Reason to get an xray on atraumatic extremity pain

A 7 y/o boy presented with 24 hrs of left knee pain. No known injury. No fever/chills, systemic signs of illness, or past medical history. Does "horse around" with older brother a lot.

PE: normal VS

Gen:awake, alert, NAD

LLE: mild swelling in distal thigh. No erythema, warmth. FROM of hip, knee. Some discomfort with active knee extension, no pain with passive extension.


MRI later showed mass suggestive of osteosarcoma vs Ewing sarcoma.