[PS: In the video I mention about Chirag, Satish and Pratik: they’re members of Blender Knowledge Base group in Facebook, where we are discussing about this issue. And please pardon my grammar, pronunciation and accent. My voice sucks :p]
The easiest way I can think of would be to switch to sculpt mode and turn on the multires modifier. Using the crease tool would help get the edge you are looking for quickly. However, this would also create a lot of vertices.
You could try adding a few more segments to your armature. At the joint, if you had 2-3 segments close together, you could probably get a good crease that way too. But you would need to add a few extra edge loops near the joint for the segments to act on.