Naik, S. -Biomechanics of Knee Complex

8/11/2019 Naik, S. -Biomechanics of Knee Complex

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KNEE COMPLEX Sagar Naik, P

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KNEE OMPLEX

Sagar Naik PT

Knee complex plays a major role in supporting the body during dynami

and static activities.In a closed kinematic chain the knee joint works in conjunctio

with the hip joint and ankle to support the body weight in the static erect postureDynamically, the knee complex is responsible for moving and supporting the body i

sitting and squatting activities and for supporting and transferring the body weigh

during locomotor activities. In an open kinematic chain the knee provides mobility fo

the foot in space. The knee is not only one of the largest joints in the body but also th

most complex.

The knee complex is composed of two distinct articulations within single joint capsule:

Tibiofemoral joint

The tibiofemoral joint is the articulation between the distal femur and th

proximal tibia.

Patellofemoral jointThe patellofemoral joint is the articulation between the patella and th

femur.

Tibiofemoral Joint:The tibiofemoral, or knee joint, is adouble condyloid jointwith 2of freedom

of motion.

Flexion and extension occur in the sagittal plane around a coronal axis

medial and lateral rotation occurs in the transverse plane about a vertica

axis.

Femoral Articular Surface:The large medial & lateral condyles on the distal femur form the proxima

articular surfaces of the knee joint.The condyles have a large and very obvious curvature anteroposteriorly bu

are also each slightly convex in the frontal plane.

The two condyles are separated by the intercondylar notch orfossathroug

most of their length, but are joined anteriorly by an asymmetrical, shallow

saddle-shaped groove called the patellar groove or surface; the patella


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surface is separated from the tibial articular surface by two slight groove

that run obliquely across the condyles.

The shaft of the femur is not vertical but is angled in such a way that femora

condyles do not lie immediately below the femoral head, but somewha

medial.Given the obliquity of the shaft of the femur, the lateral condyle lies mor

directly in line with the shaft than does the medial condyle.The articular surface of the lateral condyle is also not as long as the articula

surface of the medial femoral condyle.

When the patellofemoral surface is excluded, it can be seen that the later

tibial surface stops before the medial.

The medial condyle extends further distally than the lateral so that, despit

the angulation of the shaft of the femur, the distal end of the femur i

essentially horizontal.

Tibial Articular Surface: The articulating surfaces on the tibia that correspond to the femora

articulating surfaces are the two concave, asymmetrical medial and latera

tibial condyles or plateaus.

The proximal tibia is enlarged as compared to the shaft and overhangs th

shaft posteriorly.

The articulating surface of the medial tibial condyle is 50% larger than tha

of the lateral condyle and the articular cartilage of the medial tibial condylis three times thicker.

A roughened area and two bony spines called the intercondylar tubercle

separate the two tibial condyles.

These tubercles become lodged in the intercondylar notch of the femuduring knee extension.

Tibiofemoral Art iculation: When the large articular condyles of the femur are placed on the shallow

concavities of the tibial condyle, the incongruence of the knee joint

evident.

Each of the condyles of the knee joint has its own accessory joint structure

together known as themenisci of the knee.

Menisci: Two asymmetrical fibrocartilaginous joint discs called menisci ar

located on the tibial condyles.


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The medial meniscus is a semicircle; the lateral meniscus is four-fifths o

a ring.

Both menisci are open toward the intercondylar area, thick peripheraland thin centrally, forming concavities into which the respectiv

femoral condyles can sit.The wedge-shaped menisci increase the radius of curvature of the tibia

condyles and, therefore, joint congruence. By increasing congruence, the menisci also play an important part i

distributing weight-bearing forces, in reducing friction between the joinsegments, and serving as shock absorbers.

The menisci have multiple attachments to surrounding structures, som

common to both and some unique to each.

Each meniscus is connected around its periphery to the tibial condyle b

thecoronary ligaments, which are composed of fibres from the knee joincapsule.

Both menisci are also attached directly or indirectly to the patella via thso-called patellomeniscal or patellotibial ligaments, which are anterio

capsular thickenings.

The open ends of the menisci, which are attached to their respective tibia

intercondylar tubercles, are calledhorns.Each meniscus has an anterio

and a posterior horn.

The anterior horns of the two menisci are joined to each other by th

transverse ligament, which may be connected to the patella via the joincapsule.

The attachment site of the posterior horn of the more mobile later

meniscus had a greater zone of uncalcified fibrocartilage than th

attachment site of the posterior horn of the medial meniscus.

The attachment site of the anterior horn of the lateral meniscus had

thicker zone of cortical calcified cartilage than the attachment site of th

anterior horn of the medial meniscus.

The lateral meniscus, in addition to the connections it shares with th

medial meniscus, is attached to theposterior cruciate ligament (PCL)an

popliteus muscle via the coronary ligaments and posterior capsule, an

to the somewhat variableposterior meniscofemoral ligaments.

Some fibres from theanterior cruciate ligament (ACL) may also join th

anterior and posterior horns.


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The connections of the lateral meniscus are considered to be fairly loos

leaving the lateral menisci a fair amount of mobility on the lateral tibia

condyle.

Themedial meniscusis attached to themedial collateral ligamentand t

thesemimembranosus musclethrough its capsular connections. The medial meniscus is more firmly attached and less movable on th

tibial condyle than the lateral meniscus.

The menisci and meniscoligamentous complex are well established i

the 8-week-old embryo and during the first year of the life the menis

are well vascularized throughout.

The vascularity of the meniscal body gradually reduces from 18 month

to 18 years. Over age 50 years only periphery of meniscal body

vascularized.

The horns remain completely vascularized throughout life.In young children whose menisci have ample blood supply, the incidenc

of meniscal injuries is low. In adult the only the peripheral vascularizeregion of the meniscal body is capable of inflammation, repair, an

remodeling following a tearing injury.

The horns of the menisci and the peripheral vascularized portion of th

meniscal bodies are well innervated with free nerve endings and thre

different mechanoreceptors.

The meniscal innervation pattern indicates that the menisci are

source of information about joint position, direction of movement, anvelocity of movement as well as information about tissue deformation.

Tibiofemoral Alignment & Weight-Bearing Forces: The anatomic (longitudinal) axis of the femur is oblique, directe

inferiorly and medially from its proximal to its distal end. The anatom

axis of the tibia is directed almost vertically. Consequently, the femora

and tibial longitudinal axes normally form an angle medially at th

knee joint of 185 to 190; i.e., the femur is angled off vertical 5to 10

creating a physiologic (normal) valgus angle at the knee.

The mechanical axis of the lower extremity is the weight-bearing lin

from the center of the head of the femur to the center of the superiosurface of the head of talus.This line normally passes through the cente

of the knee joint between the intercondylar tubercles and averages 3from

the vertical given the width of the hip joints as compared to spacing of th

feet.


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Because the weight-bearing line (ground reaction force) follows th

mechanical rather than the anatomic axes, the weight-bearing stresse

on the knee joint in bilateral static stance are equally distributebetween the medial and lateral condyles, without any concomitan

horizontal shear forces.This is not necessarily the case in unilateral stance or once dynamic force

are introduced to the joint.

If the medial tibiofemoral angle is greater than 195 (165 or les

measured laterally), an abnormal condition called genu valgum (knoc

knees) exists. This condition will increase the compressive force on th

lateral condyle while increasing the tensile stresses on the media

structures.

If the medial tibiofemoral angle is 180 or less (exceeding 180 a

measured laterally), the resulting abnormality is calledgenu varum (bolegs). In this condition, the compressive stresses on the medial tibia

condyle are increased, whereas the tensile stresses are increased laterally

In genu valgum or genu varum, constant overloading of, respectively, th

lateral or medial articular cartilage may result in damage to the cartilage.

The menisci of the knee are important in distributing and absorbing th

large forces crossing the knee joint.

Although compressive forces in the dynamic knee joint ordinarily ma

reach two to three times body weight in normal gait and five to six time

body weight in activities such as running and stair climbing, the menis

assume 40% to 60% of the imposed load.

If the menisci are removed, the magnitude of the average load per un

area on the articular cartilage nearly doubles on the femur and is six t

seven times greater on the tibial condyles.

Elimination of any angulation between the femur and tibia (a mild gen

varum) will increase the compression on the medial meniscus by 25%

Five degrees of genu varum (medial tibiofemoral angle of 175) wi

increase the forces by 50%.Knee Joint Capsule:Given the incongruence of the knee joint, even with the compensation of th

menisci, stability is heavily dependent on the surrounding joint structures.

In knee flexion when surrounding passive structures tend to be lax, th

incongruence of the joint permits at least some anterior displacemen

posterior displacement, and rotation of the tibia beneath the femur.


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The knee joint capsule and its associated ligaments are critical to restrictin

such motions to maintain joint integrity and normal joint function. Althoug

muscles clearly play a role in stabilization, it is almost impossible t

effectively stabilize the knee with active muscular forces alone in th

presence of substantial disruption of passive restraining mechanisms.The joint capsule that encloses the tibiofemoral and patellofemoral joint

is large, complexly attached, and lax with several recesses.

Posteriorly, the capsule is attached proximally to the posterio

margins of the femoral condyles and intercondylar notch and distall

to the posterior margins tibial condyle. The capsule is reinforce

posteriorly by a number of muscles and by oblique popliteal and arcua

ligaments.

Medially & laterally, the capsule begins proximally above the femora

condyles to continue distally to the margins of the tibial condyle. Thcollateral ligaments reinforce the sides of the capsule.

Anteriorly, the patella, the tendon of the quadriceps muscle

superiorly, and the patellar ligament inferiorly completes the anterio

portion of the joint capsule.

Anteromedially and anterolaterally, expansions from the vastu

medialis and vastus lateralis muscles extend from the patella an

patellar ligament to the corresponding collateral ligaments and tibia

condyles.

The anteromedial and anterolateral portions of the capsule are known as thextensor retinaculumor themedial and lateral patellar retinacula.

Extensor Retinacula:Extensor retinaculum appear to be two layers,

The deeper of the two layers having longitudinally oriented fibre

connecting the capsule anteriorly to the menisci and tibia via th

coronary ligaments. These connections may be called th

patellomeniscal orpatellotibial bands.

The more superficial second layer consists of transversely oriente

fibres of which the more proximal blend with fibres of the vastu

medialis and lateralis muscles and the more distal continue to th

posterior femoral condyles.The transverse fibres connecting the patella and the femoral condyles ar

known as thepatellofemoral ligaments.


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The lateral patellofemoral ligament is connected not only to the vastu

lateralis muscle but also to the iliotibial band either directly or indirect

via an iliopatellar band.

The tendon of the biceps femoris muscle to provide superficia

reinforcement to the capsular and retinacular layers accompanies thiliotibial band and its associated fascia lata posteriorly.

Synovial Lining:The intricacy of the fibrous layer of the knee joint capsule is surpassed b

its synovial lining, the most extensive, and involved in the body.

The synovium adheres to the inner wall of the fibrous layer excep

posteriorly where the synovium invaginates anteriorly following th

contour of the femoral intercondylar notch.

The invaginated synovium adheres to the anterior aspect and sides o

the anterior cruciate ligament and the posterior cruciate ligament. Thus, anterior cruciate ligament and posterior cruciate ligament ar

intracapsularbut extrasynovial.

Embryonically, the synovial lining of the knee joint capsule is actuall

divided by septa into three separate compartments. There is initially

superior patellofemoral compartment and two separate medial and later

tibiofemoral compartments.

By 12 weeks of gestation, the synovial septa are resorbed to some degre

resulting in a single joint cavity, but retaining the posterior invaginatio

of the synovium that forms some separation of the condyles. The superior compartment continues to be recognizable as a superio

recess of the capsule known as thesuprapatellar bursa.

Posteriorly, the synovial lining may invaginate laterally between th

popliteus muscle and lateral femoral condyle. It may also invagina

medially between the semimembranosus tendon, the medial head of th

gastrocnemius muscle, and the medial femoral condyle.

When the synovial septa, which exist embryonically, are not completel

resorbed but persist into adulthood, they exist as folds or pleats o

synovial tissue known asplicaeorpatellar plicae.

These vestiges have been observed in 20% to 60% of the norm

population and are referred to, in order of most frequently to lea

frequently found, as the inferior plica (infrapatellar plica), the superio

plica (suprapatellar plica), and themedial plica (mediopatellar plica).


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The inferior plica, which also has been described as the infrapatellar fol

or ligamentum mucosum, is located below the patella anterior to th

anterior cruciate ligament.

The inferior plica extends from the anterior portion of the intercondyla

notch to attach the infrapatellar fat pad.Thesuperior plicais located between the suprapatellar bursa and the kne

joint. This plica is often bilateral and symmetrical and extends from

synovial pouch at the anterior aspect of the femoral metaphysis area tattach to the posterior aspect of the quadriceps tendon above the patella

The medial plica arises from the medial wall of the pouch of th

retinaculum and runs parallel to the medial edge of the patella to attacto the infrapatellar fat pad and synovium of the inferior plica.

Occasionally, however, the plica may become irritated and inflamed

which leads to pain, effusion, and changes in joint structure anfunction.

The plica syndrome generally does not arise from the most commo

infrapatellar plica, but from the medial or superior plicae.

The knee joint capsule is reinforced by a number of ligaments that play a

important part not only in knee joint stability but also in knee join

mobility.

Knee Joint Ligaments:

Given the lack of bony restraint to virtually any of the knee motions, thligaments are credited with resisting or controlling:

Excessive knee extension

Varus and valgus stresses at the knee

Anterior or posterior displacement of the tibia beneath the femur

Medial or lateral rotation of the tibia beneath the femur

Combinations of anteroposterior displacements and rotations of th

tibia, known as rotatory stabilization

It is also possible that the stresses may occur on the femur while the tibia

fixed (weight-bearing).In such instances, the anteroposterior displacemenand rotations will reverse; that is, anterior displacement of the tibia

equivalent to posterior displacement of the femurand so forth.

Collateral Ligaments:

The medial (tibial) collateral ligament (MCL) attaches to the medi

aspect of the medial femoral epicondyle, sloping anteriorly to insert int

the medial aspect of the proximal tibia.


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The posterior medial fibres of the ligament blend with fibres of the join

capsule and some fibres extend medially to attach to the media

meniscus.

The lateral (fibular) collateral ligament (LCL) is a strong cordlik

structure extending from the lateral femoral epicondyle and attachinposteriorly to the head of the fibula.

Unlike the medial collateral ligament,the lateral collateral ligament ha

no attachment either to the meniscus or to the joint capsule.

Both collateral ligaments are taut in full extension and, therefore, hel

resist hyperextension of the knee joint.

Medial Collateral Ligament (MCL):

The medial collateral ligament resists valgus stresses (attempte

abduction of the tibia) across the knee joint, being especial

effective in the extended knee when the ligament is taut.However, it may play a more critical role in resisting valgus stresse

in the slightly flexed knee when other structures make a lessecontribution.

The medial collateral ligament is also aligned in such a way as t

check lateral rotation of the tibia.

The medial collateral ligament is also a backup restraint to pur

anterior displacement of the tibia when the primary restraint of th

anterior cruciate ligament is absent.

Lateral Collateral Ligament (LCL):

The lateral collateral ligament resists varus stresses (attempte

adduction of the tibia)across the knee.

Given its alignment, it also appears to limit lateral rotation of th

tibia, making its most substantial contribution at about 35of flexion

in conjunction with the posterolateral capsule.

The lateral collateral ligament also resists combined lateral rotatio

with posterior displacement of the tibia in conjunction with th

tendon of the popliteus muscle.Iliotibial Band:

The iliotibial band (ITB) oriliotibial tractis formed proximally from

the fascia investing the tensor fascia lata, the gluteus maximus, and th

gluteus medius muscle.

The iliotibial band continues distally to attach to the linea aspera of th

femur via the lateral intermuscular septum and inserts into latera


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tubercle of the tibia, reinforcing the anterolateral aspect of the kne

joint.

The iliotibial band appears to be consistently taut regardless oposition of the hip joint or knee joint, although it falls anterior to th

knee joint axis in extension and posterior to the axis in flexion.The fibrous connections of the iliotibial band to the biceps femoris an

vastus lateralis muscles through the lateral intermuscular septum form

a sling behind the lateral femoral condyle, assisting the anterio

cruciate ligament in preventing posterior displacement of the femuwhen the tibia is fixed and the knee joint is near extension.

With knee flexion iliotibial band moves posteriorly, while with kneextension iliotibial band moves anteriorly.

The iliotibial band sends fibres from its anterior margin to attach to th

patella, forming an iliopatellar band.When the iliotibial band moves posteriorlyin knee flexion it exert

lateral pullon the patella resulting in a progressive laterally tiltin

as flexion increases. This is prevented by vastus medialis muscle.

Cruciate Ligaments: The anterior cruciate ligament and posterior cruciate ligament ar

intracapsularbut extrasynovialligaments.

These ligaments are named according to their tibial attachments.

Theanterior cruciate ligamentarises from the anterior aspect of the tibia

the posterior cruciate ligament arises from the posterior aspect of thtibia.

Usually both ligaments are described to have main posterolateral an

smaller anteromedial bands that behave differently in differen

movements.

Anterior Cruciate Ligament (ACL):

The anterior cruciate ligament attaches to the anterior tibia, passe

under the transverse ligament, and extends superiorly and posteriorl

to attach to the posterior part of the inner aspect of the lateral femora

condyle.

Generally, the numerous fascicles of the anterior cruciate ligament ar

grouped into ananteromedial band (AMB) and aposterolateral ban

(PLB).

Changes in the lengths of the various bands or fibres during join

motion are used as indicators of the ligaments functions.


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At 0 of knee flexion the anteromedial band is at its shortest lengt(lax)while the posterolateral band is at it longest length (taut).

Therefore, at 0 the lax anteromedial band would be able to offer th

least restraint and the taut posterolateral band would be able to offe

the most restraint.Under valgus loading the length of both bands of the anterior cruciat

ligament increases as knee flexion increases.

Anterior loading alone or combined with valgus loading causes a

increase in length of all portions of the anterior cruciate ligament wit

increases in knee flexion.

In anterior loading some portion of the anterior cruciate ligament

tight throughout the knee joint range.

In knee flexion, the anteromedial band is taut and posterolatera

band is lax. The anterior cruciate ligament is generally considered the primar

restraint to anterior displacement of the tibia on the femora

condyles.

There would appear to be essentially no anterior translation of the tibi

possible in full extension when many of the supporting passivstructures of the knee are taut.

Forces producing anterior translation of the tibia will result in maxima

excursion of the tibia at about 30 of flexion when neither of th

anterior cruciate ligament bands is particularly tensed.

The posterolateral band tends to be injured with excessive kne

hypertension, whereas the anteromedial band tends to be injure

with trauma to the flexed knee.

The anterior cruciate ligament would also appear to make at least

minor contribution to restraining both varus and valgus stresse

across the knee joint.When the medial collateral ligament is damage

and knee is flexed, the anterior cruciate ligament will make a mor

major contribution to restraining varus and valgus stresses.Both cruciate ligaments appear to play a role in producing an

controlling rotation of the tibia.

The anterior cruciate ligament appears to twist around the posterio

cruciate ligament in medial rotation of the tibia, thus checkin

excessive medial rotation.


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Injury to the anterior cruciate ligament appears to occur mo

commonly when the knee is flexed and tibia rotated in eithe

direction.

In flexion and medial rotation, the anterior cruciate ligament

tensed as it winds around the posterior cruciate ligament.In flexion and lateral rotation, the anterior cruciate ligament

tensed as it is stretched over the lateral femoral condyle. When attempting to determine whether there has been a tear of th

anterior cruciate ligament, the presence of both anteromedial an

anterolateral instability is the most diagnostic.

Hamstrings can be considered to act synergistically with the anteriocruciate ligament.

Posterior Cruciate Ligament (PCL):

Theposterior cruciate ligament, which runs superiorly and somewhanteriorly from its posterior tibial origin to attach to the inner aspect o

the medial femoral condyle, is shorter and less oblique than th

anterior cruciate ligament.

The posterior cruciate ligament blends with the posterior capsule an

periosteum as it crosses to its tibial attachment.

Usually posterior cruciate ligament is divided into an anteromedia

band (AMB) and a posterolateral band (PLB) named by the tibi

origin. The anteromedial band is lax in extension, and the posterolatera

band is taut. At 80 to 90 of flexion, the anteromedial band

maximally taut and the posterolateral band is relaxed.

The posterior cruciate ligament is primary restraint to posterio

displacement of the tibia beneath the femur, with little or n

displacement possible in full extension.

In the flexed knee, maximal displacement of the tibia with a posterio

translational force occurs at 75to 90of flexion.

The posterior cruciate ligament also has some role in restraininvarus and valgus stresses at the knee.

The posterior cruciate ligament appears to play a role in bot

restraining and producing rotation of the tibia.

Posterior translatory forces on the tibia are consistently accompanie

by concomitant lateral rotation of the tibia, with little or no rotatioproduced at the femur.


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Tension in the posterior cruciate ligament with knee extensionma

be instrumental in creating the lateral rotation of the tibia that

critical to locking of the knee for stabilization.

The popliteus muscle shares the function of the posterior cruciat

ligament in resisting posteriorly directed forces on the tibia ancontributes to knee stability when the posterior cruciate ligament

absent.

The posterior cruciate ligament, posterior joint capsule, latera

collateral ligaments, posterior oblique ligament, medial collatera

ligament with meniscus attached, posterior medial and posterio

lateral meniscotibial bands, and posterior meniscofibular ligamen

comprise a complex restraining system for knee extension.

Posterior Capsular Ligaments:

The posteromedial aspect of the capsule is reinforced by the tendinouexpansion of the semimembranosus muscle, which is known as th

oblique popliteal ligament.

This ligament passes from a point posterior to the medial tibial condy

and attaches to the central part of the posterior aspect of the joint capsule

Thearcuate popliteal ligamentreinforces the posterolateral aspect of th

capsule.

The arcuate ligament arises from the posterior aspect of the head of fibul

and passes over the tendon of the popliteus muscle to attach to th

intercondylar area of the tibia and to the lateral epicondyle of the femur.Both the oblique popliteal and the arcuate ligaments are taut in fu

extension and assist in checking hyperextension of the knee.

The arcuate and oblique popliteal ligaments play an important role i

checking varus and valgus stresses, respectively, in the extended kne

and in providing secondary restraint to other tibial motions.

The popliteofibular ligamentbecomes taut at 0, 30, 45, and 90 an

acts as a restraint to lateral rotation of the tibia when posterior force i

applied to the knee. The ligament also helps to limit posterior translatio

of the tibia.

Meniscofemoral Ligaments:The two meniscofemoral ligaments arise from the posterior horn of th

lateral meniscus and insert on the lateral aspect of the medial femora

condyle near the insertion site of the posterior cruciate ligament.

The ligament that runs anterior to the posterior cruciate ligament is calle

either the ligament of Humphrey oranterior meniscofemoral ligament.


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The ligament that runs posterior to the posterior cruciate ligament

called the ligament of Wrisberg orposterior meniscofemoral ligament.

is also known asthird cruciate ligament of Robert.

The meniscofemoral ligaments work in conjunction with the popliteu

muscle and become taut during femoral lateral rotation and maprevent posterior translation of the tibia.

Knee Joint Bursae: The extensive ligamentous apparatus of the knee joint and the larg

excursion of the bony segments set up substantial frictional forces betwee

muscular, ligamentous, and bony structures.

However, numerous bursae prevent or limit such degenerative forces.

The suprapatellar bursa, the subpopliteal bursa, and the gastrocnemiu

bursa are not usually separate entities but are either invaginations of thsynovium within the joint capsule or communicate with the capsu

through small openings.Thesuprapatellar bursalies between the quadriceps tendon and the anterio

femur; the subpopliteal bursa lies between the tendon of the popliteu

muscle and the lateral femoral condyle; and the gastrocnemius bursa lie

between the tendon of the medial head of the gastrocnemius muscle and th

medial femoral condyle.

The gastrocnemius bursa may also continue beneath the tendon of th

semimembranosus muscle to protect it from the medial femoral condyle. The lubricating synovial fluid contained in the knee joint capsule move

from recess to recess during flexion and extension of the knee, lubricatin

the articular surfaces.

In extension, the posterior capsule and ligaments are taut and th

gastrocnemius and subpopliteal bursae are compressed. This shifts th

synovial fluid anteriorly.

In flexion, the suprapatellar bursais compressed anteriorly by tension ithe anterior structures and the fluid is forced posteriorly.

When the joint is in the semiflexed position, the synovial fluid is under th

least amount of tension.

When there is an excess of fluid in the joint cavity due to injury or disease

the semiflexed knee position helps to relieve tension in the capsule an

therefore helps to reduce pain.

Several other bursae are associated with the knee but do not communicat

with the synovial capsule.


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The prepatellar bursa, located between the skin and the anterior surface o

the patella,allows free movement of the skin over the patella during flexio

and extension.

Thesubcutaneous infrapatellar bursalies between the patellar ligament an

the overlying skin.The subcutaneous infrapatellar bursa and prepatellar bursa may becom

inflamed as a result of direct trauma to the front of the knee or throug

activities like kneeling (House Maids Knee).

Thedeep infrapatellar bursa, which is located between the patellar ligamen

and the tibial tuberosity, is separated from the synovial cavity of the joint b

the infrapatellar pad of fat. The deep infrapatellar bursa helps to reduc

friction between the patellar ligament and the tibial tuberosity.

There are also several small bursae that are associated with the ligaments o

the knee joint.There is commonly abursa between the lateral collateral ligament and th

tendon of the biceps femoris muscle and between the lateral collatera

ligament and the popliteus muscle.

There is a bursa deep to the medial collateral ligament protecting it from

the tibial condyle and one superficial to the medial collateral ligamen

protecting it from the tendons of the semitendinosus and gracilis musclethat cross the medial collateral ligament.

Knee Joint Function:

Osteokinematics of Knee Joint:

The primary motions of the knee joint are flexion / extension and, t

lesser extent,medial rotation / lateral rotation.

The knee joint can also undergotibial or femoral displacement anterior

and posteriorly and some abduction and adduction through varus an

valgus forces.

The small amounts of anteroposterior displacement and valgus / varu

forces that can occur in the normal flexed knee are the result of joinincongruence and variations in ligamentous elasticity.

Excessive amounts of such motions are abnormal and generally indicat

ligamentous incompetence.

Flexion / Extension:

The axis for flexion and extension at the tibiofemoral joint passe

horizontally through the femoral condyles at an angle to th

mechanical and anatomic axes.


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The obliquity of the axis causes the tibia to move from a positio

slightly lateral to the femur in full extension to a position medial t

the femur in full flexion.

The axis of motion for flexion and extension at the knee is no

relatively fixed, but moves to a considerable extent through the ROM.The pathway of the instant axis of rotation (IAR) of the tibiofemora

joint for flexion and extension forms a semicircle, moving posteriorl

and superiorly on the femoral condyles with increasing flexion.

As many of the muscles associated with the knee are two-joint muscle

that cross both the hip and the knee, hip joint position can influenc

knee ROM.

Passive range of knee flexion is generally considered to be 130 t

140.Knee flexion may be limited to 120or less when the hip joint

simultaneously hyperextended and the stretched rectus femormuscle becomes passively insufficient.Knee flexion may also reac

as much as 160 in activities like squattingwhen the hip and knee ar

flexing at the same time and the body weight is superimposed on th

joint.

Normal gait on level ground requires approximately 60 of kne

flexion. This requirement increases to about 80for stair climbing an

to 90 or more for sitting down into a chair and arising from i

Activities beyond simple mobility tasks require 115of knee flexion omore.

Knee joint extension (hyperextension) of 5to 10is considered withi

normal limits. Excessive knee hyperextension is termed gen

recurvatum.

When the lower extremity is weight bearing and the knee is part of

closed kinematic chain, range limitations at ankle joint may caus

restriction in knee joint flexion or extension.Eg A limitation in ankle dorsiflexion (due to tight plantarflexor

may prevent the knee from being flexed; a limitation iplantarflexion (due to tight dorsiflexors) may restrict the abilit

of the knee to fully extend.

Rotation:

The knee joint rotates in two different ways that are quite differen

both structurally and functionally.

Axial rotation provides the second degree of freedom to th

tibiofemoral joint.


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There is joint rotation involved in the locking mechanism of the kne

joint, also known as terminal or automatic rotation. Rotatio

associated with the locking mechanism occurs with close packing o

the knee joint and does not contribute to degrees of freedom.

Axial rotation of the knee joint occurs around a longitudinal axthat runs through or close to the medial tibial intercondylar tubercleMedial and lateral rotations of the knee joint are named for the motio

or relative motion of the tibia.

The medial and lateral rotations available in axial rotation occu

because of articular incongruence and ligamentous laxity.

The range of knee joint rotation depends on the position of the knee.

When the knee is in full extension, it is in close-packed (locked

position and the ligaments are taut; no axial rotation is possible

The tibial tubercles are lodged in the intercondylar notch and thmenisci are tightly interposed between the articular surfaces.

As knee flexes increasing toward 90

; the capsule and ligamen

become more lax. The tibial tubercles are no longer in th

intercondylar notch and the condyles of the tibia and femur are free t

move on each other.

At 90

of knee flexion, approximately 60

to 70

of either activ

or passive rotation is possible.

The range for lateral rotation (0 to 40) is slightly greater than th

range ofmedial rotation (0to 30).

The maximum range of axial rotation is available at 90 of kneflexion, with the magnitude of axial rotation diminishing as the kne

approaches both full extension and full flexion.

Arthrokinematics of Knee Joint:

Flexion / Extension:

The large articular surface of the femur and the relatively small tibi

condyle create a potential problem as the femur begins to flex on th

tibia.If the femoral condyles were permitted to roll posteriorly on the tibi

condyle, the femur would run out of tibial condyle before much flexio

had occurred. This would result in a limitation of flexion, or the femu

would roll off the tibia.

For the femoral condyles to continue to roll with increased flexion o

the femur, the condyles must simultaneously glide anteriorlyon th


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tibial condyle to prevent them from rolling posteriorly off the tibia

condyle.

The first part of flexion of the femur from full extension (0

t

25

) is primarily rolling of the femoral condyles on the tibia

bringing the contact of the femoral condyles posteriorly on thtibial condyle.

As flexion continues, the rolling is accompanied by

simultaneous anterior glide just sufficient to create a nearly pur

spin of the femur; that is, the magnitude of posterio

displacement that would occur with the rolling of the condyles i

offset by the magnitude of anterior glide, resulting in little linea

displacement of the femoral condyles after 25

of flexion.

The anterior glide of the femoral condyles results in part from th

tension encountered in the anterior cruciate ligament as the femurolls posteriorly on the tibial condyle.

The menisci whose shape forces the femoral condyle to roll uphill

as the knee flexes may further facilitate the glide.

The menisci accompany the femoral condyles as the condyles movposteriorly on the tibial condyle, maintaining the increase

congruence the menisci provide in the fully extended knee.

The menisci cannot move in there entirely because they are attached a

their horns to the intercondylar tubercles of the tibial condyle.

Extension of the knee from flexion occurs initially as a rolling of thfemoral condyles on the tibial condyle, displacing the femor

condyles anteriorly back to neutral position.

After the initial forward rolling,the femoral condyles glide posterior

just enough to continue extension of the femur as an almost purspin (roll plus posterior glide) of the femoral condyles on the tibia

condyles.

Tension in the posterior cruciate ligament and the shape of th

menisci facilitate the intra-articular movements of the femoracondyles during knee extension.

The condyles are once again accompanied in displacement b

distortion of the wedge-shaped menisci.

As extension begins from full flexion, the posterior margins of th

menisci return to their neutral position. As extension continues, th

anterior margins of the menisci move anteriorly with the femoracondyles.


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The motion of the menisci with flexion and extension are an importan

component of the motions. Given the need of the menisci to reduc

friction and absorb forces of the large femoral condyles on the smatibial condyle, the menisci mustremain beneath the femoral condyle

to continue their function.Failure of the menisci to distort in the proper direction can als

result in limitation of joint motion. If femur literally rolls up the wedge-shaped menisci in flexio

(without either the anterior glide of the femur or the posterio

distortion of the menisci), the increasing thickness of the menisci an

the threat of rolling off the posterior margin will cause flexion to b

limited.

Similarly, failure of the menisci to distort anteriorly with the femora

condyles in extension will cause the thick anterior margins to becomwedged between the femur and tibia as the segments are draw

together in the final stages of extension. The interposition of thmenisci will prevent extension from being completed.

Locking Unlocking:

In weight bearing closed chain motion as an example, extension of th

femur on the relatively fixed tibia results in additional motions.

As the femur extends to about 30 of flexion, the shorter latera

femoral condyle completes its rolling-gliding motion.

As extension continues, the longer medial femoral condyle continue

to roll and to glide posteriorly although the lateral condyle ha

halted.

This continued motion of medial femoral condyle results in media

rotation of the femur on tibia, pivoting about the fixed lateral condyle

The medial rotatory motion of the femur is most evident in final 5oextension. Increasing tension in the knee joint ligaments as the kne

approaches full extension may also contribute to the rotation within th

joint.

As the medial rotation of the femur that accompanies the final stage

of the knee extension is not voluntary or produced by muscular force

it is referred to asautomatic orterminal rotationof the knee joint.

This rotation within the joint that accompanies the end of extensioalso brings the knee joint into the closed-packed or locked position.


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The tibial tubercles are lodged in the intercondylar notch, the menisc

are tightly interposed between the tibial and femoral condyles, and th

ligaments are taut.

Consequently, automatic rotation is also known as the lockin

mechanism orscrew home mechanismof the knee. To initiate flexion, the knee must first be unlocked; that is, th

medially rotated femur cannot flex in the sagittal plane, but mulaterally rotate before flexion can proceed.

A flexion force will automatically result in lateral rotation of thfemur because the longer medial side will move before the shorte

lateral side of the joint.

If there is an external restraint to unlocking or derotation of the femu

the joint, ligaments, and menisci can be damaged, as the femur

forced into flexion oblique to the sagittal plane in which its structureare oriented.

Automatic rotation or locking of the knee occurs in both open chai

and closed chain knee joint function.

In an open kinematic chain, the freely movingtibia laterally rotate

on the relatively fixed femur during the last 30 of extension

Unlocking, consequently, is brought about by medial rotation of th

tibia on the femurbefore flexion can proceed.

Axial Rotation:

During axial rotation of the knee joint, the longitudinal axis fo

motion lies at the medial intercondylar tubercle. Consequently, the medial condyles act as the pivot point while th

lateral condyles move through a greater arc of motion than thmedialregardless of the direction of rotation.

When lateral rotation of the tibiaoccurs at the knee joint, the media

tibial condyle moves only slightly anteriorly on the relatively fixe

medial femoral condyle while the lateral tibial condyle moves a larg

distance posteriorly on the relatively fixed lateral femoral condyle.

In medial rotation the direction of motion of the tibial condylereverses, with the medial tibial condyle moving only slightlposteriorly while the lateral condyle moves anteriorly through a large

arc of motion.

When tibia is fixed and the femur is free to move, lateral rotation o

the femur occurs as the lateral femoral condyle moves posteriorly o


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the lateral tibial condyle while the medial femoral condyle move

slightly anteriorly.

Lateral rotation of the femur on the tibia produces an opposite set o

motions.

When there is rotation between the femoral and tibial condyle(either in axial or automatic rotation), the menisci of the knee join

maintain their relationship to the femoral condyles just as they did i

flexion and extension; that is, in rotation of the knee,the menisci wi

distort in the direction of movement of the corresponding femoracondyle.

In medial rotation, the medial meniscus will distort anteriorly o

the tibial condyle to remain beneath the anteriorly movin

medial femoral condyle, and lateral meniscus will distor

posteriorly to remain beneath the posteriorly moving laterafemoral condyle.

In this way,the menisci continue to reduce friction and distribute th

forces the femoral condyles create on the tibial condyle withou

restricting motion.

Muscles of the Knee Joint:

Flexors of Knee Joint:

There are seven muscles which flexes the knee joint that are follows:Semimembranosus

Semitendinosus

Biceps Femoris

Sartorius

Gracilis

Popliteus

Gastrocnemius

All of the knee flexors, except for the short head of the biceps femoris an

the popliteus, are two-joint muscles.As two-joint muscles, their ability tproduce effective force can be influenced by the relative position of th

two joints over which they pass. The popliteus, gracilis, semimembranosus, and semitendinosus muscle

are considered to medially rotate the tibia on the fixed femur, whereas th

biceps femoris is considered to be a lateral rotator of the tibia.


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Hamstring Muscles:

The semitendinosus, semimembranosus, and the biceps femor

muscles are known collectively as thehamstrings.

These muscles all originate on the ischial tuberosity of the pelvis. Th

semimembranosus and the semitendinosus insert on the posteromediaand anteromedial aspects of the tibia, respectively.

The semimembranosus muscle has fibres that attach to the media

meniscus. This attachment assists in knee flexion by facilitatin

posterior motion of the medial meniscus during active knee flexion.The semitendinosus muscle has a fibrous septum that separates it int

distinct proximal and distal compartments. This may give it som

specificity of action at the hip joint and at the knee joint.

Most of the hamstrings, crossing the hip (as extensors) and the kne

(as flexors), work most effectively at the knee joint if they arlengthened over the flexed hip.

With active knee flexion with the body in the prone position, th

hamstrings muscles are forced to attempt to shorten over both the hi

(which will be extended) and over the knee.

The hamstrings will weaken as knee flexion proceeds because th

muscle group is approaching active insufficiencyand must overcom

the increasing tension in the rectus femoris, which is approachin

passive insufficiency.

Biceps Femoris:

The biceps femoris muscle has two heads, both of which insert on th

lateral condyle of the tibia and the head of the fibula.

The biceps femoris tendon may be attached to the iliotibial band an

retinacular fibres of the lateral joint capsule, a set of attachments tha

implies that the biceps femoris has a stabilizing role at th

posterolateral aspect of the joint.

The short head of the biceps femoris does not cross the hip joint and

therefore, has a unique action at the knee joint.

Gastrocnemius:

The gastrocnemius muscle arises from the posterior aspects of th

medial and lateral condyles of the femur by two heads. It inserts int

the calcaneus by way of the calcaneal tendon.

Except for the plantaris muscle, the gastrocnemius is the only muscl

at the knee that crosses the ankle and the knee.


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Although the gastrocnemius generates a large plantarflexor torque a

the ankle, it makes a relatively small contribution to knee flexion.

Rather than working to produce knee flexion, the gastrocnemiu

appears to be effective in preventing knee joint hyperextension.

Paralysis of the plantarflexors is classically accompanied by snapping back of the knee into hyperextension in the final stages o

single-limb support during walking.

The gastrocnemius appears to be less a mobility muscle at the kne

joint than a dynamic stabilizer.

Sartorius:

The sartorius muscle arises anteriorly from the anterior superior ilia

spine of the ilium and crosses the femur to insert the anteromedia

surface of the tibial shaft posterior to the tibial tuberosity.

Although a potential flexor and medial rotator of the tibia, activity ithe sartorius is more common with hip motion than with kne

motion.

When attached just anterior to its more usual location, it may fa

anterior to the knee joint axis, serving as a mild knee joint extenso

rather than as a knee flexor.

Gracilis:The gracilis muscle arises from the inferior half of the symphysis pub

arch and inserts on the medial tibia by way of a common tendon wit

the sartorius and the semitendinosus muscles.It is not only a hip joint flexor and adductor, but it can also flex th

knee joint and produce slight medial rotation of the tibia.

Pes Anserinus:

The gracilis, semitendinosus, and sartorius muscles attach to the tib

by a common tendon on the anteromedial aspect of the tibia. Thcommon tendon is called thepes anserinusbecause of its shape.

The three muscles of the pes anserinus appear to function effective

as a group to stabilize the medial aspect of the knee joint.

Popliteus:

Popliteus muscle originates on the posterior aspect of the latera

femoral condyle and attaches on the medial aspect of the tibia.

The popliteus muscle is a medial rotator of the tibia on the femur i

an open kinematic chain(or a lateral rotator of the femur on the tibi

in a closed kinematic chain).


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The active popliteus muscle is considered to play an important role iinitiating unlocking of the knee because it reverses the direction o

automatic rotation that occurred in the final stages of knee extension.

The popliteus muscle is commonly attached to the lateral meniscu

The lateral meniscus is drawn posteriorly by tension in the popliteuexpansion.

Extensors of Knee Joint:

The four extensors of the knee, namely

Rectus Femoris

Vastus Medialis

Vastus Intermedius

Vastus Lateralisare known collectively as the quadriceps femoris muscle.

The only portion of the quadriceps that crosses two joints is the rectu

femoris, which originates on the inferior spine of the ilium.

The vastus intermedius, vastus lateralis, and vastus medialis muscle

originate on the femur and merge into a common tendon, the quadricep

tendon.

The quadriceps tendon continues distally as the patellar ligament.

The patellar ligament runs from the apex of the patella, across the anteriosurface of the patella, into the proximal portion of the tibial tubercle.

The vastus medialis and vastus lateralis also insert directly into the mediaand lateral aspects of the patella by way of the retinacular fibres of th

joint capsule.

Together, the muscles of the quadriceps femoris extend the knee.

The different orientation of lower fibres of the vastus medialis muscle ha

resulted in reference to the upper fibres as the vastus medialis longu

(VML) and the lower fibres as the vastus medialis oblique (VMO).

Mechanically, the patella affects the efficiency of the quadriceps muscle

the patella lengthens the moment arm (MA) of the quadriceps femoris b

increasing the distance of the quadriceps tendon and patellar ligamenfrom the axis of the knee joint.

The patella, as an anatomic pulley, deflects the action line of th

quadriceps femoris away from the joint, increasing the angle of pull an

the ability of the muscle to generate a flexion torque.

Interposing the patella between the quadriceps tendon and the femora

condyles also reduces friction between the tendon and condyles.


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The position of the patella relative to the joint axis varies as th

instantaneous axis shifts and as the contour of the femoral condyle

changes.

The effect of patella on the moment arm (MA) of the quadriceps muscl

therefore, will vary through the knee joint ROM.

Naik, S. -Biomechanics of Knee Complex

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