The tibia, patella and femur are joined together at the knee to form a hinge joint, according to WebMD. The bones are held in place at the knee with an elaborate system of ligaments, and they are buffered from each other by thick pads of cartilage.
A the knee, the femur drops to press against the top of the tibia, according to WebMD. The front of the knee joint is protected by a thick, almost circular bone called the patella, or kneecap. Posterior to the joint, and somewhat exterior to it, the top of the fibula, the small bone of the lower leg, rests against the top of the tibia. The bottom of the femur is cushioned by a thick pad of cartilage, and the top of the tibia is protected by thick layers of connective tissue called the medial and lateral meniscus. Between these two pads, two ligaments help bind the knee together and keep it from twisting or deforming. These are the anterior and posterior cruciate ligaments, and they are frequent sites of injury. Two large ligaments, the medial and lateral collateral ligaments, drop down from the thigh muscles to attach to the tibia and provide additional bracing to keep the bones in place.