Knee joint – Articulatio genus
6.4
Joints
The knee joint is the most complicated synovial joint in the human body. It is a complex and compound bicondylar joint in which three bones and two menisci articulate. The knee joint has 12 articular ligaments and many associated bursae. Movements are possible in two axes, but these movements are limited when the knee is in full flexion and full extension. Type, shape and articular surfaces of the knee joint Type: both complex and compound 1 Femoropatellar joint (articulatio femoropatellaris) 1.1 Shape: plane 1.2 Articular head: the patellar surface of the femur 1.3 Articular fossa: the articular surface of the patella 2 Femorotibial joint (articulatio femorotibialis) 2.1 Shape: a combination of the trochlear and hinge joints 2.2 Articular head: the condyles of the femur 2.3 Articular fossa: the condyles of the tibia
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2.2 2.3
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Articular capsule – originates below the epicondyles of the femur – attaches to the circumference of the articular surfaces of the tibia and patella 2 Synovial membrane – lines the internal surface of the fibrous layer – does not cover the cruciate ligaments 2.1 Infrapatellar synovial fold (plica synovialis infrapatellaris) 2.1.1 Alar folds (plicae alares) – project dorsally from the ventral part of the joint 2.2 Infrapatellar fat pad (corpus adiposum infrapatellare) – a fat pad between the fibrous and synovial layers 3 Synovial bursae and articular recesses – approximately 20 bursae and 2 recesses are located in the vicinity of the knee joint Communicating with the knee joint: 3.1 Suprapatellar recess (recessus suprapatellaris) 3.2 Suprapatellar bursa (bursa suprapatellaris) 3.3 Subpopliteal recess (becessus subpopliteus) 3.4 Gastrocnemiosemimembranosus bursa (bursa gastrocnemiosemimembranosa) Not communicating with the knee joint: 3.5 Anserine bursa (bursa anserina) 3.6 Subcutaneous prepatellar bursa (bursa subcutanea prepatellaris) 3.7 Subcutaneous infrapatellar bursa (bursa subcutanea infrapatellaris)
The middle position of the knee joint is 20–30°of flexion.
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3.2 3.1
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3.7
2 3.3 2.2
Right anterior superior view of the right knee joint
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Sagittal section of the right knee joint viewed from the left
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3.5
Anterior view of the right knee joint
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3.2
The articularis genus is a standalone muscle below the quadriceps femoris. It attaches to the joint capsule, which stretches up and prevents its incarceration.
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2.1.1 2.2 3.7
In clinical practice, the tibial and fibular collateral ligaments are inaccurately termed the medial and lateral collateral ligaments.
Open right and left knee joints
• 1 Fibrous capsule
3.6
A mnemonics for remembering the positions of the cruciate ligaments: when the middle finger is crossed over the index finger and the hand placed on the ipsilateral knee, the middle finger shows the position of the anterior cruciate ligament and the index finger shows the position of the posterior cruciate ligament.
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The valve mechanism of the knee is a system of connected pouches and synovial bursae of the knee joint through which synovial fluid flows. The ventral part is formed by the suprapatellar recess and bursa, the dorsomedial part is formed by the gastrocnemius-semimembranosus bursa and the dorsolateral part by the subpopliteal recess.
Superior view of a transverse section of the right knee joint
Clinical notes The unhappy triad is a term given to concomitant damage to the anterior cruciate ligament, medial meniscus and tibial collateral ligament. The menisci, anterior cruciate ligament and collateral ligaments are the most predisposed structures of the knee to be injured. The anterior cruciate ligament is injured ten times more frequently than the posterior cruciate ligament. Baker’s cyst arises when the gastrocnemius-semimembranosus bursa becomes overfilled with synovial fluid. It is palpable in the subcutaneous tissue of the popliteal fossa. Total knee replacement is a surgical procedure that replaces severely damaged femoral and tibial condyles with artificial prostheses. This is performed when conservative therapy with analgetics, injections, and rehabilitation is not sufficient in patients with severe arthrosis. Other indications include disease of the knee caused by systemic diseases such as rheumatoid arthritis, ankylosing spondylitis disease and psoriatic arthritis.