13 year old Duggan Smith had cancer in his thigh when he was 10. The doctor amputated his leg and put it back on backwards so the kid could continue to play baseball. This is how the procedure called rotationplasty is described.
The diseased portion of the leg is removed, and then the lower portion (containing the lower shin, ankle, and foot) is turned 180 degrees and grafted back onto the upper thigh. The ankle functions as a knee, the foot becomes the upper shin, and a prosthetic leg then fills out the lower portion.
Check out the video of him playing baseball!