Knee bursa are small fluid filled sacs which contain synovial fluid. They sit between 2 surfaces, usually muscle and bone, to reduce friction, a bit like ball bearings. This allows everything to move smoothly preventing inflammation.
Bursae are found all over the body and there are approximately fourteen knee bursa.
Sometimes the 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.
We will start by looking at the five main bursa that work to protect the knee. They are:
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.
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.
This is found above the kneecap underneath the quadriceps tendon at the bottom of the thigh preventing friction from the femur.
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.
This is found at the back of the knee between the semimembranosus muscle
(one of the hamstring muscles) and the medial head of gastrocnemius
(one of the calf muscles). Inflammation of this is known as a
Bakers Cyst which often forms a small lump like a squashy orange. It often develops with knee arthritis.
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
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.
To find out more about what can go wrong with the knee bursa, 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.