Perilunate Injuries and Carpal Dislocations

Perilunate dislocations require significant force - these are not minor injuries. The energy required to cause sequential ligament rupture (or fracture through bone in greater arc injuries) indicates high-energy trauma. Always assess for associated injuries.

Progressive perilunar instability (Mayfield):

Mayfield Classification (Progressive Instability):

• Stage I: Scapholunate dissociation
• Stage II: Capitolunate dislocation
• Stage III: Lunotriquetral dissociation (Perilunate dislocation)
• Stage IV: Lunate dislocation (Lunate ejected volar into carpal tunnel)

The topic refers to a "DISI pattern" without defining it, yet the lateral carpal angles are exactly what an examiner asks you to measure on the post-reduction or chronic-instability film:

• Normal angles (true lateral): scapholunate angle about 30-60 degrees (mean ~47), capitolunate angle under about 30 degrees, radiolunate angle under about 15 degrees.
• DISI (Dorsal Intercalated Segment Instability): with scapholunate dissociation the unrestrained lunate extends/dorsiflexes (and the scaphoid flexes). Hallmarks: scapholunate angle over 70 degrees, radiolunate angle over 15 degrees dorsal, increased capitolunate angle. This is the pattern that follows a perilunate/SL injury.
• VISI (Volar Intercalated Segment Instability): typically with lunotriquetral dissociation the lunate flexes/volarflexes - scapholunate angle low (under about 30 degrees) and a volar radiolunate tilt.

Why it matters: a DISI deformity on the post-reduction lateral signals inadequate reduction or unhealed SL ligament, and persistent DISI is the radiographic forerunner of chronic instability and SLAC collapse.

Exam point: state the normal SL angle (30-60 degrees) and recognise DISI (SL angle over 70 degrees, lunate dorsiflexed - the SL/perilunate sequel) versus VISI (lunate volarflexed - the LT pattern) on the true lateral.

Do not simply write "neurovascularly intact." For this injury, explicitly document median nerve symptoms, two-point discrimination where possible, thenar power and whether symptoms improve after reduction. Persistent or progressive symptoms should trigger urgent carpal tunnel release with definitive management.

Gilula's lines are three smooth arcs on PA X-ray:

• Arc 1: Along proximal carpal row proximal surface
• Arc 2: Along proximal carpal row distal surface
• Arc 3: Along proximal capitate/hamate surfaces Disruption indicates carpal instability or dislocation.

Reduction technique:

1. Finger-trap traction for 10-15 minutes
2. Extend wrist while applying pressure to carpus
3. For lunate: direct pressure on dislocated lunate from palmar side
4. Flex wrist to lock reduction
5. Confirm with X-ray
6. Splint in slight flexion Even with reduction, surgical treatment is almost always required.

Despite optimal treatment, post-traumatic arthritis develops in up to 50% of patients over time. Carpal instability is also common. Patients should be counseled that even with good initial treatment, long-term problems may develop.

The topic repeatedly invokes "SLAC wrist" and says PRC is contraindicated when the capitate head is degenerate, but never gives the staging that drives the salvage choice. The chronic SL dissociation/DISI after a perilunate injury produces a predictable arthritic cascade:

• SLAC (ScaphoLunate Advanced Collapse) stages: I = arthritis at the radial styloid-distal scaphoid; II = whole radioscaphoid joint; III = capitolunate / midcarpal joint. The radiolunate (lunate fossa) joint is characteristically spared even in advanced disease.
• SNAC (Scaphoid Nonunion Advanced Collapse) is the analogous cascade after scaphoid nonunion (relevant to the trans-scaphoid greater-arc injury), staged the same way around the nonunion.
• Why staging dictates salvage: because the radiolunate joint and the proximal capitate/lunate cartilage are the load-bearing surfaces relied on by motion-preserving salvage - PRC needs a healthy capitate head and lunate fossa (so it fails / is contraindicated once the capitolunate joint is arthritic, i.e. SLAC/SNAC III), whereas a four-corner fusion (excise scaphoid, fuse capitate-lunate-hamate-triquetrum) is preferred when the capitolunate joint is involved but the radiolunate is spared. Total wrist fusion is the end-stage/high-demand option.

Exam point: the late perilunate/SL sequel is a SLAC (or SNAC) wrist staged I-III - the radiolunate joint is spared, so PRC suits stage I-II (healthy capitate head) and four-corner fusion suits stage III (capitolunate arthritis), with total wrist fusion for pan-carpal disease.

K-wires are typically left in place for 8-12 weeks to allow ligament healing. SL ligament is particularly slow to heal. Remove K-wires once adequate healing confirmed, then progress rehabilitation.

Greater arc injuries (trans-scaphoid) may have better long-term outcomes than lesser arc (pure ligamentous). The scaphoid fracture, once healed, provides stability. In lesser arc, the SL ligament rarely heals to normal strength.

Be prepared to discuss Mayfield stages, X-ray interpretation (especially lateral view), lesser vs greater arc, acute carpal tunnel syndrome, and surgical approach. Understanding why 25% are missed (inadequate lateral film) is commonly tested.