You don't have to convert to bones if you don't want to, although bones certainly have their benefits.
Here's a character we did with Biped, it has a similar bone structure to your emu.
His heel is the backwards-looking joint that may seem like a reversed knee. It's just that he's standing up on his toes.
We merely rotated the Foot bone up, scaling the Biped leg bones appropriately. So you can
use Biped for this if you want, although in the long run you'll be better served by using bones.
Here's a skeleton I found.
The thigh is extremely short, the knee being level with its ribcage. So the backwards-looking knee is really the heel.