There are approximately 14 knee bursa. Bursa are small fluid filled sacs found all over the body. They reduce the friction between 2 surfaces, usually muscle and bone, 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 inflammed, or it dries out so it no longer works properly.
There are 5 main bursa that work to protect the knee. They are:
This is found infront 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.
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
This is found underneath the kneecap. Inflammation 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.
This is found on the inner side of the knee approx 2 inches below the joint with the sartorius, gracilis and semitendonosis muscles. Inflammation of Pes Anserine is especially common in runners.
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 semitendonosus 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 and/or weakness which causes excessive friction on the bursa. The knee bursa can become either
1) Inflamed - ie swollen known as
2) Dried out - ie they loose the fluid inside them.
This results in more friction on the bone and muscles/tendons leading to bursa knee pain. Usually a combination of exercises, medication and/or injections helps them to recover. Visit the Bursitis of the knee section to find out more about prevention and bursitis treatment.