The knee is a central joint for human movement and stability, allowing for actions like walking, running, and bending. Understanding its structures provides insight into its complex function. This article explores the various components that contribute to the knee’s design.
The Major Bones of the Knee
The knee joint is formed by three primary bones: the femur, tibia, and patella. The femur, or thigh bone, is the longest and strongest bone in the body, connecting the hip to the knee. Its rounded lower end, called the femoral condyles, meets the tibia. The tibia, or shin bone, is the larger of the two lower leg bones and bears most of the body’s weight. Its flat upper surface, the tibial plateau, provides a stable platform for the femur.
The patella is a bone embedded within a tendon. It sits at the front of the knee, sliding in a groove on the femur as the knee bends and straightens. This position protects the knee joint and enhances the leverage of the thigh muscles. The fibula, the smaller bone running parallel to the tibia, provides attachment sites for ligaments and muscles around the knee.
Key Supporting Structures
Beyond the bones, soft tissue structures provide stability and enable smooth motion. Ligaments, strong bands of tissue, connect bones and restrict excessive movement. The knee features four major ligaments:
The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) cross inside the joint to control front-to-back motion.
The medial collateral ligament (MCL) and lateral collateral ligament (LCL) are on the sides, preventing excessive sideways movement.
Two cartilage pads, called menisci, rest on the top of the tibia. These medial and lateral menisci act as shock absorbers, distributing weight evenly across the joint and enhancing stability. Articular cartilage covers the ends of the bones within the joint. This smooth, slippery tissue minimizes friction and facilitates gliding during movement.
Tendons connect muscles to bones, enabling movement. The quadriceps tendon attaches the thigh muscles to the top of the patella, and the patellar tendon (also called the patellar ligament) extends from the bottom of the patella to the tibia. Together, these tendons work to straighten the leg.
Fluid-filled sacs called bursae are around the knee. They reduce friction between bones, tendons, and muscles, allowing for smooth gliding during motion.
Soft Tissues Behind the Knee
The region behind the knee is the popliteal fossa. This area contains major blood vessels that supply the lower leg. The popliteal artery carries oxygen-rich blood to the knee, lower leg, and foot. Running alongside it, the popliteal vein collects deoxygenated blood from these areas and returns it towards the heart.
Nerves responsible for sensation and muscle control in the lower leg traverse this space. The tibial nerve and common fibular nerve are found here. The tibial nerve supplies muscles in the calf and foot, while the common fibular nerve innervates muscles on the front and side of the lower leg.
The boundaries of the popliteal fossa are formed by several muscles. The hamstring muscles form the upper borders. At the lower boundaries, the two heads of the gastrocnemius muscle, which make up the bulk of the calf, are present. The popliteus muscle assists in unlocking the knee from a fully extended position. These muscles collectively contribute to knee flexion and overall leg movement.