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Carpal coalition refers to failure of separation of two or more carpal bones, and although the most commonly involved bones are the lunate and triquetrum, most combinations of adjacent bones can be found to be coalesced.
Carpal fusion is a misnomer, as it is the failure of normal segmentation of carpal mesenchyme that results in the anomaly 8. Carpal coalition is less contentious as its definition means a connection between two bones, it says nothing about how they came to be connected 9.
The estimated prevalence is ~0.1% in Caucasian Americans and ~1.5% in African Americans, and it tends to affect women more commonly 1,2.
There are several associated conditions, especially with multiple coalitions:
Non-syndromic congenital carpal coalition is transmitted via a Mendelian inheritance pattern. Acquired intercarpal fusion can either be a consequence of an inflammatory arthropathy (e.g. rheumatoid arthritis, psoriatic arthritis, reactive arthritis) or injury, or due to intentional surgical arthrodesis.
The two most common types are:
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