The patient complained of wrist pain after a fall. A conventional radiograph was performed (figure 1a). Lunotriquetral coalition was detected as an incidental finding. We illustrate several examples of carpal coalitions and show the most typical radiological findings.
Carpal coalitions are relatively common anomalies in which two or more carpal bones fail to segment during development, resulting in a congenital fusion that may be bony, cartilaginous, or fibrous . Carpal coalitions usually appear as an isolated phenomenon, although they may occur as a part of congenital malformative syndromes. As a rule, isolated fusions involve bones in the same carpal row, whereas syndrome-related or postinfectious coalitions involve bones in adjacents rows . Idiopathic coalitions are more common in females and African-Americans. The most common site of the isolated fusion is between the triquetrum and the lunate bones (figure 1), which is bilateral in approximately 60 per cent of patients . The spectrum of lunotriquetral coalitions was classified in four types by Minaar :
- type I: proximal fibrous or cartilaginous coalition;
- type II: incomplete bony fusion with distal notch;
- type III: complete bony fusion;
- type IV: complete bony fusion with other carpal anomalies.
A common radiological feature is the widening of the scapholunate interosseous joint space, although the scapholunate interosseous ligament is intact.
The second most frequent coalition is between capitate and hamate bones (figure 2).
Other rare fusions have also been described, such as capitate-trapezoid fusion (figure 3), trapezium-trapezoid fusion, and pisiform-hamate fusion.
Although they do not commonly produce symptoms, pain has been described in association with partial fusion and cystic changes in the adjacent bones. Massive carpal fusion, coalitions between bones of different carpal rows, or coalitions between carpal bones and distal extremities of the ulna or radius appear in association with other malformations as part of Holt-Oram syndrome, Turner syndrom, acrocephalosyndactyly syndromes, arthrogryposis or symphalangism .
Differential Diagnosis List