Just my two cents...
Cent #1: I usually get good results putting vertices like this...
Two parallel lines of interconnected vertices to maintain line art volume, and a central vertex that matches the tip and origin of the two bones that make the knee joint.
Moreover, if you were to click on the thigh mesh you'll see a similar arrangement of vertices that also have a central vertex at the joint.
Cent #2: I'm using two layers there instead of one for the whole leg. One for the thigh and another for the shin. You lose far less volume that way and can adjust that crease vertices individually so they don't end at the center of the knee.
This is how it looks when the vertices are moved...
Also, ask your artist to draw the lower limb layer (in this case the shin) to cover the whole joint so it looks rounded when it gets bent.
Please, mind that this comes only from my limited experience (five months worth). Others may have another tips to give you, incompatible with my approach. 😉
Edit: I've just realized that I've linked the already bent limb to show you how I rig... and that's not particularly clear, so let me show you the straight setup pose instead:
Later on, when you bend the limb, those vertices at the left get overlapped, but then you're supposed to fine tune weights and only after that moving the vertices themselves at key frames.
