The Knee Joint
The knee joint, a complex structure, enables human movement like walking, running, and jumping. It bears weight and endures repetitive motion, making it susceptible to wear. Its design, including bones, ligaments, tendons, and cartilage, relies on protective mechanisms for smooth function. These elements reduce friction and cushion the joint during its extensive range of motion.
Understanding Bursae
A bursa is a small, fluid-filled sac lined with a synovial membrane, like a joint capsule lining. These sacs are located throughout the body where tissues might rub. The primary function of a bursa is to reduce friction between bones, tendons, muscles, and skin. They provide a smooth, gliding surface, facilitating movement. Bursae are found in numerous joints, especially in frequently moving, high-pressure joints.
Key Knee Bursae
The knee joint contains several bursae; typically around 11 are identified, though the exact number varies. These sacs are positioned around the joint to protect specific areas. Each bursa serves a distinct purpose in knee movement.
The prepatellar bursa is on the front of the kneecap, between skin and patella. This bursa protects the kneecap from impact and reduces friction during movement. Below the kneecap, two infrapatellar bursae exist: the superficial infrapatellar bursa lies between skin and patellar tendon; the deep bursa is between the patellar tendon and tibia. Both cushion the patellar tendon, allowing smooth gliding.
On the inner side of the knee, about two inches below the joint line, lies the pes anserine bursa. It lies beneath the sartorius, gracilis, and semitendinosus tendons where they attach to the tibia. It minimizes friction between these hamstring tendons and bone. The semimembranosus bursa is behind the knee, between the semimembranosus tendon and the medial head of the gastrocnemius. It reduces friction in the posterior knee.
Common Bursa Conditions
Bursitis is the most common condition affecting bursae, characterized by inflammation. Inflamed bursae can impair normal knee function. Symptoms include localized pain, tenderness, and swelling. Inflammation can also restrict knee range of motion, making it difficult to bend or straighten the leg.
Bursitis often develops from repetitive motion, prolonged pressure, or direct trauma. For example, prolonged kneeling can irritate the prepatellar bursa, causing “housemaid’s knee.” Overuse from activities like running or cycling can also inflame other knee bursae. In some instances, bacterial infection can cause septic bursitis, requiring prompt medical attention. Initial management involves rest, ice, and leg elevation; consult a healthcare professional for accurate diagnosis and treatment.