A bursa is a small, fluid-filled sac containing lubricating synovial fluid. It functions as a cushion between bones, tendons, muscles, and skin, reducing friction during movement. The knee joint contains several bursae, which are important for smooth motion and protecting its structures.
Location and Purpose of Knee Bursae
The knee joint is surrounded by numerous bursae, each strategically positioned to minimize friction and absorb pressure. Among the most prominent are the prepatellar, infrapatellar, and anserine bursae. These fluid-filled sacs allow tendons and muscles to glide smoothly over bony surfaces as the knee bends and straightens.
The prepatellar bursa is located directly in front of the kneecap (patella), between the patella and the overlying skin. Its primary function is to protect the kneecap from friction, particularly during activities that involve kneeling. This bursa ensures the skin can move freely over the patella, preventing irritation.
Below the kneecap, the infrapatellar bursae are found. There are typically two main infrapatellar bursae: a superficial one located between the patellar ligament and the skin, and a deep one situated between the patellar ligament and the upper part of the tibia. The deep infrapatellar bursa specifically helps minimize friction between the patellar ligament and the shin bone during knee movement.
On the inner side of the knee, approximately two inches below the kneecap, lies the anserine bursa, also known as the pes anserine bursa. This bursa is positioned between the shin bone (tibia) and the conjoined tendons of three hamstring muscles: the sartorius, gracilis, and semitendinosus. Its role is to reduce friction as these tendons slide over the tibia, especially during knee flexion.
Understanding Knee Bursitis
Knee bursitis occurs when one or more of these small, fluid-filled sacs in the knee become inflamed. This inflammation leads to an increase in the fluid within the bursa, causing it to expand and put pressure on surrounding knee joint structures.
The condition can affect any of the bursae around the knee, though it most commonly impacts those located over the kneecap or on the inner side of the knee. Bursitis results from the lining of the bursa secreting more fluid than usual, leading to swelling and pain.
Common Causes of Knee Bursitis
Knee bursitis can arise from various factors, often involving repetitive stress or direct trauma to the knee. Frequent or prolonged kneeling, especially on hard surfaces, is a common cause, leading to conditions colloquially known as “housemaid’s knee” for prepatellar bursitis. Occupations like carpentry or gardening often involve such pressure.
A direct blow or fall onto the knee can also cause sudden inflammation of a bursa, leading to rapid swelling and discomfort. Overuse of the knee or strenuous activities, particularly those involving repetitive bending or jumping, can similarly irritate the bursae.
Underlying medical conditions can also contribute to the development of knee bursitis. These include inflammatory conditions like rheumatoid arthritis or gout, where crystals can accumulate in the bursa. A bacterial infection can cause septic bursitis, which typically occurs when bacteria enter the bursa through a break in the skin, such as a cut or scrape. Septic bursitis is a serious condition that requires prompt medical attention.
Recognizing and Managing Knee Bursitis
Recognizing knee bursitis involves observing specific symptoms. Common signs include pain around the knee, which often worsens with movement or direct pressure. Swelling is typically visible and palpable, feeling squishy when pressed. The skin over the inflamed bursa may also appear red and feel warm to the touch. Movement of the knee might also be limited.
Initial management often involves self-care strategies aimed at reducing pain and inflammation. Rest is important, meaning avoiding activities that aggravate the knee and minimizing pressure on the joint. Applying ice to the affected area regularly can help reduce swelling and discomfort. Compression and elevating the leg can further assist in reducing swelling. Over-the-counter pain relievers can also help manage the pain.
Seek professional medical attention if symptoms do not improve after a week or two of self-care. A doctor should also be consulted for:
Severe pain, a high fever, or chills.
Skin over the bursa that is very red, warm, or shows signs of infection, as these could indicate septic bursitis.
Inability to move the knee.
A significant change in skin color around the joint.