Name = Knee joints
Latin = articulatio genus
GraySubject = 93
GrayPage = 339
Caption = Diagram of human knee
Nerve = femoral, obturator, sciatic
MeshName = Knee
MeshNumber = A01.378.610.450
The knee is the lower extremity
jointconnecting the femur, patella, and the tibia. [EMedicineDictionary|knee+joint] Since in humans the knee supports nearly the entire weight of the body, it is the joint most vulnerable both to acute injury and the development of osteoarthritis.
Upon birth, a
babywill not have a conventional knee cap, but a growth formed of cartilage. In human females this turns to a normal bone knee cap by the age of 3, in males the age of 5.
The knee is a complex, compound, condyloid variety of a
synovial jointwhich hovers. It actually comprises two separate joints.
* The "femoro-patellar joint" consists of the
patella, or "kneecap", a so-called sesamoid bonewhich sits within the tendon of the anterior thigh muscle ("m. quadriceps femoris"), and the patellar grooveon the front of the femurthrough which it slides.
* The "femoro-tibial joint" links the femur, or thigh bone, with the
tibia, the main bone of the (lower) leg. The joint is bathed in a viscous (synovial) fluid which is contained inside the "synovial" membrane, or joint capsule.
The recess behind the knee is called the
popliteal fossa. It can also be called a "knee pit."
These are cartilaginous elements within the knee joint which serve to protect the ends of the bones from rubbing on each other and to effectively deepen the tibial sockets into which the femur attaches. They also play a role in shock absorption. There are two menisci in each knee, the
medial meniscusand the lateral meniscus. Either or both may be cracked, or torn, when the knee is forcefully rotated and/or bent.
Synovial fluid is a thick, stringy fluid found in the cavities of synovial joints. With its egg-like consistency (synovial comes from Latin for "egg"), synovial fluid reduces friction between the articular cartilage and other tissues in joints to lubricate and cushion them during movement [http://en.wikipedia.org/wiki/Synovial_fluid] .
The knee permits the following movements:
flexion, extension, as well as slight medial and lateral rotation. Also, the knee has special locking and unlocking mechanisms, related to movement by the femoral condyles on the tibial plateau. The ligaments and menisci, along with the muscles which traverse the joint, prevent movement beyond the knee's intended range of motion. It is also classified as a hinge joint.
The range of movement is as follows: Flexion is permitted up to 120º when the hip is extended, 140º when the hip is flexed and 160º when the knee is flexed passively. Medial rotation is limited to 10º and lateral rotation to 30º .
The femoral artery and the popliteal artery help form the arterial network surrounding the knee joint (articular rete). There are 6 main branches:
Superior medial genicular artery
Superior lateral genicular artery
Inferior medial genicular artery
Inferior lateral genicular artery
Descending genicular artery
Recurrent branch of anterior tibial artery
The medial genicular arteries penetrate the knee joint
In sports that place great pressure on the knees, especially with twisting forces, it is common to tear one or more ligaments or cartilages. An increasingly common victim to injury is the anterior cruciate ligament, often torn as a result of a rapid direction change while running or some other, violent twisting motion. It can also be torn by extending the knee forcefully beyond its normal range. In some such cases, other structures incur damage as well. Especially debilitating is the unfortunately common "unhappy triad" of torn medial collateral and anterior cruciate ligaments and a torn medial meniscus. This typically arises from a combination of inwards forcing and twisting.
Before the advent of
arthroscopyand arthroscopic surgery, patients having surgery for a torn ACL required at least nine months of rehabilitation. With current techniques, such patients may be walking without crutches in two weeks, and playing some sports in but a few months. In Australian rules football, knee injuries are among the most common, especially in ruck contests, involving the crashing of two knees during the leap. These injuries forced new rule changes for the 2005 season.
In addition to developing new surgical procedures, ongoing research is looking into underlying problems which may increase the likelihood of an athlete suffering a severe knee injury. These findings may lead to effective preventive measures, especially in female athletes, who have been shown to be especially vulnerable to ACL tears from relatively minor trauma. Techniques to minimize the risk of an ACL injury while skiing are published by [http://www.vermontskisafety.com/faq_skiers/faq_skiers_tips.html Vermont Safety Research]
Several diagnostic maneuvers help clinicians diagnose an injured ACL. In the
anterior drawer test, the examiner applies an anterior force on the proximal tibia with the knee in 90 degrees of flexion. The Lachman testis similar, but performed with the knee in only about twenty degrees of flexion, while the pivot-shift testadds a valgus (outside-in) force to the knee while it is moved from flexion to extension. Any abnormal motion in these maneuvers suggests a tear.
The diagnosis is usually confirmed by
MRI, the availability of which has greatly lessened the number of purely diagnostic arthroscopies performed.
In humans the knee refers to the joints between the femur, tibia and patella. In quadrupeds, particularly horses and
ungulatesthe term is commonly used to refer to the carpus, probably because of its similar hinge or ginglymusaction. The joints between the femur, tibia and patella are known as the stifle in quadrupeds. In insects and other animals the term knee is used widely to refer to any ginglymus joint.
Knee Cartilage Replacement Therapy
Partial knee replacement
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