Radial hemimelia (RH) is a rare birth defect that causes a baby to have a partially or completely missing radius, which is one of the large bones located between the elbow and the wrist (often called the forearm). Some cases are mild, causing only a shortened radius, while some are severe, causing complete absence of the radius. When the entire radius is missing, the arm is typically shorter and curved. Affected individuals may also have reduced hand, finger and elbow function, as well as abnormalities of the muscles, nerves, tendons, ligaments and blood vessels (soft tissues) of the forearm.
Other features of RH may include underdevelopment or absence of the fingers, specifically the thumb. RH is present at birth (congenital) and affects both arms (bilateral) in half of the cases. When RH only affects one arm (unilateral), it is seen more often in the right arm than the left. RH can occur alone (isolated RH) or can be seen in combination with other birth defects or health complications as part of a syndrome, such as chromosome abnormalities, thrombocytopenia-absent radius (TAR) syndrome, or Fanconi anemia.
The exact cause of isolated RH is not known at this time. However, most forms resulting from a syndrome do have a known genetic cause. Doctors typically diagnose RH before or at birth with ultrasounds, physical exams, and X-rays. Treatment usually includes surgery to help make the affected arm more functional. Amputation to remove the affected forearm may be recommended in severe cases. If your child has been diagnosed with RH, talk to a doctor about all treatment options. Support groups can provide more information and connect you with affected families.