Wikipedia
Rotationplasty
Rotationplasty is a type of autograft wherein a portion of a limb is removed, while the remaining limb below the involved portion is rotated and reattached. This procedure is used when a portion of an extremity is injured or involved with a disease, such as cancer.
Typically, the ankle joint becomes the knee joint. The limb is rotated because the ankle flexes in the opposite direction compared to the knee. The benefit to the patient is that they have a functioning knee joint and can run and jump.
The operation is also called a Van Nes rotation.