Fibular hemimelia (FH) is a rare birth defect that causes a baby to have a partially or completely missing fibula, which is the small bone located below the knee next to the shinbone (often called the calf bone). Affected individuals may also have lower limb abnormalities or absence of bones in the femur, knee, shinbone, ankle and foot. Abnormalities in the ankle and foot can cause the foot to point down or inward (clubfoot). FH is present at birth (congenital) and usually affects only one leg (unilateral), but can affect both legs (bilateral). When FH is unilateral, it is seen more often in the right leg than the left. FH seems to affect males more often than females.
The exact cause of FH is uncertain. Most cases are random (sporadic) but a very small number seem to have a genetic factor, as they occur in more than one person in a family. A specific gene has not yet been associated with FH but the genetic form seems to be inherited in an autosomal dominant way, which means a mutation in one of the two gene copies a person has is enough to cause FH.
Doctors typically diagnose FH before (prenatal) or at birth with ultrasounds, physical exams, and X-rays. Treatment usually includes surgery to help make the affected leg more functional. In severe cases, amputation to remove the affected part of the leg may be necessary. If your child has been diagnosed with FH, talk to a doctor about the most current treatment options. Support groups can provide more information and connect you with affected families.