paradoxical extension phenomenon of the little finger due to repetitive trauma to the palm. Hand Surg 2012;17(2):255-7.PMID: 22745095
  3. Lilly, SI and Messer, TM. Complications after treatment of flexor tendon injuries. J Am Acad Orthop Surg 2006;14(7):387-96.PMID: 16822886
  4. Schuind, FA, Moungondo, F and Van Wetter, P. A New Clinical Sign of Lumbrical Plus Finger. J Hand Surg Am 2018;43(6):573 e1-573. PMID: 29223629
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