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In
human Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A speci ...

human
s and other
primate A primate ( ) (from Latin , from 'prime, first rank') is a eutherian mammal constituting the Taxonomy (biology), taxonomic order (biology), order Primates (). Primates arose 85–55 million years ago first from small Terrestrial animal, ...

primate
s, the knee joins the
thigh In Outline of human anatomy, human anatomy, the thigh is the area between the hip (pelvis) and the knee. Anatomically, it is part of the Human leg, lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong ...

thigh
with the
leg A leg is a weight-bearingIn orthopedics Orthopedic surgery or orthopedics, is the branch of surgery concerned with conditions involving the musculoskeletal system. Orthopedic surgeons use both surgical and nonsurgical means to treat muscul ...
and consists of two
joint A joint or articulation (or articular surface) is the connection made between bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of th ...

joint
s: one between the
femur The femur (; ), or thigh bone, is the proximal Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek language, Greek roots and used to describe s ...

femur
and
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. ...

tibia
(tibiofemoral joint), and one between the femur and
patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as mo ...
(patellofemoral joint). It is the largest joint in the human body. The knee is a modified
hinge joint A hinge joint (ginglymus or ginglymoid) is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, r ...

hinge joint
, which permits
flexion Motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon in which an object changes its position (mathematics), position over time. Motion is mathematically described in terms of ...

flexion
and extension as well as slight internal and external rotation. The knee is vulnerable to injury and to the development of
osteoarthritis Osteoarthritis (OA) is a type of degenerative joint disease An arthropathy is a disease of a joint. Signs and symptoms Arthralgia, Joint pain is a common but non-specific sign of joint disease. Signs will depend on the specific disease, and may ...

osteoarthritis
. It is often termed a ''compound joint'' having tibiofemoral and patellofemoral components. (The
fibular collateral ligament The fibular collateral ligament (long external lateral ligament or lateral collateral ligament, LCL) is a ligament A ligament is the fibrous connective tissue Connective tissue is one of the four basic types of animal Animals (also calle ...
is often considered with tibiofemoral components.) Ligaments Of Knee Joint:- 1.Capsular Ligament 2.Ligamentum patellae 3.Tibial collateral ligament 4.Fibular collateral ligament 5.Oblique popliteal ligament 6.Arcuate popliteal ligament 7.Anterior cruciate ligament 8.Posterior cruciate ligament 9.Medial meniscus 10.Lateral meniscus 11.Transverse ligament 12.POPLITEOFIBULAR LIGAMENT 13.FABELLOFIBULAR LIGAMENT By:-Aniket Rathod


Structure

The knee is a modified
hinge joint A hinge joint (ginglymus or ginglymoid) is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, r ...

hinge joint
, a type of
synovial joint A synovial joint, also known as diarthrosis, joins bones or cartilage with a fibrous joint capsule In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In ...
, which is composed of three functional compartments: the patellofemoral articulation, consisting of the
patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as mo ...
, or "kneecap", and the
patellar groove The intercondylar fossa of femur (intercondyloid fossa of femur, intercondylar notch of femur) is a deep notch between the rear surfaces of the medial and lateral epicondyle of the femur The lateral epicondyle of the femur The femur (, pl. ''femur ...
on the front of the
femur The femur (; ), or thigh bone, is the proximal Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek language, Greek roots and used to describe s ...

femur
through which it slides; and the medial and lateral tibiofemoral articulations linking the femur, or thigh bone, with the
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. ...

tibia
, the main bone of the lower leg., p. 390 The joint is bathed in
synovial fluid Synovial fluid, also called synovia, elp 1/sup> is a viscous, non-Newtonian fluid A non-Newtonian fluid is a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, ...
which is contained inside the
synovial membrane The synovial membrane (also known as the synovial stratum, synovium or stratum synoviale) is a specialized connective tissue that lines the inner surface of capsules of synovial joint A synovial joint, also known as diarthrosis, joins bones or car ...
called the
joint capsule In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint.posterolateral corner Posterolateral corner injuries (PLC injuries) of the knee In humans and other primates, the knee joins the thigh with the human leg, leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur an ...
of the knee is an area that has recently been the subject of renewed scrutiny and research. The knee is the largest joint and one of the most important joints in the body. It plays an essential role in movement related to carrying the body weight in horizontal (running and walking) and vertical (jumping) directions. At birth, the
kneecap The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee In human Humans (''Homo sapiens'') are the most p ...
is just formed from
cartilage Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue Elastic is a word often used to describe or identify certain types of elastomer An elastomer is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-m ...

cartilage
, and this will
ossify Ossification (or osteogenesis) in is the process of laying down new material by named s. It is synonymous with formation. There are two processes resulting in the formation of normal, : is the direct laying down of bone into the primitiv ...
(change to
bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubit ...

bone
) between the ages of three and five years. Because it is the largest
sesamoid bone In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...
in the human body, the
ossification Image:Bonemetabolism.svg, 300 px, Bone is broken down by osteoclasts, and rebuilt by osteoblasts, both of which communicate through cytokine (TGF-β, Insulin-like growth factor, IGF) signalling. Ossification (or osteogenesis) in bone remodeling ...
process takes significantly longer.


Articular bodies

The main articular bodies of the femur are its
lateral Lateral is a geometric term of location {{unreferenced, date=March 2014 Geometric terms of location describe directions or positions relative to the shape of an object. These terms are used in descriptions of engineering, physics, and other scienc ...
and
medial Medial may refer to: Mathematics * Medial magma, a mathematical identity in algebra Geometry * Medial axis, in geometry the set of all points having more than one closest point on an object's boundary * Medial graph, another graph that repres ...
condyle A condyle ( or ;Entry "condyle"
in
The radius of the condyles' curvature in the
sagittal plane In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...

sagittal plane
becomes smaller toward the back. This diminishing radius produces a series of
involute In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It ...

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. The pair of tibial condyles are separated by the intercondylar eminence composed of a lateral and a medial tubercle. The
patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as mo ...
also serves an articular body, and its posterior surface is referred to as the trochlea of the knee. It is inserted into the thin anterior wall of the joint capsule. On its posterior surface is a lateral and a medial articular surface, both of which communicate with the patellar surface which unites the two femoral condyles on the anterior side of the bone's distal end.


Articular capsule

The articular capsule has a synovial and a
fibrous Fiber or fibre (from la, fibra, links=no) is a natural Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of space and time and their contents, including ...
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 (ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period (), and the period (). Ancient Greek wa ...
or recess extends the joint space proximally. The suprapatellar bursa is prevented from being pinched during extension by the
articularis genus muscle The articularis genus (also known as the subcrureus muscle) is a small skeletal muscle located anteriorly on the thigh just above the knee. Structure It arises from the anterior surface of the lower part of the body of the femur, deep to the vas ...
. 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.


Bursae

Numerous
bursae A synovial bursa (plural bursae or bursas) is a small fluid-filled sac lined by synovial membrane The synovial membrane (also known as the synovial stratum, synovium or stratum synoviale) is a specialized connective tissue that lines the inner su ...
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 A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant ...

tendon
, and others are sometimes present.


Cartilage

Cartilage Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue Elastic is a word often used to describe or identify certain types of elastomer An elastomer is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-m ...

Cartilage
is a thin, elastic
tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubitata'', a species of geometer mot ...
that protects the
bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubit ...

bone
and makes certain that the
joint A joint or articulation (or articular surface) is the connection made between bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of th ...

joint
surfaces can slide easily over each other. Cartilage ensures supple knee movement. There are two types of joint cartilage in the knees: fibrous cartilage (the meniscus) and
hyaline cartilage Hyaline cartilage is the glass-like (hyaline) but translucent cartilage found on many joint surfaces. It is also most commonly found in the ribs, nose, larynx, and trachea. Hyaline cartilage is pearl-grey in color, with a firm consistency and has a ...

hyaline cartilage
. Fibrous cartilage has tensile strength and can resist pressure. Hyaline cartilage covers the surface along which the joints move. Collagen fibres within the articular cartilage have been described by Benninghoff as arising from the subchondral bone in a radial manner, building so called Gothic arches. On the surface of the cartilage these fibres appear in a tangential orientation and increase the abrasion resistance. There are no blood vessels inside of the hyaline cartilage, the alimentation is performed per diffusion. Synovial fluid and the subchondral bone marrow serve both as nutrition sources for the hyaline cartilage. Lack of at least one source induces a degeneration. Cartilage will wear over the years. Cartilage has a very limited capacity for self-restoration. The newly formed tissue will generally consist of a large part of fibrous cartilage of lesser quality than the original hyaline cartilage. As a result, new cracks and tears will form in the cartilage over time.


Menisci

The
articular disk The articular disk (or disc) is a thin, oval plate of fibrocartilage Fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its inflexibility and toughness to the former of these co ...
s of the knee-joint are called menisci because they only partly divide the joint space. These two disks, the medial meniscus and the
lateral meniscus The lateral meniscus (external semilunar fibrocartilage) is a fibrocartilaginous band that spans the lateral side of the interior of the knee joint. It is one of two meniscus (anatomy), menisci of the knee, the other being the medial meniscus. It ...
, 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. 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

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


Intracapsular

The knee is stabilized by a pair of
cruciate ligament Cruciate ligaments (also cruciform ligaments) are pairs of ligament A ligament is the Connective tissue#Types, fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibr ...
s. The
anterior cruciate ligament#REDIRECT Anterior cruciate ligament {{Redirect category shell, 1= {{R from other capitalisation ...
(ACL) stretches from the
lateral condyle of femur The lateral condyle is one of the two projections on the lower extremity of the femur The lower extremity of femur (or distal extremity) is the lower end of the femur The femur (, pl. ''femurs'' or ''femora'' ), or thigh bone, is the proximal Sta ...
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 The posterior cruciate ligament (PCL) is a ligament in each knee of humans and various other animals. It works as a counterpart to the anterior cruciate ligament (ACL). It connects the posterior intercondylar area of the tibia to the Medial condyle ...
(PCL) stretches from
medial condyle of femur The medial condyle is one of the two projections on the lower extremity of femur, the other being the lateral condyle. The medial Condyle (anatomy), condyle is larger than the lateral (outer) condyle due to more weight bearing caused by the centr ...
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 The lateral meniscus (external semilunar fibrocartilage) is a fibrocartilaginous band that spans the lateral side of the interior of the knee joint. It is one of two meniscus (anatomy), menisci of the knee, the other being the medial meniscus. It ...
to the medial meniscus. It passes in front of the menisci. It is divided into several strips in 10% of cases. The two menisci are attached to each other anteriorly by the ligament. , p. 200 The posterior and anterior meniscofemoral ligaments stretch from the posterior horn of the 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. The meniscotibial ligaments (or "coronary") stretches from inferior edges of the menisci to the periphery of the tibial plateaus.


Extracapsular

The
patellar ligament The patellar tendon is the distal portion of the common tendon of the quadriceps femoris, which is continued from the patella to the tibial tuberosity. It is also sometimes called the patellar ligament as it forms a bone to bone connection when the ...
connects the
patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as mo ...
to the
tuberosity of the tibia The tuberosity of the tibia or tibial tuberosity or tibial tubercle is an elevation on the proximal, anterior aspect of the tibia The tibia (plural tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior ...
. It is also occasionally called the patellar tendon because there is no definite separation between the
quadriceps tendon In human anatomy The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis In biology Biology is the natura ...
(which surrounds the patella) and the area connecting the patella to the tibia. This very strong ligament helps give the patella its mechanical leverage , p. 194 and also functions as a cap for the condyles of the femur. Laterally and medially to the patellar ligament the lateral and medial retinacula connect fibers from the and to the tibia. Some fibers from the
iliotibial tract The iliotibial tract or iliotibial band (also known as Maissiat's band or the IT band) is a longitudinal fibrous reinforcement of the fascia lata. The action of the muscles associated with the ITB ( tensor fasciae latae and some fibers of gluteu ...
radiate into the lateral retinaculum and the medial retinaculum receives some transverse fibers arising on the medial femoral epicondyle. The
medial collateral ligament The medial collateral ligament (MCL), or tibial collateral ligament (TCL), is one of the four major ligaments of the knee. It is on the Human anatomical terms#Anatomical directions, medial (inner) side of the knee joint in humans and other primate ...
(MCL a.k.a. "tibial") stretches from the
medial epicondyle of the femur The medial epicondyle of the femur is an epicondyle, a bony protrusion, located on the medial side of the femur at its Lower extremity of femur, distal end. Located above the medial condyle of the femur, medial condyle, it bears an elevation, the a ...
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 The semimembranosus muscle () is the most medial of the three hamstring muscles in the thigh. It is so named because it has a flat tendon of origin. It lies posteromedially in the thigh, deep to the semitendinosus muscle. It Anatomical terms of mot ...
passes under it. 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
fibular collateral ligament The fibular collateral ligament (long external lateral ligament or lateral collateral ligament, LCL) is a ligament A ligament is the fibrous connective tissue Connective tissue is one of the four basic types of animal Animals (also calle ...
(LCL a.k.a. "fibular") stretches from the
lateral epicondyle of the femur The lateral epicondyle of the femur The femur (, pl. ''femurs'' or ''femora'' ), or thigh bone, is the proximal Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive f ...
to the head of fibula. It is separate from both the joint capsule and the lateral meniscus. It protects the lateral side from an inside bending force (a varus force). The
anterolateral ligament The anterolateral ligament (ALL) is a ligament on the Anatomical terms of location#Left and right (lateral), and medial, lateral aspect of the human knee, anterior to the fibular collateral ligament. Perhaps the earliest account of the ALL was wri ...
(ALL) is situated in front of the LCL. Lastly, there are two ligaments on the dorsal side of the knee. The
oblique popliteal ligament The oblique popliteal ligament (posterior ligament) is a broad, flat, fibrous band, on the posterior knee. Structure The oblique popliteal ligament originates from the Adductor tubercle of femur, adductor tubercle of the medial side of the femur. ...
is a radiation of the tendon of the
semimembranosus The semimembranosus muscle () is the most medial of the three hamstring muscles in the thigh. It is so named because it has a flat tendon of origin. It lies posteromedially in the thigh, deep to the semitendinosus muscle. It Anatomical terms of mot ...
on the medial side, from where it is direct laterally and proximally. The
arcuate popliteal ligament The arcuate popliteal ligament is an extracapsular ligament A ligament is the Connective tissue#Types, fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament ...
originates on the apex of the head of the fibula to stretch proximally, crosses the tendon of the
popliteus muscle The popliteus muscle in the leg is used for unlocking the knees when walking, by laterally rotating the femur The femur (, pl. ''femurs'' or ''femora'' ), or thigh bone, is the proximal Standard anatomical terms of location deal unambiguously ...
, and passes into the capsule.


Muscles

The muscles responsible for the movement of the knee joint belong to either the
anterior Standard anatomical terms of location deal unambiguously with the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient ...
,
medial Medial may refer to: Mathematics * Medial magma, a mathematical identity in algebra Geometry * Medial axis, in geometry the set of all points having more than one closest point on an object's boundary * Medial graph, another graph that repres ...
or posterior compartment of the thigh. The extensors generally belong to the anterior compartment and the flexors to the posterior. The two exceptions to this is gracilis, a flexor, which belongs to the medial compartment and sartorius, a flexor, in the anterior compartment.


Extensors


Flexors

Posterior compartment Medial compartment:


Blood supply

The
femoral artery The femoral artery is a large in the and the main arterial supply to the thigh and leg. The femoral artery gives off the deep femoral artery or and descends along the anteromedial part of the thigh in the . It enters and passes through the , ...
and the
popliteal artery The popliteal artery is a deeply placed continuation of the femoral artery The femoral artery is a large in the and the main arterial supply to the thigh and leg. The femoral artery gives off the deep femoral artery or and descends along th ...

popliteal artery
help form the arterial network or
plexus A plexus (from the Latin for "braid") is a branching network of vessels or nerves. The vessels may be blood vessels (veins, capillaries) or lymphatic vessels. The nerves are typically Axon, axons outside the central nervous system. The standard ...
, surrounding the knee joint. There are six main branches: two
superior genicular arteries The superior genicular arteries (superior articular arteries), two in number, arise one on either side of the popliteal artery, and wind around the femur immediately above its Condyle (anatomy), condyles to the front of the knee-joint. The medial su ...
, two
inferior genicular arteries The inferior genicular arteries (inferior articular arteries), two in number, arise from the popliteal beneath the gastrocnemius. On the inside of the knee, is the medial inferior genicular artery, and on the outer side is the lateral inferior genic ...
, the descending genicular artery and the recurrent branch of anterior tibial artery. The medial genicular arteries penetrate the knee joint.


Function

The knee permits
flexion Motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon in which an object changes its position (mathematics), position over time. Motion is mathematically described in terms of ...

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 Lateral is a geometric term of location {{unreferenced, date=March 2014 Geometric terms of location describe directions or positions relative to the shape of an object. These terms are used in descriptions of engineering, physics, and other scienc ...
meniscus move over the tibia during rotation, while the femur rolls and glides over both menisci during extension-flexion. 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.


Extended position

With the knee extended, both the
lateral Lateral is a geometric term of location {{unreferenced, date=March 2014 Geometric terms of location describe directions or positions relative to the shape of an object. These terms are used in descriptions of engineering, physics, and other scienc ...
and
medial collateral ligament The medial collateral ligament (MCL), or tibial collateral ligament (TCL), is one of the four major ligaments of the knee. It is on the Human anatomical terms#Anatomical directions, medial (inner) side of the knee joint in humans and other primate ...
s, as well as the anterior part of the
anterior cruciate ligament#REDIRECT Anterior cruciate ligament {{Redirect category shell, 1= {{R from other capitalisation ...
, 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 The iliotibial tract or iliotibial band (also known as Maissiat's band or the IT band) is a longitudinal fibrous reinforcement of the fascia lata. The action of the muscles associated with the ITB ( tensor fasciae latae and some fibers of gluteu ...
and is caused by the stretching of the anterior cruciate ligament. Both cruciate ligaments are slightly unwinded and both lateral ligaments become taut.


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°.


Clinical significance

Knee pain is caused by trauma, misalignment, and degeneration as well as by conditions like
arthritis Arthritis is a term often used to mean any disorder that affects joints A joint or articulation (or articular surface) is the connection made between bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of th ...
. 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 Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical or dental specialty that uses operative manual and instrumental techniques on a person to investigate or t ...
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 Prepatellar bursitis is an inflammation of the prepatellar bursa at the front of the knee. It is marked by swelling at the knee, which can be tender to the touch and which generally does not restrict the knee's range of motion. It can be extremel ...
also known as ''housemaid's knee'' is painful inflammation of the
prepatellar bursa The prepatellar bursa is a Bursa of the knee joint#Frontal, frontal bursa of the knee joint. It is a superficial bursa (anatomy), bursa with a thin synovium, synovial lining located between the skin and the patella. Pathology

Prepatellar burs ...

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 Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue Elastic is a word often used to describe or identify certain types of elastomer An elastomer is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-m ...

Cartilage
lesions can be caused by: *Accidents (fractures) *Injuries *The removal of a meniscus *
Anterior cruciate ligament#REDIRECT Anterior cruciate ligament {{Redirect category shell, 1= {{R from other capitalisation ...
injury *
Posterior cruciate ligament The posterior cruciate ligament (PCL) is a ligament in each knee of humans and various other animals. It works as a counterpart to the anterior cruciate ligament (ACL). It connects the posterior intercondylar area of the tibia to the Medial condyle ...
injury *
Posterolateral corner Posterolateral corner injuries (PLC injuries) of the knee In humans and other primates, the knee joins the thigh with the human leg, leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur an ...
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 Muscle weakness is a lack of muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A gi ...
and
overweight Being overweight or fat is having more body fat Adipose tissue, body fat, or simply fat is a loose connective tissue Connective tissue is one of the four basic types of animal tissue (biology), tissue, along with epithelial tissue, muscle ...

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 120lb at age 18 years, before her three pregnancies, and now weighs 285lb, had added 660lb of force across her patellofemoral joint with each step.


Common injuries due to physical activity

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

The
anterior cruciate ligament#REDIRECT Anterior cruciate ligament {{Redirect category shell, 1= {{R from other capitalisation ...
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 A joint or articulation (or articular surface) is the connection made between bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of th ...

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

Knee fractures are rare but do occur, especially as a result of
road accident A traffic collision, also called a motor vehicle collision, car accident or car crash, occurs when a vehicle A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles ( ...

road accident
. Knee fractures include a
patella fracture A patella fracture is a bone fracture, break of the patella, kneecap. Symptoms include pain, swelling, and bruising to the front of the knee. A person may also be unable to walk. Complications may include injury to the tibia, femur, or knee ligamen ...
, and a type of
avulsion fracture An avulsion fracture is a bone fracture which occurs when a fragment of bone tears away from the main mass of bone as a result of physical trauma. This can occur at the ligament by the application of forces external to the body (such as a fall o ...
called a
Segond fracture The Segond fracture is a type of avulsion fracture An avulsion fracture is a bone fracture which occurs when a fragment of bone tears away from the main mass of bone as a result of physical trauma. This can occur at the ligament by the applicat ...
. There is usually immediate pain and swelling, and a difficulty or inability to stand on the leg. The muscles go into
spasm A spasm is a sudden involuntary contraction of a muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist ...
and even the slightest movements are painful.
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Moti ...

X-ray
s 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 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 Physical therapy (PT), also known as physiotherapy, is one of the allied health professions Allied health professions are health care Health care, health-care, or healthcare is the maintenance or improvement of health via the preventive h ...

physical therapy
.


Overuse

Overuse injuries of the knee include
tendonitis Tendinopathy, also known as tendinitis or tendonitis, is a type of tendon A tendon or sinew is a tough band of fibrous connective tissue that connects muscle to bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes p ...
,
bursitis Bursitis is the inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogen In biology Biology is the natural science that studies life and living o ...

bursitis
, muscle strains, and . 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

There are two disorders relating to an abnormal angle in the
coronal plane A coronal plane (also known as the frontal plane) is any vertical plane that divides the body into ventral and Dorsum (anatomy), dorsal (belly and back) sections. It is one of the three main Anatomical terms of location#Planes, planes of the body ...
at the level of the knee: *''
Genu valgum ''Genu valgum'', commonly called "knock-knee", is a condition in which the knee In humans and other primates, the knee joins the thigh with the human leg, leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and o ...

Genu valgum
'' is a
valgus deformity A valgus deformity is a condition in which the bone segment distal Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek language, Greek roots and ...
in which the tibia is turned outward in relation to the femur, resulting in a knock-kneed appearance. *''
Genu varum Genu, a Latin word for "knee," may refer to: * Genu of internal capsule The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere The vertebrate Vertebrates () comprise all species of ani ...

Genu varum
'' is a
varus deformity A varus deformity is an excessive inward angulation ( medial angulation, that is, towards the body's midline) of the distal Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used general ...
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 The ankle, or the talocrural region, is the region where the foot The foot (plural: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a Limb (anatomy), limb which bears weight and allows Animal locomotio ...
. It is normally between 1.0° and 1.5° of varus in adults. Normal ranges are different in children. File:Hip-knee-ankle angle by age.png, ''Hip-knee-ankle angle'' by age, with 95%
prediction interval In statistical inference, specifically predictive inference, a prediction interval is an estimate of an interval in which a future observation will fall, with a certain probability, given what has already been observed. Prediction intervals are ...
.


Surgical interventions

Before the advent of
arthroscopy Arthroscopy (also called arthroscopic or keyhole surgery) is a minimally invasive surgical procedure on a joint A joint or articulation (or articular surface) is the connection made between bones in the body which link the skeletal system into ...
and
arthroscopic surgery Arthroscopy (also called arthroscopic or keyhole surgery) is a minimally invasive surgical procedure on a joint A joint or articulation (or articular surface) is the connection made between bones in the body which link the skeletal system into ...
, 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 The aim of an articular cartilage repair treatment is to restore the surface of an articular joint A joint or articulation (or articular surface) is the connection made between bones in the body which link the skeletal system into a functional wh ...
treatment: *
Arthroscopic Arthroscopy (also called arthroscopic or keyhole surgery) is a minimally invasive surgical procedure Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical or d ...
debridement Debridement is the medical removal of dead, damaged, or infected tissue (biology), tissue to improve the healing potential of the remaining healthy tissue. Removal may be surgery, surgical, mechanical, chemical, Autolysis (biology), autolytic ...
of the knee (
arthroscopic lavage The washing out or cleaning out the contents (blood, fluid or loose debris) inside a joint space is generally termed as Arthroscopic lavage. Lavage is a general term referring to the therapeutic washing, cleaning or rinsing. Medical uses Excessive ...
) * Mosaïc-plasty *Microfracture (Ice-picking) * Autologous chondrocyte implantation *Osteochondral
Autograft Autotransplantation is the organ transplantation, transplantation of Organ (anatomy), organs, Biological tissue, tissues, or even particular proteins from one part of the body to another in the same person (''wikt:auto-, auto-'' meaning "self" in ...
and
Allografts Allotransplant (''allo-'' meaning "other" in Greek) is the transplantation of cells, tissues, or organs to a recipient from a genetically non-identical donor of the same species. The transplant is called an allograft, allogeneic transplant, or ...
* PLC Reconstruction


Other animals

In humans, the term "knee" refers to the joints between the femur, tibia, and patella, in the leg. In
quadruped Quadrupedalism is a form of terrestrial locomotion Terrestrial locomotion has evolved Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits f ...
s such as dogs, horses, and mice, the homologous joints between the femur, tibia, and patella, in the
hind leg A hind is a female deer, especially a red deer. Places * Hind and al-Hind, a Persian and Arabic name for the Indian subcontinent * Hind (crater), a lunar impact crater * 1897 Hind, an asteroid Military * , numerous Royal Navy ships * Mil Mi- ...
, are known as the
stifle joint The stifle joint (often simply stifle) is a complex joint in the hind limbs of quadruped The zebra is a quadruped. Quadrupedalism is a form of terrestrial locomotion where a tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-l ...
. Also in quadrupeds, particularly horses,
ungulate Ungulates ( ) are members of the diverse Ungulata which primarily consists of large mammals with . These include s such as s, es, and s; and s such as , s, s, s, , , and es. s such as , , and are also classified as even-toed ungulates, althoug ...
s, and elephants, the layman's term "knee" also commonly refers to the forward-facing joint in the
foreleg A forelimb or front limb is one of the bilateral symmetry, paired joint, articulated appendages (limb (anatomy), limbs) attached on the cranial (anterior (anatomy), anterior) end of a terrestrial animal, terrestrial tetrapod vertebrate's torso. Wi ...
, the , which is homologous to the human
wrist In human anatomy The human body is the structure of a human being Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and ...

wrist
. In
birds Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , and a strong yet lightweight . Birds live worldwide and range in size from the to the . There ar ...

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 The ankle, or the talocrural region, is the region where the foot The foot (plural: feet) is an anatomical Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and liv ...

ankle
. In insects and other animals, the term knee widely refers to any
hinge joint A hinge joint (ginglymus or ginglymoid) is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, r ...

hinge joint
.


See also

* Arthrofibrosis *
Articular cartilage repair The aim of an articular cartilage repair treatment is to restore the surface of an articular joint A joint or articulation (or articular surface) is the connection made between bones in the body which link the skeletal system into a functional wh ...
* Autologous chondrocyte implantation * Chondromalacia patellae *
Fibular collateral ligament The fibular collateral ligament (long external lateral ligament or lateral collateral ligament, LCL) is a ligament A ligament is the fibrous connective tissue Connective tissue is one of the four basic types of animal Animals (also calle ...
*
GeniculumA geniculum is a small ''wikt:genu, genu'', or angular knee-like structure. It is often used in anatomical nomenclature to designate a sharp knee-like bend in a small structure or organ. For example, in the facial canal, the genicular ganglion is ...
*
Genuflection Genuflection or genuflexion is the act of bending a knee to the ground, as distinguished from kneeling which more strictly involves both knees. From early times, it has been a gesture of deep respect for a superior. Today, the gesture is common in ...
*
Knee arthritis Arthritis of the knee is typically a particularly debilitating form of arthritis. The knee may become affected by almost any form of arthritis. The word ''arthritis'' refers to inflammation of the joints. Types of arthritis include those related t ...
* Knee cartilage replacement therapy * Knee examination *
Kneecapping Kneecapping is a form of malicious wounding, often as torture Torture (from Latin language, Latin ''tortus'': to twist, to torment) is the act of deliberately inflicting severe physical or psychological suffering on someone by another as a puni ...
*
Kneeling Kneeling is a basic human position where one or both knees touch the ground. Kneeling is defined as “to position the body so that one or both knees rest on the floor,” according to Merriam-Webster. Kneeling when only composed of one knee, and n ...

Kneeling
* Knésetja *
Medial collateral ligament The medial collateral ligament (MCL), or tibial collateral ligament (TCL), is one of the four major ligaments of the knee. It is on the Human anatomical terms#Anatomical directions, medial (inner) side of the knee joint in humans and other primate ...
*Partial knee replacement unicompartmental knee arthroplasty * Posterolateral corner injuries *
Reflex hammer In biology, a reflex, or reflex action, is an involuntary, unplanned, sequence of action and nearly instantaneous movement in response to a Stimulus (physiology), stimulus. A reflex is made possible by neural pathways called reflex arcs which can ...

Reflex hammer


Additional images

File:Real-time MRI - Knee (central).ogv, Real-time MRI- Knee File:Knie ct.gif, Knee MR File:Knie mr.jpg, Knee MR File:Knie-roentgen-r-seite.jpg, Knee X-ray File:Knee Front X-ray.jpg, Knee X-ray (Front) File:Legamenti crociati.jpg, Cruciate ligaments File:Gray348.png, Left knee-joint from behind, showing interior ligaments. File:Gray351.png, Capsule of right knee-joint (distended). Lateral aspect. File:Knee skeleton lateral anterior views.svg, Anterior and lateral view of knee. File:Slide2CAC.JPG, Anterior view of knee.


References


External links

*
Animation of bones and ligament in the kneeMRI anatomy of a normal knee
{{Authority control Articles containing video clips *Knee