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{{Infobox Anatomy |
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Name = Knee joints |
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Latin = articulatio genus |
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GraySubject = 93 |
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GrayPage = 339 |
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Image = Male Knee by David Shankbone.jpg |
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Caption = A knee |
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Image2 = |
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Caption2 = |
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Precursor = |
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System = |
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Artery = |
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Vein = |
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Nerve = [[femoral nerve|femoral]], [[obturator nerve|obturator]], [[sciatic nerve|sciatic]] |
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Lymph = |
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MeshName = Knee |
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MeshNumber = A01.378.610.450 |
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Dorlands = five/000056558|
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DorlandsID = Knee|
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}}
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The '''knee''' [[joint]] joins the thigh with the [[leg]] and consists of two articulations: one between the [[femur]] and [[tibia]], and one between the femur and [[patella]].<ref>{{EMedicineDictionary|knee+joint}}</ref> It is the largest and most complicated joint in the human body.<ref>Kulowski (1932), p 618</ref> The knee is a mobile trocho-ginglymus (i.e. a pivotal hinge joint),<ref>See [[trochoid]] and [[Hinge joint|ginglymus]].</ref> which permits [[flexion]] and [[extension]] as well as a slight medial and lateral rotation. 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]].
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== Human anatomy ==
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[[Image:Gray246.png|thumb|Articular surfaces of femur.]]
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[[Image:Gray257.png|thumb|Articular surfaces of tibia.]]
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The knee is a complex, compound, condyloid variety of a [[synovial joint]]. It actually comprises three functional compartments: the femoropatellar articulation consists of the [[patella]], or "kneecap", and the [[patellar groove]] on the front of the [[femur]] through which it slides; and the medial and lateral femorotibial articulations linking the femur, or thigh bone, with the [[tibia]], the main bone of the lower leg.<ref name="Burgener-390">Burgener (2002), p 390</ref> The joint is bathed in [[synovial fluid]] which is contained inside the [[synovial membrane]] called the [[Articular capsule of the knee joint|joint capsule]].
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Upon birth, a [[baby]] will 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.
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=== Articular bodies ===
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The articular bodies of the femur are its [[lateral condyle of femur|lateral]] and [[Medial condyle of femur|medial]] [[condyle]]s. These diverge slightly distally and posteriorly, with the lateral condyle being wider in front than at the back while the medial condyle is of more constant width.<ref name="Platzer-206">Platzer (2004), p 210</ref> The radius of the condyles' curvature in the [[sagittal plane]] becomes smaller toward the back. This diminishing radius produces a series of [[involute]] midpoints (i.e. located on a spiral). The resulting series of transverse axes permit the sliding and rolling motion in the flexing knee while ensuring the collateral ligaments are sufficiently lax to permit the rotation associated with the curvature of the medial condyle about a vertical axis.<ref name="Platzer-194">Platzer (2004), pp 194-195</ref>
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The pair of tibial condyles are separated by the intercondylar eminence<ref name="Platzer-206" /> composed of a lateral and a medial tubercle<ref name="Platzer-202">Platzer (2004), p 202</ref>.
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The [[patella]] is inserted into the thin anterior wall of the joint capsule.<ref name="Platzer-206" /> On its posterior surface is a lateral and a medial articular surface<ref name="Platzer-194" />, both of which communicate with the [[Patellar surface of femur|patellar surface]] which unites the two femoral condyles on the anterior side of the bone's distal end.<ref name="Platzer-192">Platzer (2004), p 192</ref>
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=== Articular capsule ===
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{{double image|right|Gray351.png|100|Gray352.png|100|Lateral and posterior aspects of right knee}}
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{{main|Articular capsule of the knee joint}}
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The articular capsule has a [[Synovial fluid|synovial]] and a [[fibrous]] membrane separated by fatty deposits. Anteriorly, the synovial membrane is attached on the margin of the cartilage both on the femur and the tibia, but on the femur, the suprapatellar bursa or recess extends the joint space proximally. Behind, the synovial membrane is attached to the margins of the two femoral condyles which produces two extensions similar to the anterior recess. Between these two extensions, the synovial membrane passes in front of the two cruciate ligaments at the center of the joint, thus forming a pocket direct inward.
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<ref name="Platzer-210">Platzer (2004), p 210</ref>
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=== Bursae ===
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{{main|Bursae of the knee joint}}
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Numerous [[bursa (anatomy)|bursae]] surround the knee joint. The largest communicative bursa is the [[suprapatellar bursa]] described above. Four considerably smaller bursae are located on the back of the knee. Two non-communicative bursae are located in front of the patella and below the patellar tendon, and others are sometimes present.
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<ref name="Platzer-210" />
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=== Menisci ===
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The [[articular disk]]s of the knee-joint are called [[meniscus (anatomy)|menisci]] because they only partly divide the joint space.<ref name0"Platzer-26>Platzer (2004), p 26</ref> These two disks, the [[medial meniscus]] and the [[lateral meniscus]], consist of connective tissue with extensive collagen fibers containing cartilage-like cells. Strong fibers run along the menisci from one attachment to the other, while weaker radial fibers are interlaced with the former. The menisci are flattened at the center of the knee joint, fused with the synovial membrane laterally, and can move over the tibial surface.
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<ref name="Platzer-208">Platzer (2004), p 208</ref>
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The menisci 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, and may be cracked, or torn, when the knee is forcefully rotated and/or bent.
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=== Ligaments ===
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[[Image:Knee diagram.svg|thumb|Anterolateral aspect of knee.]]
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[[Image:Knee medial view.gif|thumb|Anteromedial aspect of knee]]
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The ligaments surrounding the knee joint offer stability by limiting movements and, together with several menisci and bursae, protects the articular capsule.
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==== Intracapsular ====
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The [[anterior cruciate ligament]] (ACL) stretches from the [[lateral condyle of femur]] to the [[anterior intercondylar area]] The ACL is critically important because it prevents the tibia from being pushed too far anterior relative to the femur. It is often torn during twisting or bending of the knee. The [[posterior cruciate ligament]] (PCL) stretches from [[medial condyle of femur]] to the [[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.
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The [[Transverse ligament of knee|transverse ligament]] stretches from the [[lateral meniscus]] to the [[medial meniscus]]. It passes in front of the menisci. Is divided into several strips in 10% of cases.<ref name="Platzer-208" /> The two menisci are attached to each others anteriorly by the ligament.<ref>Diab (1999), p 200</ref> The [[posterior meniscofemoral ligament|posterior]] and [[anterior meniscofemoral ligament]]s stretch from posterior horn of lateral meniscus to the medial femoral condyle. They pass posteriorly behind the posterior cruciate ligament. The posterior meniscofemoral ligament is more commonly present (30%); both ligaments are present less often.<ref name="Platzer-208" /> The [[Coronary ligament of the knee|meniscotibial ligaments]] (or "coronary") stretches from inferior edges of the mensici to the periphery of the tibial plateaus.
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==== Extracapsular ====
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The [[patellar ligament]] connects the [[patella]] to the [[tuberosity of the tibia]]. It is 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.<ref>MedicineNet.com, ''Definition of Patellar tendon''</ref> This very strong ligament helps give the patella its mechanical leverage<ref name="Moore-954">Moore (2006), p 194</ref> and also functions as a cap for the condyles of the femur.
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Laterally and medially to the patellar ligament the [[lateral patellar retinaculum|lateral]] and [[medial patellar retinaculum|medial patellar retinacula]] connect fibers from the [[Vastus lateralis muscle|vasti lateralis]] and [[Vastus medialis muscle|medialis muscles]] to the tibia. Some fibers from the [[iliotibial tract]] radiates into the lateral retinaculum and the medial retinaculum receives some transverse fibers arising on the medial femoral epicondyle.
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<ref name="Platzer-206" />
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The [[medial collateral ligament]] (MCL a.k.a. "tibial") stretches from the [[medial epicondyle of the femur]] to the [[medial tibial condyle]]. It is composed of three groups of fibers, one stretching between the two bones, and two fused with the medial meniscus. The MCL is partly covered by the [[Pes anserinus (leg)|pes anserinus]] and the tendon of the [[semimembranosus muscle|semimembranosus]] passes under it.<ref name="Platzer-206" /> It protects the medial side of the knee from being bent open by a stress applied to the lateral side of the knee (a [[valgus deformity|valgus]] force).
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The [[lateral collateral ligament]] (LCL a.k.a. "fibular") stretches from the [[lateral epicondyle of the femur]] to the [[head of fibula]]. It is separated from both the joint capsule or the lateral meniscus.<ref name="Platzer-206" />. It protects the lateral side from an inside bending force (a [[varus deformity|varus]] force).
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Lastly, there are two ligaments on the dorsal side of the knee. The [[oblique popliteal ligament]] is a radiation of the tendon of the [[Semimembranosus muscle|semimembranosus]] on the medial side, from where it is direct laterally and proximally. The [[arcuate popliteal ligament]] originates on the apex of the head of the fibula to stretch proximally, crosses the tendon of the [[popliteus muscle]], and passes into the capsule.<ref name="Platzer-206" />
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=== Movements ===
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{| class="wikitable" align="right"
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|+ Maximum movements<ref name="Thieme-Atlas-398">''Thieme Atlas of Anatomy'' (2006), pp 398-399</ref> and muscles<ref name="Platzer-252">Platzer (2004), p 252</ref>
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|-
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! Extension 120-150° !! Flexion 5-10°
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|-
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| [[Quadriceps femoris muscle|Quadriceps]] (with<br />some assistance from<br />the [[Tensor fasciae latae]])
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| (In order of importance)<br />[[Semimembranosus muscle|Semimembranosus]]<br />[[Semitendinosus muscle|Semitendinosus]]<br />[[Biceps femoris muscle|Biceps femoris]]<br />[[Gracilis muscle|Gracilis]]<br />[[Sartorius muscle|Sartorius]]<br />[[Popliteus muscle|Popliteus]]<br />[[Gastrocnemius muscle|Gastrocnemius]]
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|-
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! External rotation* 30-40° !! Internal rotation* 10°
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|-
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| (In order of importance)<br />Semimembranosus<br />Semitendinosus<br />Gracilis Sartorius<br />Popliteus
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| Biceps femoris
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|-
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| colspan="2" | *(knee flexed 90°)
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|}
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The knee permits [[flexion]] and [[extension]] about a virtually transversal 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 [[meniscus (anatomy)|menisci]] move over the tibia during rotation, while the femur rolls and glides over the menisci during extension-flexion.<ref name="Platzer-212">Platzer (2004), pp 212-213</ref>
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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, why 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 of several parameters such as soft-tissue restraints, active insufficiency, and hamstring tightness.<ref name="Thieme-Atlas-398" />
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===== Extended position =====
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With the knee extended both the [[lateral collateral ligament|lateral]] and [[medial collateral ligament]]s, as well as the anterior part of the [[anterior cruciate ligament]], are taut. During extension, the femoral condyles glide 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 the [[iliotibial tract]] and is caused by the stretching of the anterior cruciate ligament. Both cruciate ligaments are slightly unwinded and both lateral ligaments become taut.<ref name="Platzer-212" />
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===== Flexed position =====
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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 unwounded 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°.<ref name="Platzer-212" />
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===Blood supply===
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[[Image:Gray552.png|thumb|Arteris of the knee]]
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The femoral artery and the popliteal artery help form the arterial network surrounding the knee joint (articular rete). There are 6 main branches:
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* 1. [[Superior medial genicular artery]]
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* 2. [[Superior lateral genicular artery]]
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* 3. [[Inferior medial genicular artery]]
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* 4. [[Inferior lateral genicular artery]]
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* 5. [[Descending genicular artery]]
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* 6. [[Recurrent branch of anterior tibial artery]]
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The medial genicular arteries penetrate the knee joint.
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==Disorders and injury==
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[[Image:Prothese-genou-IMG 0033.jpg|thumb|Model demonstrating parts of an artificial knee]]
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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(ACL), 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|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.
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Before the advent of [[arthroscopy]] and [[arthroscopic surgery]], patients having surgery for a torn ACL required at least nine months of rehabilitation. With [[Anterior cruciate ligament reconstruction|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 [[Ruckman (AFL)|ruck]] contests, involving the crashing of two knees during the leap. These injuries forced new rule changes for the 2005 season.
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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.
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There are disorders of the knee which are not necessarily the result of injury, for example [[patellofemoral syndrome]] and [[arthritis]].
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==Diagnosis==
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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.
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The diagnosis is usually confirmed by [[MRI]], the availability of which has greatly lessened the number of purely diagnostic [[arthroscopy|arthroscopies]] performed.
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== Animal anatomy ==
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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 joint|stifle]] in quadrupeds. In insects and other animals the term knee is used widely to refer to any ginglymus joint.
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== See also ==
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{{Wiktionarypar|knee}}
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{{commonscat|Knees}}
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{{commonscat|Knee joint}}
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* [[Cartilage]]
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* [[Knee Cartilage Replacement Therapy]]
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* [[Knee examination]]
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* [[Leglock#Kneebar|Kneebar]]
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* [[Reflex hammer]]
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* [[Partial knee replacement]]
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==Additional images==
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<gallery>
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Image:Knie ct.gif|Knee MR
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Image:Knie mr.jpg|Knee MR
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Image:Knie-roentgen-r-seite.jpg|Knee X-ray
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Image:Legamenti crociati.jpg|Cruciate ligaments
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Image:Gray348.png|Left knee-joint from behind, showing interior ligaments.
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Image:Gray351.png|Capsule of right knee-joint (distended). Lateral aspect.
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Image:Knee skeleton lateral anterior views.svg|Anterior and lateral view of knee.
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</gallery>
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== Notes ==
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{{reflist|2}}
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==References==
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* {{cite book
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| url = http://books.google.com/books?id=brsH_IqPzzoC&pg=PA390
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| title = Differential Diagnosis in Magnetic Resonance Imaging
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| first = Francis A. | last = Burgener | coauthors = Meyers, Steven P.; Tan, Raymond K.
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| publisher = Thieme | date = 2002
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| isbn = 1588900851<!--- 9781588900852 --->
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}}
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* {{cite book
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| title = Lexicon of Orthopaedic Etymology
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| url = http://books.google.com/books?id=fstFQVnw8-wC&pg=PA200
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| first = Mohammad | last = Diab
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| publisher = Taylor & Francis | date = 1999
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| isbn = 9057025973
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}}
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* {{cite journal
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| url = http://www.ejbjs.org/cgi/reprint/14/3/618.pdf
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| title = Flexion Contracture of the Knee: The Mechanics of the Muscular Contracture and the Turnbuckle Cast Method of Treatment
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| first = Jacob | last = Kulowski
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| publisher = [[Journal of Bone and Joint Surgery]]
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| year = 1932 | issue = 14 < pages = 618-630
  +
}}
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* {{cite book
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| url = http://books.google.com/books?id=SxuA3T7JbQkC&pg=PA594
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| title = Clinically Oriented Anatomy
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| first = Keith L. | last = Moore | coauthors = Dalley, Arthur F.: Agur, A. M. R.
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| publisher = [[Lippincott Williams & Wilkins]] | year = 2006
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| isbn = 0781736390
  +
}}
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* {{cite book
  +
| first = Werner | last = Platzer
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| title = Color Atlas of Human Anatomy, Vol. 1: Locomotor System
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| publisher = [[Thieme Medical Publishers|Thieme]] | isbn = 3-13-533305-1<!---US: 1-58890-159-9--->
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| year = 2004 | edition = 5th | pages = 206-213
  +
}}
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* {{cite web
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| url = http://www.medterms.com/script/main/art.asp?articlekey=34200
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| title = Definition of patellar tendon
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| publisher = MedicineNet.com | accessdate = 2008-12-11
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}}
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* {{cite book
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| title = Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System
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| publisher = Thieme | year = 2006 | isbn = 1-58890-419-9
  +
}}
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{{Joints of lower limbs}}
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{{human anatomical features}}
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[[Category:Joints (anatomy)|*Knee]]
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Latest revision as of 00:58, 4 April 2009

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Knee joints
File:Male Knee by David Shankbone.jpg
A knee
Latin articulatio genus
Gray's subject #93 339
System
MeSH A01.378.610.450
[[Image:|190px|center|]]

The knee joint joins the thigh with the leg and consists of two articulations: one between the femur and tibia, and one between the femur and patella.[1] It is the largest and most complicated joint in the human body.[2] The knee is a mobile trocho-ginglymus (i.e. a pivotal hinge joint),[3] which permits flexion and extension as well as a slight medial and lateral rotation. 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.

Human anatomy

File:Gray246.png

Articular surfaces of femur.

File:Gray257.png

Articular surfaces of tibia.

The knee is a complex, compound, condyloid variety of a synovial joint. It actually comprises three functional compartments: the femoropatellar articulation consists of the patella, or "kneecap", and the patellar groove on the front of the femur through which it slides; and the medial and lateral femorotibial articulations linking the femur, or thigh bone, with the tibia, the main bone of the lower leg.[4] The joint is bathed in synovial fluid which is contained inside the synovial membrane called the joint capsule.

Upon birth, a baby will 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.

Articular bodies

The articular bodies of the femur are its lateral and medial condyles. These diverge slightly distally and posteriorly, with the lateral condyle being wider in front than at the back while the medial condyle is of more constant width.[5] The radius of the condyles' curvature in the sagittal plane becomes smaller toward the back. This diminishing radius produces a series of involute midpoints (i.e. located on a spiral). The resulting series of transverse axes permit the sliding and rolling motion in the flexing knee while ensuring the collateral ligaments are sufficiently lax to permit the rotation associated with the curvature of the medial condyle about a vertical axis.[6]

The pair of tibial condyles are separated by the intercondylar eminence[5] composed of a lateral and a medial tubercle[7].

The patella is inserted into the thin anterior wall of the joint capsule.[5] On its posterior surface is a lateral and a medial articular surface[6], both of which communicate with the patellar surface which unites the two femoral condyles on the anterior side of the bone's distal end.[8]

Articular capsule

File:Gray351.png File:Gray352.png
Lateral and posterior aspects of right knee
Main article: Articular capsule of the knee joint

The articular capsule has a synovial and a fibrous membrane separated by fatty deposits. Anteriorly, the synovial membrane is attached on the margin of the cartilage both on the femur and the tibia, but on the femur, the suprapatellar bursa or recess extends the joint space proximally. Behind, the synovial membrane is attached to the margins of the two femoral condyles which produces two extensions similar to the anterior recess. Between these two extensions, the synovial membrane passes in front of the two cruciate ligaments at the center of the joint, thus forming a pocket direct inward. [9]

Bursae

Main article: Bursae of the knee joint

Numerous bursae surround the knee joint. The largest communicative bursa is the suprapatellar bursa described above. Four considerably smaller bursae are located on the back of the knee. Two non-communicative bursae are located in front of the patella and below the patellar tendon, and others are sometimes present. [9]

Menisci

The articular disks of the knee-joint are called menisci because they only partly divide the joint space.[10] These two disks, the medial meniscus and the lateral meniscus, consist of connective tissue with extensive collagen fibers containing cartilage-like cells. Strong fibers run along the menisci from one attachment to the other, while weaker radial fibers are interlaced with the former. The menisci are flattened at the center of the knee joint, fused with the synovial membrane laterally, and can move over the tibial surface. [11]

The menisci 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, and may be cracked, or torn, when the knee is forcefully rotated and/or bent.

Ligaments

File:Knee diagram.svg

Anterolateral aspect of knee.

File:Knee medial view.gif

Anteromedial aspect of knee

The ligaments surrounding the knee joint offer stability by limiting movements and, together with several menisci and bursae, protects the articular capsule.

Intracapsular

The anterior cruciate ligament (ACL) stretches from the lateral condyle of femur to the anterior intercondylar area The ACL is critically important because it prevents the tibia from being pushed too far anterior relative to the femur. It is often torn during twisting or bending of the knee. The posterior cruciate ligament (PCL) stretches from medial condyle of femur to the 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.

The transverse ligament stretches from the lateral meniscus to the medial meniscus. It passes in front of the menisci. Is divided into several strips in 10% of cases.[11] The two menisci are attached to each others anteriorly by the ligament.[12] The posterior and anterior meniscofemoral ligaments stretch from posterior horn of lateral meniscus to the medial femoral condyle. They pass posteriorly behind the posterior cruciate ligament. The posterior meniscofemoral ligament is more commonly present (30%); both ligaments are present less often.[11] The meniscotibial ligaments (or "coronary") stretches from inferior edges of the mensici to the periphery of the tibial plateaus.

Extracapsular

The patellar ligament connects the patella to the tuberosity of the tibia. It is 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.[13] This very strong ligament helps give the patella its mechanical leverage[14] and also functions as a cap for the condyles of the femur. Laterally and medially to the patellar ligament the lateral and medial patellar retinacula connect fibers from the vasti lateralis and medialis muscles to the tibia. Some fibers from the iliotibial tract radiates into the lateral retinaculum and the medial retinaculum receives some transverse fibers arising on the medial femoral epicondyle. [5]

The medial collateral ligament (MCL a.k.a. "tibial") stretches from the medial epicondyle of the femur to the medial tibial condyle. It is composed of three groups of fibers, one stretching between the two bones, and two fused with the medial meniscus. The MCL is partly covered by the pes anserinus and the tendon of the semimembranosus passes under it.[5] It 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). The lateral collateral ligament (LCL a.k.a. "fibular") stretches from the lateral epicondyle of the femur to the head of fibula. It is separated from both the joint capsule or the lateral meniscus.[5]. It protects the lateral side from an inside bending force (a varus force).

Lastly, there are two ligaments on the dorsal side of the knee. The oblique popliteal ligament is a radiation of the tendon of the semimembranosus on the medial side, from where it is direct laterally and proximally. The arcuate popliteal ligament originates on the apex of the head of the fibula to stretch proximally, crosses the tendon of the popliteus muscle, and passes into the capsule.[5]

Movements

Maximum movements[15] and muscles[16]
Extension 120-150° Flexion 5-10°
Quadriceps (with
some assistance from
the Tensor fasciae latae) 		(In order of importance)
Semimembranosus
Semitendinosus
Biceps femoris
Gracilis
Sartorius
Popliteus
Gastrocnemius
External rotation* 30-40° Internal rotation* 10°
(In order of importance)
Semimembranosus
Semitendinosus
Gracilis Sartorius
Popliteus 		Biceps femoris
*(knee flexed 90°)

The knee permits flexion and extension about a virtually transversal 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 menisci move over the tibia during rotation, while the femur rolls and glides over the menisci during extension-flexion.[17]

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, why 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 of several parameters such as soft-tissue restraints, active insufficiency, and hamstring tightness.[15]

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 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 the iliotibial tract and is caused by the stretching of the anterior cruciate ligament. Both cruciate ligaments are slightly unwinded and both lateral ligaments become taut.[17]

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 unwounded 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°.[17]

Blood supply

File:Gray552.png

Arteris of the knee

The femoral artery and the popliteal artery help form the arterial network surrounding the knee joint (articular rete). There are 6 main branches:

  • 1. Superior medial genicular artery
  • 2. Superior lateral genicular artery
  • 3. Inferior medial genicular artery
  • 4. Inferior lateral genicular artery
  • 5. Descending genicular artery
  • 6. Recurrent branch of anterior tibial artery

The medial genicular arteries penetrate the knee joint.

Disorders and injury

File:Prothese-genou-IMG 0033.jpg

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. An increasingly common victim to injury is the anterior cruciate ligament(ACL), 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.

There are disorders of the knee which are not necessarily the result of injury, for example patellofemoral syndrome and arthritis.

Diagnosis

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.

The diagnosis is usually confirmed by MRI, the availability of which has greatly lessened the number of purely diagnostic arthroscopies performed.

Animal anatomy

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.

See also

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Additional images

Notes

  1. ↑ Dictionary at eMedicine knee+joint
  2. ↑ Kulowski (1932), p 618
  3. ↑ See trochoid and ginglymus.
  4. ↑ Burgener (2002), p 390
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 Platzer (2004), p 210
  6. ↑ 6.0 6.1 Platzer (2004), pp 194-195
  7. ↑ Platzer (2004), p 202
  8. ↑ Platzer (2004), p 192
  9. ↑ 9.0 9.1 Platzer (2004), p 210
  10. ↑ Platzer (2004), p 26
  11. ↑ 11.0 11.1 11.2 Platzer (2004), p 208
  12. ↑ Diab (1999), p 200
  13. ↑ MedicineNet.com, Definition of Patellar tendon
  14. ↑ Moore (2006), p 194
  15. ↑ 15.0 15.1 Thieme Atlas of Anatomy (2006), pp 398-399
  16. ↑ Platzer (2004), p 252
  17. ↑ 17.0 17.1 17.2 Platzer (2004), pp 212-213

References


v·d·e
Joints and ligaments of lower limbs
Coxal/hip

iliofemoral - pubofemoral - ischiofemoral - head of femur - transverse acetabular

Knee-joint

patellar - popliteal (oblique, arcuate) - collateral (medial/tibial, lateral/fibular) - cruciate (anterior, posterior) - menisci (medial, lateral)

Tibiofibular

Superior tibiofibular: anterior of the head of the fibula - posterior of the head of the fibula
Inferior tibiofibular: anterior of the lateral malleolus - posterior of the lateral malleolus

Talocrural/ankle

deltoid - external lateral of the ankle-joint (anterior talofibular, posterior talofibular, calcaneofibular)

Foot - intertarsal

Subtalar/talocalcaneal: anterior talocalcaneal - posterior talocalcaneal - lateral talocalcaneal - medial talocalcaneal - interosseous talocalcaneal
Talocalcaneonavicular: dorsal talonavicular
Calcaneocuboid: dorsal calcaneocuboid - bifurcated - long plantar - plantar calcaneocuboid
Transverse tarsal: plantar calcaneonavicular/spring

Foot - other

Cuneonavicular, Cuboideonavicular, Intercuneiform and cuneocuboid, Tarsometatarsal/Lisfranc, Intermetatarsal, Metatarsophalangeal, Interphalangeal
Arches of the foot (Longitudinal, Transverse)

Human anatomical features
Human body features

HEAD: Forehead – Eye – Ear – Nose – Mouth – Tongue – Teeth – Jaw – Face – Cheek – Chin

NECK: Throat – Adam's apple

TORSO: Shoulders – Spine – Chest – Breast – Ribcage – Abdomen – Belly button

Sex organs (Penis/Scrotum/Testicle or Clitoris/Vagina/Ovary/Uterus) – Hip – Anus – Buttocks

LIMBS: Arm – Elbow – Forearm – Wrist – Hand – Finger (Thumb - Index finger - Middle finger - Ring finger - Little finger) – Leg – Lap – Thigh – Knee – Calf – Heel – Ankle – Foot – Toe (Hallux)

SKIN: Hair


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