The femur or thigh bone is the biggest bone in the body. It connects the pelvis to the leg via the hip and knee joints. The femur is one of the strongest bones in the body.
The femur forms the top of the knee. At the knee joint there are two rounded prominences called condyles. The one toward the inner thigh is the medial femoral condyle and the one toward the outer thigh is the lateral femoral condyle. The “valley” between the two condyles is called the trochlear groove. All of these are covered by articular or joint lining cartilage.
The shape of the condyles allows the knee to lock into place when it is straight but also to rotate slightly when it is bent. The patella or knee cap articulates with the trochlear forming the patellofemoral joint.
The femur is joined to the tibia and fibula by a series of ligaments including the collateral (medial and lateral) and cruciate (anterior and posterior) ligaments. These ligaments govern the directional mobility of the knee and limit excessive stretching and rotation. In a standing position, the femur bone extends at a very slight angle with the head slightly deeper than the far end. This stance allows the femur and knee joint to absorb the majority of the body’s weight without putting undue stress on the bones of the lower leg and feet.
Flexion (bending) & extension (straightening) of knee joint are not simple hinge movements but take place through a constantly changing centre of rotation (polycentric rotation).
As the knee is extended, the femoral condyles roll on the tibial condyles & menisci as well as sliding to move in the correct way. The ligaments of the knee control this movement and are essential for normal functioning of the knee.
The exact ratio of rolling to gluiding differs between individuals and does not remain constant throughout the range of motion of the knee. The joint lining cartilage tends to wear out differently in different disease processes and can be damaged as a result of a sporting injury or from age related degeneration of the knee.