Whenever I treat limb problems I always have a look at the equivalent joint in the contralateral (i.e. other side) and contramedian (i.e. other end) limb. I'll look and palpate for tender areas and channel changes and needle appropriately. I first got introduced to this concept with the success of techniques such as the Balance Method.
It got me interested in what the science behind such a technique might be. The clearest reasoning for why this should be, is simply balance.
Animals who walk on all fours can't have both legs on one side in the air at the same time because otherwise they'd fall over and look pretty stupid. I'm not sure how much animals care about looking stupid but I imagine staying up is important to them.
The process of staying upright is subconscious and is found in very primitive animals: as such it will be a function of the spinal cord and brainstem. The spinal cord and brainstem do have very peculiar patterns of nerves crossing over, but thankfully we don't need to go into that much
From an acupuncturist point of view though we don't really need to know about the nerves because things are much better (and simpler) explained by understanding fascia (Jing Luo system) and Qi (energy of organisation).
In animals this balancing trick can be understood as trains of fascia which cross from upper to lower and keep the body tense and stable. Most importantly, in pathology, these will get tight and painful in predictable places. These become the spots we look for and treat.
Whilst humans don't walk on all fours (unless very small or exceedingly drunk) the same patterns will be present as in animals to keep the body balanced.