My Armature model is a biped creater that has 4 bones per leg. thigh,calf, foot and then an IK bone.
I have the x and y axis locked but as you can see with the blue line the z axis should allow the knee to move in the right direction.  However If you look in the picture the blue line show it should allow the knee to bend like a human knee. Any advice would be appreciated.
[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/0bpJPk6C.png
Here's the blend file.  The right leg when you are looking at the cannon head on is the one with the axis locks.

[<img src="https://blend-exchange.com/embedImage.png?bid=JbYjv0oB" />](https://blend-exchange.com/b/JbYjv0oB/)