Author: Gordana Sendic•Reviewer: Declan Tempany BSc (Hons)Last reviewed: September 30, 2021Reading time: 25 minutes

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Knee joint (Articulatio genu)

The knee joint is a synovial joint that connects three bones; the femur, tibia and also patella. The is a facility hinge joint written of two articulations; the tibiofemoral joint and patellofemoral joint. The tibiofemoral share is an articulation between the tibia and also the femur, when the patellofemoral share is an articulation between the patella and also the femur.

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The knee share is the largest and also arguably the most stressed share in the body. The arrangement of the skeleton in the joint gives a fulcrum that translates the action of the flexor and extensor muscles of the knee. The arrangement of the extracapsular and intracapsular and ligaments, as well as extensions that muscles that cross the joint, provide the much needed stability that counters the substantial biomechanical stress brought upon the joint. As a hinged joint, the knee joint mostly allows movement follow me one axis in terms of flexion and also extension of the knee in the sagittal plane. The also allows slight medial rotation throughout flexion and also the last stage of extension of the knee, and also lateral rotation when “unlocking” the knee.

Key facts about the knee joint
TypeTibiofemoral joint: Synovial hinge joint; uniaxialPatellofemoral joint: plane joint
Articular surfacesTibiofemoral joint: lateral and also medial condyles of femur, tibial plateausPatellofemoral joint: patellar surface of femur, posterior surface ar of patella
Ligaments and also MenisciExtracapsular ligaments: patellar ligament, medial and lateral patellar retinacula, tibial (medial) collateral ligament, fibular (lateral) collateral ligament, oblique popliteal ligament, arcuate popliteal ligament, anterolateral ligament (ALL)Intracapsular ligaments: anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial meniscus, lateral meniscus
InnervationFemoral nerve (nerve come vastus medialis, saphenous nerve) tibial and common fibular (peroneal) nerves, posterior department of the obturator nerve
Blood supplyGenicular branches that lateral circumflex femoral artery, femoral artery, posterior tibial artery, anterior tibial artery and popliteal artery
MovementsExtension, flexion, medial rotation, lateral rotation

This write-up will comment on the anatomy and duty of the knee joint.


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The tibiofemoral share is an expression between the lateral and also medial condyles that the distal end of the femur and also the tibial plateaus, both of which space covered through a thick layer of hyaline cartilage.

The lateral and also medial condyles space two bony projections located at the distal end of the femur, which have actually a smooth convex surface, and also are be separate posteriorly by a deep groove well-known as the intercondylar fossa. The medial condyle is larger, more narrow and also further projected 보다 its lateral counterpart, which accounts because that the angle in between the femur and also the tibia. The roughened external surfaces that the medial and lateral condyles are defined as medial and lateral epicondyles, respectively. Follow me the posterior aspect of the distal femur, there are paired turbulent elevations above the medial and also lateral epicondyles known as the medial and lateral supracondylar ridges.

The tibial plateaus are the two slightly concave exceptional surfaces of the condyles located at the proximal finish of the tibia, and also are be separate by a bony protuberance recognized as the intercondylar eminence. The medial tibial articular surface ar is somewhat oval shaped along its anteroposterior length, while the lateral articular surface is an ext circular in shape

The articular surface of the tibiofemoral joint are typically incongruent, for this reason compatibility is listed by the medial and lateral meniscus. These are crescent-shaped fibrocartilaginous frameworks that permit a more even circulation of the femoral push on the tibia.

The patellofemoral joint


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The patellofemoral joint is a saddle joint formed by the coupling of the patellar surface ar of femur (also known as the trochlear groove the femur) and the posterior surface ar of patella. The patellar surface ar of femur is a groove on the anterior next of the distal femur, i m sorry extends posteriorly right into the intercondylar fossa.

The patella is a triangular shaped bone, through a bent proximal base and also a pointed distal apex. Its articular surface is defined by medial and also lateral facets which space concave articular surfaces extended with a special layer the hyaline cartilage and separated by a vertical ridge. Medial come the medial facet is a 3rd minor facet, known as the ‘odd’ facet which lacks hyaline cartilage.

Being a sesamoid bone, the patella is tightly embedded and also held in ar by the tendon that the quadriceps femoris muscle. Top top the distal component of the patella, an expansion of the quadriceps femoris tendon forms a central band referred to as the patellar ligament. That is a strong, thick ligament the extends native the patellar apex come the premium area that the tibial tuberosity.

To solidify her knowledge, take it a quiz on the skeleton contributing to the knee joint!


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skeleton articulating at the knee share for a wider topic focus, try this customizable quiz.

Joint capsule

The joint capsule of the knee joint is among a composite nature, mainly developed by muscle tendons and also their expansions, forming a thick ligamentous sheath around the joint. The capsule is relatively weak and also attached to the spare part of the femoral and tibial articular surfaces. The anterior portion of the capsule features an opening, whose margins attach to the boundaries of the patella. A 2nd gap is also present in the lateroposterior section of the capsule to offer passage come the tendon that the popliteus muscle.

The capsule is created from an external fibrous great (which is constant with adjacent tendons) and an inside synovial membrane that lubricates the articular surfaces, to reduce friction in enhancement to offering nourishment come the cartilage. The joint capsule creates several liquid filled pouches called bursae, that reduce friction in ~ the knee joint. Remarkable bursa of the knee joint incorporate the:

Suprapatellar bursa - located superior to the patella between the femur and the tendon that the quadriceps musclePrepatellar bursa- Lies in former of the patella between the patella and also the skinInfrapatellar bursa - located under the patella between the patellar ligament and the tibia
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Ligaments and also menisci

The ligaments of the knee joint can be divided into 2 groups; extracapsular ligaments and also intracapsular ligaments. These ligaments affix the femur and tibia, holding them in place, giving stability, and preventing dislocation.

Extracapsular ligaments are discovered outside the share capsule and also include the patellar ligament, fibular (lateral) and tibial (medial) collateral ligaments, and oblique and also arcuate popliteal ligaments. Intracapsular ligaments are discovered inside the joint capsule, with the cruciate ligaments gift the most famous of this subgroup.

Patellar ligament


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The patellar ligament is a strong, special fibrous band that is a distal extension of the quadriceps femoris tendon. The is uncovered superficial/anterior to the infrapatellar bursa and also extends native the apex the patella to the tibial tuberosity.

Along its external margins, the patellar ligament blends with the medial and also lateral patellar retinacula, which are extensions of the vastus medialis and lateralis muscles, respectively, as well as the overlying fascia. The patellar ligament plays a major role in stabilizing the patella and preventing that is displacement.

Lateral (fibular) collateral ligament


The fibular collateral ligament is a solid ligament that originates native the lateral epicondyle of the femur, just posterior to the proximal attachments of the popliteus, and also extends distally to connect on the lateral surface of the fibular head.

As that attaches to the fibular head, the ligament splits the tendon of biceps femoris muscle in two. The fibular collateral ligament is discovered deep come the lateral patellar retinaculum, and superficial come the tendon that popliteus muscle, i m sorry separates the ligament indigenous the lateral meniscus.

Medial (tibial) collateral ligament

The tibial collateral ligament is the strong, level ligament that the medial element of the knee joint. The tibial collateral ligament, in addition to its fibular counterpart, acts to secure the knee joint and prevent extreme sideways activity by restricting external and internal rotation of the prolonged knee. The tibial collateral ligament is sometimes divided the literature right into superficial and deep parts:

Superficial part: originates simply proximal the medial epicondyle that the femur. This ligament has actually two attachment points; a proximal attachment on the medial condyle that the tibia, and also a distal attachment on the medial obelisk of the tibia. Anteriorly, the superficial part blends through the medial patellar retinaculum and the medial patellofemoral ligament, which process from the medial femoral condyle to connect onto the medial border that the patella.Deep part: a vertical thickening the the knee share capsule discovered underneath the superficial component of the tibial collateral ligament. The originates native the area of the distal femur, then attaches to the medial meniscus, and terminates on the proximal tibia. These two components of the ligament are defined as meniscofemoral and meniscotibial ligaments (see below).

Oblique popliteal ligament


The tilt popliteal ligament (Bourgery ligament) is an expansion of the semimembranosus tendon i beg your pardon originates posterior come the medial tibial condyle and also reflects superiorly and also laterally to affix on the lateral condyle of the femur.

As that spans the intercondylar fossa, the tilt popliteal ligament reinforces the posterior part of the share capsule and also blends v its main portion.

Arcuate popliteal ligament

Arcuate popliteal ligament is a thick, fibrous band the arises on the posterior aspect of the fibular head and arches superiorly and medially to affix on the posterior side of the joint capsule that the knee. The arcuate popliteal ligament reinforces the posterolateral part of the joint capsule, and along with the slope popliteal ligament, prevents overextension that the knee joint.

Cruciate ligaments


The paired cruciate ligaments acquired their name due to the fact that they overcome each various other obliquely within the joint in a way that each other a overcome (latin = crux), or a letter X. They overcome within the share capsule, yet remain exterior to the synovial cavity. The cruciate ligaments are split as follows:

Anterior cruciate ligament: arises from the anterior intercondylar area the the tibia simply behind the attachment of the medial meniscus, and also extends posterolaterally and also proximally to affix on the posterior part of the medial surface of the lateral femoral condyle. As it crosses to the other side that the knee joint, the ligament passes underneath the transverse ligament (see below) and blends v the anterior horn of the lateral meniscus. The anterior cruciate ligament is crucial to prevent posterior rolling and displacement of the femoral condyle throughout flexion, and also to prevent hyperextension the the knee joint.Posterior cruciate ligament: occurs from the posterior intercondylar area of the tibia and extends anteromedially and proximally to attach on the anterior part of the lateral surface ar of the medial femoral condyle. This ligament is practically twice as strong and has much better blood supply 보다 the anterior cruciate ligament. The posterior cruciate ligament has actually the opposite function of the anterior cruciate ligament, offer to prevent anterior rolling and also displacement that the femoral condyle throughout extension, and also to avoid hyperflexion of the knee joint.

Menisci


The menisci are fibrocartilaginous crescent-shaped bowl found between the articular surfaces of the femur and also tibia and also serve to administer their congruence and also shock absorption. The menisci room thick and vascularized in their outer one third, while your inner 2 thirds space thinner and also avascular. Additionally, the inner two thirds contain radially organized collagen bundles, vice versa, the outer 3rd contains bigger circumferentially i ordered it bundles. Thus, that is believed that the inner section is more adapted for weight-bearing and also resisting compressive forces, while the outer portions room suited because that resisting tensional forces. The menisci are separated as follows:

Medial meniscus: a C-shaped, nearly semicircular fibrocartilaginous plate the overlies the surface ar of the medial tibial plateau. The anterior horn attaches on the anterior intercondylar area of tibia and blends with the anterior cruciate ligament. Its posterior horn is attached come the posterior intercondylar area the the tibia, between the attachments that the lateral meniscus and also the posterior cruciate ligament.Lateral meniscus: an practically circular fibrocartilaginous plate the overlies the surface of the lateral tibial plateau. The anterior horn likewise attaches to the anterior intercondylar area of tibia and also partially blends with the anterior cruciate ligament. Similarly, that is posterior horn attaches to the posterior intercondylar areas anterior to the posterior horn that the medial meniscus.

The menisci are held in place by numerous ligaments, including the transverse ligament, meniscofemoral ligaments and also meniscotibial (coronary) ligaments. By stability the menisci, this ligaments are likewise indirectly connected in staying clear of displacement the the knee joint.

Transverse ligament: associate the menisci anteriorly expanding from the anterior margin that the lateral meniscus come the anterior horn of the medial meniscus. The exact role is uncertain yet it is believed that this ligaments stabilizes the menisci during knee movements and decrease tension produced in the longitudinal circumferential fibres.Meniscofemoral ligaments: room the superior parts of the distal tibial collateral ligament expanding from the posterior horn the the lateral meniscus to the lateral aspect of the medial femoral condyle. Lock are separated into two ligaments; one anterior meniscofemoral ligament (of Humphry) that courses anterior to the posterior cruciate ligament; and a posterior meniscofemoral ligament (of Wrisberg), that runs posterior come the posterior cruciate ligament.Meniscotibial (coronary) ligaments: space the inferior sections of the distal tibial collateral ligament, extend between the margin of the lateral meniscus and the peripheral area of the tibial condyles. It is made up of a medial and lateral meniscotibial (coronary) ligament.Patellomeniscal ligament: comprised of a medial and also lateral patellomeniscal ligament, often explained as merely medial and also lateral ligaments. These ligaments run from the inferior 3rd of the patella come insert ~ above the anterior portion of the medial and also lateral meniscus, respectively.

Other ligaments

Some other noteworthy ligaments the the knee joint include ligamentum mucosum, popliteofibular and also fabellofibular ligament.

Ligamentum mucosum: is composed of 2 alar crease that connect onto the infrapatellar fat pad, holding that in position. This framework is one embryonic remnant that separates the medial and lateral compartments the the knee.Popliteofibular ligament: located on the posterolateral facet of the knee joint, prolonging from the popliteus muscle to the medial element of the fibula.Fabellofibular ligament: arises from a tiny sesamoid bone ~ above the posterior aspect of the lateral supracondylar ridge of the femur and also inserts distally top top the posterolateral sheet of the styloid process of the fibula.

Innervation

The knee joint receives innervation indigenous the femoral nerve, via the saphenous nerve and also muscular branches. The joint likewise receives contributions from the tibial and common fibular (peroneal) nerves, and also the posterior division of the obturator nerve.

Blood supply

The knee joint has a rich vascularization stemming from the genicular anastomosis developed by numerous arterial blood vessels. Over there are about ten arteries affiliated in the formation of the genicular anastomosis:

In current years however, a examine by Sabalbal et al. Has rejected the classic textbook representation of the genicular anastomosis described above. During their study of ten cadaver lower limbs, they uncovered that “robust straight communications between branches that the femoral and popliteal arteries did not exist”, and that vasculature that this region was subject to a interindividual variation.


Being a hinge joint, the main movements in the knee joint are flexion and extension of the knee in the sagittal plane. It likewise allows limited medial rotation in a flexed position and also in the last stage of extension, as well as lateral rotation when “unlocking” and flexing the knee. Uneven the elbow joint, the knee joint is no a true hinge due to the fact that it has actually a rotational component, an accessory movement that accompanies flexion and also extension, hence it is termed as a modified hinge joint.

The level of possible knee flexion counts on the place of the i know well joint and whether the movement is active or passive. When the i know good is flexed, a maximum degree of flexion that 140° is achievable in the knee joint, whereas an extended hip permits for just 120°. This is as result of the fact that the hamstrings room both extensors that the hip and flexors the the knee, therefore they lose some the their performance to flex the knee if the hip is extended, and also vice versa. In addition, a more comprehensive range of activity in the knee joint is completed with passive flexion of the knee, increasing it come 160°. The contact of the posterior leg (calf) v the thigh is the significant limiting factor of flexion of the knee. In addition, the capsular sample of the knee joint, in state of many restriction, is flexion and extension to a lesser degree.

As you can see, the knee share is deceptively simple but complete of complex anatomy. Rather of passively reading and also re-reading about it, begin using active recall to cement the details and also review it an ext efficiently!

During motion of the knee native flexion to extension, the femoral condyles roll and also glide posteriorly over the tibial plateaus fan to their greater articular surface area. The posterior gliding activity is important since without it, the femur would simply roll turn off the tibia prior to full expansion is complete. Additionally, as the articular surface ar of the lateral femoral condyle is much less than its medial counterpart, the posterior gliding the the medial condyle throughout the last degrees of expansion results in medial rotation of the femur on the tibia.

During the last couple of degrees that extension, the femoral condyle rotates medially top top the tibial plateau “locking” the knee. This is referred to as the the “screw-home mechanism”, which enables for an extensive weight-bearing without the aid from the muscles of the knee. The full expansion of the knee in addition to the medial rotation of the femoral condyle placed the knee in a so referred to as “close packed position”, in i m sorry there are no extr movements possible. In order to flex the knee again, the knee have to be “unlocked” by the contraction of the popliteus, which reasons lateral rotation the the femur on the tibia. The flexion the the knee puts that in the “open packed position”, i beg your pardon is less stable and has much more laxity than the “close packed position”.

In the patellofemoral joint, the key motion is gliding of the posterior surface of the patella over the patellar surface of the femur as much as the intercondylar notch. The main duty of the patella is to carry out a bigger moment arm for the quadriceps femoris muscle, i beg your pardon is the distance between the axis of the muscle and also the facility of the joint. That does therefore by acting prefer a sheave for the quadriceps femoris, boosting its mechanical benefit and providing greater angular force.

Some accessory movements in the knee joint space possible, yet depend on the place of the knee. Because that example, adduction and also abduction is prevented by the interlocking of the femoral andtibial condyles, as well as collateral ligaments and cruciate ligaments when the knee is fully extended. Top top the various other hand, as soon as the knee is contempt flexed, limited adduction and abduction room possible. Movements in the longitudinal axis, together in medial and lateral rotation, are similarly affected by the amount of share flexion, and are possible if the knee share is contempt flexed.

For much more videos, articles, illustrations and also quizzes explaining the knee joint, take it a look at below:


Muscles acting on the knee joint

Muscles acting on the knee joint
FlexionBiceps femoris, semitendinosus and semimembranosus; initiated by popliteus; helped by gracilis and also sartorius
ExtensionQuadriceps femoris (rectus femoris, vastus lateralis, vastus medialis and vastus intermedius) helped by tensor fasciae latae
Medial rotationPopliteus, semimembranosus and semitendinosus, helped by sartorius and gracilis.
Lateral rotationBiceps femoris

The prime flexors of the knee joint space biceps femoris, semitendinosus and also semimembranosus, whereas popliteus initiates flexion of the “locked knee” and gracilis and sartorius aid as weak flexors.

The primary extensor of the knee share is quadriceps femoris, helped by the tensor fasciae latae. Quadriceps femoris of 4 muscle bellies; rectus femoris, vastus lateralis, vastus medialis and vastus intermedius, all innervated by the femoral nerve.

Medial rotation, as discussed earlier, occurs when the knee is in the last phase of extension, v some also occurring as soon as the knee is flexed. The is primarily produced by the action of popliteus, semimembranosus and also semitendinosus, i m sorry are aided by sartorius and also gracilis. Lateral rotation is developed by biceps femoris and likewise occurs when the knee is flexed.

Now that you have settled all points knee joint, why not test your new knowledge with our quiz!


Clinical significance

As the knee share is a complicated structure subjected to significant biomechanical stress every day, that is a usual site that injury. As it is mainly stabilized through the ligaments pointed out above, any kind of unnatural movement of the knee such together twisting, pivoting, sudden adjust of direction, or a forceful blow can cause injury to this structures. Typical conditions include:

Patellar tendinitis: is one inflammation of the patellar ligament because of overuse anxiety on the patellofemoral joint. It is also called “jumper’s knee” since it frequently occurs in sporting activities such as basketball or volleyball, where the football player exhibit a sudden impact on the joint once landing ~ a jump. It is also an ext common in overweight individuals, together the knee is subjected to much more stress.Anterior cruciate ligament (ACL) injury: ranging from a gentle sprain to complete tear of the ligament, this injury is common amongst athletes in call sports, such together football or football occuring due to a sudden adjust of direction or improper landing after a jump. ACL injury causes pain, swelling and instability of the knee joint.Collateral ligament tears: this injuries take place most generally in call sports due to a punch on the next of the knee. The tibial collateral ligament can be injured by a direct blow to the lateral next of the knee that pushes the knee inwards. Whereas a fibular collateral ligament tear occurs due to a straight blow come the medial side of the knee.Terrible triad: a knee injury identified by tears of the cruciate ligament, the tibial collateral ligament, and the medial meniscus. The is frequently caused by a lateral blow to the knee, if the foot is addressed on the ground. This injury frequently occurs in sporting activities such together rugby or football.

Sources

References:

Hall, S. J. (2015). An easy biomechanics (7th ed.). New York, NY: McGraw-Hill Education.Palastanga, N., & Soames, R. (2012). Anatomy and also human movement: framework and function (6th ed.). Edinburgh: Churchill Livingstone.Lippert, L. S. (2011). Clinical Kinesiology and Anatomy (5th ed.). Philadelphia, PA: F. A. Davis Company.Standring, S. (2016). Gray"s Anatomy (41tst ed.). Edinburgh: Elsevier Churchill Livingstone.Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.Nordin, M., & Frankel V. H. (2012). Basic biomechanics that the musculoskeletal system (4th ed.). Philadelphia, PA: Wolters Kluwer Health/Lippincott, Williams & Wilkins.Sabalbal, M, Johnson, M., McAlister, V. (2013), lack of the genicular arterial anastomosis together generally shown in textbooks. Annals that the royal College that Surgeons, England, 95, 405–409. DOI: 10.1308/003588413X13629960046831

Illustrations:

Knee share (Articulatio genu) - Liene ZnotinaKnee joint (sagittal view) - Paul Kim

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