The articular capsule of the knee joint is the wide and lax

joint capsule In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint.knee In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the hu ...

. It is thin in front and at the side, and contains the

patella The patella (: patellae or patellas), also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in m ...

ligament A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have liga ...

s, menisci, and bursae of the knee.Platzer (2004), p 206 The capsule consists of an inner

synovial membrane Synovial () may refer to: * Synovial fluid * Synovial joint A synovial joint, also known as diarthrosis, joins bones or cartilage with a fibrous joint capsule that is continuous with the periosteum of the joined bones, constitutes the outer bou ...

, and an outer fibrous membrane separated by fatty deposits anteriorly and posteriorly.Platzer (2004), p 210

Synovial membrane

Anteriorly, the reflection of the synovial membrane lies on the

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

; located at some distance from the cartilage because of the presence of the suprapatellar bursa. Above, the reflection appears lifted from the bone by underlying periosteal

connective tissue Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesod ...

. In a standing posture, the suprapatellar bursa is seemingly redundant. It is however also referred to as the ''suprapatellar synovial recess'' as it gradually unfolds as the knee is flexed; to open up completely when the knee is flexed 130 degrees.''Thieme Atlas of Anatomy'', pp 400-401 The suprapatellar bursa is prevented from being pinched during extension by the

articularis genus muscle The articularis genus (also known as the subcrureus muscle) is a small skeletal muscle located anteriorly on the thigh just above the knee. Structure It arises from the anterior surface of the lower part of the body of the femur, deep to the v ...

. On the

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

, the anterior reflection and attachment of the synovial membrane is located near the cartilage. Anteriorly, the infrapatellar fat pad is inserted below the patella and between the two membranes. It extends from the lower margin of the patella above, to the infrapatellar synovial fold below. With its free upper margin, this fold extends dorsally through the joint space to surround the two cruciate ligaments from the front, thus dividing the surrounding joint space into two chambers. Laterally of this are a pair of alar folds. Posteriorly, the femoral attachment of the synovial membrane is located at the cartilaginous margin of the

lateral Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...

and medial femoral condyles, where the joint space has two dorsal extensions. Between these, the synovial membrane passes in front of the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

and

posterior cruciate ligament The posterior cruciate ligament (PCL) is a ligament in each knee of humans and various other animals. It works as a counterpart to the anterior cruciate ligament (ACL). It connects the posterior intercondylar area of the tibia to the Medial condyl ...

s, why these ligaments are both intracapsular and extra-articular with their tibial attachment located exactly on the cartilage margin. Both the

and medial meniscus are, however, located within the synovial capsule.

Fibrous membrane

It is a thin, but strong, fibrous membrane which is strengthened in almost its entire extent by bands inseparably connected with it. Above and in front, beneath the tendon of the quadriceps femoris, it is represented only by the synovial membrane. Its chief strengthening bands are derived from the

fascia lata The fascia lata is the deep fascia of the thigh. It encloses the thigh muscles and forms the outer limit of the fascial compartments of thigh, which are internally separated by the medial intermuscular septum and the lateral intermuscular sept ...

and from the

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

s surrounding the joint.

Bursae

The numerous bursae surrounding the knee joint can be divided into the ''communicating'' and the ''non-communicating'' bursae: * Communicating bursae: ** The suprapatellar bursa, the largest bursa, extends the joint space anteriorly and proximally. ** The subpopliteal recess and semimembranosus bursa are located posteriorly and are much smaller ** The

and medial subtendinous bursae of gastrocnemius are located at the origin of the two heads of the

gastrocnemius muscle The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It is located superficial to the soleus in the posterior (back) compartment of the leg. It runs from its t ...

. * Non-communicating bursae: ** The subcutaneous prepatellar bursa is located in front of the patella. ** The eep infrapatellar bursa is located under the patella, between the patellar ligament and the fibrous membrane of the joint capsule. It is communicating with the joint space in particular cases. ** Other less regularly present bursae include the subfascial prepatellar, the subtendinous prepatellar, and the subcutaneous prepatellar bursae. Adding to the complex structure of the knee space, there are remnants of three embryonic septal divisions of the knee space called synovial plicae:Burgener (2002), p 390 * The ''suprapatellar plica'' dividing the suprapatellar recess * The ''infrapatellar plica'', in front of the

anterior cruciate ligament The anterior cruciate ligament (ACL) is one of a pair of cruciate ligaments (the other being the posterior cruciate ligament) in the human knee. The two ligaments are called "cruciform" ligaments, as they are arranged in a crossed formation. In ...

, reaches from the intercondylar notch to the infrapatellar fat pad * The ''medial patellar plica'', located adjacent to the patella's medial facet, runs vertically along the medial joint capsule

Additional images

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Notes

References

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External links

*
knee/ligaments/ligamen2
at the

Dartmouth Medical School The Geisel School of Medicine is the medical school of Dartmouth College located in Hanover, New Hampshire. The fourth oldest medical school in the United States, it was founded in 1797 by New England physician Nathan Smith. It is one of the sev ...

's Department of Anatomy {{Joints of lower limbs Animal anatomy Knee