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An 11yo girl presents with 2 weeks of right knee pain and limp after falling off a bicycle. She has had no fever, rash, other trauma. Vital signs are: temperature 37.5, HR 80, RR 16, BP 110/60. Her exam is normal except for: a 1/6 musical systolic ejection murmur at the LLSB, acanthosis nigricans, and gait with a noticeable limp. Her right knee has no effusion, deformity, erythema, or warmth appreciable.

The appropriate initial diagnostic work-up for this patient is: