Knee Anatomy in General
The knee is a confluence of three bones, two most important of whom are the tibia or the shin bone, and the femur or the thigh bone. The patella or the knee cap sits in front of these two bones. The patella acts as a lever for the quadriceps muscle. The knee joint is a synovial joint. Synovial joints are enclosed by a ligament capsule and contain a fluid, called synovial fluid, that lubricates the joint.
The end of the femur joins the top of the tibia to create the knee joint. Two round knobs called femoral condyles are found on the end of the femur. These condyles rest on the top surface of the tibia. This surface is called the tibial plateau. The outside half (farthest away from the other knee) is called the lateral tibial plateau, and the inside half (closest to the other knee) is called the medial tibial plateau. The patella glides through a special groove formed by the two femoral condyles called the patellofemoral groove.
Articular cartilage is the material that covers the ends of the bones of any joint. This material is about one-quarter of an inch thick in most large joints. It is white and shiny with a rubbery consistency. Articular cartilage is a slippery substance that allows the surfaces to slide against one another without damage to either surface. The function of articular cartilage is to absorb shock and provide an extremely smooth surface to facilitate motion. We have articular cartilage essentially everywhere that two bony surfaces move against one another, or articulate. In the knee, articular cartilage covers the ends of the femur, the top of the tibia, and the back of the patella.
Ligaments and Tendons
Ligaments are tough bands of tissue that connect the ends of bones together. Two important ligaments are found on either side of the knee Ligaments are tough bands of tissue that connect the ends of bones together. Two important ligaments are found on either side of the knee joint. They are the medial collateral ligament (MCL) and the lateral collateral ligament (LCL).
Inside the knee joint, two other important ligaments stretch between the femur and the tibia: the anterior cruciate ligament (ACL) in front, and the posterior cruciate ligament (PCL) in back. The MCL and LCL prevent the knee from moving too far in the side-to-side direction. The ACL and PCL control the front-to-back motion of the knee joint.
The ACL keeps the tibia from sliding too far forward in relation to the femur. The PCL keeps the tibia from sliding too far backward in relation to the femur. Working together, the two cruciate ligaments control the back-and-forth motion of the knee. The ligaments, all taken together, are the most important structures controlling stability of the knee.
Two special types of ligaments called menisci sit between the femur and the tibia. These structures are sometimes referred to as the cartilage of the knee, but the menisci differ from the articular cartilage that covers the surface of the joint.
The two menisci of the knee are important for two reasons: (1) they work like a gasket to spread the force from the weight of the body over a larger area, and (2) they help the ligaments with stability of the knee.
Imagine the knee as a ball resting on a flat plate. The ball is the end of the thighbone as it enters the joint, and the plate is the top of the shinbone. The menisci actually wrap around the round end of the upper bone to fill the space between it and the flat shinbone. The menisci act like a gasket, helping to distribute the weight from the femur to the tibia.
Without the menisci, any weight on the femur will be concentrated to one point on the tibia. But with the menisci, weight is spread out across the tibial surface.
Dr. Santosh Kumar
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