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Updated: Aug 7 2022

Scapholunate Ligament Injury & DISI

Images - AP - Terry Thomas sign and cortical ring_moved.jpg clenched fist.jpg - lateral_moved.jpg
  • Summary
    • Scapholunate Ligament Injury is a source of dorsoradial wrist pain with chronic injuries leading to a form of wrist instability (DISI deformity).
    • Diagnosis is made with PA wrist radiographs showing widening of the SL joint. Diagnosis of DISI deformity can be made with lateral wrist radiographs showing a scapholunate angle > 70 degrees. 
    • Treatment of acute SL ligament injuries may be immobilization versus operative repair/reconstruction depending on degree of displacement. Chronic DISI deformities may be indicated for fusion procedures depending on degree of arthritis and patient symptoms. 
  • Epidemiology
    • Incidence
      • acute injury
        • occurs in approximately 10-30% of intra-articular distal radius fractures or carpal fractures
      • degenerative injury
        • degenerative tears in >50% of people over the age of 80 years old
    • Anatomic location
      • ligament has 3 components that span between the scaphoid and lunate bones
      • dorsal, proximal and volar components
      • incomplete tears > complete tears
  • Etiology
    • Pathophysiology
      • mechanism of injury
        • sudden impact force applied to the hand and wrist causing SLIL injury and scapholunate dissociation
        • injury occurs most commonly with wrist positioned in extension, ulnar deviation and carpal supination
      • pathoanatomy
        • osseous
          • SLIL tearing will position the scaphoid in flexion and lunate extension
        • ligamentous
          • diastasis of the scapholunate complex occurs with complete SLIL tears and capsule disruption.
    • Associated injuries
      • DISI (dorsal intercalated segmental instability)
        • scapholunate dissociation causes the scaphoid to flex palmar and the lunate to dorsiflex
        • if left untreated the DISI deformity can progress into a SLAC wrist
          • DISI deformity may also develop secondary to distal pole of the scaphoid excision for treatment of STT arthritis
        • DISI is a form of carpal instability dissociative
  • Anatomy
    • Scapholunate interosseous ligament
      • location
        • c-shaped structure connecting the dorsal, proximal and volar surfaces of the scaphoid and lunate bones
        • dorsal fiber thickened (2-3mm) compared to volar fibers
      • biomechanics
        • dorsal component provides the greatest constraint to translation between the scaphoid and lunate bones
        • proximal fibers have minimal mechanical strength
    • Overview of wrist ligaments and biomechanics
  • Presentation
    • History
      • acute FOOSH injury vs. degenerative rupture
        • age, nature of injury, duration since injury, degree of underlying arthritis, level of activity
    • Symptoms
      • usually dorsal and radial-sided wrist pain
      • pain increased with loading across the wrist (e.g. push up position)
      • clicking or catching in the wrist
      • may be associated with wrist instability or weakness
    • Physical exam
      • inspection
        • may see swelling over the dorsal aspect of the wrist
      • palpation
        • tenderness in the anatomical snuffbox or over the dorsal scapholunate interval (just distal to Lister's tubercle)
      • motion
        • pain increased with extreme wrist extension and radial deviation
      • provocative tests
        • Watson test
          • when deviating from ulnar to radial, pressure over volar aspect of scaphoid subluxates the scaphoid dorsally out of the scaphoid fossa of the distal radius, and a clunk is palpated when pressure is released as the scaphoid reduces back over the dorsal rim of the radius
            • a painful clunk during this maneuver may indicate insufficiency of scapholunate ligament
  • Imaging
    • Radiographs
      • recommended views
        • AP and lateral views of the wrist
      • additional views
        • radial and ulnar deviation views
        • flexion and extension views
        • clenched fist (can exaggerate the diastasis)
      • findings
        • AP radiographs
          • SL gap > 3mm with clenched fist view (Terry Thomas sign)
          • cortical ring sign (caused by scaphoid malalignment)
          • humpback deformity with DISI associated with an unstable scaphoid fracture
          • scaphoid shortening
        • Lateral radiographs
          • dorsal tilt of lunate leads to SL angle > 70° on neutral rotation lateral
          • capitolunate angle > 20°
        • DISI
          • normal carpal alignment
          • increased SL angle
    • Arthrography
      • indications
        • may be used as screening tool for arthroscopy
      • views
        • radiocarpal and midcarpal views
        • always assess the contralateral wrist for comparison
      • findings
        • may demonstrate the presence of a tear but cannot determine the size of the tear
        • positive finding of a tear may indicate the need for wrist arthroscopy
    • MRI
      • indications
        • often overused as a screening modality for SLIL tears
      • findings
        • requires careful inspection of the SLIL by a dedicated radiologist to confirm diagnosis
        • low sensitivity for tears
    • Arthroscopy
      • indications
        • considered the gold standard for diagnosis
  • Differential 
    • LT ligament injury & VISI deformity
    • Carpal instability nondissociative (CIND)
  • Treatment
    • Nonoperative
      • NSAIDS, rest +/- immobilization
        • indications
          • acute, undisplaced SLIL injuries
          • chronic, asymptomatic tears
        • technique
          • splinting and close follow-up with repeat imaging and clinical response with acute injuries
        • outcomes
          • most people feel casting alone is insufficient
          • may be effective with incomplete tears
    • Operative
      • scapholunate ligament repair
        • indications
          • acute scapholunate ligament injury without carpal malalignment
          • chronic but reducible scapholunate ligament injuries (can peform if < 18 months from the time of injury)
          • ligament pathoanatomy is ammenable to repair
      • scapholunate reconstruction
        • indications
          • acute scapholunate ligament injury without carpal malalignment where pathoanatomy is not ammenable to repair
          • reducible scapholunate ligament injuries > 18 months from the time of injury
      • scaphoid ORIF vs. CRPP (+/- arthroscopic assistance)
        • indications
          • if pathoanatomy of SL ligament injury is a scaphoid fx than repair with ORIF vs. CRPP (+/- arthroscopic assistance)
      • stabilization with wrist fusion (STT or SLC)
        • indications
          • rigid and unreducible DISI deformity
          • DISI with severe DJD
        • technique
          • scaphotrapezialtrapezoidal (STT) fusion
          • scapholunocapitate (SLC) fusion
          • scapholunate fusion alone has highest nonunion rate
  • Technique
    • Scapholunate ligament direct repair SLIL with k-wires
      • approach
        • small incision is made just distal to the radial styloid
        • care to avoid cutting the radial sensory nerve branches
      • methods
        • SL joint pinning with k-wires
        • suture anchors with k-wires
        • Blatt dorsal capsulodesis
          • often added to a ligament repair and remains a viable alternative for a chronic instability when ligament repair is not feasible
      • repair technique
        • place two k-wires in parallel into the scaphoid bone
        • reduce the SL joint by levering the scaphoid into extension, supination and ulnar deviation and lunate into flexion and radial deviation
        • pass the k wires into the lunate
        • confirm reduction of the SL joint under fluoroscopy
        • place patient in short arm cast
      • post-operative care
        • remove k-wires in 8-10 weeks
        • no heavy labor for 4-6 months
    • Scapholunate ligament reconstruction
      • approach
        • same as for repair
      • reconstruction
        • FCR tendon transfer (direct SL joint reduction)
        • ECRB tendonosis (indirect SL joint reduction)
        • weave not recommended due to high incidence of late failure
  • Complications
    • Disease progression (e.g. SLAC wrist)
    • Arthritis
    • Post-operative pain, stiffness, fatigue
    • Reduced grip strength
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