Anatomy   [back to the Category]

The Knee   [read the french version]

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The knee joint is an important musculo-ligamentary crossroads.
It joins the femur to the tibia and the femur to the patella.
The lower extremity of the femur is joined, on the one hand, by its anterior section - trochlea - to the patella and, on the other hand, by its posterior section - condyle - to the upper extremity of the tibia.
The knee joint is, therefore, composed of the femoral trochlea, the femoral condyles, the upper extremity of the tibia, the patella, the medial and lateral menisci - the menisci are the semilunar fibrocartilages that provide a better articular congruence between the femoral condyles and the upper extremity of the tibia -, an articular capsule and ligaments.
The main ligaments are the:
- lateral and medial patellar retinaculum which go from the patella to the femoral condyles,
- collateral ligaments: the tibial collateral ligament which extends from the medial femoral condyle to the tibia and the fibular collateral ligament which extends from the lateral femoral condyle to the fibula,
- cruciate ligaments: anterior and posterior which cross over in the intercondylar area between the femur and the tibia.

The knee joint has two axes-of-freedom: flexion - extension, and internal rotation - external rotation. It is the centre of a muscular quadrant with the quadriceps at the front.

Periarticular muscles

The quadriceps is on the front of the thigh. It is attached by its patellar tendon to the patella and the anterior section of the tibia known as the tuberosity of the tibia; the quadriceps femoris acts as extensor for the knee and, by its anterior part known as rectus femoris, acts as flexor for the hip.

The sartorius, gracilis and semitendineus muscles are on the inner side of the thigh. Their lower insertions are to be found on the medial side of the upper extremity of the tibia. They stabilize the medial compartment of the knee and participate in the flexion of the knee. The sartorius muscle also participates in flexion of the hip.

The tensor fasciae latae (T.F.L.) and the biceps are on the lateral side of the thigh. The T.F.L. form active defence for the lateral compartment of the knee. These muscles act as external rotator for the tibia and flexor for the hip. Their lower insertions are to be found on the lateral edge of the patella and on Gerdy's tubercle, located on the lateral section of the upper extremity of the tibia. The lower insertions of the biceps femoris are to be found on the upper extremity of the fibula and on the lateral side of the upper extremity of the tibia. The biceps femoris acts as external rotator.

The popliteus, the biceps surae and the semimembranosus are at the back of the knee. The semimembranosus is attached to the postero-medial section of the upper section of the tibia; it acts with the popliteus as internal rotator for the tibia under the femur. The biceps consists of the medial and lateral gemellus muscles which have their upper insertions on the femoral condyles and participate in the locking of the knee.

The tibial knee is, therefore, where internal and external rotation take place. Its stability is controlled by the collateral and the cruciate ligaments and by the periarticular muscles.
As for the patellar knee, it is part of the extensor apparatus, together with the quadriceps, the quadriceps' tendon, the patella, the patellar tendon and the tuberosity of the tibia.