A bursa is a small, thin sac filled with synovial fluid, a natural lubricant found in joints. These sacs function as cushions between tissues. The knee joint is surrounded by numerous bursae that are essential for smooth, pain-free movement.
Identifying the Knee’s Major Bursae
The knee contains up to a dozen bursae, but four are most commonly involved in injury and inflammation due to their superficial positioning. The prepatellar bursa sits directly in front of the kneecap (patella), positioned between the skin and the bone. Because of this location, it is highly susceptible to irritation from direct pressure, such as prolonged kneeling.
Located just below the kneecap are the infrapatellar bursae, separated into two distinct sacs: superficial and deep. The superficial bursa is situated between the skin and the patellar tendon. The deep bursa lies between the patellar tendon and the shinbone (tibia). These sacs absorb strain from activities like jumping and running.
A fourth significant bursa is the pes anserine bursa, found on the inner side of the knee, slightly below the joint line. This bursa provides cushioning between the shinbone and the conjoined tendons of three hamstring muscles (sartorius, gracilis, and semitendinosus). Irritation here is often associated with runners or individuals with tight hamstrings.
How Bursae Protect the Joint
The purpose of a bursa is to reduce friction between moving anatomical structures. Each sac contains lubricating synovial fluid, which allows tissues to glide effortlessly over one another. Without this fluid-filled cushion, the movement of tendons, muscles, and skin across bony prominences would result in significant wear and tear.
When the knee bends and straightens, the bursae compress and change shape to accommodate the joint’s motion. They act as pressure distributors, preventing tendons from snapping against bone and protecting the skin from abrasive contact during repetitive activities. This mechanism helps maintain the integrity of the surrounding soft tissues, allowing for a full range of motion.
Understanding Knee Bursitis
Bursitis is the inflammation and swelling of a bursa, causing it to enlarge and become painful. This condition occurs when the thin bursal lining becomes irritated, leading to an overproduction of fluid within the sac. The most common causes are acute trauma from a direct blow or chronic, repetitive pressure, such as frequently kneeling on hard surfaces.
Knee bursitis is categorized into two types: aseptic and septic. Aseptic bursitis is non-infectious, stemming from overuse, injury, or underlying conditions like gout, rheumatoid arthritis, or osteoarthritis. Symptoms include localized swelling, tenderness, and pain that worsens with movement or direct pressure.
Septic bursitis is a concerning condition where the bursa becomes infected with bacteria, usually Staphylococcus entering through a break in the skin. This form presents with intense symptoms, including rapid onset of swelling, warmth, and redness over the affected area. A high fever and a general feeling of being unwell indicate an infection, requiring immediate medical evaluation. The prepatellar bursa is susceptible to septic infection due to its superficial location.
Treatment and Recovery Strategies
For most cases of aseptic bursitis, conservative home treatments are effective for managing symptoms. The standard approach involves resting the knee and avoiding activities that aggravate the bursa, such as kneeling or extensive bending. Applying ice to the swollen area for 15 to 20 minutes several times a day helps reduce inflammation and pain.
Using a compression wrap or sleeve can help control swelling. Elevating the leg above heart level encourages the drainage of excess fluid. Over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen, may be used for short-term pain and inflammation relief. Most acute cases improve within a couple of weeks with consistent self-care.
If symptoms persist, a doctor may recommend a corticosteroid injection directly into the bursa to suppress inflammation. For significant fluid buildup or suspected infection, a procedure called aspiration may be performed using a needle to drain the excess fluid. If fluid analysis confirms septic bursitis, a course of antibiotics is prescribed to clear the bacterial infection. Surgical removal of the bursa is a rare measure, reserved for chronic cases that fail to respond to other treatments or for persistent infections.