The composition of the knee joint.

- Mar 27, 2020-

The composition of the knee joint.


The knee joint is the largest and most complex joint in the body. It consists of tibia and femoral joints and patellofemoral joints. It bears the main weight of the body, maintains good flexibility, and is vulnerable to injury. The main activities of the knee joint are flexion, straightening, and internal and external rotation of the lower leg.


Knee joint composition: femoral condyle, tibial plateau, sacrum, synovium, bursa, joint capsule, ligament, meniscus, muscle.


 In the knee joint, the flexion is often accompanied by a small and significant rotation, but it has special stability due to the strong bursa, ligaments and muscles around the joint. The ligaments around the knee joint are only loaded under tension, and they passively support the joint. The muscles around the knee joint also actively support the joint when loaded under tension. The bones around the knee joint support and counteract pressure loads. Therefore, the functional stability of the knee joint comes from the passive contraction of the ligaments, the joint geometry, the active exertion of the muscles, and the load-bearing effect of the bones.

(1) Patella

   The sacrum provides two important biomechanical functions to the knee: it helps the knee to straighten by extending the arm of the quadriceps muscle throughout the range of motion; and it improves the pressure distribution on the femur by increasing the contact surface between the sacrum and the femur.

(2) Articular cartilage

   Patellofemoral joint cartilage is the thickest cartilage in the human body. The maximum thickness can reach 7㎜. The patellar-femoral joint cartilage is not uniform in thickness, and the thickest part of the cartilage is located at the epiphysis. 60% are located on the lateral articular surface of the sacrum, and about 20% are distributed on the medial side. The characteristics of articular surface cartilage thickness help to increase the suitability of patellofemoral articular surface.


(1) Structure and function of knee joint meniscus

①The meniscus is a meniscus-shaped fibrocartilage disc cushioned between the knee joint femur and tibia. The edges of the meniscus are thick, the middle is thin, the top is depressed, and the bottom is flat. They are called inner and outer menisci. The medial meniscus is larger, with a "C" shape, the front feet are narrow and thin, and the rear angle is wider and slightly thicker. The lateral meniscus is smaller, similar to an "O" shape, and the distance between the front and back angle It is very close, and the lateral margin is also connected to the joint capsule.

② Function: A. Conductive load: When the knee joint is reduced, the contact surfaces do not match, which increases the contact area and uniform pressure distribution. B. Maintain stability: Deepen the tibial condylar articular surface, and always maximize the contact area of the knee joint during forward and backward movement. C. Reduce shock: play a certain buffer function, can absorb a certain load shock


Knee ligament

(1) There are extracapsular ligaments and intracapsular ligaments. That is: patellar ligament, fibular collateral ligment, tibial collateral ligament, oblique popliteal ligament, and cruciate ligaments of knee.

(2) Many ligaments are attached to ensure the stability of knee joint movement.

(3) The collateral ligament is tightened when the knee joint is fully straightened, and the joint is only vulnerable when it is in this state. When the knee joint is abducted violently, it can cause the tibial collateral ligament to be partially or completely torn, and excessive adduction force can cause the peroneal collateral ligament to be damaged.

(4) In severe adduction or abduction injuries, the cruciate ligament can be torn with the collateral ligament. The anterior cruciate ligament can be torn when the knee is overextended or the tibia is dislocated forward. The posterior cruciate ligament was torn during posterior dislocation. If both cruciate ligaments are torn, the knee joint will move abnormally forward and backward; if the range of forward movement is only increased, it indicates that the anterior cruciate ligament is broken or loose. If the range of backward movement is increased, then Indicates a posterior cruciate ligament rupture or relaxation.


Knee pain is a common problem in the clinic. Common knee osteoarthritis, meniscus injury, medial / lateral collateral ligament injury, anterior cruciate ligament injury, patellar softening disease, bursitis, etc. are common. The knee joint is a weighing joint of the human body. The surrounding muscles have little fat content and are mainly wrapped by ligaments. The knee joint is stably supported by ligaments and muscles. However, the main manifestation of knee injury is ligament injury. In the treatment of knee joint injuries, after professional physical examination and imaging data, local anti-inflammatory and analgesic are generally applied to the injured area. Patients with severe injuries often do not have good results. Because of the weight-bearing and flexible role of the knee joint, as well as the local ligaments, the local ligament tension is too high in daily activities, and the poor blood supply of the ligaments further aggravates the difficulty of recovery after injury.