EXTENSOR CARPI ULNARIS (ECU) SUBLUXATION

Subluxation of the extensor carpi ulnaris (ECU) tendon is regarded as a relatively uncommon injury. It typically results from forced supination, volar flexion, and ulnar deviation of the wrist, which disrupts the ECU subsheath and subluxes the ECU tendon out of its groove in the distal ulna. These injuries are most common in athletes, especially golf and tennis players, which is due to the swing and stroke mechanics involved in these sports. Owing to its fairly generic presentation of ulnar-sided wrist pain, many ECU subluxations are missed on initial evaluation, which often leads to poor long-term outcomes. When properly diagnosed, conservative treatment is usually recommended for most acute injuries, while surgery is reserved for chronic cases and those that fail to improve after a conservative regimen. 1-4

Pathophysiology

• The ECU subsheath stabilizes the ECU during forearm rotation, and subluxation is thought to result from insufficiency of the subsheath. 5
• The injury mechanism of ECU subluxation is usually forced supination, volar flexion, and ulnar deviation of the wrist, which disrupts the ECU subsheath. This can occur in sports like golf and tennis, from a fall on an outstretched hand (FOOSH) injury or potentially from repetitive forceful supination, palmar flexion and ulnar deviation of the wrist.
  • Once the subsheath is damaged, the ECU tendon can sublux and slide under the intact extensor retinaculum.
  • The ECU tendon dislocates during supination and relocates with pronation. 2,3

  Related Anatomy

  • ECU tendon
  • Extensor retinaculum (superficial to the ECU subsheath and not attached to the distal ulna)
  • ECU subsheath
  • Dorsal extensor compartments
  • Fibro-osseous tunnel of the distal ulna
  • Deep antebrachial fascia
  • Distal radioulnar joint
  • Ulnar styloid
  • Ulnar capitulum
  • Pisiform
  • Triquetrum

  Inoue and Tamura created a classification system that grouped ECU subluxation and dislocation into the following 3 types:

  • Type A: the fibro-osseous sheath is torn at its ulnar side, and the tendon may lie beneath the fibrous sheath
  • Type B: the fibro-osseous sheath is disrupted from the radial wall and lies in the groove beneath the tendon
  • Type C: there is detachment of the groove’s periosteum from the ulnar side in continuity with the fibro-osseous sheath, thus forming an expanded and redundant false pouch into which the tendon is dislocated 6

  Incidence and Related Conditions

  • Traumatic ECU subluxations and dislocations are considered to be rare, but their incidence may actually be much higher, because many cases are missed or misdiagnosed. 2
  • The prevalence of ECU subluxation is particularly high in athletes who forcibly flex, supinate, and ulnar deviate their wrist—especially golf and tennis players—and the number of cases is expected to continue to rise in young, active individuals. 4
    • One study found the annual prevalence of ECU tendon injury in tennis players to be 1 in 18, and 42% of affected players also had ECU instability. 7

    Differential Diagnosis

    • ECU dislocation
    • ECU tendinopathy
    • Triangular fibrocartilage complex (TFCC) injury
    • Lunotriquetral (LT) instability
    • Distal radioulnar joint (DRUJ) injury
    • Flexor carpi ulnaris (FCU) tendinopathy
    • Pisotriquetral (PT) joint injury
    • Distal ulnar fracture
    • Ulnar collateral ligament sprain