Perilunate Dislocation and Scapholunate Dissociation: Terry-Thomas Sign, Mayfield Stages, and Wrist Reconstruction
In short
High-energy perilunate disruptions tear carpal ligaments in a predictable circle of perilunate instability; early reduction and proprioceptive retraining prevent SLAC wrist.
In this guide (4 sections)
The Biomechanics of Carpal Instability and Mayfield's Four Stages
Perilunate dislocations and carpal ligament dissociations represent devastating high-energy injuries, frequently resulting from high-velocity motor vehicle collisions or falls from substantial heights. The wrist carpus functions through coordinated intercarpal row mechanics governed by primary intrinsic ligaments, foremost among which is the Scapholunate Interosseous Ligament (SLIL).
Mayfield described the pathomechanics of perilunate instability as a progressive sequential disruption traveling around the lunate in four distinct stages: Stage I involves rupture of the SLIL (scapholunate dissociation); Stage II involves capitohamate dislocation through the Space of Poirier; Stage III involves lunotriquetral ligament disruption (perilunate dislocation); and Stage IV involves extrusion of the lunate into the carpal tunnel (volar lunate dislocation, 'spilled teacup sign').
Mayfield Staging and Radiographic Instability Criteria
| Mayfield Instability Stage | Ligamentous Disruption & Anatomical Path | Radiographic Hallmarks on Standard Views | Surgical & Rehabilitation Directives | |
|---|---|---|---|---|
| Stage I: Scapholunate Dissociation | Complete rupture of dorsal, interosseous, and volar SLIL bands | 'Terry-Thomas Sign' (SL gap > 3 mm on clenched-fist AP view) | Open dorsal SLIL anchor repair + dorsal capsulodesis (Blatt) or 3-ligament tenodesis | |
| Stage II: Perilunate Dislocation | Stage I plus disruption of lunocapitate and radioscaphocapitate ligaments | Capitate displaced dorsal to lunate on lateral X-ray; 'ring sign' on AP | Urgent closed reduction; open dorsal/volar reconstruction with K-wire pinning | |
| Stage III: Midcarpal Dislocation | Stage II plus lunotriquetral interosseous ligament (LTIL) rupture | Triquetrum overlaps lunate; total midcarpal dissociation | Extensive bicompartmental repair; rigid immobilization in neutral wrist for 8-10 wks | |
| Stage IV: Volar Lunate Dislocation | Complete lunate enucleation; dorsal radiocarpal ligament avulsion | 'Spilled Teacup Sign' (lunate tipped volar into carpal tunnel on lateral view) | EMERGENCY: Immediate open reduction and carpal tunnel release to decompress median nerve |
Standardized Clinical Rehabilitation Protocols and Dart-Thrower's Training
- Post-Surgical Pin Care and Neutral Cast Immobilization (Weeks 0 to 8): Maintain rigid immobilization in a short-arm fiberglass cast or custom thermoplastic splint with the wrist in neutral alignment; monitor K-wire pin sites for signs of superficial infection; maintain complete active range of motion across all digital MCP and IP joints.
- Early Protected Dart-Thrower's Motion Plane (DTM) Following Pin Removal: Following K-wire removal at Week 8 to 10, initiate active wrist motion strictly confined to the dart-thrower's plane (radial extension to ulnar flexion); DTM minimizes strain across the reconstructed scapholunate interval while restoring midcarpal functional mobility.
- Sensorimotor Proprioceptive and Perturbation Training: Introduce carpal neuromuscular re-education using unstable wobble boards, laser-pointer target tracking, and rhythmic stabilization with elastic bands to activate dynamic carpal stabilizers (flexor carpi radialis and extensor carpi radialis longus).
Frequently Asked Questions
What is the 'Terry-Thomas sign' on a wrist X-ray?
Named after a famous British comedian with a wide gap between his front teeth, the Terry-Thomas sign describes an abnormally wide gap (greater than 3 millimeters) between two wrist bones (the scaphoid and lunate). It proves that the main ligament holding them together has completely torn.
Why does a dislocated wrist bone require emergency surgery right away?
In severe wrist dislocations (Mayfield Stage IV), the lunate bone pops completely out of its socket and gets shoved forward into your carpal tunnel. This crushes your median nerve, risking permanent numbness and paralysis of your thumb muscles if not decompressed within hours.
Will my wrist ever bend completely normally after a perilunate dislocation surgery?
Because saving the wrist requires heavy surgical stitching and metal pins to lock the bones in place while ligaments heal, some permanent loss of wrist bending is normal (patients usually regain about 60% to 75% of normal motion). However, this leaves you with a strong, stable, and pain-free wrist.
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