--is that yes, foot drop will not be eliminated by surgery in those whose cause for it is something systemic, such as CMT, another hereditary neuropathic process, or even a condition such as diabetes (and there are some people some people with diabetes whose de-enervation has progressed to the point that their motor functions are affected and they show foot drop; this is not uncommon in conditions such as CIDP, either).

But, if the foot drop is caused by nerve compression at the lumbosacral nerve roots, or if the compression is farther down the tracts of some of the long nerves of the leg, proper surgical technique might relieve the foot drop, if it is not of too long standing (e.g., the compressed nerves have not been damaged severely over a long period of time).

The Wikipedia explanation of this is actually pretty comprehensive:

http://en.wikipedia.org/wiki/Foot_drop