Knee Kinesiography

Knee : Understanding Anatomy and Function

A large percentage of medical consultations are related to knee pain. This can be explained because of the role and complex anatomy of the knee. The knee plays a vital role in shock absorption and leg stability. It is both sturdy and mobile during our daily activities but remains vulnerable to injury.

The knee connects three bones: the thigh bone (femur), the leg bone (tibia) and finally, the patella. To ensure its function, the knee uniquely moves along 3 axes of rotation: flexion-extension, adduction-abduction and internal-external rotation.

The function of the muscles (images below) is both to stabilize and move the joint. The quadriceps represent the muscles at the front of the thigh and are responsible for the extension of the knee while the hamstrings are the muscles at the back of the thigh that are responsible for flexion of the knee. The muscles are attached to the bones via the tendons. These structures are resistant but remain susceptible to injury during repetitive movements.

The ligaments (green in the picture below) are resistant connective tissues that connect the bones together. They therefore limit slippage and excessive movement between bones. The knee has four main ligaments: the anterior cruciate ligament (ACL), the posterior cruciate ligament and two collateral ligaments (internal and external).

The menisci (pink in the picture below) act as cushions and shock absorbers between the femur and the shin. They improve the congruence between the bones to increase the stability of the knee and they allow to distribute the loads on the articulation in an adequate way.

Finally, to ensure good sliding between the bones, the articular surfaces (femur and tibia extremities) are covered with cartilage. It is an elastic and smooth layer that ensures the fluidity of movement and an adequate distribution of loads on the knee.

Because of its irregular bone geometry (i.e. not a smooth fit), knee stability in these 3 movements depends on the proper functioning of surrounding structures such as muscles, ligaments, and soft tissues.

An injury to one of these structures will affect the stability or mobility of the knee and conversely a deficit in the mobility of the knee could cause significant pain to these structures. Our next column will deal with a pathology often diagnosed in runners, the patellofemoral syndrome. We will explain the different symptoms, the links with the biomechanical deficits of the knee as well as the various possible treatments.