Knee Bursas and Their Significance

Knee bursas is the term for the bursas around the knee. Bursa, a fluid-filled structure that is present between two apposing surfaces to reduce the friction between the two surfaces.

Bursas are generally are located around large joints such as the shoulder, knee, hip, and elbow. Knee bursas or bursae are of two types. Those which are around patella and those that are elsewhere.

Types of Knee Bursas

Following are present around the patella

• Prepatellar bursa
• Superficial infrapatellar bursa
• Deep infrapatellar bursa
• Suprapatellar bursa.

Other major knee bursas are

• Pes anserine bursa
• Iliotibial bursa
• Bursas of tibial and fibular collateral ligament bursae
• Gastrocnemius-semimembranosus bursa

Another way to group knee bursas is by their location

Anterior

• Suprapatellar
• Prepatellar
• Superficial infrapatellar
• Deep infrapatellar

Medial/Posteromedial

• Pes anserine
• Tibial collateral
• Semimembranosus-tibial collateral
• Semimembranosus-gastrocnemius

Lateral and Posterolateral

• Iliotibial
• Popliteal recess
• Fibular collateral-biceps femoris

The main function of these knee bursas is to reduce friction between adjacent moving structures.

Different Knee Bursas

Anterior Knee Bursas

Prepatellar Bursa

This bursa is located between the patella and the overlying subcutaneous tissue and thus is superficial to quadriceps. it is usually centered in the midline though it may extend slightly medially or laterally relative to the patella.

Prolonged or repeated trauma as in kneeling can cause leads to inflammation and hemorrhagic bursitis which is presented as swelling over the patella. Prepatellar bursitis is known as housemaid’s knee.

[Read more about Prepatellar bursitis]

Infrapatellar Bursa

Infrapatellar bursae can be superficial or deep.

The superficial infrapatellar bursa is located between the anterior tibial tubercle and the skin. It thus lies superficial or anterior to patellar tendon insertion.

The deep infrapatellar bursa is located between the posterior aspect of the patellar tendon and the tibia. Thus, it lies deep to the patellar tendon. None of these knee bursas communicate with the knee joint.

Superficial infrapatellar bursitis is also known as the clergyman’s knee.

Infrapatellar bursitis is inflammation of the infrapatellar bursa, a fluid-filled sac located just below the patella or kneecap. The superficial infrapatellar bursa is located between the patellar tendon and the skin. It lies anterior to patellar tendon and is subcutaneous.

Suprapatellar Bursa

This bursa is between the quadriceps tendon and the femur.

It is located deep to the distal quadriceps tendon and superficial to the pre-femoral fat pad and distal femur.

Suprapatellar bursa communicates widely with the knee joint in most adults. Thus it functions as a recess that is formed due to the involution of an embryonic septum that exists between the bursa and the remaining joint,

Swelling in this knee bursa presents as a mass in the pre-femoral region.

Medial and Posteromedial Knee Bursae

Pes Anserine Bursa

The pes anserine bursa separates the pes anserine tendons [sartorius, gracilis, and semitendinosus] from tibial collateral ligament and the bony surface of the medial tibial condyle.

The pes anserine bursa is located anteromedially, about 3-4 cm distal to the joint line. Normally, it does not communicate with the joint.

The name comes from the webbed configuration of the above tendons which resembles a goose’s foot or pes anserinus.

Anserine bursitis results from overuse of pes anserine bursa.

Collateral Ligament Bursa [Tibial Collateral Ligament Bursa]

The medial collateral ligament bursae are located between the superficial and deep layers of the collateral ligament.

Medial collateral ligament bursitis is typically vertically oriented well defined fluid collection extending along the medial aspect of the femoral and tibial cortices.

It is centered deep to the superficial medial collateral ligament or tibial collateral ligament. It could also be between the superficial medial collateral ligament and deep medial collateral ligament [the meniscofemoral and meniscotibial ligaments]

[Read more about ligaments of the knee]

Its bursitis can be confused with medial parameniscal cysts [are centered more posteriorly and are often more loculated]

Semimembranosus-Gastrocnemius Bursa

The Semimembranosus-gastrocnemius bursa also called a semimembranosus-gastrocnemius recess,  is between the semimembranosus tendon and the medial head of the gastrocnemius, within the posteromedial popliteal fossa.

Often, it is proximal to the joint line at the level of the upper medial femoral condyle though they may extend distally.

This bursa communicates with the knee joint in most persons.

Inflammation of this knee bursa is popularly called as  Baker cyst.

Lateral and Posterolateral Knee Bursae

Iliotibial Bursa

The iliotibial bursa is located between the distal part of the iliotibial band near its insertion on the Gerdy tubercle and the adjacent tibial surface.

It is believed to be an adventitial bursa [those which can develop in adulthood in response to friction] b

Popliteus Recess

The Popliteus Recess or popliteus hiatus is present the posterolateral corner of the knee. It is posterior to the posterior horn lateral meniscus around the popliteus tendon and routinely communicates with the knee and may also communicate with the proximal tibiofibular joint in one tenth of population.

Fibular Collateral- Biceps Femoris

This bursa has an inverted J shape in the axial plane. The curved short arm extends around the anteromedial portion of the distal fibular collateral ligament near the insertion. The larger arm lies along the superficial lateral aspect of the fibular collateral ligament.

References

• Image Credit: Radsource
• Steinbach LS, Stevens KJ. Imaging of Cysts and Bursae About the Knee. Radiologic Clinics of North America. 2013;51:433–54.
• Lee KR, Neff R, Arnett R. Cystic Masses of the Knee: Arthrographic and CT Evaluation. Knee, The. 1987;(February):329–34.