hip joint effusion

I recently had an MRI with a diagnosis of small  hip joint effusion.  There is no deterioration of the hip joint.  What  is a hip effusion, what is the cause, and how  is it treated?   The Orthopedic I was referred to gave me  a cortisone injection in the joint under sedation which after two weeks  has not been effective; there was no reduction of pain.  With this condition, my hip feels  like  it is going to give way when I get up from sitting to walk.  I also have pain in the groin as well as the front of the hip and sometimes on the side of the hip.  Is there any help for me?
Thank you, Jackie