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Updated: Feb 2 2024

Snapping Extensor Carpi Ulnaris (ECU)

  • Summary
    • Snapping ECU is a clinical condition characterized by pain over the ulnar wrist caused by instability and tendonitis of the ECU tendon secondary overuse.
    • Diagnosis is made with clinical examination with palpation of the ECU tendon and noting a painful snap while moving the wrist from pronation to supination.
    • Treatment is usually rest and wrist splinting. In refractory cases ECU subsheath reconstruction may be considered.
  • Epidemiology
    • Incidence 
      •  common with sporting activities 
    • Risk factors
      • tennis
      • golf
      • rupby
  • Etiology
    • Pathoanatomy
      • ECU subluxation is secondary to attenuation or rupture of the ECU subsheath (6th dorsal compartment)
      • attenuation
        • remains intact but is stripped at ulnar/palmar attachment to produce a false pouch that the ECU tendon can subluxate/dislocate into
      • rupture
        • ulnar sided ECU subsheath tears
          • ECU subluxates on supination, and reduces on pronation
        • radial sided ECU subsheath tears
          • ECU subluxates on supination, and lies on top of the torn subsheath on pronation
      • subluxation and snapping can lead to ECU tendonitis
  • Anatomy
    • Extensor tendon compartments
      • Compartment 1 (De Quervain's Tenosynovitis )
        • APL
        • EBP
      • Compartment 2 (Intersection syndrome )
        • ECRL
        • ECRB
      • Compartment 3
        • EPL
      • Compartment 4
        • EIP
        • EDC
      • Compartment 5 (Vaughan-Jackson Syndrome )
        • EDM
      • Compartment 6 (Snapping ECU )
        • ECU
    • ECU tendon
      • ECU tendon inserts onto the 5th metacarpal base
      • ECU subsheath is part of the TFCC that is most critical to ECU stability
      • ECU lies dorsal during supination and translates ulnar during pronation
        • in pronation, the ECU tendon exits the wrist in a straight direction.
        • in supination, the tendon exits the sixth compartment at an angle of approximately 30°
        • tension on the ECU retinaculum and subsheath is therefore greater during activities involving supination
      • ECU subluxates during ulnar deviation, supination, wrist flexion
        • this position has the greatest angulation of the ECU tendon with respect to the ulna
  • Presentation
    • Symptoms
      • pain and snapping over dorsal ulnar wrist
    • Physical exam
      • flexion and supination of the wrist elicit a painful snap
      • ECU tendon reduces with pronation
  • Imaging
    • Radiographs
      • unremarkable
    • Ultrasound
      • can dynamically assess ECU stability
    • MRI
      • can show tendonitis, TFCC pathology, or degenerative tears of ECU
  • Differential
    • TFCC tear
    • Hook of hamate fracture
    • Ulnar styloid fracture
    • Ulnar styloid impaction syndrome
    • Ulnar tunnel syndrome
    • Pisotriquetral arthritis
  • Diagnosis
    • Clinical
      • diagnosis is made with careful history and physical examination
  • Treatment
    • Nonoperative
      • wrist splint or long arm cast
        • indications
          • first line of treatment
        • technique
          • arm immobilized in pronation and slight radial deviation
    • Operative
      • ECU subsheath reconstruction +- wrist arthroscopy
        • indications
          • if nonoperative management fails
        • technique
          • direct repair in acute cases
          • chronic cases may require a extensor retinaculum flap for ECU subsheath reconstruction
          • wrist arthroscopy shows concurrent TFCC tears in 50% of cases
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