Determining the cause of residual limb pain in amputees can be very challenging. To appropriately investigate and treat pain in the residual limb, the prosthetist must identify the nature of pain (neuropathic, musculoskeletal, or somatic) before socket modification is undertaken. Amputees will experience pain at the residual site of amputation. Although common in prosthetic clinical practice, few studies describe its incidence or prevalence. Residual limb pain differs from phantom limb pain in that it is felt only in the residual limb and not in the absent limb.1 Phantom pain is usually neuropathic in character and originates from nervous tissue. Although residual limb pain can also have a neuropathic component, it usually originates in other tissues. It can be caused by inflamed bursae, localized soft-tissue inflammation,2 or bone pain. MRI can demonstrate additional causes of residual limb pain including scar formation, fat in atrophied muscles, soft tissue abscesses, osteomyelitis, and hematomas.3 Another rare cause of residual limb pain is complex regional pain syndrome.4
A 48-year-old man was referred to our consultation service for severe left residual limb pain (described as 12/10 in severity) that was not responding to high doses of opioid analgesia and pregabalin. An elective transtibial amputation was performed 1 month previously for symptoms related to complex regional pain syndrome—a complication of a motorcycle accident that occurred 17 years previously. His immediate postoperative recovery was uneventful. Two weeks after the amputation, he sought help for increasingly worsening nonneuropathic residual limb pain. He was admitted to hospital when the wound dehisced and bled (Fig. 1). This provided temporary relief of his pain, but was subsequently followed by rapid worsening of his pain.
Physical examination revealed a tender residual limb with tense, indurated skin. The wound had dehisced and was healing by secondary intention. An area on its posteromedial aspect was extremely tender but not pulsatile. Range of motion was limited in flexion but otherwise normal. Sensation was normal.
Ultrasound imaging revealed a large, well-circumscribed mass measuring approximately 8.0 by 5.3 cm. Both solid and echogenic components with cystic areas were seen within it. There was increased flow centrally with large amounts of clot. Color Doppler-imaging revealed a classic to-and-fro flow pattern of blood5 that resembled a “ying-yang” sign of blood in the perivascular mass (Fig. 2). The angiogram showed widely patent femoral, profunda femoris, and superficial femoral arteries. The anterior tibial artery had an abrupt cutoff approximately 2 cm distal to its origin where there was a filling of a sizeable pseudoaneurysm (Fig. 3).
Management included vessel embolization with three platinum coils ranging from 3 to 6 mm in size. After treatment, digital subtraction imaging revealed that the vessel was completely occluded and no further filling of the pseudoaneurysm was occurring (Fig. 4).
Because of the severity of pain, prosthetic evaluation was deferred pending further investigations which demonstrated the pseudoaneurysm formation. Subsequent to the repair procedure, the patient's pain levels decreased to 5/10 in severity and narcotic medications were reduced. The pain further diminished after several months of therapy. He was subsequently fitted with a patellar tendon bearing socket, neoprene sleeve, and Safe II foot. Early limb fluctuation attributed to the healing pseudoaneurysm was accommodated by various ply socks and enlarging the prosthesis. He is currently a functional prosthetic user experiencing no further pain symptoms.
A pseudoaneurysm, also termed false aneurysm, forms when blood leaks from an artery into the surrounding tissue.6 It persists through a communication between the feeding artery and the surrounding blood filled cavity. The body of the aneurysm is initially composed of fibrous tissue. However, over a period of time, the surrounding tissue may mature resembling a vessel wall. As a consequence of arterial pressure, pseudoaneurysms tend to enlarge in size.7 Clinically, pseudoaneurysms can be associated with pain, a bruit and a pulsatile mass on palpation.8
Pseudoaneurysms are often missed and are commonly the result of an arterial injury9 especially from the femoral artery.10 They may form as a result of procedures which involve catheter puncture of an artery (incidence of 0.6%–6%11), from anastomoses of arterial bypass grafts or dialysis, after direct trauma to an artery,12,13 arterial wall infection, cardiac catheterization,14 and intravenous drug abuse.15 Complications can include rupture,16 nerve compression,17 and amputation.18 Lesions may be mistaken for an infection or abscess19 or may also simulate the presence of a mesenchymal tumor.20
A literature search of databases PubMed, CINAHL, and OVID encountered only two reports of pseudoaneurysm formation after transtibial amputation.21,22 They have also been found to complicate other amputations such as digital amputation,23 Lisfranc amputation,24 and rotationplasty.25
Radiographic examination may show a nonspecific tissue mass, later followed by rim calcification.26 Rarely, involvement of adjacent bone can occur.27 Ultrasonography is the most common method for diagnosis with a sensitivity of 94% and a specificity of 97%.28 Spectral waveforms and color Doppler show a characteristic to-and-fro flow pattern.29 Ultrasound is also useful for distinguishing between hematoma and aneurysm.30 Angiography is most sensitive for detection and diagnosis with contrast filling the aneurysm being a typical finding.31 MRI discriminates between hematoma and tumor. On spin-echo sequences, a persistent flow void into the aneurysm can be seen.32
Most pseudoaneurysms are small and undergo spontaneous thrombosis, which resolve over time without treatment.33 Spontaneous resolution is related to size (<1.8 cm in diameter)34 and whether the patient is using anticoagulation or antiplatelet therapy. Until recently, pseudoaneurysms were treated surgically by ligation and grafting.35 Recognized indications for surgical repair included a rapidly expanding or infected pseudoaneurysm, distal ischemia or neuropathy and failure of percutaneous treatment.36–38 Profuse bleeding may be encountered intraoperatively.39
Ultrasound-guided compression was first described by Fellmeth et al. in 199139 but has been superseded by the development of thrombin and coil embolization. Coil embolization was the preferred method by the interventional radiologist in this case. The technique involves filling the aneurysm with metallic coils to occlude flow.40 Recently, duplex guided thrombin injection has been proven safe and effective.41,42 Thrombin can be introduced transarterially or percutaneously with or without balloon occlusion. With this technique, an occlusion rate of 93% to 100% of the pseudoaneurysm can be achieved.
Pseudoaneurysm formation can cause significant pain after a transtibial amputation. This rare entity should be considered by the prosthetist in the differential for pain that does not conform to the neuropathic or musculoskeletal paradigm and does not resolve with prosthesis modification. It does not resemble neuropathic pain and should be considered in severe residual limb pain not responding to high doses of pain medication. Diagnosis can be made with standard Doppler ultrasound equipment. Preferred treatment can include coil or thrombin embolization.
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