The knee joint is the largest synovial (lined by synovial membrane) joint of the body. It is a major weight bearing joint of the body and is made of three bones. On the top is the thigh bone(femur) below it the shin bone (tibia) and in the front is the knee cap (patella).

    Keeping all these bones in place are various ligaments (tough band or cord like structures), muscles and the joint capsule (tough flexible fibrous structure that surrounds the joint).

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    The part of the femur that forms the knee joint is expanded side ways and behind to form two oval structures called condlyes. Similarly the part of the tibia forming the knee is expanded and forms two condyles that articulate with the corresponding femur condyles. The one on the outer side is called the lateral condyle and the one on the inner side is called the medial condyle On the front the patella articulates with the femur.

    Clinicians also divide the knee joint into compartments. The medial condyles form the medial compartment. The lateral condyles form the lateral compartment. Anterior compartment is between the patella and femur. So there can arthritis of the lateral, medial or anterior compartment, individually

    knee joint model showing bones and ligaments

    The bone ends are covered with cartilage (tough, smooth and resilient structure). Function of the cartilage is to provide a smooth surface, for the bones to move easily over one another. It also acts as a shock absorber.

    This joint also contains two semi-circular disc like structures, made of fibrous cartilage that are called menisci. They help to provide a congruent surface for the thigh bone to move on the shin bone.

    The knee is a hinge joint, meaning that it allows movement in one plain only. Flexion (bend) and extension (straighten the knee). Though slight amounts of rotation and translation also occur.

    Internally the whole surface of this joint (excluding cartilage), is covered with a thin membrane (sheet or film like) structure called synovium. The function of synovium is to secrete a fluid, that lubricates the joint and provides nourishment to the avascular (having no blood supply) cartilage.

    Cross sectional anatomy of the knee joint

    In the front (anteriorly), the bones of the knee joint can easily be felt beneath the skin, but behind they are covered by bulky muscles and are difficult to feel. Due to this, even mild swelling in the knee is easily appreciated. This is opposite to the hip joint where slight swelling is not obvious as it is surrounded by many muscles.

    Four main ligaments stabilize this joint. Medially (on the inner side) the medial collateral ligament. Laterally (on the outer side) the lateral collateral ligament. These ligaments stabilize the knee against angulation (tend to wedge open the joint) and translation (tend to slide the bones in opposite direction) forces.

    knee anatomy - ligaments knee ligaments - posterior view

    The other two ligaments are the anterior and posterior cruciate ligaments. There main function is to stabilize the joint against translation forces.

    Muscles acting on this joint are extensors (straighten) and flexors (bend the joint). Extensors include the Quadriceps muscle. Flexors include Semitendenosus, Semimembranosus and the Biceps femoris (collectively called Hamstring muscles).

    This joint is also surrounded by small sac like structures, that have an inner lining of synovial membrane called bursae. The function of these is to allow, smooth movement of various ligaments and tendons (cord like structures that attach muscles to bone) over bone.

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    I hope the information provided was helpful. If you have any query about the knee joint anatomy you can ask me at the contact me page.

    This page was last updated on 28th December 2010.

    Causes of knee pain include...

    Knee Osteoarthritis

    Knee Bursitis

    Meniscal Injury

    Ligament Injury

    Knee Fracture

    Patella Fracture

    Tibial Plateau Fracture

    Osgood Schlatter Disease

    Knee Replacement Surgery

Go from Knee Joint Anatomy to Knee Pain


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