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Scapholunate Ligament Injury & DISI

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Topic updated on 08/26/14 9:29pm
Introduction
  • 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 extention
      • 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  
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 fibres 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 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
      • LT shuck test (aka ballottement test) post
        • grasp the lunate between the thumb and index finger of one hand while applying alternative dorsal and palmar loads across the triquetrum with the thumb and index of the other hand
        • positive test elicits pain, crepitus or increased laxity, suggesting LT interosseous injury
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 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 
        • radiolunate angle > 15°
      • 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
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 or SL reconstruction (if repair not possible)
      • indications
        • acute scapholunate ligament injury without carpal malalignment
        • chronic but reducible scapholunate ligament injuries
        • primary repair can be performed up to 18 months from the time of injury
      • techniques
        • primary repair
          • 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
        • tendon reconstruction
          • FCR tendon transfer (direct SL joint reduction)
          • ECRB tendonosis (indirect SL joint reduction)
          • weave not recommended due to high incidence of late failure
        • if pathoanatomy is scaphoid fx than 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
  • 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
    • 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 fluroscophy
      • place patient in short arm cast
    • post-operative care
      • remove k-wires in 8-10 weeks
      • no heavy labour for 4-6 months

 

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(SBQ07.38) A 32-year-old professional baseball player presents with wrist pain after a fall on his outstretched wrist 10 days ago. He initially thought it was a sprain, but presents due to continued pain worsened by push-ups. His physical exam shows dorsal wrist tenderness and is positive for the provocative test shown in Figure V. Standard PA radiograph of the wrist is normal. Which of the following radiographic views shown in Figures A to E would be most helpful in establishing the diagnosis? Topic Review Topic
FIGURES: V A   B   C   D   E  

1. A
2. B
3. C
4. D
5. E

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