BIOMECHANICS

THE KNEE COMPLEX

Sreeraj S R

KNEE JOINT

Sreeraj S R

INTRODUCTION

� FUNCTIONS OF KNEE ARE:1. Provide mobility2. Support body during Dynamic & Static

activities.3. In closed K chain it works with hip & ankle

joints to support body wt. in static erect posture.

4. Dynamically, support during sitting & squatting activities and transferring body wt. during locomotor activities.

5. In open K chain knee provides mobility for foot in space.

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ARTICULATIONS

� Knee complex composed of 2 articulations within a single capsule:

1. The tibiofemoral joint2. The patellofemoral joint

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TIBIOFEMORAL JOINT

1. Is a double condyloid joint with medial & lateral articular surfaces.

2. Flexion and Extension occur in sagittal plane around a coronal axis.

3. Medial & Lateral rotation occur in transverse plane & vertical axis.

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FEMORAL ARTICULAR SURFACE

� Medial & Lateral femoral condyles forms proximal articular surface.

� Patellar groove.

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TIBIAL ARTICULAR SURFACE

� This corresponds to femoral articular surface.

� They are 2 concave medial and lateral asymmetrical plateaus.

� Medial condyle is 50% larger than lateral condyle.

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MENISCI

� Two asymmetrical fibro cartilaginous joint disks called MENISCI are located on tibial condyles that enhances the congruence of knee joint.

� Med.Men. is semi circle.� Lat.Men. is 4/5 of a ring.� Both men. open towards intercondylar

area.� They are thick peripherally & thin centrally

forming concavities.

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MENISCI

� USES.1. Increases joint congruence.2. Distribute weight bearing forces.3. Reduces friction between joints.4. Serve as shock absorbers.

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MENISCI

� ATTATCHMENTS:1.Both Men. are attached to,� Intercondylar tubercles of tibia.� Tibial condyle via coronary lig.� Patella via patellomeniscal & patellofemoral ligs.� Transverse lig.� ACL.2.Med. Men. attached to,� MCL.� Semitendinous muscle.3.Lat. Men. attached to,� Ant. & Post. menisco femoral ligs.� PCL.� Popliteus muscle.

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MENISCI

OTHER FACTS� Meniscal complex is well established in 8 weeks old

embryo.� Well vascularised in 1st yr. of life.� Vascularity gradually reduces from 18 months to 18 yrs.� Over age 50 only periphery is vascularised.� The horns remain vascularised throughout life.� Whole meniscal complex is well innervated.� Innervation is denser in post. horns. May be due to greater

load on post. horns.� The meniscal innervation is a source of information about:1. Joint position.2. Movt. Direction.3. Movt. Velocity.4. Tissue formation.

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TF ALLIGNMENT & WEIGHT

BEARING FORCES

� Anatomical or Longitudinal axis of femur is oblique falling medially & inferiorly.

� Anatomical axis of tibia is almost vertical.

� These 2 lines forms an angle of 185-190° medially at the knee i.e. physiologic valgus angle.

� Mechanical axis of lower extremity falls from head of femur to sup. Surface of head of talus.

� This line passes through the knee joint in bilateral static stance giving equal forces to both the condyles.

� If the med.TF angle is more than 195˚(>165˚lat.) it is Genu Valgum or Knock Knee.

� If the med.TF angle is less than 180˚(<180˚ lat.) it is Genu Varum or Bow Legs.

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TIBIOFEMORAL JOINT

REACTION FORCE

� JRF reach 2-3 times body weight in normal gait.

� JRF reach 5-6 times B W in running, stair climbing etc.

� This time menisci assume 40-60% of imposed load.

� In the absence of menisci JRF doubles on femur & increase 6-7 times on tibial condyle.

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KNEE JOINT CAPSULE

� Restrict various movts.� To maintain joint integrity and normal joint function.ATTATCHMENTS� Postly. :proximally to post. margins of femoral condyles

and inter condylar notch. Distally to post.tibial condyle.� Med. & Lat. :Prox. above femoral condyle & dist. margins of

tibial condyle.� Collateral ligs. reinforce sides of capsule.� Antly. : Patella,Q’ceps muscle superiorly and patellar lig.

inferiorly.� Anterolaterally & anteromedially expansions from vastus

med. & vastus lat. From patella to collateral ligs. And tibial condyles

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EXTENSOR RETINACULUM

� Anteromedial & anterolateral portions of capsule are known as Extensor retinaculum or medial & lateral patellar retinacula.

� Have 2 layers. Deeper and Superficial.� Deeper longitudinal fibers connects capsule

anteriorly to menisci and tibia via coronary ligs.This is known as patellomeniscal bands.

� Superficial transverse fibers blend with fibers of vastus medialis & lateralis and to post. tibial condyles.

� The transverse fibers connecting patella and femoral condyle are known as patellofemoral ligs.

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SYNOVIAL LINING

� Most extensive and involved in the body.� Anteriorly synovium adheres to inner wall of the

joint.� Posteriorly synovium invaginate anteriorly

following the contour of femoral intercondylar notch & adheres to the ant. aspect and sides of ACL & PCL.

� Embryonically synovial lining is divided by septa into 3 compartments.• Superior PF compartment.• Medial TF compartment.• Lateral TF compartment.

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SYNOVIUM (cont )

� By 12 weeks of gestation synovial septa resorbed resulting in a single joint cavity.

� The superior compartment remain as a superior recess of capsule known as Suprapatellar bursa.

� Posteriorly the synovial lining may invaginate :• Laterally between popliteus muscle and lat. Femoral

condyle.• Medially invaginate between semimembranosus tendon,

med. head of gastrocnemius tendon and med. femoral condyle.

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SYNOVIUM (cont )

PLICAE� Synovial septa which are not resorbed into adulthood exist as

folds or pleats of synovial tissue known as Plicae.� They are composed of loose, pliant and elastic fibrous

connective tissue.� They easily passes back and forth over femoral condyles as the

knee flexes and extends.� Observed in 20 to 60% of population.� Commonly known plicae are:1. Inferior/Infrapatellar plica extends from ant. portion of

intercondylar notch to infrapatellar fat pad.2. Superior/Suprapatellar plica is located between suprapatellar

bursa and knee joint.3. Medial/ Mediopatellar plica arises from medial wall of

retinaculum to infrapatellar fat pad.� Plica can become irritated and inflamed, leads to pain, effusion

and changes in joint structure and function.

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KNEE JOINT LIGAMENTS

The knee ligaments are credited with restricting and controlling:

1. Excessive knee motion2. Varus and valgus stresses at knee3. Anterior and posterior displacement of

tibia beneath femur4. Medial and lateral rotation of tibia

beneath femur5. Stabilization in anteroposterior

displacements and rotations of tibia known as rotary stabilization.

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COLLATERAL LIGAMENTS

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CRUCIATE LIGAMENTS

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Anatomy of the ACL

� 3 strands

� Anterior medial tibia to posterior lateral femur

� Prevent anterior tibial displacement on femur

� Secondarily, prevents hyperextension, varus & valgus stresses

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Biomechanics of the ACL

� Most injuries occur in Closed Kinetic Chain

� Least stress on ACL between 30-60 degrees of flexion

� Anteromedial bundle tight in flexion & extension

� Posterior lateral bundle tight only in extension

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Posterior Cruciate Ligament

� Two bundles• Anteromedial, taut in flexion

• Posterolateral, taut in extension

� Orientation prevents posterior motion of tibia

� PCL larger & stronger than ACL

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PCL Biomechanics

� Functions:• Primary stabilizer of the

knee against posterior movement of the tibia on the femur

• Prevents flexion, extension, and hyperextension

� Taut at 30 degrees of flexion• posterior lateral fibers

loose in early flexion

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PCL Biomechanics

� PCL• Primary restraint to

post. Displacement -90%

• relaxed in extension, tense in flexion

• reinforced by Humphreys/ant. MF lig. or Wrisberg/post.MF lig.

• restraint to varus /valgus force

• resists rotation, especially int. rotn. of tibia on femur

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KNEE JOINT MOTION

� Flexion/Extension

� The axis for these movements lies medially oblique through the joint

� This causes the tibia to move from a position slightly lateral to the femur in full extension to a position medial to the femur in full flexion

� Passive ROM 0-130˚� Normal gait on level ground needs 60˚ of flexion� 80° for stair climbing� 90° for sitting down on a chair� Excessive knee hyper extension is termed as Genu

recurvatum

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ARTHROKINEMATICS

flexion/extension

� Femur rolling & gliding at 25°

� Anterior glide is due to

1. Tension of ACL2. The menisci� Extension is reverse

roll, spin and glide1. Tension of PCL2. menisci

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LOCKING AND UNLOCKING

� DURING KNEE EXTENSION

� The tibia glides anteriorly on the femur.

� During the last 20 degrees of knee extension, anterior tibial glide persists on the tibia's medial condyle because its articular surface is longer in that dimension than the lateral condyle's.

� Prolonged anterior glide on the medial side produces external tibial rotation, the "screw-home" mechanism.

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LOCKING AND UNLOCKING

� DURING KNEE FLEXION� When the knee begins to flex from

a position of full extension, posterior tibial glide begins first on the longer medial condyle.

� Between 0 deg. extension and 20 deg. of flexion, posterior glide on the medial side produces relative tibial internal rotation, a reversal of the screw-home mechanism.

� popliteus is the muscle that ‘unlocks’ the knee at the beginning of flexion of the fully extended knee. As the extended and locked knee prepares to flex (when beginning to descend into a squat position), the popliteus provides an external rotation torque to the femur that mechanically unlocks the knee. Since the knee is mechanically locked by a combo of extension and slight IR of the femur on a fixed tibia, unlocking the knee requires that the femur ER on the fixed tibia.

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KNEE JOINT MOTION

� Rotation: in 2 different ways�Axial rotation : occurs around a

longitudinal axis. Med. and lat. rotn. are possible. This occur in flexed position. Approximately 60-70° of active or passive ROM is possible

�Terminal or automatic rotation : associated with locking mechanism

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ARTHROKINEMATICS

Axial rotation� Longitudinal axis for axis

rotation lies at medial intercondylar tubercle

� i.e. med. Condyle act as pivot point while the lat. condyle move through a greater arc of motion

� When lat. and med. rotation of tibia occurs at knee joint

� When lat. and med. rotation of femur occurs at knee joint

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Knee Muscles

� Knee Extension

• Rectus Femoris• Vastus Medialis• Vastus Lateralis• Vastus Intermedius

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Rectus Femoris

� Two-jointed, bipennateACTIONS� May contribute to lateral

rotation and abduction of hip� Extends knee and flexes hipEFFECTS OF WEAKNESS� Decreases knee extension

strengthEFFECTS OF TIGHTNESS� Limits knee flexion range of

motion (ROM) with hip extended

� Hip abduction reduces stretch of rectus femoris.

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Vastus Medialis

� Consists of longitudinal (vastus medialis longus [VML]) and oblique (vastus medialis oblique [VMO]) portions

ACTIONS� Knee extension� Patellar stabilization� Active with other heads

throughout knee extensionEFFECTS OF WEAKNESS� Decreased knee extension

strength� Few data support the belief that

specific vastus medialis weakness contributes to patellar tracking abnormalities. And, the VMO has been refuted to contribute to the last 15 deg of knee extension.

EFFECTS OF TIGHTNESS� With rest of quadriceps, limits

knee flexion ROM

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Vastus Lateralis� Largest head of quadriceps

in many individualsACTIONS

� Knee extensionEFFECTS OF WEAKNESS

� Significant weakness in knee extension

EFFECTS OF TIGHTNESS

� Decreased knee flexion ROM

� May contribute to patellofemoral dysfunction

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Vastus Intermedius

� Unipennate and deepACTIONS

� Extends knee and pulls capsule proximally

EFFECTS OF WEAKNESS

� Significant loss of knee extension strength 15-40% of PCSA

EFFECTS OF TIGHTNESS

� Decreased knee flexion ROM regardless of hip position

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Knee Muscles

� Knee Flexion—

• Biceps Femoris• Semitendinosous• Semimembranosus• Gastrocnemius• Plantaris

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HamstringsACTIONS� Knee flexion� Active knee flexion without

rotation requires simultaneous contraction of medial and lateral hamstrings.

� Contribute to knee joint stability� Hip extension throughout ROM of

hip� May also adduct and rotate hipEFFECTS OF WEAKNESS� Knee flexion weakness� Larger impairment may be

weakness of hip extension.EFFECTS OF TIGHTNESS� Decreased knee extension ROM

with the hip flexed� May contribute to knee flexion

contractures and posterior rotation of pelvis

� Considerable evidence from cadaver studies indicating that the hamstings muscles decrease the stress/strain on the ACL

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Hamstring and Gait

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Rotation of the Knee and

hamstrings

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� Tightness of hamstrings can pull the pelvis into a posterior pelvic tilt, flattening the lumbar spine

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Popliteus

ACTIONS� Small muscle� Increased activity with

combined knee flexion and medial rotation of tibia

� Medially rotates knee� Adds stability to tibiofemoral

jointEFFECTS OF WEAKNESS� Difficult to determine� Injured with extensive

posterolateral ligamentous structures

EFFECTS OF TIGHTNESS� Difficult to discern but would

contribute to knee flexion contractures

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MEDIAL ROTATORS OF THE

KNEE

� Sartorius and Gracilis, in addition to medial hamstrings and popliteus

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Sartorius

� Strap muscle with very long muscle fibers

ACTIONS� Hip flexion with large moment

arms to also abduct and laterally rotate hip

� Knee flexion� Inactive with isolated medial

rotation of kneeEFFECTS OF WEAKNESS� Isolated weakness may have

little effectEFFECTS OF TIGHTNESS� Small effect but may

contribute to flexion contracture

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Gracilis

ACTIONS

� Medial rotation and flexion of knee

� Adduction of hipEFFECTS OF WEAKNESS

� No reports but may affect hip adduction and knee flexion and medial rotation strengths

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Pes Anserinus

� Semitendinosus, sartorius, and gracilis attach to tibia by a common tendon on the anteromedial aspect of the tibia.

� They effectively stabilize the medial aspect of the knee.

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LATERAL ROTATORS OF THE

KNEE

� Tensor fasciae latae with lateral hamstrings

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Tensor Fasciae Latae

ACTIONS� Flexes, abducts, and medially

rotates hip� Extends and laterally rotates

knee� Participates in gait with other

abductors, perhaps to stabilize pelvis or progress pelvis over stance limb

EFFECTS OF WEAKNESS� Effects small, but reduced hip

abduction, flexion, and medial rotation strength and decreased knee extension strength

EFFECTS OF TIGHTNESS� Decreased hip adduction and

lateral rotation ROM� Associated with knee and

patellofemoral pain and dysfunction

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Patellofemoral Joint

� Patella is a true sesamoid bone

� Posterior surface of the patella is covered with thick hyaline cartilage

� The patella slides within the trochlear groove

� Function of the patella• 1) Aids knee extension by

producing anterior displacement of quadriceps tendon and lengthening the lever arm of the quad muscle force

• 2) Allows wider distribution of compressive stress on the femur by increasing area of contact between patellar tendon and femur

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PATELLAR MOVEMENTS

� In full extension the patella sits on ant. Surface of femur

� In flexion , the patella slides distally on the femoral condyles

� In full flexion the patella sinks into the intercondylar notch

� The patella in extended knee has little contact with femoral sulcus beneath it

� First contact made at 10-20°of flexion on inferior margin of patella

� By 90° flexion all patella got some contact except odd facet

� Above 90° odd facet gain contact

� At 125° flexion contact is on lateral facet

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PMJ STABILITY

� PFJ is under control of two restricting mechanisms that cross each other at right angles

1. Transverse group of stabilizers

2. Longitudinal group of stabilizers

� In a so called patellar tracking both the transverse and Longitudinal structures will influence the medial and lateral positioning of the patella within the femoral sulcus

� Medial – lateral forces1. Pull of VL is 12-15° lateral

on long axis of femur2. Pull of VM is 15-18° medial

with 50-55° pulling of VMO

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Q-Angle

� The Q-angle is the angle formed by a line from the anterior superior spine of the ilium to the middle of the patella and a line from the middle of the patella to the tibial tuberosity.

� Males typically have Q-angles between 10 to 14°

� Females between 15-17°� A Q- angle of more than

20° or more is considered to be abnormal creating excessive lateral forces on the patella.

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PF joint reaction forces

� The patella is pulled simultaneously by the quadriceps tendon superiorly and by the patella tendon inferiorly

� In normal full extension the patella is suspended between them

� Even a strong contraction of quadriceps produce no PF compression

� – Minimal quad forces are required during upright and relaxed standing (center of gravity almost directly above knee)

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PF joint reaction forces

� As knee flexion increases, the center of gravity shifts posterior, increasing flexion moments required

� Knee flexion affects angle between patellar tendon force and quadriceps tendon force

� The total joint reaction force depends on

1. Magnitude of active or passive pull of quadriceps

2. Angle of knee flexion� 10-15deg flexion: 50% of

BW� Increase flexion, increased

muscle activity up to 3.3xBW� Mechanical advantage is the

biggest between 30-70deg flexion