a 51-year - old female patient ( bmi 39.3 ) was referred our clinic , complaining of tactile allodynia , coldness , and electric shock - like pain on her right ankle . mechanical allodynia was assessed with a brush ( visual analogue scale [ vas ] score of 7/10 ) and thermal allodynia was assessed by applying ice and hot water to the affected area ( vas score of 2 - 3/10 ) . her pain developed about 1 year earlier after an ankle fracture and subsequent surgery , and gradually worsened . she had already been diagnosed as crps type 2 , and nerve conduction velocity and electromyographic studies revealed lesions of the spn and sural nerve . she was treated with medication and physical therapy but it did not relieve her pain at all . a lumbar sympathetic block and subsequent lumbar sympathetic neurolysis was done and the coldness and electric shock - like pain was reduced from a vas score of 7 - 8/10 to 2 - 3/10 . however , the allodynia was not diminished ( a vas score of 7/10 ) . as her pain was mainly confined to the anterior ankle and foot dorsum , the spn block was tried with 3 ml of 1% mepivacaineat in the mid - calf area using an in - plane ultrasound guided approach with a 6 - 13 mhz linear array transducer ( sonosite s - nerve , sonosite inc . , bothell , wa ; linear 613 mhz ) and it relieved her pain by about 70% ( the vas decreased from 7 - 8/10 to 2 - 3/10 ) . however , as the reduction of pain lasted only for a few days , we decided to apply prf on the spn . we used a tcu 410 tc - electrode inside the 22 g disposable cannula of 0.9  150 mm cannula with an active tip of 5 mm , and the electrode was connected to a radiofrequency lesion generator ( neuro n50 , stryker leibinger gmbh , freiburg , germany ) . after applying local anesthesia to the skin , the needle was inserted under ultrasound guidance close to the spn ( fig . prf was applied for 120 seconds at 45 v , with an electrode tip temperature not exceeding 42 , and it was repeated three times . the treatment resulted in a reduction of the vas of the allodynia from 7 - 8/10 to 2 - 3/10 at the 2-week follow up . pain relief was maintained during the 4-month follow - up , but was slightly exacerbated to a vas score of 5 - 6 . a 20-year - old male patient ( bmi 19.8 ) who presented with complaints of tactile allodynia and coldness in his right foot visited our clinic . he could not undergonerve conduction velocity and electromyographic studies because of severe allodynia in affected area . the assessment of the allodynia was also impossible because of his fear of anyone touching the affected foot . according to the patient , he had a history of treatment with medication , physical therapy , intravenous ketamine therapy , a lumbar sympathetic block , and lumbar sympathetic neurolysis , but their effects had not been satisfactory , especially in the management of the allodynia . we tried superficial peroneal nerve blocks using ultrasound and nerve stimulator guidance because his complaint about allodynia was dominant on the dorsal aspect of the right foot . it provided the reduction of allodynia symptom ( the vas decreasedfrom 7 - 8/10 to 3 - 4/10 ) but it lasted only a few days . prf on the spn underultrasound guidance was done in the same manner as described in case 1 . the vas of the allodynia was decreasedfrom 7 - 8/10 to 3 - 4/10 at the 2-week follow up , and he could put on his socks , unlike previous visits with barefoot . the vas was maintained at 3 - 4/10 at the 3-month follow - up , but gradually returned to the baseline level of pain after that . a 51-year - old female patient ( bmi 39.3 ) was referred our clinic , complaining of tactile allodynia , coldness , and electric shock - like pain on her right ankle . mechanical allodynia was assessed with a brush ( visual analogue scale [ vas ] score of 7/10 ) and thermal allodynia was assessed by applying ice and hot water to the affected area ( vas score of 2 - 3/10 ) . her pain developed about 1 year earlier after an ankle fracture and subsequent surgery , and gradually worsened . she had already been diagnosed as crps type 2 , and nerve conduction velocity and electromyographic studies revealed lesions of the spn and sural nerve . she was treated with medication and physical therapy but it did not relieve her pain at all . a lumbar sympathetic block and subsequent lumbar sympathetic neurolysis was done and the coldness and electric shock - like pain was reduced from a vas score of 7 - 8/10 to 2 - 3/10 . however , the allodynia was not diminished ( a vas score of 7/10 ) . as her pain was mainly confined to the anterior ankle and foot dorsum , the spn block was tried with 3 ml of 1% mepivacaineat in the mid - calf area using an in - plane ultrasound guided approach with a 6 - 13 mhz linear array transducer ( sonosite s - nerve , sonosite inc . , bothell , wa ; linear 613 mhz ) and it relieved her pain by about 70% ( the vas decreased from 7 - 8/10 to 2 - 3/10 ) . however , as the reduction of pain lasted only for a few days , we decided to apply prf on the spn . we used a tcu 410 tc - electrode inside the 22 g disposable cannula of 0.9  150 mm cannula with an active tip of 5 mm , and the electrode was connected to a radiofrequency lesion generator ( neuro n50 , stryker leibinger gmbh , freiburg , germany ) . after applying local anesthesia to the skin , the needle was inserted under ultrasound guidance close to the spn ( fig . prf was applied for 120 seconds at 45 v , with an electrode tip temperature not exceeding 42 , and it was repeated three times . the treatment resulted in a reduction of the vas of the allodynia from 7 - 8/10 to 2 - 3/10 at the 2-week follow up . pain relief was maintained during the 4-month follow - up , but was slightly exacerbated to a vas score of 5 - 6 . a 20-year - old male patient ( bmi 19.8 ) who presented with complaints of tactile allodynia and coldness in his right foot visited our clinic . he could not undergonerve conduction velocity and electromyographic studies because of severe allodynia in affected area . the assessment of the allodynia was also impossible because of his fear of anyone touching the affected foot . according to the patient , he had a history of treatment with medication , physical therapy , intravenous ketamine therapy , a lumbar sympathetic block , and lumbar sympathetic neurolysis , but their effects had not been satisfactory , especially in the management of the allodynia . we tried superficial peroneal nerve blocks using ultrasound and nerve stimulator guidance because his complaint about allodynia was dominant on the dorsal aspect of the right foot . it provided the reduction of allodynia symptom ( the vas decreasedfrom 7 - 8/10 to 3 - 4/10 ) but it lasted only a few days . prf on the spn underultrasound guidance was done in the same manner as described in case 1 . the vas of the allodynia was decreasedfrom 7 - 8/10 to 3 - 4/10 at the 2-week follow up , and he could put on his socks , unlike previous visits with barefoot . the vas was maintained at 3 - 4/10 at the 3-month follow - up , but gradually returned to the baseline level of pain after that . crps occurs mainly in the limbs and is characterized by abnormal pain , motor symptoms , sweating , edema , and autonomic changes of the skin such as hypertrichosis and abnormal sudomotor activity . several pharmacological and interventional therapies for the treatment of crps have been introduced , but there are no definitive treatment modalities established at this point . mechanical allodynia is pain due to a mechanical stimulus which does not normally provoke pain . it may cause functional impairment of daily activity and result in a declining quality of life . the mechanisms of allodynia are not fully understood but central sensitization is generally the accepted mechanism of allodynia like most neuropathic pain symptoms . thus , medical treatments such as anticonvulsants , antidepressants , and opioids , or invasive interventional treatments , including sympathetic ganglion neurolysis / radiofrequency denervation , spinal cord stimulation , and the intrathecal pump , are generally accepted as the treatments of choice . however , systemic administration of these medications produce frequent side effects , and interventional treatments are relatively invasive and expensive . meanwhile , in addition to peripheral sensitization , the peripheral mechanism has been suggested as a cause for allodynia . and there are some reports that peripheral applied treatments can reduce the symptoms of crps patients including intradermal / subcutaneous botulinum toxin a , topical ketamine , and lidocaine patches . prf treatments are usually performed on the dorsal root ganglion or medial branch of spinal dorsal ramus , but prf treatments on the peripheral nerves for the treatment of chronic pain have gained popularity in recent years . . however , the exact mechanism of prf in pain relief is still not known , but it is thought that the electromagnetic field may cause a neuromodulatory effect which can interrupt the gene expression of the sensory neurons and molecules involved in sensitization without damaging the surrounding tissue . mechanical allodynia is known to be mediated by altered low - threshold a- fiber functions such as phenotypic switching , sprouting , and the opening of polysynaptic excitatory synaptic pathways . in our opinion , prf treatment may affect the a- input signal , and it can reduce dynamic mechanical allodynia symptoms , although the precise mechanism is not known . additional controlled trials for proving the efficacy of prf are needed , especially in neuropathic pain . in conclusion , we report our experience with 2 patients with crps of the foot and ankle treated with prf on spn , and to our knowledge , this is the first report of applying prf treatment on the spn .
the superficial peroneal nerve is vulnerable to damage from ankle sprain injuries and fractures as well as surgery to this region . and it is also one of the most commonly involved nerves in complex regional pain syndrome type ii in the foot and ankle region . 
 we report two cases of ultrasound - guided pulsed radiofrequency treatment of superficial peroneal nerve for reduction of allodynia in crps patients .