A lunotriquetral coalition, also known as lunotriquetral fusion or synostosis, is a type of carpal coalition and represents a congenital lack of separation of the lunate and triquetral bones of the carpus.
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Terminology
The term coalition is preferred over fusion for congenital coalitions, as during development the discrete carpal bones form by a process of separation, i.e. the lunate and triquetral do not form and then later fuse, they just never separate or only do so partially (hence incomplete coalitions) 9.
Epidemiology
The lunotriquetral coalition is the most common type of carpal coalition with a prevalence of 0.1%. It is more common in females (F:M = 2:1) and African Americans.
Diagnosis
The diagnosis can be established by typical findings on imaging.
Clinical presentation
Whilst osseous coalitions of the lunate and the triquetrum are known to be asymptomatic, fibrocartilaginous lunotriquetral coalitions can present as an uncommon cause of ulnar-sided wrist pain often due to pseudarthrosis or a post-traumatic disruption 3,8.
Pathology
- the coalition may be fibrous, cartilaginous or osseous 5
- commonly bilateral 4
Carpal coalitions can follow an autosomal dominant route of inheritance
Classification
de Villiers classified lunotriquetral coalition into four types 6:
- incomplete (or fibrocartilaginous) fusion - resembles a pseudoarthrosis
- incomplete osseous fusion
- complete osseous fusion
- complete osseous fusion with other carpal abnormalities
Radiographic features
Plain radiograph
- incomplete or complete fusion of the lunate and triquetrum
- possibly accompanied by a widened scapholunate interval 4
Treatment and prognosis
A lunotriquetral coalition is most commonly an incidental finding and does not require treatment if not symptomatic. It might occasionally be the cause of chronic wrist pain (especially in types 1 and 2 6) and can be fractured.
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