A 66-year-old K4 functional level male presented to our university pain clinic with persistent and uncontrolled PAP following a traumatic right transtibial amputation approximately 42 years ago. The patient reported multiple surgeries, including a revision one week post-amputation as well as surgery two years post-amputation to address heterotopic ossification in his residual limb. He then underwent a saphenous neuroma excision 5 years later that reduced PLP greatly but did not eliminate it.

Upon presentation to our clinic, he occasionally experienced PLP, but his biggest complaint was acute episodes of burning and aching pain over the lateral half of the distal portion of his residual limb and right buttocks. These pains were routinely provoked by activity and often reached an 8/10 NRS. Despite longstanding pain, he felt his PAP had markedly increased in the last 3 years, which he attributed partly to a neuroma of the right CPN.

Initial physical exam revealed a well-appearing gentleman who had a residual right lower extremity limb with intact skin that had no signs of wounds or pressure injury. Oral medications were discussed, but he did not want to risk potential cognitive side effects. Given the patient had exhausted conservative therapies, he was offered a diagnostic peripheral nerve block of the right CPN to assess candidacy for RFA. After an ultrasound-guided block of the right CPN with a 15 mL mixture of 0.25% bupivacaine and preservative-free normal saline yielded 100% pain reduction, the patient was quickly scheduled for RFA.

A combination of fluoroscopic and ultrasound guidance for this novel procedure was utilized to adequately identify CPN location. After the patient was placed in the prone position, a Fujifilm SonoSite X-Porte ultrasound machine was used to identify the neuroma of his right CPN and our target, which was approximately 1.5 cm proximal to the neuroma.

The skin above this area was anesthetized with 2 mL of 1% lidocaine utilizing a 27G 1.5-inch needle. A Nimbus Electrosurgical RF Multi-tined Expandable Electrode (Tip Type: Black Bevel, Active Tip: 10mm, Tip OD: 1.47mm, length: 50mm, Ref NM-050-10BB) was advanced through the skin under ultrasound guidance. A second electrode was inserted in close proximity (Fig. 1A and B).

Motor stimulation up to 1.7V applied through the electrodes was consistent with peroneal nerve supply as we observed contraction of the tibialis anterior muscle. Once appropriate positioning was confirmed, a mixture of 0.25% bupivacaine and 2% lidocaine was injected through the cannulas. A Nimbus Probe Disposable RF Thermocouple Electrode (Length 5cm, Ref NDP-50-27-SS) was then inserted into each cannula. A Cosman G4 generator was set to bipolar, thermal ablation mode for 90 seconds at 80° Celsius. After the first cycle, the needles were moved ~3 mm laterally. Another lesion was performed here at the same settings.

(Fig. 3). After this, the needles were redirected more anterior to the nerve and 2 more thermal RFA cycles were completed, one medially (Fig. 2A and D) and one laterally (Fig. 2B and C). After a total of 4 locations were ablated, the needles were withdrawn uneventfully.

The patient tolerated the procedure very well; he was able to walk with minimal discomfort before being discharged and was advised to call the pain clinic or seek emergency care in case of unexpected extremity weakness, paresthesia, or other worsening of his clinical condition. While previous pain upon activity was rated 8/10 on NRS, RFA of the right CPN was followed by 0/10 pain upon activity with no return of symptoms for 9 months. Despite the procedure resulting in total paralysis of the tibialis anterior and partial paralysis of other residual limb muscles, the patient expressed he was able to use his prosthetic with dramatically improved function throughout this time. His pain eventually recurred 9 months later, but intensity and frequency were still much lower than prior to RFA.