5. Remember in Three Stories when they explained House's infarction? They didn't remove the muscle entirely - the option they chose was to remove as much of the dead muscle as they could, limiting the amount of pain while still retaining some muscle function. Kind of a middle ground.

I think that implicit in this is that House's limp is mostly due to pain, not due to lack of muscle. It's like the muscle can't relax fully because it's so painful. Ketamine is an analgesic - it may reduce the pain enough to give him use of the leg again.

See this article for similar situations.