Bursae are fluid-filled cavities located at tissue sites where tendons or muscles pass over bony prominences near joints, such as the elbow. The function of a bursa is to facilitate movement and reduce friction between moving parts. Update Date: 08/11/2008Linda Vorvick, MD, Seattle Site Coordinator, Lecturer, Pathophysiology, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.