膝関節

The knee joint consists of three articulations formed by three bones: the femur, tibia, and patella. Two tibiofemoral joints connect the femur and tibia, while one patellofemoral joint connects the patella and femur. The femur's medial and lateral condyles roll and glide over the tibial plateau at the tibiofemoral joints, enabling smooth hinge movement. The patella glides along the patellar groove in the patellofemoral joint.

The anterior and posterior cruciate ligaments cross each other within the articular capsule between the femur's condyles. The anterior cruciate ligament prevents hyperextension of the knee, while the posterior cruciate ligament supports the knee during weight bearing. Together, these ligaments provide rotational stability and limit front-to-back movement, protecting the joint from excessive motion.

The lateral and medial menisci are crescent-shaped fibrocartilage pads positioned between the femur and tibia. They absorb shock, distribute weight evenly across the joint, and cushion the articulating bones. These structures enable smooth movement between the femur and tibia while protecting the joint from impact during weight-bearing activities.

Bursae are thin connective tissue sacs filled with lubricating liquid that prevent friction between bones and overlying muscle tendons or skin. The suprapatellar bursa separates the quadriceps tendon from the distal femur above the knee, while the prepatellar bursa allows skin to move smoothly over the patella. These structures reduce wear and enable comfortable joint movement.

The medial and lateral collateral ligaments are positioned outside the articular capsule on either side of the knee. They resist excessive side-to-side movement of the femur at the knee joint, preventing lateral instability. Together with the cruciate ligaments and other supporting structures, they maintain the knee's alignment during movement and weight bearing.

The knee is a synovial joint because it has a thin articular capsule enclosing a joint cavity filled with lubricating fluid. It functions as a hinge joint because the tibiofemoral articulations allow primarily flexion and extension movements, with slight rotation. This structural classification reflects both its anatomical features and its functional movement patterns.

The patella covers the anterior surface of the knee joint and glides along the intercondylar or patellar groove of the femur in the patellofemoral joint. This plane joint allows the patella to move smoothly over the femur during knee flexion and extension. The patella also protects the underlying joint structures and improves the mechanical efficiency of the quadriceps muscle.