Tibial hemimelia (TH) is a rare birth defect that causes a baby to have a partially or completely missing tibia, which is the large bone located below the knee (often called the shin bone). Affected individuals can also have issues with the knee, such as missing ligaments that support the knee and trouble straightening the knee. Other features may include foot deformities and feet with additional or webbed toes (syndactyly). Part of the ankle may be missing, causing the foot to point down or inward (clubfoot). An opening or split in the lip (cleft lip) and/or an opening in the roof of the mouth (cleft palate) has been seen in some children with TH.
TH is present at birth (congenital) and can affect either one leg (unilateral) or both legs (bilateral). It can occur alone (isolated TH) or can be seen in combination with other birth defects or health complications as part of a syndrome. There are different types of TH that describe whether a person is missing the entire tibia, the top of the tibia, or just the bottom of the tibia.
The cause of TH is uncertain. Many cases are random (sporadic) but some seem to be genetic, as they occur in more than one person in a family. Most of the genetic cases are inherited in an autosomal recessive way, which means a change (mutation) in both copies of a gene a person has is needed to have TH. However, a specific gene has not yet been associated with TH. Doctors typically diagnose TH before or at birth with ultrasounds, physical exams, and X-rays. There is no cure for TH. Treatment usually includes surgery to help make the affected leg more functional. In severe cases, an amputation just above or below the knee may be necessary. If your child has been diagnosed with TH, talk to a doctor about the most current treatment options. Support groups can help connect you with families also affected by tibial hemimelia.