Osteosarcoma of the Proximal Femur Mimicking Septic Arthritis of the Hip: A diagnostic dilemma.

Septic arthritis is a surgical emergency requiring prompt drainage of the accumulation of pus in the joint. We report an eight-year-old boy who was referred to the Armed Forces Hospital, Salalah, Oman, in 2016 with limping and pain in his right hip along with an abduction deformity. He was initially diagnosed with synovitis and underwent conservative management. However, two weeks later, he presented to another centre due to persistent pain. Magnetic resonance imaging was suggestive of septic arthritis or osteomyelitis. Eight weeks later, the patient presented again to the Armed Forces Hospital. An arthrotomy was performed, during which an amount of what appeared to be frank pus was drained; however, cultures of the intraoperative samples returned no growth. A histopathological analysis revealed an osteosarcoma. The patient was subsequently referred elsewhere and underwent neoadjuvant chemotherapy and limb salvage surgery. Several months later, he relapsed and developed extensive pulmonary metastasis and died as a result of progressive deterioration.