This is a question everyone asks. Don't assume your doctor knows answers either. I was at a conference not long ago and asked the Drug Rep for Lidoderm, and SHE said the company doesn't know either and gives no advice!

Well, armed with that nugget of optimism, I do have some suggestions that I have learned over the years by experimenting with mine. I started with Lidoderm when they first became available in US. I had at that time a severe case of Meralgia Paresthetica that I was enduring with much agony. It was the result of a C-section when I had my son. I had the vertical long incision because they were looking for a tumor at the time. Somehow that nerve -- the lateral femoral nerve--got damaged.

I found the right spot for that problem after a few days, and after about 2 weeks of continuous daily use, the nerve settled down and I didn't need them anymore for that purpose! This told me that nerves might be firing when the original trauma is over, but for some reason they get stuck in the "on" position.

Lidoderms work for sensory pain very well. They do not affect motor functions normally (there might be exceptions to this, but I don't think so). They were originally made for post-shingles pain, which lingers for some patients for life. Slowly other studies came out. One for example comparing knee pain relief with Celebrex and Lidoderm, and the Lidoderms were found to be fairly equal in relief.
http://www.zhion.com/joint_bone/Lidoderm.html

I do not think Lidoderms work at the endpoints where we feel pain. At the tips of the nerves the cells are tiny and spaced around. I think the nerves travel along and conjoin like tree roots to turn into a major sized nerve which then carries the messages to the spine. I found a nice 3D graph of the leg (and other body parts too) at this link:
http://www.healthline.com/vpbody/ner...-spine-to-foot

There is a slide toggle at the bottom which you can move back and forth, to see 360 degrees around the foot and leg.
Moving to the left, rotates the leg showing the inner aspect of the ankle (medial) and this shows the tibial nerve, supplying the heel, arch and big toe. Just above the ankle is the junction for that area, and a patch here (1/2 patch...placed vertically will reach those sensory parts. Turning the picture to the right, lateral aspect of the foot, shows the tibial and peroneal nerves feeding the other parts of the foot. So you can intercept those at the lateral ankle area before they go up the calf.
I sometimes use 1/2 patch on the top of each foot, for burning issues... if you turn the graph facing you --you can see all the nerves on the instep area going to the toes. Sometimes I use that placement for big time global burning(when my Biofreeze does not work well.)

Looking up the leg you can see behind the knee, another junction where the peroneal splits off the sciatic. This is another spot, right above the bend of the knee on the back side of the thigh to try if you have calf pain, or knee pain in addition to foot pain. Sometimes I think foot pain can refer from the knee.
This spot behind the knee is where people get pressure palsies from crossing the legs too much. So it is a good spot to try the patches for some people.

Way at the top of the lower back, is the sacral plexus. I have luck with this location too. But it usually needs a full sized patch.
Leg pain, groin pain, and recently I have noticed some foot pain generates for me at this level too. So for some it is worth trying a patch there too.

Lidoderms are expensive which is difficult for some patients.
So experimenting may be expensive. That is why I put my experiences here, so that you may find quicker relief. I prefer this topical method instead of oral meds for pain. Most of the time it works for me. Sometimes I have to take Tylenol, or Aleve liquigels in addition, but not always.

At that 3D website are other body views, showing nerves as well, and the principles are the same if you want to try shoulder, back etc...use the various views to give you a location for your placement. If you have had EMGs or X-rays showing pathology, get your results, and look them up on the graph.
This will help you map out, your placement and get the most results for your expense and time.

Any questions or comments are welcome on this thread.
The smallest I cut the Lidoderms is into 3rds. For the feet you can get away with that size and save $$. The Ankle needs at least 1/2 patch. The knee works with 1/2 patch, and the back needs a whole one, for me. Keep the rest of the patch not used in the closed zip lock with its backing intact.

I have heard that if your patches dry out some with age..say past the Exp.date, you can rehydrate them with a little fine mist spritz of water. If they don't feel cold going on anymore, they might not work. I have old patches and I've used them successfully. They sometimes don't stick well however. Using medical tape is okay with them to help that. If you have very oily skin you might clean it off with alcohol, and then dry it, and then apply. You cannot wear them in showers or swimming. They will fall off. The adhesive is aqueous and moist. So too much sweating makes them fall off too.

Follow manufacturers suggestions with Lidoderm, the timing of 12 hrs on and 12 hrs off, and proper disposal, since active drug remains in the patches when you discard them. Fold them over sticky sides together so pets or small children cannot get to them. Do not apply over broken or open skin areas either. This would affect the absorption of the lidocaine and expose you to more than allowed.
We don't get many comments about rashes. I've never had them with these patches.