The common peroneal nerve was released distally, resected as far proximally as allowed by surgical exposure, and then retracted cephalad into the biceps femoris muscle. The resected end of the nerve appeared hyperemic and swollen under direct vision, confirming the diagnosis of common peroneal neuroma.
The patient was followed after the procedure for 9 months and did not report any neuropathic pain in the stump region. He required hydrocodone in the immediate postoperative period for about 4 weeks and did not require any further opioids for pain control. Nine months later, he reported medial stump scar pain, rated 8 of 10, which was treated surgically by scar revision (under sciatic nerve block and spinal anesthesia). He has had no recurrence of his lancinating neuropathic pain in the common peroneal nerve distribution. He has not been using any opioids and has been able to use his prosthesis regularly.
Clinical treatment of postamputation stump pain can be difficult to manage and frustrating for both patient and physician. Various causes of postamputation stump pain include protruding bone edge, heterotopic calcification, osteomyelitis, tumor recurrence, phantom pain, and neuropathic pain from neuroma formation. Neuroma pain usually starts 2 to 3 months after the initial surgery.2 While the pathophysiology and etiology of neuroma stump pain are unclear, the distal end of a transected nerve likely regenerates abnormally3,4 resulting in a tangled architecture of axons, Schwann cells, endoneurial cells, and perineurial cells within the surrounding scar tissue.3,4 This leads to increased sensitivity to any stimulation from traction on the nerve from scar tissue, compression of the entangled nerve ending, or ischemia of the nerve tissue.
Diagnosis of stump neuroma pain is made clinically, with the classic Tinel sign allowing for localizing it to a single peripheral nerve. Sciatic neuromas are typically easier to detect than those arising from the smaller nerve branches within the thigh.5 MRI is the accepted standard for detection of a neuroma.5 Neuromas have low signal intensity on T1-weighted images and intermediate to high signal intensity on T2-weighted images; they also demonstrate variable enhancement after administration of gadopentetate dimeglumine.5 In patients with above-knee amputation, MRI has been used to detect stump neuromas as heterogeneous masses with intermediate intensity. However, in below-knee amputees, the compactness of musculature, along with fatty atrophy, interferes with the ability of MRI to detect many lesions.6 This was probably the scenario in our patient. It should also be noted that to be radiographically detected, most neuromas need to be 1.0 to 3.5 cm in diameter.6–9
With ultrasound, stump neuromas appear as hypoechoic/anechoic structures, with the surrounding scar tissue appearing hyperechoic. This is in contrast to normal nerves identified as echogenic, cord-like structures with internal linear echoes in longitudinally oriented scans and as an oval-to-round echogenic sections on transverse scans.10 In perioperative settings, ultrasound appears to be more easily available as an alternative to diagnose peripheral neuromas. Ultrasound can also trace the mass to an adjacent nerve, which is helpful in definitive diagnosis.11
Postamputation pain is typically treated conservatively before surgical intervention, but the success rate is mixed.12 Our patient was medically treated for 6 months before seeking surgical cure. Ultrasound guidance has allowed for therapeutic local anesthetic/steroid blocks into neuroma previously localized by MRI,13 but this may require multiple blocks.
To our knowledge, there is no standard guideline on surgical decision making regarding neuroma excision. The incidence of painful neuromas in 1 retrospective study on unilateral traumatic lower limb amputees in Chile was reported to be 12.5%.14 Diagnosis of a suspected neuroma with local anesthetic infiltration under ultrasound guidance could be used before excision, as demonstrated by our case report.
Our case is unique in that the neuroma could not be identified by either MRI or ultrasound. However, we used an ultrasound-guided common peroneal nerve diagnostic block to identify the nerve causing neuropathic pain. This was followed by common peroneal nerve resection and retraction into the biceps femoris, yielding complete relief from the neuropathic pain.
As exemplified in our report, BKA neuromas are difficult to detect by standard diagnostic testing. If the patient receives complete pain relief after ultrasound-guided selective peripheral nerve block, resection of the involved nerve can be undertaken to potentially treat intractable neuropathic pain.
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© 2014 International Anesthesia Research Society
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