Research study to determine if putting local anesthetic-or numbing medication-through one or two tiny tube(s) placed next to the nerves that go to an amputated limb will decrease phantom limb and/or stump pain.

Specific Aim 1: To determine if, compared with current standard-of-care treatment, the addition of an ambulatory continuous peripheral nerve block decreases post-amputation phantom limb and stump pain.

Hypothesis 1: Following upper or lower extremity amputation, phantom limb and/or stump pain will be significantly decreased four weeks following a multiple-day ambulatory continuous peripheral nerve block as compared with patients receiving standard-of-care treatment (as measured on the 11-point numeric rating scale).

Specific Aim 2: To investigate the possible relationship between the addition of a multiple-day ambulatory continuous peripheral nerve block to standard-of-care treatment of post-amputation phantom limb and/or stump pain and cortical reorganization.

Hypothesis 2: Following upper or lower extremity amputation with subsequent phantom limb pain/sensation and/or stump pain, the addition of a multiple-day ambulatory continuous peripheral nerve block to standard-of-care treatment will result in cortical reorganization during and four-weeks following the perineural infusion (as measured by MRI).

Inclusion Criteria:

• previous upper or lower limb amputation including at least one metacarpal or metatarsal bone, respectively
• age 18 years or older
• phantom limb and/or stump pain described as at least a 2 on the NRS for the previous week [and pain occurring on a weekly basis over the previous month]
• willing to have an ambulatory perineural infusion for 6 days
• willing to avoid additional "new" analgesic interventions from 4 weeks prior to at least 4 weeks following catheter placement, and preferably to 6 months following catheter placement
• the availability of a "caretaker" who will transport the subject home following the procedure and remain with the subject for the first night of the infusion

Exclusion Criteria:

• known hepatic or renal insufficiency
• allergy to the study medications
• possessing a contraindication to perineural catheter placement or perineural local anesthetic infusion