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Around the knee there are several sacs that contain a slippery substance. The medical term for then is “bursae“. When they get  inflammation, the physician diagnoses them as “bursitis”. Normally a bursa does not hurt, but bursitis does hurt a lot. There is an accumulation of fluid in the bursa due to inflammation, which is painful. Repetitive movement or kneeling can cause such a bursitis. The carpenter’s knee (orinfrapatellar bursitis; thanks to for the image) is common in carpenters, tile setters or other workers who do a lot of kneeling.

Prepatellar bursitis 

Injury of the prepatellar bursa can happen with a blow to the patella and is another form of bursitis. As this bursa lies just underneath the skin surface, the redness really shows and often patient and physician alike think it might be a skin infection, when in reality it is an inflammatory condition originating from the prepatellar bursa. Protection with an elastic bandage and avoiding further irritation is often what heals these in a 3 to 4 week period. Anserine bursitis is a condition where a bursa, which lies underneath the pes anserinus, a common tendon at the medial aspect of the knee below the knee cap, becomes tender and inflamed. This condition occurs in middle aged and elderly patients. The diagnosis is made clinically and the therapy is injection of a small amount of corticosteroid injection into the affected area (Ref. 2, p.17).

Baker’s cyst

A Baker’s cyst is a cyst in the knee that was there prior to the painful swelling and was part of a degenerative process of the knee joint. When the knee cyst (medically termed “popliteal cyst”) gets closed off and inflamed, there can suddenly be a lot of fluid collection in this structure to the point where it makes movement in the affected knee almost impossible. A period of immobilization with treatment using ANSAIDs or COX-2 inhibitors will usually lead to an uneventful recovery. At other times the condition resolves itself by a spontaneous rupture of the cyst, at which time there is an acute pain in the calf area where the fluid is discharged to. The physician will want to rule out a deep vein thrombosis by doing a doppler ultrasound study of the affected lower extremity.


1. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 157.

2. ABC of rheumatology, second edition, edited by Michael L. Snaith , M.D., BMJ Books, 1999. Chapter 4.

3. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 270.

4. Wheeless’ Textbook of Orthopaedics:

5. Goldman: Cecil Textbook of Medicine, 21st ed.(©2000)W.B.Saunders

6. Ferri: Ferri’s Clinical Advisor: Instant Diagnosis and Treatment, 2004 ed., Copyright © 2004 Mosby, Inc.

7. Rakel: Conn’s Current Therapy 2004, 56th ed., Copyright © 2004 Elsevier

8. Suzanne Somers: “Breakthrough” Eight Steps to Wellness– Life-altering Secrets from Today’s Cutting-edge Doctors”, Crown Publishers, 2008

Last modified: June 22, 2019

This outline is only a teaching aid to patients and should stimulate you to ask the right questions when seeing your doctor. However, the responsibility of treatment stays in the hands of your doctor and you.