A bursa is a fluid-filled space lined by endothelium. They function to permit free movement between apposing tendon, bone and skin.
There are a number of well-defined bursae:
- olecranon bursa
- pre-patellar bursa
- infra-patellar bursa
- ischial bursa
- trochanteric bursa
- gluteofemoral bursa
Also, bursae may form at the sites of repeated friction between two layers: adventitious bursae.
Bursae may become inflamed or infected.