Multiple imaging modalities are currently used to evaluate pathologic conditions of the knee including,conventional radiography,fluroscopy,CT,U/S,nuclear medicine,and MRI. The ideal initial imaging device after plain radiography is U/S because it provides economic and non invasive imaging of tissue.The sonographer can image tissues in both static and dynamic state.It is cost effective because it can be utilized as an extension of the clinical examination.There are no limitation as to the number of joints that may be examined and how frequently such studies may be performed beyond time and patient tolerance. Several procedures may be performed under U/S guidance including aspiration of a cyst,fluid collection or abscess,biopsy,steroid injection of bursae and the tendon sheaths in patients with a chronic inflammatory arthropathy,and arthrocentesis.