Knee
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In human anatomy, the knee is the leg joint connecting the femur and the tibia.
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Human anatomy
The knee is a complex, compound, condyloid variety of a synovial joint. 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 muscles, 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 fluid which is contained inside the "synovial" membrane, or "joint capsule". The area behind the knee is called the popliteal fossa.
Ligaments
The human knee is associated with the following ligaments: Anterior Cruciate Ligament (ACL), Posterior Cruciate Ligament (PCL), Capsular Ligament, Ligamentum Patellae, Tibial Collateral Ligament (Medial Collateral Ligament, or MCL), Fibular Collateral Ligament(Lateral Collateral Ligament, or LCL), and Oblique Popliteal Ligament. The MCL protects the inside of the knee from being bent open by a stress applied to the outside of the knee, while conversely the LCL protects the outside from an inside bending force. The critically important ACL prevents the tibia from being pushed too far forward relative to the femur.
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. 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.
Movements
The knee permits the following movements: flexion, extension, locking, unlocking, and slight rotation. The ligaments and menisci, along with the muscles which traverse the joint, prevent movement beyond the knee's intended range of motion.
Injury
In sports such as skiing and soccer, or other sports that involve great stress to the knees, it is common to tear one or more ligaments or cartilages. Especially debilitating is the unfortunately common triad of torn medial collateral and anterior cruciate ligaments and a torn medial meniscus. Before the advent of arthroscopy and arthroscopic surgery, patients having surgery for this injury 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 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 (http://www.vermontskisafety.com/faq_skiers/faq_skiers_tips.html)
Non-biped anatomy
Leg joints of quadruped mammals and of insects that have functions similar to the human knee are also referred to as knees, despite important differences. In particular, the homologies in the limbs of bipeds and of quadupeds are extensive, but often the parts serving corresponding functions are not homologous to each other, and the homologous parts have different functions, to the extent that thinking of horses as running on their tiptoes and fingertips can be a step toward abandoning misconceptions.
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