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Extensor Carpi Ulnaris (ECU) Subluxation

Exams and Signs

Historical Overview

  • Extensor carpi unlaris (ECU) subluxation is a partial dislocation of the ECU. Bunnell claimed that ECU tendon dislocation is “not common unless the fascial tunnel for the ulnaris has been torn.”3

Description

  • ECU subluxation is secondary to rupture of the ECU subsheath in the 6th dorsal compartment. It may cause pain and clicking on the ulnar side of the wrist.1

Pathophysiology

  • ECU subluxation may arise from injury, tendonitis or rheumatoid arthritis.

Instructions

  1. Place the patient’s forearm in a supinated position
  2. Ask the patient to ulnarly deviate his/her wrist
  3. Palpate the ECU to check for subluxation

Variations

  • Dynamic ultrasound of the 6th dorsal compartment may also contribute to a confirmation of ECU tendon subluxation.3

Related Signs and Tests

  • ECU synergy test
  • Magnetic resonance imaging (MRI)

Diagnostic Performance Characteristics

  • The possibility of coexistent injuries can make physical examination maneuvers unreliable, so that it is difficult to differentiate between intra- and extra-articular pathology.4
  • ECU subluxation test should be used in conjunction with other tests (eg, ECU synergy test) to improve reliability.
Definition of Positive Result
  • A positive result occurs when there is visible or palpable subluxation of the dorsal ulnar side of the wrist, which may cause pain.1
Definition of Negative Result
  • A negative result occurs when there is no visible or palpable subluxation of the dorsal ulnar side of the wrist. 
Comments and Pearls
  • A shallow ECU groove could make patients more susceptible to subsequent ECU instability.2
  • Using the ECU synergy test in conjunction with the ECU subluxation test may help some patients avoid having to undergo MRI and wrist arthrography.4
Diagnoses Associated with Exams and Signs
References
  1. Culp R, Jacoby S. Musculoskeletal Examination of the Elbow, Wrist and Hand: Making the Complex Simple. New Jersey: SLACK Incorporated, 2012.
  2. Iorio ML, Bayomy AF, Huang JI. Morphology of Extensor Carpi Ulnaris Groove and Tendon. J Hand Surg Am 2014;39(12):2412-6. PMID: 25306505
  3. MacLennan AJ, Nemechek NM, Waitayawinyu T, Trumble TE. Diagnosis and anatomic reconstruction of Extensor Carpi Ulnaris Subluxation. J Hand Surg Am 2008;33(1):59-64. PMID: 18261666
  4. Ruland RT, Hogan CJ. The ECU Synergy Test: An Aid to Diagnose ECU Tendonitis. J Hand Surg Am 2008;33(10):1777-82. PMID: 19084177
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