Knee Joint 2a

Joint Capsule: • Encloses the tibiofemoral & patellofemoral joints • It is large complex and possess several recesses • Collaterals reinforce the sides of the capsule • Anteromedial and anterolateral portions of capsule are known as medial and lateral patellar retinacula

Ligaments: • As the joint lacks bony restraint to any motions, ligaments are credited with resisting or controlling c. Excessive extension d. Varus and valgus stress e. Anterior and posterior displacement of tibia beneath the femur f. Medial or lateral rotation of of tibia beneath the femur g. Combinations of anteroposterior displacements and rotations of tibia – rotatory stabilization

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Collateral Ligaments: Are taught in full extension and help resist hyper extension of knee joint Medial collateral ligament: Extends from medial femoral epicondyle to medial aspect of proximal tibia Resists valgus stress Backup restraint to pure anterior displacement of tibia when ACL is absent

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Lateral collateral ligament: Extends from lateral femoral epicondyle to head of fibula Resists varus stress

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Cruciate ligaments: Two in number and named according to their tibial attachments

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Anterior cruciate ligament: arises from anterior aspect of tibia passes under the transverse ligament and extends superiorly and posteriorly and attaches to posterior part of inner aspect of lateral femoral condyle primary restraint to anterior displacement of tibia on femoral condyles fascicles are grouped into anteromedial band (AMB) and posterolateral band(PLB)

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Posterior cruciate ligament: arises from posterior aspect of tibia and attaches to inner aspect of medial femoral condyle is shorter and less oblique primary restraint to posterior displacement of tibia beneath the femur fascicles are grouped into anteromedial band (AMB) and posterolateral band(PLB)

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Posterior Capsular Ligaments: Postero medial aspect of capsule is reinforced by oblique popliteal ligament expansion of semimebranous muscle Postero lateral aspect of capsule is reinforced by arcuate popliteal ligament expansion of popliteus muscle Both check hyperextension

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Meniscofemoral Ligaments: Two in number, arise from posterior horn of lateral meniscus and insert on the lateral aspect of medial femoral condyle near insertion site of PCL Ligament that runs anterior to PCL is lig. of Humphrey/anterior meniscofemoral ligament Ligament that runs posterior to PCL is lig.of Wrisberg/ posterior meniscofemoral ligament

Bursae: • Supra patellar bursa • Sub popliteal bursa • Gastronemius bursa • Prepatellar bursa • Infrapatellar bursa • Deep infrapatellar bursa

Synovial fluid contained in knee capsule moves from recess to recess during movements of knee • In extension fluid is shifted anteriorly • In flexion fluid is forced posteriorly • In semiflexed position fluid is under least tension •

Knee Joint Motion: • Primary movements are flexion/extension and to lesser extent medial/lateral rotation Osteokinematics: Flexion/extension: • As many two joint muscles pass knee they can affect the ROM with changes in hip position

Knee Flexion: Passive 130° - 140°. • Range is limited to 120° if hip is hyperextended as hamstring becomes actively insufficient • Gait requires about 60° of knee flexion • This increases to about 80° for staircase climbing and 90° for sitting down into a chair Knee Extension: 5° - 10° normal

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Excessive hyperextension is called as Genu Recurvatum

Rotation: • Knee rotates in 2 different directions • Axial rotation provides second degree of freedom to tibiofemoral joint • Medial and lateral rotation are named for the relative motion of tibia • Occurs due to ligament laxity and articular incongruencies • Depends on joint position • In full extension there is no axial rotation • As the knee flexes towards 90° the ligaments lax and the condyles are free to move • Maximum axial rotation is available at 90° • Lateral Rotation: 0 - 40° • Medial Rotation: 0 - 30°

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Large articular surface of femur and relatively small tibial condyle creates a potential problem as femur begins to flex on tibia If femoral condyles were permitted to roll posteriorly on tibial condyle femur would run out of tibial condyles before much flexion could occur – this would result in limitation of flexion or femur would roll of tibia

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For femoral condyles to continue to roll with increased flexion of the femur the condyles must simultaneously glide anteriorly on tibial condyle to prevent them from rolling posteriorly off the tibial condyle

Knee flexion: • First part of flexion of femur from full extension (0-25°) is primarily rolling of femoral condyles on the tibia bringing the contact of femoral condyles posteriorly on tibial condyle • As flexion continues the rolling is accompanied by an anterior glide just sufficient to create a nearly pure spin of the femur • That is, the magnitude of posterior displacement that would occur with the rolling of condyles is offset by the anterior glide • This results in a linear displacement after 25° of flexion

The anterior glide is controlled by tension encountered in the ACL as the femur rolls posteriorly only on the tibial condyles • The glide is facilitated by the wedge shape of the meniscus • The femur and the menisci create shear force with respect to one another, thus the menisci accompany the femoral condyles as they move posteriorly on the tibial condyles • The lateral meniscus moves more than the medial •

Knee extension: • Occurs initially as a rolling of the femoral condyles over the tibial condyles displacing the femoral condyles anteriorly back to the neutral position • After the initial forward rolling, femoral condyles glide posteriorly just enough to continue extension of the femur as a pure spin • Tension in the PCL and the shape of the menisci facilitate the intra articular movements of femoral condyles during knee extension

Motion (or distortion) of menisci are an important component of the movements • Failure to distort would result in limitation of ROM •

Locking and unlocking: • Although the incongruence of the femoral condyles and the tibial condyles results in a rolling and gliding of the condylar surfaces on each other, the asymmetry in the size of medial and lateral condyles also causes complex intra-articular motions Locking: • In weight bearing closed chain position extension of the femur on a fixed tibia results in additional motion to the earlier explained ones

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As the femur extends to about 30° of flexion, the shorter lateral condyles complete its rolling – gliding motion As extension continues the longer medial femoral condyle continues to roll and glide posteriorly although the lateral condyle has halted This continued motion of medial femoral condyles results in medial rotation of the femur on tibia, pivoting about the fixed lateral condyle This medial rotation is most evident in the final stages of knee extension (5°) Increasing tension in the joint ligaments as the knee approaches full extension may also contribute to the rotation with in the joint

Since the medial rotation of the femur that accompanies the final stages of knee extension is not voluntary or produced by muscular forces, it is referred to as automatic or terminal rotation • This rotation brings the knee in close-packed or locked position • The tibial tubercles are lodged in the intercondylar notch, the ligaments become taut and the menisci are interposed tightly between the condyles - locking mechanism or screw home mechanism •

Unlocking: • To initiate flexion knee must be unlocked • For the knee to flex, unlocking occurs by lateral rotation of the femur • A flexion force will automatically result in lateral rotation since the longer medial side will move before the shorter lateral side • The longer medial side moves just compared to the lateral side

In open chain - Tibia rotates laterally on a fixed femur during the last 30° of extension –LOCKING • Tibia rotates medially on a fixed femur before flexion can proceed - UNLOCKING •

Muscles II. Flexors: c. Semimembranosus d. Gastrocnemius • Sartorius f. Gracilis ∗ Gracilis, semitendinosis and sartorius are inserted on the tibia by means of a common tendon called as ‘Pes Anserinus’ h. Popletius

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Extensors: Quadriceps femoris Only muscle which crosses two joints is rectus femoris

Patella increases the efficiency of quadriceps • Efficiency of the quadriceps muscle is affected by the patella • Patella lengthens the moment arm of quadriceps by increasing the distance of the quadriceps tendon and patellar ligament from the axis of the knee joint

Patella acting as an anatomic pulley deflects the action line of the quadriceps femoris away from the joint that increases the angle of pull and the ability of the muscle to generate torque • It helps to reduce friction between the tendon and the condyles • Substantial decreases in the strength of quadriceps of upto 49% occurs following patellectomy •

Patellofemoral joint : • Patella is primarily an anatomic pulley and reduces friction between quadriceps and femoral condyles • Ability of patella to perform its functions with out restricting the knee motion depends on its mobility Patellar flexion: • In full extension patella sits on anterior surface on distal femur • With knee flexion patella slides distally on femoral condyles,seating itself between femoral condyles • In full flexion patella sinks into the intercondylar notch

Patellar extension: • Knee extension reverses the sliding of the patella and brings it back to the patella surface of femur Patellar tilt: • Tilts medially from 0°-30° • Tilts laterally between 20° -100°

Patellar Rotation : • Medial rotation of the patella involves movement of the inferior patellar pole with medial rotation of the tibia • Lateral rotation of the patella involves movement of the inferior pole of patella with lateral rotation of the tibia

Patellar Shift: • Mediolateral translation that the patella under goes during knee movement • Patella shifts medially in flexion and laterally in extension

Failure of patella to slide,tilt,rotate,or shift can lead to restriction of ROM,instability,or pain ∀ ∴ passive mobility of patella is often assessed clinically •

Articular surfaces: • Patellofemoral joint is the least congruent joint in the body

Articular surface of patella

Femoral articular surface

Joint Congruence: • In fully extended knee patella lies on femoral sulcus Patella alta – abnormally high position of patella on femoral sulcus due to excessively long patellar tendon • In extended knee patella has little or no contact wit femoral sulcus • First consistent contact of patella is made at 10° – 20° of flexion • Over all the range of knee flexion, medial patellar facet normally receives the most consistent contact with the femoral surfaces where as the odd facet receive the least

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Most common cartilaginous changes on patella are found on medial and odd facets

Patella femoral Joint Reaction Force: • Patella is pulled on simultaneously by quadriceps tendon superiorly and patellar tendon inferiorly • In extension when pulls of these two are vertical or in line with each other patella may be suspended between them making no contact with the femur • Even a strong contraction of quadriceps in full extension will produce little or no patellofemoral compression

This is the basis for the use of SLR in strengthening the quadriceps without increasing forces on the joint • As flexion occurs from full extension pull of quadriceps(FQ) tendon and patellar ligament (Fpl) becomes oblique compressing patella into the femur • Compression creates a joint reaction force across the patellofemoral joint • The magnitude of joint reaction force (R) depends upon: a. Magnitude of pull of quadriceps b. Angle of knee flexion •

Patellofemoral joint reaction force in gait when foot first contacts the ground and knee flexes to 10°-15° is 50% of body weight • During stair case climbing and running hills knee flexion goes up to 60° and thus increases patellofemoral joint reaction force to 3.3times body weight • Joint reaction force many reach up to 7.8times of body weight at 130° of knee flexion in such activities as deep knee bends • Medial facet bears the brunt of compressive forces •

Joint stability: • Two stabilizing groups are present • Longitudinal stabilizers - quadriceps tendon superiorly and patellar ligament inferiorly • Transverse stabilizers - medial and lateral patellar retinaculae join the vastus medialis and vastus lateralis respectively • Both structures help in medial-lateral positioning of patella within the femoral sulcus called as ‘Patellar Tracking’ from extension to flexion

Q (quadriceps) angle: • Defined as the angle between the quadriceps muscle (primarily the rectus femoris) and the patellar tendon and represents the angle of quadriceps muscle force • Used to clinically assess the net pull of quadriceps and patellar tendon • Angle formed between a line connecting ASIS to the midpoint of patella • A line connecting the tibial tubercle and midpoint of patella

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Normal-men is 14° and in women is 17°

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> 20° considered to be abnormal, creating excessive lateral forces on the patella

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An increased Q angle is a risk factor for patellar subluxation and patellar dislocation

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Anything that may increase the obliquity of the resultant pull of the quadriceps or the obliquity of the patellar ligament may increase the lateral force on the patella

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Q angle is increased in

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genu valgum

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increased femoral anteversion

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external tibial torsion

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laterally positioned tibial tuberosity

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tight lateral retinaculum

Knee Injury and Disease • Injury can be due to ligaments, menisci, bones, soft tissue, bursae and tendon • Menisci: Medial meniscus is more injured and is due to medial rotation of the femur on a fixed tibia on a flexed knee • Ligaments: Motion exceeding normal can be due to ligament laxity which can occur due to aging, disease, immobilization, reduced vascularity • Bursitis: Common in prepatellar and superficial infrapatellar bursa (Housemaid’s Knee). This is due to indirect blow/prolonged compressive stress or areas of high friction

PF Joint Instability: Due to -Imbalance in Quadriceps muscle -Tension/shortening of the lateral retinaculum -Tight IT band • Chondromalacia Patella: softening articular cartilage of patella •

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