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Articular Capsule of Knee Joint (Left)
Connective Tissue

Articular Capsule of Knee Joint (Left)

Capsula articulationis genus

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The knee joint is surrounded by an articular capsule composed of a fibrous layer lined internally by a synovial membrane. The fibrous layer contains fibrous dense connective tissue of variable thickness and encloses the articular ends of the femur and tibia that participate in the knee joint. The synovial membrane lining the fibrous layer of the articular capsule is composed of loose connective tissue with a free smooth surface that faces the joint cavity. It is responsible for secreting synovial fluid.

There are gaps within the fibrous layer of the articular capsule through which the synovial membrane may protrude as small fluid filled sacs called bursae. These might or might not remain in contact with the joint cavity.

The fibrous layer of the articular capsule is supported externally by several supporting ligaments, such as the tibial and fibular (or medial and lateral) collateral ligaments and the patellar ligament.

The innervation for the fibrous capsule arises from the nerves supplying muscles acting on the joint. Some nerves are thought to be proprioceptive, whereas others have free nerve endings at their attachments, which contribute to the intense pain following injuries to the joint ligaments.

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Anatomical Relations

Anteriorly, the articular capsule is deficient and is replaced by the patellar ligament. The capsule does not pass proximal to the patellar region. Anterolaterally, it lies deep to the patellar retinacula, which are expansions of vastus medialis and lateralis muscles that are attached anteriorly to the margins of the patella and patellar tendon, and extend posteriorly to the collateral ligaments.

Laterally, the capsule is related to the iliotibial tract. Posterolaterally, the capsule is related to the tendon of popliteus muscle, which pierces the capsule to insert into the lateral femoral condyle. Posteromedially, the capsule is related to an oblique popliteal ligament, which is considered as an extension of the tendon of the semimembranosus muscle.


The articular capsule is vital to the function of synovial joints. It seals the joint space, provides passive stability by limiting joint movements, provides active stability via its proprioceptive nerve endings, and may form articular surfaces for the joint. It varies in thickness according to the stresses to which it is subjected to. Local thickenings form capsular ligaments. It also incorporates tendons (e.g., the popliteal tendon) to aid in its functions.

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Complete Anatomy