Lunate dislocations are an uncommon traumatic wrist injury that require prompt management and surgical repair. The lunate is displaced and rotated volarly. The rest of the carpal bones are in a normal anatomic position in relation to the radius.
These should not be confused with perilunate dislocations where the radiolunate articulation is preserved and the rest of the carpus is displaced dorsally.
Lunate dislocations typically occur in young adults with high energy trauma resulting in loading of a dorsiflexed wrist. Overall, carpal dislocations comprise less than 10% of all wrist injuries. Lunate dislocations are far less common than the less severe perilunate dislocation.
Patients present with wrist pain following a fall. Volar wrist swelling is usually prominent. The swelling often causes a decrease in 2-point discrimination in the median nerve distribution due to acute carpal tunnel syndrome. Patients often prefer to hold their fingers in partial flexion due to pain on extension.
Lunate dislocations typically occur due to a fall on an out-stretched hand (or during a motor vehicle injury) where there is forceful dorsiflexion of the wrist 3.
There is injury of all of the perilunate ligaments, most significantly the dorsal radiolunate ligament. Mayfield et. al. have proposed a 4 stage process to describe perilunar wrist instability (see carpal dislocation) where lunate dislocation represents stage IV. 2
- AP radiograph
- dislocation is often overlooked
- disruption of the normally smooth line made by tracing the proximal articular surfaces of the hamate and capitate
- lunate overlaps the capitate and has a 'triangular' or 'piece of pie' appearance.
- lateral radiograph
In addition to stating that a lunate dislocation is present, a number of features should be sought and commented upon:
- ensure that radiolunate alignment is disrupted, and that you are not looking at a perilunate dislocation (stage II carpal dislocation)
- evaluate and comment on the degree or palmar rotation of the lunate (this can be up to 270 degrees) 4
- ensure that the capitate remains co-linear with the long axis of the radius
- any additional fractures
Treatment and prognosis
Urgent reduction and surgical repair of disrupted ligaments is required to prevent long-term joint dysfunction. Despite treatment, there remains a high risk of future degenerative arthritis and wrist instability.
The most important differential is of other carpal dislocations, particularly:
- 1. Wrist Dislocation by Kadeer M Halimi from emedicine.com. Wrist Dislocation
- 2. Mayfield JK, Johnson RP, Kilcoyne RK. Carpal dislocations: pathomechanics and progressive perilunar instability. J Hand Surg Am. 1980;5 (3): 226-41. - Pubmed citation
- 3, Greenberg MI. Greenberg's text-atlas of emergency medicine. Philadelphia : Lippincott Williams & Wilkins, c2005. (2005) ISBN:0781745861. Read it at Google Books - Find it at Amazon
- 4. Schmitt R, Lanz U, Buchberger W. Diagnostic Imaging of the Hand. Thieme Medical Pub. (2008) ISBN:1588904539. Read it at Google Books - Find it at Amazon
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Dislocation of the lunate||✗|
|Dislocation of lunate||✗|