The secret is partly the Joint Editor, and partly a touch of cheating. The above pic is the PT (possibly the worst knees in all Poser-dom) .. as Daz released her (top) and after a bit of work on the joints (lower pic). No postwork .. just rigging. The cheating part .. don't forget you can move the shins sideways. Limits are set at 0 or very small values, so you'll have to turn Limits off. But a few points to the side can get the calf muscle in view, and that's usually easier to postwork than if the thigh is hiding the calf.