Ulnar hemimelia (UH) is a rare birth defect that causes a baby to have a partially or completely missing ulna bone, which is the smaller of the two forearm bones located between the elbow and the wrist. Some cases are mild, causing only a shortened ulna bone, while some cases are severe, causing complete absence of the ulna bone. Most affected people have shortening of the forearm and limited arm and hand function. In affected individuals, the position of the hand is usually located more toward the ulnar-side (outside) of the wrist. The extension of the elbow is typically limited, depending on the severity.
UH is present at birth (congenital) and 70% of cases affect one arm (unilateral), while the rest affect both arms (bilateral). Unilateral cases usually affect the right arm. UH can occur alone (isolated UH) or can be seen in combination with other birth defects or health complications as part of a syndrome. Several conditions that have UH as a possible symptom include Gorlin-Goltz syndrome, Schinzel syndrome, Klippel-Feil syndrome, and Cornelia de Lange syndrome. The exact cause of isolated UH is not known at this time. However, most forms resulting from a syndrome do have a known genetic cause.
Doctors typically diagnose UH before or at birth using ultrasounds, physical exams, and X-ray images. Treatment usually includes physical therapies and surgery to help the affected arm become more functional. If your child has been diagnosed with UH, talk to a doctor about all treatment options. Support groups can provide more information and connect you with affected families.