= Solution
\b[The <knee> is a compound <synovial joint> comprising tibiofemoral and patellofemoral articulations.] It permits chiefly flexion and extension, with controlled rotation and translation. The head of the <fibula> provides important ligamentous attachments nearby but does not form a principal articular surface of the <knee> cavity.
The medial and lateral femoral condyles articulate with the corresponding superior surfaces of the <tibia>. Anteriorly, the <patella> articulates with the femoral patellar surface. These load-bearing surfaces are covered by <hyaline cartilage>. The relatively incongruent tibiofemoral surfaces are supplemented by the medial and lateral <knee menisci>, wedges of <fibrocartilage> whose thicker outer borders attach towards the capsule and tibial margins. Their anterior and posterior roots attach in the intercondylar tibial region. The medial <meniscus of the knee> is more C-shaped and relatively less mobile; the lateral is more nearly circular and more mobile. An anterior transverse connection may join them.
The fibrous capsule encloses the articulations but is strengthened and partly replaced by neighbouring tendons and ligaments. Anteriorly, the extensor apparatus includes the <quadriceps tendon>, <patella>, <patellar ligament> to the tibial tuberosity, and medial and lateral patellar retinacula. Posteriorly, the capsule is reinforced by the <oblique popliteal ligament>, an expansion related to <semimembranosus>, and the arcuate posterolateral complex. The <popliteus tendon> passes in relation to the posterolateral capsule and lateral meniscus.
The <tibial collateral ligament> extends from the medial femoral side to the medial <tibia> and is closely related to the capsule and medial <meniscus of the knee>. The cord-like <fibular collateral ligament> runs from the lateral femoral epicondyle to the fibular head. It is separated from the lateral meniscus by the <popliteus tendon>. Thus the two collateral ligaments do not have identical meniscal attachments.
The <anterior cruciate ligament> runs from the anterior intercondylar tibial area towards the inner surface of the lateral femoral condyle. The <posterior cruciate ligament> runs from the posterior intercondylar tibial area towards the inner surface of the medial femoral condyle. They cross within the fibrous capsule but lie outside the synovial cavity proper. The <anterior cruciate ligament> checks excessive anterior displacement of the <tibia> relative to the <femur> and contributes to rotational control; the <posterior cruciate ligament> checks excessive posterior displacement. Their effects depend on joint position and interact with the collateral ligaments and muscular support.<Anatomy, Bony Pelvis and Lower Limb, Knee (StatPearls)>[Structure and Function: articulations, menisci, capsule and cruciate/collateral attachments]{ref}
The <synovial membrane> lines the inner non-articular capsule, reflects around the cruciate region and the <infrapatellar fat pad>, and forms recesses. The fat pad is intracapsular but excluded from the synovial cavity by the membrane covering it. The <suprapatellar recess> extends above the <patella> beneath the quadriceps. The <prepatellar bursa> and the superficial and deep <infrapatellar bursae> reduce friction outside the principal cavity and should not all be described as compulsory communications with it. Posterior bursal communications are variable.
The <quadriceps femoris> extends the <knee>; the <hamstrings> and other crossing <muscles> contribute to flexion and dynamic stability. Rotation is freer in flexion than in full extension. Terminal extension includes a coupled locking movement, commonly described as external rotation of the unloaded <tibia> or the corresponding internal rotation of the loaded <femur>. <Popliteus> helps initiate unlocking. This is a constrained three-dimensional articulation rather than a simple door hinge.<Anatomy and Physiology 2e by J. Gordon Betts and others/9.6 Anatomy of Selected Synovial Joints>[Knee Joint: ligaments, menisci and movements]{ref}
The genicular arterial anastomoses, chiefly associated with <popliteal artery> branches and contributions from neighbouring arterial systems, supply the region; accompanying <veins> drain it. Articular sensory supply comes from branches of the <femoral nerve>, <obturator nerve>, <tibial nerve> and <common fibular nerve>. Their relation to the <muscles> crossing the articulation illustrates the connection between movement, stabilization and sensation. Dissection with the joint flexed and extended, and inspection of a section through the cruciate and synovial reflections, reveal relations that a single external view cannot show.
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