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Subsections
Scapholunate Dissociation

Orthopedics

Scapholunate Dissociation

Background

  1. Definition
    • A pathologic disruption of scapholunate ligament leading to spreading apart of scaphoid and lunate
      • AKA: rotary subluxation of the scaphoid, scapholunate interosseous ligament (SLIL) injury
  2. Synopsis
    • Scapholunate dissociation is the most common cause of degenerative arthritis of the wrist
    • Often implies severe injury to the scapholunate interosseous ligament and other stabilizing ligaments
    • Without early diagnosis and treatment ⇒ proximal migration of the capitate between the scaphoid and lunate
    • Treatment
      • Must be differentiated from simple wrist sprain
      • Immobilize in thumb spica splint or cast
      • Surgical Rx can avert progression
        • Consider surgical repair of torn ligaments or selected fusion

Pathophysiology

  1. Mechanism
    • Abnormal orientation of the scaphoid relative to the lunate caused by direct trauma to the hand/wrist
      • Typical pattern of scapholunate dissociation consists of:
        • Relative flexion (volar rotation) of the scaphoid
        • Relative extension (dorsal rotation) of the lunate
      • Major injury of the SLIL (i.e., complete tear of dorsal component) and radiolunate ligament ⇒ scapholunate dissociation
        • Complete SLIL transection does not result in permanent dissociation
          • Presence of secondary scaphoid stabilizers
            • Palmar radioscaphoid-capitate
            • Scaphoid capitate
            • Anterolateral scaphotrapeziotrapezoid ligaments
          • Long-term wear on these secondary ligamentous stabilizers ⇒ permanent deformity and/or SLAC
    • Anatomy
      • The scapholunate interosseous ligament (SLIL) is a U-shaped ligament is divided into 3 anatomic components
        • Dorsal component:
          • Strongest, 3 mm thick, composed of short, transversely-oriented collagen fibers
          • Important in resisting volar-dorsal translation
        • Intermediate component:
          • Primarily composed of fibrocartilage
          • Homologous to the meniscus of the knee
        • Volar component:
          • 1 mm thick
  2. Etiology/Risk Factors
    • Most commonly results from trauma
      • Hyperextended wrist in ulnar deviation after fall on an outstretched hand
    • Risk factors
      • Spastic paresis
      • Rheumatoid arthritis
      • Congenital ligament laxity
  3. Epidemiology
    • Incidence/Prevalence
      • ~5% of all wrist sprains have an associated SL tear
        • SL ligament injuries often associated with distal radius fracture (~40%)
    • Mortality/Morbidity
      • Most common cause of carpal instability
      • Acute carpal tunnel syndrome has been reported in up to 46% of dislocations
      • Leading cause of SLAC (scapholunate advanced collapse) wrist
        • SLAC wrist is most common pattern of osteoarthritis in the wrist

Diagnostics

  1. History/Symptoms
    • Pain at the radial (thumb) side of the wrist
      • Pain with hyperextension
    • Swelling
    • Stiffness
    • Numbness
    • Clicking sensation
    • Weakness of the wrist
  2. Physical Exam/Signs
    • Clinical findings vary significantly
    • "Snapping or clicking" sensation with wrist deviation
    • Joint instability
      • Scaphoid shift test
    • Tenderness at site of injury
    • Compromise of the nerve in the carpal tunnel
      • Median nerve injury
        • Reduced sensation in the thumb, index, middle fingers, and radial half of the ring finger
        • Decreased strength of thumb flexion, opposition, and abduction
  3. Labs/Tests
    • Blood labs are usually not indicated unless suspect other etiology
  4. Imaging
    • Xray
      • Standard PA and lateral wrist radiographs
      • Bilateral clenched-fist comparison views
        • Dorsal intercalated segment instability (DISI)
        • Relative widening of scapholunate interval on affected side
      • Often takes 3-12 months after trauma before SL dissociation is noted radiologically
      • SL angle > 60° and SL gap > 3 mm on clenched-fist or ulnar-deviation radiographs
      • SLAC ⇒ arthrosis pattern showing progression of injury
    • CT
    • MRI
      • Often unnecessary
      • May reveal thinning of the articular surfaces of the proximal scaphoid
  5. Other Tests/Criteria
    • Assess balance/fall risk in elderly
    • Geissler's classification
      • Grade I
        • Attenuation and/or hemorrhage of the interosseous ligament
        • No incongruence of carpal alignment in MC space
        • Treatment by immobilization
      • Grade II
        • Attenuation and/or hemorrhage of the interosseous ligament
        • Incongruence and/or step-off as observed from MC joint
        • A slight gap (< 2 mm) between the carpal bones may be present
        • Treatment by reduction and pinning
      • Grade III
        • Incongruence and/or step-off of the carpal alignment
        • Gap > 2 mm between the carpal bones
        • Treatment by arthroscopic reduction or open reduction and pinning or repair
      • Grade IV
        • Incongruence and/or step-off of the carpal alignment
        • Gross instability with manipulation is noted
        • 2.7 mm gap between the carpal bones ("drive-through phenomena")
        • Treatment by open re-insertion or ligament reconstruction
    • Watson and Ballet SLAC stages
      • Stage I:
        • Localized arthrosis of scaphoid fossa begins at the styloid tip (radial styloid beaking)
      • Stage II:
        • Progressive joint space narrowing and sclerosis affecting entire scaphoid fossa of distal radius
      • Stage II:
        • Sclerosis and narrowing joint space between lunate and capitate
        • Eventual migration of capitate proximally into space created by scapholunate dissociation
        • Synonymous with "Terry Thomas sign"
          • Lunate dorsiflexed (dorsal intercalated segment instability) and scaphoid flexed
  6. Differential Diagnosis
    • Carpal Tunnel Syndrome
    • Scaphoid fracture
    • Distal radial fractures
    • Dorsal ganglion cyst
    • Septic arthritis
    • Avascular necrosis of the scaphoid
    • Gout
    • Pseudogout
    • Rheumatoid arthritis
    • Tear of the triangular fibrocartilage complex
    • Kienbock disease
    • Tenosynovitis
    • Lunate fracture vs dislocation
    • Dorsal intercalated segmental instability

Treatment

  1. Initial/Prep/Goals
    • ABCs, ATLS as needed
    • Splint affected wrist
      • Thumb spica splint
      • Radial gutter
      • Short arm volar splint
    • Pain medication
    • Urgent referral to hand specialist
      • Immediate reduction if lunate or perilunate dislocation
        • Immediate orthopedic or hand surgery consultation
        • Reduction, stabilization
          • Arthroscopically guided reduction
  2. Medical/Pharmaceutical
  3. Surgical/Procedural
    • May require urgent surgical intervention (< 6 weeks)
      • Decrease risk of severe/debilitating wrist dysfunction
      • Closed reduction with percutaneous pinning or open reduction
      • Short-arm cast postoperatively
  4. Complications
    • Stiffness
    • Chronic pain
    • If untreated ⇒ SLAC

Disposition

  1. Admission Criteria
    • Usually not indicated unless pre-Op
  2. Consult(s)
    • Orthopedist
    • Hand surgeon
  3. Discharge/Follow-up Instructions
    • K-wires are removed in 8-10 weeks
    • No heavy lifting using the wrist for 4-6 months post-injury

References

  1. Bentley TP, Hope N, Journey JD. Wrist Dislocation. StatPearls [Internet]. Available at: https://www.ncbi.nlm.nih.gov/books/NBK507712/. [Accessed March 2024]
  2. Stevenson M, Levis JT. Image Diagnosis: Scapholunate Dissociation. Perm J. Mar 1, 2019; 23(2): 18-237
  3. Andersson JK. Treatment of scapholunate ligament injury. EFORT Open Rev. Sep 2017; 2(9): 382-393
  4. Lane R, Tafti D, Varacallo M. Scapholunate Advanced Collapse. StatPearls [Internet]. Available at: https://www.ncbi.nlm.nih.gov/books/NBK537124/. [Accessed March 2024]

Contributor(s)

  1. Ho, Nghia, MD

Updated/Reviewed: March 2024