Knee Bursa

Written By: Chloe Wilson, BSc(Hons) Physiotherapy
Reviewed by: KPE Medical Review Board

Knee bursa are small fluid filled sacs which contain synovial fluid. 

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.

1. Prepatellar Bursa

The prepatellar knee bursa is found directly in front of the kneecap, just underneath the skin. It provides protection and cushioning for the kneecap

Repetitive or prolonged, forwards kneeling places a great deal of pressure and friction on the prepatellar knee bursa which can lead to inflammation.

Inflammation here is known as prepatellar bursitis, or Housemaids Knee. It commonly affected people who spend lots of time kneeling and today is more common in trades such as roofers and carpet fitters than housewives!

2. Infrapatellar Bursa

There are actually two infrapatellar knee bursa, known as the deep and superficial infrapatellar bursa.

They are both found just below the kneecap protecting the patellar tendon and the tibial tuberosity, a bony prominence where the patellar tendon attaches to the tibia.

Inflammation of either of these knee bursa is known as infrapatellar bursitis, or Clergyman's Knee. These knee bursa also tend to cause problems for people who kneel lots, but is usually caused by more erect kneeling than with prepatellar bursitis - visit the infrapatellar bursitis section to find out more.

4. Semimembranosus Bursa

The semimembranosus bursa is found at the back of the knee. It sits between one of the hamstring muscles (semimembranosus) and the medial head of one of the calf muscles (gastrocnemius).

Inflammation of this knee bursa is known as semimembranosus bursitis, or, more commonly, a Bakers Cyst, which can be extremely painful.

A Bakers cyst usually develops when by excess fluid in the knee, usually from an injury or arthritis, leaks back into the bursa causing it to swell. A lump forms behind the knee, like a squashy orange. 

Problems usually develop in the knee bursa when there is muscle tightness or weakness which causes excessive friction on the bursa and can lead to knee bursitis.

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 underlying bone and the muscles/tendons leading to bursa knee pain. Usually a combination of strengthening and stretching exercises, medication and injections helps the knee bursa 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.