Ulnar ray deficiency: a review of the classification systems, the clinical features in 72 cases, and related developmental biology.

Ulnar ray deficiency is rare and has a variable presentation. As a result, there are many different classification systems for this anomaly. Furthermore, the developmental biology of the anomaly is still not fully understood. The aim of this article is to review the previous classification systems, present the clinical features in 72 cases and discuss the developmental biology of ulnar ray deficiency.