X-ray hip (AP & bilateral frog-leg view), femur, knee
Consider CBC, ESR, total CK
Consider:
Ultrasound to evaluate for effusion
CT to evaluate for abscess
Ultrasound to evaluate for effusion
CT to evaluate for abscess
ESR > 40 mm/hr
WBC > 12,000/microliter
Refusal or inability to weight bear on affected joint
Fever 38.5° C or greater
Limp 
Acute rheumatic fever
Hirudins
Developmental dysplasia of hip
Tdap
Femur fracture
CURB-65
Juvenile idiopathic arthritis