https://upload.orthobullets.com/topic/6041/images/DISI - AP - Terry Thomas sign and cortical ring_moved.jpg
https://upload.orthobullets.com/topic/6041/images/reivew clenched fist.jpg
https://upload.orthobullets.com/topic/6041/images/DISI - lateral_moved.jpg
  • Scapholunate ligament is important for carpal stability
    • chronic scapholunate deficiency leads to DISI (see below)
  • 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
    • location
      • ligament has 3 components that span between the scaphoid and lunate bones
      • dorsal, proximal and volar components
      • incomplete tears > complete tears
  • 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 topic
      • DISI is a form of carpal instability dissociative  
  • 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 
  • 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 post
        • when deviating from ulnar to radial, pressure over volar aspect of scaphoid produces a clunk secondary to dorsal subluxation of the scaphoid over the dorsal rim of the radius
          • dorsal wrist pain or a clunk during this maneuver may indicate instability of scapholunate ligament
  • Radiographs
    • recommended views
      • AP and lateral views of the wrist
    • additional views
      • radial and ulnar deviation views
      • flexion and extension views 
      • clenched fist  (can attenuate 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
  • 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
        • f 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 
  • 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
  • Disease progression (e.g. SLAC wrist)
  • Arthritis
  • Post-operative pain, stiffness, fatigue
  • Reduced grip strength

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