Knee Bursa

Knee bursa are small fluid filled sacs which contain synovial fluid. Here we will look at knee bursa anatomy, where they are found, how they are injured and how to treat knee bursitis

Bursa are found all over the body and there are approximately fourteen around the knee. They sit between two surfaces, usually muscle and bone, to reduce friction, a bit like ball bearings. This allows everything to move smoothly preventing inflammation.

Sometimes the knee bursa get damaged, known as bursitis, which can cause pain. This is usually when there is excessive friction over the bursa causing it to either become inflamed, or when it dries out so it no longer works properly.

So lets have a look at knee bursitis anatomy, particularly focusing on the 5 main knee bursa, which are the ones that are most commonly injured. Then we will look at what can go wrong with the bursa.

1) Prepatellar Bursa

This is found in front of the kneecap. Inflammation of this occurs when there is repeated friction over the kneecap, such as with prolonged forward kneeling. This is known as Housemaids Knee but today is more common in trades such as roofers and carpet fitters.

2) Infrapatellar Bursa

There are actually two infrapatellar bursa both found underneath the kneecap protecting the patellar tendon. They are known as the deep and superficial infrapatellar bursa.  Inflammation of these is known as Clergyman's Knee and is usually caused by more erect kneeling than with prepatellar bursitis.

3) Suprapatellar bursa

This is found above the kneecap underneath the quadriceps tendon at the bottom of the thigh preventing friction from the femur.

4) Pes Anserine Bursa

This is found on the inner side of the knee approximately two inches below the joint between the tendons of the sartorius, gracilis and semitendinosis muscles and the medial collateral ligament. Inflammation of Pes Anserine is especially common in runners and swimmers - visit the pes anserine bursitis section to find out more.

5) Semimembranosus Bursa

The semimembranosus bursa is found at the back of the knee. Excess fluid in the knee, usually from an injury or arthritis, can leak back into the bursa causing it to swell. A lump forms behind the knee, like a squashy orange. 

Inflammation of the semimembranosus bursa is known as a Bakers Cyst which can be extremely painful. The bursa sits between the semimembranosus muscle (one of the hamstring muscles) and the medial head of gastrocnemius (one of the calf muscles).   

The other bursa knee locations are:

Anteriorly (front of the knee): pretibial and deep infrapatellar bursa

Medially (inner side): medial gastrocnemius bursa, the bursa between semitendinosus tendon and the head of the tibia and occasionally there is a bursa between the tendons of semimembranosus and semitendinosus

Laterally (outer side): lateral gastrocnemius, fibular, fibulopopliteal and the subpopliteal bursae

Problems usually develop in the bursa when there is muscle tightness or weakness which causes excessive friction on the bursa. The knee bursa can become either:

1) Inflamed: i.e. swollen known as bursitis or
2) Dried out: i.e. they lose the fluid inside them

This results in more friction on the bone and muscles/tendons leading to bursa knee pain. Usually a combination of strengthening and stretching exercises, medication and injections helps them to recover. 

Inflammation and irritation of the knee bursa is a common cause of knee pain. To find out more about what can go wrong, visit the bursitis of the knee section to find out more about prevention and bursitis treatment.

To find out more about this different structures in the knee, including the muscles, ligaments and cartilage, visit the anatomy section.

Alternatively, if you have a problem with your knee and would like help working out what is causing it, visit the knee pain diagnosis section.

Go to Anatomy Guide or Homepage