Pulsed electromagnetic field therapy is a possible method of pain control involving the application of electromagnetic energy (also termed nonthermal, pulsed, shortwave radiofrequency therapy). Food and Drug Administration-cleared devices have been in clinical use for over 70 years. For decades, available devices consisted of a large signal generator and bulky coil applicator that were not portable and produced significant electromagnetic interference, making them impractical for common use. However, small, lightweight, relatively inexpensive, noninvasive, Food and Drug Administration-cleared devices that function for 30 days are now available to treat acute and chronic pain, decrease inflammation and edema, and hasten wound healing and bone regeneration. Therefore, it has the potential to concurrently improve analgesia and decrease or even negate opioid requirements, only without the limitations of opioids and peripheral nerve blocks. The purpose of this pilot study is to explore the possibility of treating chronic post-amputation pain with nonthermal, pulsed shortwave (radiofrequency) therapy, optimize the study protocol, and estimate the treatment effect in preparation for developing subsequent definitive clinical trials.

The proposed study will be a randomized, participant- and observer-masked, sham-controlled, crossover, human participants pilot study with two primary aims:

Specific Aim 1: To determine the feasibility and optimize the protocol for subsequent clinical trials that will compare the addition of nonthermal, pulsed shortwave therapy to usual and customary analgesia for post-amputation phantom and residual limb pain.

Specific Aim 2: To estimate the treatment effect of adding nonthermal, pulsed shortwave therapy to usual and customary analgesia for post-amputation phantom and residual limb pain. This will provide an idea of the optimal amputee characteristics amenable to this analgesic technique and allow determination of the required sample sizes of subsequent definitive clinical trials.

Hypothesis: Nonthermal, pulsed shortwave therapy will decrease pain in the 28 days following application for post-amputation pain.

This will be a single-center (University of California San Diego), randomized, participant- and observer-masked, sham-controlled, crossover human subjects pilot study.

Enrollment. Participants will be consenting adults experiencing post-amputation phantom and/or residual limb pain. Study inclusion will be proposed after an amputee contacts the investigators. If an individual desires study participation, written, informed consent will be obtained using a current University of California San Diego Institutional Review Board-approved informed consent form. The study population of interest includes adult women and men of all races, ethnicity, sexual identity, and socioeconomic status.

Procedures. Following written, informed consent, we will record baseline anthropometric information (age, sex, height, weight, amputation details and current pain levels).

Treatment Group Assignment. Each participant will be randomized to one of two treatment groups: Active or Sham treatment. There are sham devices produced that are identical to active devices, only they do not deliver pulsed electromagnetic energy. Randomization will be in block sizes of 2. The computer-generated randomization lists will be created by the University of California San Diego Investigational Drug Service in a 1:1 treatment group ratio using opaque envelopes. The active and sham devices are indistinguishable in appearance, and therefore investigators, participants, and all clinical staff other than the individual who opens the randomization envelope and chooses a sham or active device will be masked to treatment group assignment for the duration of the data collection period. An Investigational Drug Service pharmacist will open the envelope and provide the investigators with the appropriate device, keeping all investigators masked to treatment group assignment. Upon completion of data collection, the pharmacist will provide the investigators with a masked list of the treatment groups (e.g., "Treatment A" and "Treatment B"), and the active/sham lists only following analysis for that subgroup, resulting in a triple-masked study (investigators, participants, statistician).

Study intervention. The pulsed shortwave devices used are over-the-counter (Model 088, BioElectronics, Frederick, Maryland) and 2 devices (both the same treatment group) will be shipped to the patient either in or out of California who will then contact an investigator for assistance in self-placement of the device on the residual limb. The optimal location to treat phantom pain is currently unknown and will partially informed by the results of this pilot study, and patients will be encouraged to move the devices to a new anatomic location every two days until relief is experienced.

Supplemental analgesics. In addition to the pulsed shortwave device(s), participants will receive standard-of-care supplemental analgesics which can include acetaminophen, ibuprofen, ketorolac, opioids, gabapentin (this is provider- and patient-dependent). Therefore, all patients of this study-regardless of the treatment arm they are randomized to-will continue to receive current usual and customary analgesia: all will receive the same combination of supplemental analgesics they would regardless of study participation. Participants will be provided with verbal and written instructions, and the telephone and pager numbers of an investigator available during business hours throughout the treatment period. Participants can shower with the device in place, but not submerge it during swimming or a bath, as advised by the manufacturer.

Amputees will return their initial devices in pre-addressed and -stamped envelopes that we provide. They will be sent a second device which is the opposite treatment of the initial device: participants who initially received sham will subsequently receive active, and vice versa. These will be applied on (approximately) Day 35 and the same protocol will be repeated as for the initial device, with additional data collected for 35 days after placement of the second device. The second device will be discarded in the trash.

Of note, if a device is reported lost or nonfunctional during the study, it will be replaced by the investigators by mail if more than 7 days of treatment remain.

Primary end points: This is an exploratory pilot study to assist in planning subsequent definitive trials and we therefore have no data analysis plan. We will enroll a convenience sample of up to 40 participants. The outcome measures of primary interest will be (1) the change in "average" residual and phantom limb pain scores between baseline and Day 28 of the initial treatment, as well as (2) the Patient Global Impression of Change on Day 28 of the initial treatment.

Inclusion Criteria:

• adult patients of at least 18 years of age [19 years in Alabama and Nebraska]
• with an upper or lower limb amputation at least 12 weeks prior to enrollment distal to the shoulder or hip (femoral head remaining), respectively, and including at least one metacarpal or metatarsal bone, respectively
• experience at least moderate residual and/or phantom limb pain-defined as a 3 or higher on the Numeric Rating Scale (NRS; 0-10, 0= no pain; 10=worst imaginable pain)-at least daily for the previous 2 months
• willing to avoid both changes to their analgesic regimen as well as elective surgical procedures for 70 days after initiation of treatment with PEMF therapy

Exclusion Criteria:

• concurrent use of an implanted pulse generator (e.g., cardiac pacemaker)
• pregnancy
• incarceration

For participants who had only the initial treatment, the follow-up was 35 days. For participants who participated in both the initial and crossover treatments, the follow-up was 70 days.

The Investigational Drug Service will create the randomization tables and provide the investigators with the appropriate device (active or sham), leaving all participants, investigators, and the statistician masked to treatment group assignment.