Structures of the Knee Joint
The knee joint is formed by the thighbone, or femur, and the tibia, the larger of the two lower leg bones. The fibula, the smaller of the lower leg bones, fits into a depression of the tibia. The knee joint permits both a hinge-like motion between the upper and lower leg and a slight side-to-side motion.
The kneecap, called the patella, is not joined directly to any other of the bones, but rather it is held in place by muscles and ligaments. The quadriceps muscles extend from the hip along the front of the femur to the knee. The hamstring muscles extend from the hip along the back of the femur to the knee.
The muscles are connected to the bones of the knee by tough, cord-like tissues, called tendons.
The quadriceps tendon connects the quadriceps to the patella. The patellar tendon connects the patella to the tibia. Additional strength is provided to the knee joint by the ligaments which connect the bones from front to back and side to side.
The cruciate ligaments (anterior and posterior) are located along the front and back inside surfaces of the knee, while the collateral ligaments (medial and lateral) are located on the outside surfaces of the knee.
A synovial capsule surrounds the knee joint, contributing to the connection between the femur and the tibia. Synovial fluid, which is secreted into the capsule, nourishes the joint surfaces and reduces friction and stress during joint movement.
Two crescent-shaped pads or discs of tough connective tissue, called menisci, serve to cushion the bony surfaces of the tibia and femur and help to absorb the shock produced by joint movement and weight-bearing.