Orthopedics
Scapholunate Dissociation
Background
- 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
- 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
- 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:
- 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
- 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
- History/Symptoms
- Pain at the radial (thumb) side of the wrist
- Swelling
- Stiffness
- Numbness
- Clicking sensation
- Weakness of the wrist
- Physical Exam/Signs
- Clinical findings vary significantly
- "Snapping or clicking" sensation with wrist deviation
- Joint instability
- 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
- Labs/Tests
- Blood labs are usually not indicated unless suspect other etiology
- 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
- Other Tests/Criteria
- 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
- 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
- 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
- Medical/Pharmaceutical
- 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
- Complications
- Stiffness
- Chronic pain
- If untreated ⇒ SLAC
Disposition
- Admission Criteria
- Usually not indicated unless pre-Op
- Consult(s)
- 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
- Bentley TP, Hope N, Journey JD. Wrist Dislocation. StatPearls [Internet]. Available at: https://www.ncbi.nlm.nih.gov/books/NBK507712/. [Accessed March 2024]
- Stevenson M, Levis JT. Image Diagnosis: Scapholunate Dissociation. Perm J. Mar 1, 2019; 23(2): 18-237
- Andersson JK. Treatment of scapholunate ligament injury. EFORT Open Rev. Sep 2017; 2(9): 382-393
- 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)
- Ho, Nghia, MD
Updated/Reviewed: March 2024