Hemimelia is a partial or total absence of a bone in either the lower leg or the forearm. It is a rare condition that is present at birth.

It is also known as a congenital longitudinal deficiency of the fibula, tibia, radius or ulna.

It usually occurs for no apparent reason, but some types of hemimelia can be inherited and/or be part of a syndrome. Occasionally, hemimelia may also be caused by other factors, such as ionizing radiation or certain medications during pregnancy.

The main aim of any treatment is to ensure that the arm or leg is functional. Treatment varies and depends upon which bone is affected and how the limb is affected.