The knee joint is the largest and one of the most complex joints in the body. It is predominantly a hinge joint and joins the thigh with the lower leg.
It is formed from the articulation between the condyles of the femur and those of the tibia, with the patella at the front. Usually, stability and mobility are incompatible functions for a joint, with the majority of joints sacrificing one for the other. However, at the knee both functions are secured by the interaction of ligaments and muscles, and complex gliding and rolling movements at the articular surfaces.
The knee joint plays an important role in locomotion. With powerful muscles, it acts with the ankle joint as a strong forward propeller of the body. It receives and absorbs vigorous stresses which the body’s movement creates.
Each knee has to support the weight of the body whilst allowing for movement. During walking, four times the body’s weight will be transferred through the knee.
Most commonly we refer to the tibiofemoral joint as the knee joint. The anatomy of the knee is shown below:
Because the top of the thigh bone (femur) overhangs the shaft, the anatomical axis of the femur and tibia do not coincide, but form an outward opening angle. However the hip, knee and ankle all lie in a straight line. These two axis coincide to create a slight angle. This angle is larger the wider the pelvis, as in females.
With age, pathological conditions or trauma, this angle may be increased or decreased to give the appearance of ‘bowlegs’ or ‘knock knees’. This is displayed in the picture below. This angle can have a significant impact on the biomechanical function of the joint.
The menisci are so called because of their ‘moon’ shape. They are found between the articular surfaces of the knee joint (femur and tibia). There are two, medial and lateral, the medial being the larger of the two. The functions of the menisci are to provide joint stability and act as a shock absorber between the two joint surfaces.
In the second part of this blog I will go on to discuss the important role the ligaments play in supporting the knee.