<prompt> Commonest true benign tumor of bone?OsteoblastomaChondroblastomaOsteoid osteomaGCT  <response>: Ans. c Osteoid osteoma Ref. Maheshwari orthopedics 4th1215Osteoid osteoma It is the commonest true benign bone tumor. Please note that otherwise the most common benign bone tumor is osteochondroma! Osteochondroma is synomymous with exostosis. Not a premalignant condition. Tibia is most commonly affected bone. Posterior elements of vertebrae is a common site. Affects 5-25 years of age. Classical clinical presentation is nagging pain during nighttime, relieved by aspirin.Radiological features: Generally in diaphysis. Usually cortical. Typically seen as a radiolucent nidus usually 1 cm surrounded by reactive sclerosis. May have central fleck of target calcification in the centre. Spinal lesions: Most often affects lamina. 60 are in lumbar spine. Mature sclerotic lesion may present as sclerotic Ivory pedicle or ivory lamina. Radionuclide bone scan may show double density sign . Q CT remains the best modality to detect most sensitively the nidus, which is defining feature. Rx:- Complete excison of nidus with sclerotic bone.- RFA.OSTEOBLASTOMA 1 of all primary bone tumors Mean age: 6-30 years 90 Lesion 1.5 cm; smaller lesions are classified as osteoid osteoma Radiological features:Similar to osteoid osteoma:- Radiolucent nidus 2 cm in size.- Well demarcated.- Stippled ringlike flecks of matrix calcification. MC Location spine in posterior elements followed by long bone diaphysis e.g., femur.CHONDROBLASTOMA Codman tumor 1 of primary bone neoplasms, and epiphyseal in origin. Peak in 2nd decade. Histologically,chicken wire calcification pericellular deposition of calcification is virtually PATHOGNOMONIC. MC location long bones 80; 23 in lower extremity, 50 about knee. Radiological features:- eccentric medullary, subarticular location with open growth plate 98 begin within epiphysis DD: Giant cell tumor usually larger less well demarcated, not calcified, older age group with closed growth plate, 