The knee is a complex, compound, condyloid variety of a synovial joint which hovers. It actually comprises two separate joints.
The recess behind the knee is called the popliteal fossa. It can also be called a "knee pit."
|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. It is often torn during twisting or bending of the knee.|
|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 displacement of the tibia relative to the femur.|
|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||-||Tendinous expansion of the semimembranosus muscle. Strengthens the back of the capsule|
|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.|
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:
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 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, 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 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 test is similar, but performed with the knee in only about twenty degrees of flexion, while the pivot-shift test adds 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.