Role of percutaneous CT-guided radiofrequency ablation in treatment of intra-articular, in close contact with cartilage and extra-articular osteoid osteomas: comparative analysis and new classification system

Purpose We investigated procedural safety, technical and clinical outcomes of the percutaneous image-guided radiofrequency ablation (PRFA) of intra-articular (IA), intra-articular close to cartilage (IACC), and extra-articular (EA) osteoid osteomas (OO). We proposed a new radiologic classification for osteoid osteoma depending on the degree and location of sclerosis which may correlate with technical failure and/or difficulties. Material and methods According to the inclusion criteria, we enrolled consecutive patients who were referred to the investigation center from June 2018 to January 2022. After clinical and CT imaging features were suggestive for the diagnosis of OO, all the patients were treated by percutaneous CT-guided RFA with a standardized technique. Biopsy of the lesion was not performed in all patients. A retrospective analysis was conducted to assess the procedure's technical, primary clinical, and secondary clinical successes, recurrence rate, and complications. We classified all the OOs according to a new proposed classification of the site and the amount of sclerosis. Results A total number of 55 patients were enrolled in our study according to the inclusion criteria. The mean age of the enrolled patients was 24.07 +/- 14.71 years (ranges from 7 to 57 years). The M/F ratio was roughly 2:1. The mean follow-up was 20.18 +/- 12.60 months (ranges from 2 to 44 months). EA group included 36 patients, IA included 5 and IACC included 14 patients. Technical success was achieved in all cases of IA and IACC groups. Technical success in the EA group was 97.22% (1 technical failure). Primary clinical success was 100%, 92.85%, and 91.66% for IA, IACC, and EA groups, respectively. Accordingly, the recurrence rate was 5.88% in EA, and 7.14% in IACC, while no recurrence occurred in the IA group. No complications occurred. The secondary success rate of the 3 cases of recurrence was 100%. Conclusions PRFA proved to be a safe procedure with a high rate of success for OO treatment even in intra-articular lesions in close contact with cartilage. This study showed that the results in terms of technical and clinical success are comparable for IA OO, IACC OO, and EA OO, even if the recurrence rate was higher in EA OO. Our proposed new classification of the degree and location of sclerosis may correlate to technical failure, but further studies with a larger number of patients are needed for validation.