Knee joint

Nicole Wendler holds a PhD in biology in the field of oncology and immunology. As a medical editor, author and proofreader, she works for various publishers, for whom she presents complex and extensive medical issues in a simple, concise and logical manner.

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The knee joint is the largest and most complicated joint in our body. As a swivel-hinge joint, it can switch between bending, stretching and slightly rotating movements. However, the complex structure and constant stress also make it prone to serious problems. Read everything you need to know about the knee joint!

What is the knee joint?

The knee is a multi-part structure made up of bones, cartilage, muscles, tendons and ligaments. When we speak of the knee joint (articulatio genus), strictly speaking, we only mean the bones, cartilage and the capsule that holds the joint together. The knee joint actually consists of two joints: the kneecap joint (femoropatellar joint, articulatio femoropatellaris) between the thighbone and the kneecap and the knee joint between the thighbone and the shinbone (femorotibial joint, articulatio femorotibialis).

bone

The three bony components of the knee joint include the thigh, kneecap and shin, but not the fibula. A total of six joint surfaces lie closely together here: the kneecap, three surfaces of the femur and two of the tibia.

cartilage

The ends of the thigh and tibia (condyles) are covered by articular cartilage (hyaline cartilage). Two cartilage discs, the menisci (fiber cartilage), are embedded between the two bones. The back of the kneecap is also provided with cartilage.

Joint capsule

The entire knee joint is surrounded by a joint capsule made of connective tissue (capsula articularis). This consists of two layers, the stabilizing fiber layer and the synovial membrane. The joint capsule is filled with a highly viscous joint fluid (synovial fluid).

Despite their close proximity, the thighbones (femur) and shinbones (tibia) only meet in a few places. The joint head sits relatively "loosely" in the socket and therefore needs numerous ligaments that protect the knee from dislocation. Although these are not located directly in the joint space of the knee, they are crucial for its function. The most important are:

• Inner band (MCL)
• Outer band (LCL)
• Anterior cruciate ligament
• Posterior cruciate ligament

Some tendons close to the knee are necessary for power transmission:

• Patellar tendon
• Biceps tendon
• Quadriceps tendon

Numerous muscles (such as the thigh and shin muscles) start in the area of ​​the knee joint. Below the kneecap and to the side of the knee joint are bursa that reduce friction between the skin, tendons, muscles and ligaments with the bone. The knee joint is supplied by arteries and nerves and is equipped with lymph nodes.

What is the function of the knee joint?

For every type of locomotion, whether swimming, cycling, running or jumping, we need a knee joint that is easy to move. Bones and cartilage, as well as adjacent muscles, ligaments, tendons, and bursae work closely together to enable smooth knee movement. We can bend and straighten our knees and, when bent, turn them slightly outwards. The synovial fluid acts as a lubricant and supplies the articular cartilage with nutrients. The cartilage surfaces at the ends of the bones and the menisci reduce friction and cushion an impact.

Where is the knee joint located?

The knee joint is the articulated connection between the upper and lower leg.

What problems can the knee joint cause?

The knee joint and its surrounding structures are prone to numerous injuries, inflammations and degenerative processes (signs of wear and tear).

Common traumatic injuries in the knee joint are:

• Contusion: ligaments, cartilage, bones, muscles and skin are crushed by impact, impact, blow or fall.
• Strain (distortion): fine tears in the tissue due to overstretching.
• Torn capsule / ligament: Result of a severe strain. In the case of strong ligaments, their anchorage to the bone usually tears (bony tear).
• Meniscal tear
• Dislocation (dislocation): Joint surfaces are no longer correctly positioned after excessive rotation; often favored by slack ligaments; usually associated with a ligament or capsule tear.

Inflammatory processes that can affect the knee include:

• Inflammation of the bones (osteitis, osteomyelitis)
• Joint inflammation (arthritis): rheumatism, gout (hyperuricemia)
• Inflammation of the bursitis (bursitis)
• Inflammation of the lining of the joint (synovitis)
• Tendinitis (tendosynovitis)

One of the most common forms of joint wear affects the knee joint (knee joint osteoarthritis = gonarthrosis). Common bone diseases such as benign or malignant tumors, osteoporosis, and osteomalacia can also affect the knee joint. Last but not least, congenital malformations (musculoskeletal deformities) or misalignments of the leg or hip can impair the functioning of the knee joint.

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