The synovial membrane of the knee joint forms several fluid-filled synovial sacks and pockets around the joint that are called bursae (singular: bursa). Four of these bursae typically communicate with the synovial cavity of the knee joint, and these are:

Suprapatellar bursa - located between the femur and the tendon of the quadriceps femoris muscle;
Popliteus bursa - lies between the tendon of the popliteus muscle and the lateral condyle of the tibia;
Anserine bursa - separates the tendon of the sartorius muscle, tendon of the gracilis muscle and tendon of the semitendinosus muscle from the tibia and the tibial collateral ligament;
Semimembranosus-Gastrocnemius bursa - located in front of the proximal attachment of the tendon of the medial head of the gastrocnemius muscle.

There are several more bursae that are not connected with the synovial cavity, including:

Subcutaneous prepatellar bursa - lies between the skin and the anterior surface of the patella;
Subcutaneous infrapatellar bursa - located between the skin and the tibial tuberosity;
Deep infrapatellar bursa - lies between the patellar ligament and the anterior surface of the tibia; this bursa may be connected to the synovial cavity in some cases.

NOTE: Some of the leg muscles have been moved away from the bone in order to better visualize the bursae in the 3D model.

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Bursae of knee joint