Presentation
Incidental finding. Presented with crushed finger, to rule out fracture.
Patient Data
Lunotriquetral coalition.
Jewelry artifact.
No acute bony injury.
Case Discussion
Lunotriquetal coalition is the commonest of the carpal bone coalitions, representing more than 9 out of 10 of all cases. Although, overall it is not a common finding, being found in 0.1% white and 1.6% black populations respectively.
Like other carpal coalitions, it is inherited in an autosomal dominant fashion. The NOG gene, coding for the noggin protein is responsible in most cases
It is interesting to recognize that calling this phenomenon "carpal bone fusion" is erroneous as the wrist bones form by a failure of larger progenitor cartilaginous elements to separate during development. Failure of the lunate and triquetrum to divide into two separate bones by 10 weeks' gestational age results in this particular coalition.
This finding is common but is thought to be asymptomatic. Conversely, a fibrocartilaginous lunotriquetral coalition may present with pain, in particular if there has been a traumatic disruption or a pseudoarthrosis has formed.
Lunotriquetral coalitions have been subclassified by the Minnaar classification system into four discrete types. Complete bony coalition, without any coexisting carpal bone abnormalities, as here, is a type 3.
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