Perilunate Dislocations are devastating closed wrist injuries, non-uncommonly missed on initial imaging. Below are some of the characteristics of this condition and how they’re spotted in readings.
Perilunate Dislocation Xray
Potentially devastating closed wrist injuries
Non-uncommonly missed on initial imaging.
Dislocation of carpus relative to lunate
Lunate remains in normal alignment with the distal radius
NOT to be confused with LUNATE Dislocation = lunate is dislocated volarly and thereofore abnormal radiolunate articulation.
Carpal dislocations – less than 10% of all wrist injuries.
High energy trauma
Loading of hyperextended/ulnarly deviated hand
Fall on dorsiflexed wrist
60% of perilunate dislocations associated with ascaphoid fracture which is then termed a trans-scaphoid perilunate dislocation.
Triangular orientation of the lunate
Dislocation most easily appreciated on this view
Lunate in anatomic position to Radius
Capitate dorsal to the lunate
Plain film normally sufficient to diagnose dislocation
CT is important to diagnose associated occult fractures
The most common and important associated = scaphoid fracture
Treatment and Prognosis
If Untreated = High risk of:
- Median nerve palsy
- Pressure necrosis
- Compartment syndrome and long-term wrist dysfunction
- Perilunate dislocation should be reduced ASAP
- Prompt open reduction with ligamentous repair recommended
Long-term risk of:
Degenerative arthritis is high (~60%).
Dissociative and non-dissociative carpal instability (DISI or VISI)
Higher rate of nonunion of scaphoid fractures when associated with perilunate dislocation
The most important differential diagnosis is that of Lunate Dislocation which can mimic a Perilunate dislocation on AP projection.
Therefore ALWAYS look at the LATERAL XRAY
TAKE HOME MESSAGE:
DO NOT MISS Perilunate Dislocations
Communicate Positive Findings of Perilunate Dislocation ASAP
Look for associated SCAPHOID FRACTURE
The LATERAL VIEW will help DIFFERENTIATE Perilunate from Lunate Dislocations
Remember- “The Eyes Will Not See What The Brain Does Not Know”