Wrist #3 - Answers

1. Isolated congenital failure of segmentation anomaly of lunate and triquetrum

Findings

1. Absence of a lunatotriquetral joint space (other than a very small vestigial space).
2. Common medullary space of the lunate and triquetrum.

Brief Discussion

This congenital anomaly may occur either as an isolated finding or as part of a syndrome. In general, the isolated form occurs between bones on the same carpal row, and bones on different rows are involved in syndromes.

The lunatotriquetral form shown above is the most common form of this anomaly, involving about 0.1 % of Caucasian Americans and about 1.6 % of African Americans. The lunatotriquetral form of this anomaly has little or no clinical significance, and has very little effect on wrist motion.

The second most common type of this anomaly is the capitate-hamate form. Other forms are much rarer, and include trapezium-trapezoid, capitate-trapezoid, pisiform-hamate, and others.

In this particular patient, the term "carpal fusion" does not make sense here, since that would imply that the two bones were once apart. However, it should be noted that there are indeed acquired forms of carpal fusion, including surgical fusion, prior trauma, and inflammatory disease such as rheumatoid arthritis. In the right clinical setting, these causes should be considered.

References:

1. Poznanski AK. The hand in radiologic diagnosis, WB Saunders, Philadelphia, 1974.

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