2D Sprite Bone Rigging Rotation Causing Deformity

Hi,

Admitedly this is not my strong subject, but I’ve been watching a few tutorials on YouTube. I have a basic 32x32 sprite that I’m trying to animate with bones, but the rotating the lower bone on the leg causes the sprite to rotate in 3D space:

(Resting)

(Rotating)
image

Where have I gone wrong here?