The knee joint is the junction of three bones:
- the thighbone, or femur
- the shin bone, or tibia, the larger front bone of your calf
- the kneecap, or patella.
At its lower end, the femur divides into two rounded knobs called condyles that support the body's weight on the bone of the lower leg, the tibia. The top of the tibia is rather flat with a middle bump. Unlike the beautiful fit between bones found in many other joints, the knee's mismatch in shape allows for complex movement but is quite unstable, like two doorknobs balanced on an uneven plate. Stability is supplied by strong ligaments on the inside and outside of the joints.
The patella is a small, flat bone that floats in front of the knee joint. The patella moves within a groove between the two condyles of the femur. Your patella protects other knee structures and applies leverage to help straighten the joint.