ischiummedial surface of tibiaprofunda femoris, gluteal arterysciatic nerveflexes knee, extends hip joint, medially rotates leg at kneequadriceps muscle gastrocnemiusmedial and lateral condyle of the femurcalcaneussural arteriestibial nerve from the sciatic, specifically, nerve roots s1, s2minor flexion of knee and plantarflexiontibialis anterior muscle plantarislateral supracondylar ridge of femur above lateral head of gastrocnemiustendo calcaneus (medial side, deep to gastrocnemius tendon)sural arteriestibial nerveflexes knee and plantar flexes foottibialis anterior muscle popliteusmiddle facet of the lateral surface of the lateral femoral condyleposterior tibia under the tibial condylespopliteal arterytibial nervemedial rotation and flexion of knee medial compartment: muscleorigininsertionarterynerveactionantagonist gracilisinferior pubic ramuspes anserinusobturator arteryanterior branch of obturator nerveflexion and medial rotation of knee; adduction of hip, flexion of hip, blood supply arteries of the knee the femoral artery and the popliteal artery help form the arterial network or plexus, surrounding the knee joint. there are six main branches: two superior genicular arteries, two inferior genicular arteries, the descending genicular artery and the recurrent branch of anterior tibial artery. the medial genicular arteries penetrate the knee joint. function maximum movements : 398–399 and muscles: 252 extension 5–10°flexion 120–150° quadriceps (withsome assistance fromthe tensor fasciae latae) (in order of importance)semimembranosussemitendinosusbiceps femorisgracilissartoriuspopliteusgastrocnemius internal rotation* 10°external rotation* 30–40° (in order of importance)semimembranosussemitendinosusgracilissartoriuspopliteus biceps femoris *(knee flexed 90°) the knee permits flexion and extension about a virtual transverse axis, as well as a slight medial and lateral rotation about the axis of the lower leg in the flexed position. the knee joint is called "mobile" because the femur and lateral meniscus move: 399 over the tibia during rotation, while the femur rolls and glides over both menisci during extension-flexion.: 212–213 the center of the transverse axis of the extension/flexion movements is located where both collateral ligaments and both cruciate ligaments intersect. this center moves upward and backward during flexion, while the distance between the center and the articular surfaces of the femur changes dynamically with the decreasing curvature of the femoral condyles. the total range of motion is dependent on several parameters such as soft-tissue restraints, active insufficiency, and hamstring tightness.: 398 extended position with the knee extended, both the lateral and medial collateral ligaments, as well as the anterior part of the anterior cruciate ligament, are taut. during extension, the femoral condyles glide and roll into a position which causes the complete unfolding of the tibial collateral ligament. during the last 10° of extension, an obligatory terminal rotation is triggered in which the knee is rotated medially 5°. the final rotation is produced by a lateral rotation of the tibia in the non-weight-bearing leg, and by a medial rotation of the femur in the weight-bearing leg. this terminal rotation is made possible by the shape of the medial femoral condyle, assisted by contraction of the popliteus muscle and the iliotibial tract and is caused by the stretching of the anterior cruciate ligament. both cruciate ligaments are slightly unwound and both lateral ligaments become taut.: 212 flexed position in the flexed position, the collateral ligaments are relaxed while the cruciate ligaments are taut. rotation is controlled by the twisted cruciate ligaments; the two ligaments get twisted around each other during medial rotation of the tibia—which reduces the amount of rotation possible—while they become unwound during lateral rotation of the tibia. because of the oblique position of the cruciate ligaments, at least a part of one of them is always tense and these ligaments control the joint as the collateral ligaments are relaxed. furthermore, the dorsal fibers of the tibial collateral ligament become tensed during extreme medial rotation and the ligament also reduces the lateral rotation to 45–60°.: 212 clinical significance lateral trauma to the knee can tear the medial collateral ligament, anterior cruciate ligament, and medial meniscus knee pain is caused by trauma, misalignment, degeneration, and conditions producing arthritis. the most common knee disorder is generally known as patellofemoral syndrome. the majority of minor cases of knee pain can be treated at home with rest and ice, but more serious injuries do require surgical care. one form of patellofemoral syndrome involves a tissue-related problem that creates pressure and irritation in the knee between the patella and the trochlea (patellar compression syndrome), which causes pain. the second major class of knee disorder involves a tear, slippage, or dislocation that impairs the structural ability of the knee to balance the leg (patellofemoral instability syndrome). patellofemoral instability syndrome may cause either pain, a sense of poor balance, or both. prepatellar bursitis also known as housemaid's knee is painful inflammation of the prepatellar bursa (a frontal knee bursa) often brought about by occupational activity such as roofing. age also contributes to disorders of the knee. particularly in older people, knee pain frequently arises due to osteoarthritis. in addition, weakening of tissues around the knee may contribute to the problem. patellofemoral instability may relate to hip abnormalities or to tightness of surrounding ligaments. cartilage lesions can be caused by: accidents (fractures) injuries the removal of a meniscus anterior cruciate ligament injury posterior cruciate ligament injury posterolateral corner injury medial knee injuries considerable strain on the knee. any kind of work during which the knees undergo heavy stress may also be detrimental to cartilage. this is especially the case in professions in which people frequently have to walk, lift, or squat. other causes of pain may be excessive on, and wear off, the knees, in combination with such things as muscle weakness and overweight. common complaints: a painful, blocked, locked or swollen knee. sufferers sometimes feel as if their knees are about to give way, or may feel uncertain about their movement. overall fitness and knee injury physical fitness is related integrally to the development of knee problems. the same activity such as climbing stairs may cause pain from patellofemoral compression for someone who is physically unfit, but not for someone else (or even for that person at a different time). obesity is another major contributor to knee pain. for instance, a 30-year-old woman who weighed 120 lb at age 18 years, before her three pregnancies, and now weighs 285 lb, had added 660 lb of force across her patellofemoral joint with each step. common injuries due to physical activity model demonstrating parts of an artificial knee in sports that place great pressure on the knees, especially with twisting forces, it is common to tear one or more ligaments or cartilages. some of the most common knee injuries are those to the medial side: medial knee injuries. anterior cruciate ligament injury main article: anterior cruciate ligament injury the anterior cruciate ligament is the most commonly injured ligament of the knee. the injury is common during sports. twisting of the knee is a common cause of over-stretching or tearing the acl. when the acl is injured a popping sound may be heard, and the leg may suddenly give out. besides swelling and pain, walking may be painful and the knee will feel unstable. minor tears of the anterior cruciate ligament may heal over time, but a torn acl requires surgery. after surgery, recovery is prolonged and low impact exercises are recommended to strengthen the joint. torn meniscus injury the menisci act as shock absorbers and separate the two ends of bone in the knee joint. there are two menisci in the knee, the medial (inner) and the lateral (outer). when there is torn cartilage, it means that the meniscus has been injured. meniscus tears occur during sports often when the knee is twisted. menisci injury may be innocuous and one may be able to walk after a tear, but soon swelling and pain set in. sometimes the knee will lock while bending. pain often occurs when one squats. small meniscus tears are treated conservatively but most large tears require surgery. fractures radiography to examine eventual fractures after a knee injury knee fractures are rare but do occur, especially as a result of a road accident. knee fractures include a patella fracture, and a type of avulsion fracture called a segond fracture. there is usually immediate pain and swelling, and a difficulty or inability to stand on the leg. the muscles go into spasm and even the slightest movements are painful. x-rays can easily confirm the injury and surgery will depend on the degree of displacement and type of fracture. ruptured tendon tendons usually attach muscle to bone. in the knee the quadriceps and patellar tendon can sometimes tear. the injuries to these tendons occur when there is forceful contraction of the knee. if the tendon is completely torn, bending or extending the leg is impossible. a completely torn tendon requires surgery but a partially torn tendon can be treated with leg immobilization followed by physical therapy. overuse overuse injuries of the knee include tendonitis, bursitis, muscle strains, and iliotibial band syndrome. these injuries often develop slowly over weeks or months. activities that induce pain usually delay healing. rest, ice and compression do help in most cases. once the swelling has diminished, heat packs can increase blood supply and promote healing. most overuse injuries subside with time but can flare up if the activities are quickly resumed. individuals may reduce the chances of overuse injuries by warming up prior to exercise, by limiting high impact activities and keep their weight under control. varus or valgus deformity hip-knee-ankle angle. there are two disorders relating to an abnormal angle in the coronal plane at the level of the knee: genu valgum is a valgus deformity in which the tibia is turned outward in relation to the femur, resulting in a knock-kneed appearance. genu varum is a varus deformity in which the tibia is turned inward in relation to the femur, resulting in a bowlegged deformity. the degree of varus or valgus deformity can be quantified by the hip-knee-ankle angle, which is an angle between the femoral mechanical axis and the center of the ankle joint. it is normally between 1.0° and 1.5° of varus in adults. normal ranges are different in children. hip-knee-ankle angle by age, with 95% prediction interval. surgical interventions before the advent of arthroscopy and arthroscopic surgery, patients having surgery for a torn acl required at least nine months of rehabilitation, having initially spent several weeks in a full-length plaster cast. with current techniques, such patients may be walking without crutches in two weeks, and playing some sports in 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, especially in female athletes, who have been shown to be especially vulnerable to acl tears from relatively minor trauma. articular cartilage repair treatment: arthroscopic debridement of the knee (arthroscopic lavage) mosaïc-plasty microfracture (ice-picking) autologous chondrocyte implantation osteochondral autograft and allografts plc reconstruction imaging mri both anterior cruciate ligament (acl) and posterior cruciate ligaments (pcl) are hypointense on both t1 and t2 weighted images of mri. however, some high signal striations are often seen at the distal part of the acl, making acl higher intensity than pcl on mri scans. knee mri (pd tse fs sagittal) knee mri (t1 tse sagittal) knee mr x-ray knee x-ray knee x-ray (weight bearing) knee x-ray (weight bearing, flexion) illustrations cruciate ligaments left knee-joint from behind, showing interior ligaments. capsule of right knee-joint (distended). lateral aspect. anterior and lateral view of knee. anterior view of knee. other animals in humans, the term "knee" refers to the joints between the femur, tibia, and patella, in the leg. in quadrupeds such as dogs, horses, and mice, the homologous joints between the femur, tibia, and patella, in the hind leg, are known as the stifle joint. also in quadrupeds, particularly horses, ungulates, and elephants, the layman's term "knee" also commonly refers to the forward-facing joint in the foreleg, the carpus, which is homologous to the human wrist. in birds, the "knee" refers to the joints between the femur and tibiotarsus, and also the patella (when present). the layman's term "knee" may also refer to the (lower and often more visible due to not being covered by feathers) joint between the tibiotarsus and tarsometatarsus, which is homologous to the human ankle. in insects and other animals, the term knee widely refers to any hinge joint.