Knee Joint Bursae

Because almost all tendons at the knee lie parallel to the bone and pull lengthwise across the joint, bursae are numerous (Fig 3, page 61, The adult knee).  Bursae are potential sacs separating tendons from bones and skin.  They contain a microscopic fluid layer and allow tendons to move over bones smoothly.  They can become inflamed and fill with fluid to form lumps around the knee. 

The suprapatellar bursa lies between the quadriceps tendon and the anterior femur. Three other bursae are associated with the patella and its ligament. The prepatellar bursae located between the skin and the anterior surface of the patella allows free motion of the skin over the patella during flexion and extension. The subcutaneous infrapatellar bursa lies between the patellar tendon and the overlying skin. Both these bursae can become inflamed during repetitive activities such as kneeling or the result of direct trauma.  The deep infrapatellar bursa located between the patellar ligament and the tibial tuberosity is separated from the synovial cavity of the joint by the infrapatellar fat pad and helps to reduce friction between the patellar ligament and the tibial tuberosity.

Medially the bursa anserina lies deep to the pes anserinus tendons (sartorius, gracilis and semi tendinosis) and separates them from the tibial collateral ligament.  The bursa of the semi membranosis muscle lies between the muscle and the tibia.

Posteriorily there are two large bursae associated with the medial and lateral heads of the gastrocnemius muscle.  The bursa of the medial head of the gastrocnemius underlies the medial head separating it from the capsule and generally communicates with the knee joint. This bursa is the most common site of the occurrence of a Baker's cyst.

There are numerous other bursae around the knee, many of which can communicate with the knee joint to produce swellings around the knee.