Actually, they can keep your leg numb but then you can't walk on it and movement is important. The same peripheral nerve block used during the operation can be used afterwards as well.

The problem is there's no way to separate out the sensory from the motor portion of the nerve. The patient's leg is both numb and unable to move under voluntary control. Injury from an insensate leg is a real concern. And there is a risk for toxicity from the anesthesia to persist.

Patients must be selected carefully for this kind of treatment. Patient education is very important. For patients to go home with continuous nerve blocks there must be close supervision to prevent accidents and injuries.

Studies are underway to find drugs that can do exactly what you suggest. With a time-released capsule, patients could go home under their own steam but with far less pain. Nerve blocking drugs that last 48 to 96 hours would be very helpful.