Suggest Treatments For Frequent Tightness In My Daughters Leg

My 7 year old daughter sometimes cannot straighten her right or left leg. It caused her to walk like a cripple and sometimes it last for 3-5 days. X-ray has been done and series of blood lab test yet the cause of which was not yet determine. May I know if this symptom may result to a permanent crippledness? Is it a sign of juvenile arthirtis? How is it treated?