Knee

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Knee joints

Diagram of human knee
Latin	articulatio genu
Gray's	subject #93 339
Nerve	femoral, obturator, sciatic
MeSH	Knee

For other uses, see Knee (disambiguation).

In human anatomy, the knee is the lower extremity joint connecting the femur and the tibia. Since in humans the knee supports nearly the entire weight of the body, it is vulnerable both to acute injury and to the development of osteoarthritis.

1 Function of the knee
2 Human anatomy
3 Animal anatomy
4 Trivia
5 See also
6 Additional images
7 External links

[edit] Function of the knee

The knee functions as a living, self-maintaining, biologic transmission, the purpose of which is to accept and transfer biomechanical loads between the femur, tibia, patella, and fibula (The previous sentence is ambiguous, and may be correct, but no one should be of the impression that the fibula is part of the knee joint). In this analogy the ligaments represent non-rigid adaptable sensate linkages within the biologic transmission. The articular cartilages act as bearing surfaces, and the menisci as mobile bearings. The muscles function as living cellular engines that in concentric contraction provide motive forces across the joint, and in eccentric contraction act as brakes and dampening systems, absorbing loads.

[edit] Human anatomy

The knee is a complex, compound, condyloid variety of a synovial joint which hovers. It actually comprises two separate joints.

The femoro-patellar joint consists of the patella, or "kneecap", a so-called sesamoid bone which sits within the tendon of the anterior thigh muscle (m. quadriceps femoris), and the patellar groove on the front of the femur through 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.

[edit] Ligaments

Name	Capsule	From	To	Description
anterior cruciate ligament (ACL)	inside	lateral condyle of femur	anterior intercondylar area	The critically important ACL prevents the tibia from being pushed too far anterior relative to the femur.
posterior cruciate ligament (PCL)	inside	medial condyle of femur	posterior intercondylar area	Injury to this ligament is uncommon but can occur as a direct result of forced trauma to the ligament. This ligament prevents posterior displacment of the tibia relative to the femur.
capsular ligament	-	-	-	-
patellar ligament	outside	patella	tuberosity of the tibia	- Also occasionally called the patellar tendon because there is no definite separation between the quadriceps tendon (which surrounds the patella) and the area connecting the patella to the tibia. This very strong ligament helps give the patella its mechanical leverage and also functions as a cap for the condyles of the femur.
medial collateral ligament (MCL a.k.a. "tibial")	outside	medial epicondyle of the femur	medial tibial condyle	The MCL protects the medial side of the knee from being bent open by a stress applied to the lateral side of the knee (a valgus force).
lateral collateral ligament (LCL a.k.a. "fibular")	outside	lateral epicondyle of the femur	head of fibula	The LCL protects the lateral side from an inside bending force (a varus force).
oblique popliteal ligament	outside	medial condyle of tibia	-	-
arcuate popliteal ligament	outside	Intercondylar area of tibia, and lateral condyle of femur, to below head of fibula	Connects to the medial portion of the fibular head	-This ligament strengthes the knee posterolaterally and usually when injured is in combination with a PCL and popliteus tendon injury.

[edit] Menisci

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 meniscus and the lateral meniscus. Either or both may be cracked, or torn, when the knee is forcefully rotated and/or bent.

[edit] Movements

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.

[edit] Injury

artificial knee

In sports that place great stress on the knees, especially with twisting forces, it is common to tear one or more ligaments or cartilages. The anterior cruciate ligament is often torn as a result of a rapid direction change while running or as a result of some other type of violent twisting motion. It can also be torn by being extended forcefully beyond its normal range, or as a result of being forced sideways. In such cases, other structures will 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 arthroscopy and 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, with a great deal of controversy caused in ruck contests, where the crashing of two knees during the leap has caused injuries to numerous players. This forced new rule changes in the AFL 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. Techniques to minimize the risk of an ACL injury while skiing are published by Vermont Safety Research

[edit] Animal anatomy

Look up knee in Wiktionary, the free dictionary.

In humans the knee refers to the joints between the femur, tibia and patella. In quadrupeds, particularly horses and ungulates the term is commonly used to refer to the carpus, probably because of its similar hinge or ginglymus action. 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.

[edit] Trivia

The medical phobia for knees is called Genuphobia.

[edit] See also

[edit] Additional images

Knee MR	Knee MR	Knee X-ray	Cruciate ligaments
Female knee	Left knee-joint from behind, showing interior ligaments.	Capsule of right knee-joint (distended). Lateral aspect.