<prompt> The most likely diagnosis for the tumor at upper end of tibia is:-GCTUBCABCCB  <response>: Giant cell tumor - It is the only tumor to involve the joint. It is seen in 20-40 years of age after skeletal maturity. It occurs in epiphysis mainly and extends into metaphysis, so called as epiphyseal-metaphysis tumor Unicameral bone cyst -Unilocular cystic bone cavity filled with serosanguinous fluid. X-ray shows fallen leaf sign. It often abuts but does not cross the physis. Aneurysmal bone cyst -Blood-filled cystic spaces. X-ray shows expansile, lytic cystic lesions and MRI shows fluid-fluid levels within the lesion. Chondroblastoma - presence of chicken-wire calcification is pathognomonic. 