a boy with limping and hip pain

We presented a 5-year-old boy with fever, limping, and hip pain for six days. there was no abnormal past medical history. he kept his left leg immobile and slightly flexed, and externally rotated in the hip joint. laboratory findings showed leukocytosis and elevated esr and crp. hip sonography was normal. hip magnetic resonance imaging (mri) found no joint effusion but elucidated signs of inflammation in muscles of the periarticular and proximal femoral area (iliopsoas and gluteus maximus), and no collection could be noticed. we provided a thorough discussion on differential diagnoses and approaches to the patient.