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Knee joint

Synonym: articulatio genus
German: Kniegelenk

1 Definition

The knee is the articulated connection between the femur (femur), tibia (tibia) and patella (patella).

2 Anatomy

2.1 Structure of the joint

The knee joint is made up of two parts. The articulation of the femur and tibia is termed femoro-tibial joint (articulatio femorotibialis). The connection between the femur and patella is called femoropatellar joint (articulatio femoropatellaris).

The cartilaginous articular surfaces of the femur and tibia are called condyles. The femur additionally has an articular surface (facies patellaris) to the cartilage-covered facies articularis kneecap.

2.2 Menisci

Between the condyles of the thigh and leg bones are the fibrocartilaginous menisci fused in their growth to the joint capsule: the meniscus medialis (medial meniscus) and the lateral meniscus (lateral meniscus). The lateral meniscus is semicircular, the medial meniscus appears sickle-shaped and grown together with the medial lateral ligament, resulting in lower mobility in the bending and extension of the knee, as well as increased susceptibility to injury. The anterior protrusions of both menisci are connected to one another by the ligamentus transverwum genus.

The tasks of the menisci include enlargement of the contact surface between the tibia and femur and well as balancing the incongruity between the condyles.

2.3 Ligaments

The knee joint is secured by complex band-like structures (ligaments).

2.3.1 Lateral ligaments

The lateral ligaments are used to stabilise the knee against varus and valgus stress. Due to tension during extension they also prevent internal and external rotation, so that these actions are only possible in the bent knee position and with untensed ligaments. They include:

2.3.2 Cruciate ligaments

The ligamentum cruciatum anterius (ACL) runs in the joint cavity from posterior, superior and lateral toward anterior, inferior and medial. The ligamentum cruciatum posteriorius (PCL) from top medial to bottom lateral. In internal rotation, the cruciate ligaments wrap around one another, in external rotation they yield from one another. In flexion the cruciate ligaments prevent slippage of the femoral condyles toward the dorsal and/or ventral.

Click and drag to move the 3D model around the page.

2.3.3 Other ligaments

The joint is secured anteriorly by the so called ligamentum patellae tendo continuation of the quadriceps femoris, and by the retinaculum patellae. For stabilisation the lateral lying tractus iliotibialis, and the dorsal lying ligaments ligamentum popliteum obliquum and ligament popliteum arcuatum also contribute here.

For some orthopaedic surgeons the existence of an ligament anterolateral ligaments (ALL) is also postulated in the knee joint. The existence of this ligament is controversial.

2.4 Joint capsule

The wide capsule (capsula articularis) encompasses all joint surfaces of the knee, including the patella. It consists of two layers:

  • membrana fibrosa: the stabilising fibre layer
  • membrana synovialis: which inwardly lines the knee joint synovia In horizontal section it has joint space enclosed by the two membranes with a horseshoe-shaped configuration, whereby the posterior cruciate ligament lies outside the joint capsule.

The joint capsule is most stable on the dorsal side of the knee joint. Laterally it forms a passage point for the musculus popliteus. Distally the capsule is attached at the edges of the tibia condyles and there it is fused with the menisci. Ventrally the joint capsule is firmly fixed to the ligaments of the knee cap (liagamentum patellae).

In the area included in the capsule there is a fatty substance (corpus adiposum infrapatellar), which is used for padding underneath the synovium. It is also called Hoffa fat pad/intrapatellar fat pad and is located between the membrana fibrosa and the synovium (membrana synovialis). In addition, the joint cavity is traversed by mucosal folds (plicae synoviales), which segment its various component regions. They include the plica suprapatellaris (SPP), the plica mediopatellaris (MPP) and the plica infrapatellaris (IPP).

2.5 Bursa

The knee joint is surrounded by numerous bursae (bursae), which can increase in size in the instance of inflammation and can change the appearance of the leg surface. It partly communicates with the joint capsule, and is partially independent of it.

2.6 Arterial supply

The arterial supply of the knee joint occurs via a variety of arteries, which form anastomoses with one another and so from a dense collateral network. These include the following:

2.7 Topography

Ventral to the knee joint - ie on the extensor side - is the regio genus anterior. The corresponding region of the body on the flexor side is the regio genus posterior. One finds the fossa poplitea (knee pit) here. Through this run important blood vessels and nerves, including the arteria poplitea and nervus tibialis. In addition, one finds here some lymph nodes (nodi lymphatici poplitei).

3 Biomechanics

3.1 Femorotibial joint

The Femorotibial joint is a connection between a trochoid joint and hinge joint, which is referred to as rotation angle joint or bicondylar joint. It allows a combination of rolling and sliding movement of the joint bodies involved.

There are four possible movement ranges around the vertical axis and horizontal axis:

3.1.1 Extension (stretching) - flexion (bending)

In the initial phase of bending (up to 25°) the femoral condyles roll. In any instance of more acute bending, the roll movement is largely eliminated, the condyles slide increasingly posteriorly. At maximum flexion, the contact area between the upper and lower leg bones can be found at the rear edge of the lower leg bone.

The menisci move dorsally during flexion whereby the the lateral meniscus travels a longer distance due to its greater mobility.

The active flexion of the flexor muscle cannot exceed 125° on account of active incapacity. By stretching the flexor muscles with additional flexion in the hip, flexion of 140° can be achieved. Due to the effect of pressing together of the dorsal thigh and calf muscles, passive flexion is limited to 160°.

A stretch can be extended out to 0°; passively, an overstretching of 5-10° can be achieved. During extension the menisci move back in a ventral direction, in a neutral zero position they are pushed to the side.

3.1.2 External rotation - internal rotation

In an extension position, rotations are prevented by the lateral ligaments. In the bent joint position the lower leg can be more externally rotated (about 30°), since internal rotation is inhibited by the winding up of the cruciate ligaments (up to 10°). During an external rotation, the lateral meniscus moves forward while the medial meniscus is moved back. With internal rotation, the movements are reversed.

3.2 Femoropatellar joint

In the stretched knee joint, the patella lies on the bursa suprapatellaris, a bursa, and touches the articular surface of the femur only with its lower margin.

During flexion it glides 5-7cm over the femur in a caudal direction, the resulting force is an increasing one and can reach more than six times the body weight. For this reason injuries and degenerations of retropatellar cartilage are among the most common cartilage damage.

4 Clinic observations

4.1 Diseases

The knee is primarily affected by degenerative diseases or injuries (knee trauma). In addition to osteoarthritis, damage to the ligaments (eg cruciate ligament rupture, lateral ligament rupture) or to the menisci (meniscus rupture) is particularly prominent, for example as part of a Unhappy triad.

4.2 Diagnostics

Diagnosis includes, among other things clinical knee examination, as well as imaging (x ray, CT, MRI) and endoscopic procedures (knee arthroscopy). Clinical examinations include verifying the presence of the following signs or conducting the following tests:

4.3 Joint replacement

Like the hip, the knee can also be replaced by total endoprosthesis n (TEP), so-called knee prostheses (knee TEP).

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