osteoid osteoma is a benign bone tumor consisting of an osteoid nidus in a highly vascular connective tissue stroma . these tumors are exquisitely painful , and demonstrate characteristic findings on clinical and radiographic examinations . the major drawback of this traditional approach is prolonged surgery and hospital stay , weakening of the bone requiring a prophylactic fixation , and its subsequent removal and additional time off school due to open surgery . to overcome this drawback , different minimally invasive techniques have been described as alternative therapeutic options ( radiofrequency ablation , laser photocoagulation , and percutaneous resection ) . computed tomography ( ct ) guidance has become a very useful and easy method for the percutaneous treatment of these lesions . we started using ct guided radiofrequency ablation for osteiod osteoma 5 years ago and immediately noted many beneficial effects in terms of duration of hospital stay , morbidity , and overall patient comfort prompting us to do this study . we report our experience with ct - guided percutaneous radiofrequency ablation ( rfa ) of osteoid osteoma in common and technically challenging locations in 30 pediatric patients and evaluate technical and clinical results . this is a retrospective observational study of 30 pediatric and adolescent patients who underwent ct - guided percutaneous rfa of osteoid osteoma between june 2009 to may 2014 . all patients reported severe pain that usually increased at night and required nonsterioidal anti - inflammatory drugs for pain relief . the osteoid osteoma was diagnosed from clinical and imaging findings ( radiography , ct , and/or magnetic resonance imaging ( mri ) scan ) , demonstrating a nidus and other findings that are typical of osteoid osteoma . patients and their legal guardians were fully informed of the procedure as well as of the surgical and medical alternatives , and informed consent was obtained . all procedures were performed under general anesthesia in the ct room on six slice ct scanner ( philips brilliance , massachusetts , usa ) . a guidewire ( k - wire ) was drilled into the center of the nidus using either a hand drill ( aesculap inc . b braun , center valley , pa ) or a battery operated drill ( stryker corp . , kalamazoo , mi ) with a cannulated drill bit ( 2.54.5 mm ) ( zimmer , warsaw , in ) along the planned tract by the pediatric orthopedist ; keeping the cannulated drill bit in nidus of osteoid osteoma , k - wire was exchanged for the stiff end of the amplatz wire ; a 5f sheath which was cut near hub and a linear cut along its entire length was made to allow it to expand and peel off when rfa probe was inserted through ; subsequently , a 4 mm cannulated bone drill was exchanged for a 5f sheath over an amplatz wire . ( 17 gauge 2 cm diameter , 12 cm long , three tines ) angiodynamics , inc . , ga , usa ] was inserted into the nidus of osteoid osteoma through the sheath . sheath was withdrawn approximately 2 cm back , and the tines were opened and confirmed to be within the lesion with check ct sections . using the radiofrequency waves from rf generator ( model 1500x ; angiodynamics , inc . , ga , usa ) , the tines were heated to a target temperature of 90c and power of 60100 w and the peak temperature was maintained for 6 min . after 6 min , the tines were withdrawn into the probe and then the rf probe was removed . the treatment success was evaluated in terms of pain relief before and after procedure ( 1 day , 1 month , and 3 months ) . patients were also contacted by telephone at 6 months for follow - up regarding complications or recurrence of pain . technical success was defined as the ability to localize the radiolucent nidus and placement of an electrode under ct guidance with ablation performed for the desired period . clinical success was defined as complete relief of pain without the use of oral pain medication within 1 month of the procedure . from june 2009 to may 2014 , 30 pediatric patients underwent ct - guided rfa of osteoid osteoma . there were 25 boys and 5 girls , with a male - to - female ratio of 5:1 . their age ranged between 4 years to 20 years with a mean age of 13.16 years . lesions were grouped into common and challenging location . among the common location ( n = 25 ) , lesions were located in the femur ( n = 21 ) [ figure 1 ] and tibia ( n = 4 ) . among the challenging locations ( n = 5 ) , four were near articular surface ( one each at glenoid fossa of right scapula , head of right radius , talocalcalcaneal joint of right calcaneum [ figure 2 ] and left femoral head ) and one was in the left sacrum . radiography ( a ) and ct scan bone window axial image ( b ) show a radiolucent nidus and surrounding reactive sclerosis . ( d ) ct scan post procedure shows rf ablation tract a 17-year - old boy with a right calcaneal osteoid osteoma near the talocalcaneal joint margin . ( a ) magnetic resonance imaging ( stir ) sagittal image shows central nidus surrounded by hypointense reactive sclerosis . rest of the surrounding calcaneum appear hyperintense due to reactive edema due to osteoid osteoma . ( b ) ct scan shows rfa probe in situ in nidus technical success was achieved in all patients ( 100% ) . primary clinical success was 96.66% ( 29 of total 30 patients ) , despite pediatric population and challenging location . one patient with an osteoid osteoma in the shaft of right femur had persistent pain after 1 month and was treated successfully with a second procedure ( secondary success rate 100% ) . one patient from the challenging location group with osteoid osteoma at right radial head had immediate post - procedure weakness of wrist and finger extension because the lesion was very close to posterior interosseous nerve , which slowly recovered with physiotherapy . since the promising results of rosenthal et al . , in the management of osteoid osteoma with rfa , a large number of studies evaluating rfa of osteoid osteoma have been reported in the literature . most of these studies found very high technical success rates ( 100% ) and good primary success rates with a single session of ablation ranging from 76% to 100% . hence , this minimally invasive technique has become the method of choice for treatment of osteoid osteomas , provided that the diagnosis is based on a typical clinical , scintigraphy , and ct presentation . to our knowledge , there are few reports in the literature regarding the role of percutaneous rfa in treating osteoid osteomas in children at atypical locations . our technical success rate was 100% , which is similar to most of the other studies ( 100% ) . in our study in the pediatric population , the primary and secondary clinical success ratings were 96.66% and 100% , respectively , which are comparable to success rates in most other studies among adults , where primary success and secondary success ranged from 76% to 100% and 87% to 100% , respectively . in a study done by donkol et al . on the efficacy of rfa of osteiod osteoma in children showed that the technical success , primary clinical success , and secondary clinical success rates were 91.3% , 78.2% , and 82.6% respectively . and vanderschueren et al . , in their studies , showed that lower age can be a risk factor for lower clinical success rate . this can be explained by the greater technical difficulty during ablation of osteoid osteoma in children due to the small body mass , difficulty in positioning and fixation of the needle , and shorter ablation time ( range : 26 min in their study ) for each procedure . our study showed that if technical success is 100% and if strict desired temperature ( 90c ) can be maintained for desired time ( 6 min ) using controlled power ( wattage ) delivery ( 60100 w ) then high clinical success can be achieved even in pediatric population similar to adult population . in our study , this happened in a child with radial head ( technically challenging position ) osteoid osteoma who had developed an immediate post procedure weakness of wrist and finger extension as the lesion was very close to posterior interosseous nerve . there are few case reports of likely articular cartilage damage in weight bearing joints such as acetabulum following ct - guided percutaneous rfa of juxta - articular osteoid osteoma , however , it was not confirmed whether the articular cartilage was damaged only by head due to rfa or if it had also been weakened before by the osteiod osteoma . on rfa of intra - articular osteoid osteoma of the hip showed that there is good ossification and bone regeneration following rfa and that it is a safe and effective treatment even for intra - articular lesions . no delayed complications were observed in our study . in comparison to percutaneous ct - guided curettage of osteiod osteoma , during rfa there is lack of confirmation of histological diagnosis . however , there are other disadvantages of curettage technique that it is little more traumatic with complications of neuropraxia , skin abrasions , damage to blood vessels especially in femur leading to avascular necrosis , and frequently incomplete curettage . we suggest that when the clinical and radiological features are not typical , the technique should be supplemented with a core biopsy from the nidus area . this is specially indicated when the differential diagnosis is infection as management will be required . limitations of our study are that it is an observational study , lack of confirmation of histological diagnosis , and lack of imaging follow - up . percutaneous ct - guided rf ablation is a relatively safe , highly effective , and minimally invasive procedure for the treatment of osteoid osteoma in pediatric population despite atypical location .
context : percutaneous radiofrequency ablation ( rfa ) of osteoid osteoma has a high technical and clinical success rate . however , there is limited data on its use in the pediatric population , especially in technically challenging locations.objective:to assess the safety and efficacy of computed tomography ( ct)-guided percutaneous rfa of osteoid osteoma in pediatric population.patients and methods : from june 2009 to may 2014 , 30 patients with osteoid osteoma were treated with ct - guided rfa in common ( 25 cases ) and technically challenging ( five cases : four near articular surface and one in sacrum ) locations . 
 therapy was performed under general anesthesia with a three - array expandable rf probe for 6 min at 90c and power of 60100 w. the patients were discharged next day under instruction . the treatment success was evaluated in terms of pain relief before and after ( 1 day , 1 month , and 6 months ) treatment.results:technical success was achieved in all patients ( 100% ) . 
 primary clinical success was 96.66% ( 29 of total 30 patients ) , despite the pediatric population and atypical location . 
 one patient had persistent pain after 1 month and was treated successfully with a second procedure ( secondary success rate was 100% ) . 
 one patient had immediate complication of weakness of right hand and fingers extension . 
 no delayed complications were observed.conclusions:ct-guided rfa is relatively safe and highly effective for treatment of osteoid osteoma in pediatric population , even in technically difficult locations .