A bursa is a lubricated sac or pocket that exists within mobile tissues to facilitate a limb's movement.
Bursae (plural) are usually closely related to tendons where there is a lot of frictional movement.
Bursae of the knee
In the knee there are several bursae (plural of bursa), the main ones being:
- suprapatellar bursa
- pre-patellar bursa
- infrapatellar bursa
- deep infrapatellar bursa
- pes anserine bursa
Occasionally bursae become inflamed and distended with fluid. They can also become infected. The condition of an inflamed bursa is called bursitis.