Biomech of Knee & tkr knee

BIOMECHANICSOF

NORMAL &

REPLACED KNEE

BIOMECHANICSOF

NORMAL &

REPLACED KNEE

BIOMECHANICSBIOMECHANICS

KNEE :Force closed mechanism

HIP :Self closed mechanism

The Axis Of Lower Limb

The Axis Of Lower Limb

•Vertical Axis•Mechanical Axis•Anatomical Axis of Femur

•Anatomical Axis of Tibia

•Vertical Axis•Mechanical Axis•Anatomical Axis of Femur

•Anatomical Axis of Tibia

Tibio-Femoral Motion

Tibio-Femoral Motion•Flexion – Extension

•Abduction – Adduction

•Internal – External Rotation

•Flexion – Extension

•Abduction – Adduction

•Internal – External Rotation

Instantaneous centre of motion

Instantaneous centre of motion

FLEXION - EXTENSIONFLEXION -

EXTENSION

Instantaneous center pathway

Instantaneous center pathway


EXTENSION

Sliding/RockingSliding/Rocking


EXTENSION

Sliding/Rocking of femurSliding/Rocking of femur

Gliding/Rolling


EXTENSION

Gliding/Rolling of femur


EXTENSION

Knee glides & SlidesRocks & Rolls!

Knee glides & SlidesRocks & Rolls!

ROTATION OF KNEEROTATION OF KNEE

•Screw home

movement

•Rotation increases

as knee is flexed

•Arc ranges 30 – 60

•Screw home

movement

•Rotation increases

as knee is flexed

•Arc ranges 30 – 60

Abduction - AdductionAbduction - Adduction•Normal angulation

of 7 Degrees with knee extended

•Motion permitted by cruciate and collaterals

•No movement in flexion

•Normal angulation of 7 Degrees with knee extended

•Motion permitted by cruciate and collaterals

•No movement in flexion

FlexionFlexion40

0

40ExtensionExtension

HS

FFFF

HO

TOTO

Flexion - ExtensionFlexion - Extension

•Sit & Rise from a chair90 -110 degrees

•Sit & Rise from a chair90 -110 degrees


•Descending stairs 90 degrees•Descending stairs 90 degrees


•Ascending stairs 82 degrees•Ascending stairs 82 degrees

Int – Ext RotationInt – Ext Rotation

•Normal 30-60 Degrees

•13 degrees in normal walking

•More in stair walking•More on rough

ground walking

•Normal 30-60 Degrees

•13 degrees in normal walking

•More in stair walking•More on rough

ground walking

Loads Applied to Knee

Loads Applied to Knee

•3X - in Level Walking•4X – in Stair Climbing•Area of Contact is less in Flexion•Medial side bears more weight

•3X - in Level Walking•4X – in Stair Climbing•Area of Contact is less in Flexion•Medial side bears more weight

STABILITYSTABILITY• Surface geometry• Muscles

crossing the joint

• Ligaments and capsule

• Menisci

• Surface geometry• Muscles

crossing the joint

• Ligaments and capsule

• Menisci

SURFACE GEOMETRYSURFACE

GEOMETRY

Femur is convexTibia is concave mediallyTibia is convex laterally

Tibial eminence aids in stability

Femur is convexTibia is concave mediallyTibia is convex laterally

Tibial eminence aids in stability

•Resists deforming force

•Resists slow forces

•Increase joint compression

•Increase stability

•Resists deforming force

•Resists slow forces

•Increase joint compression

•Increase stability

MUSCLES

MUSCLES

•Resists motion

•Resists translatory movement

•Resists excessive rotation

•Resists motion

•Resists translatory movement

•Resists excessive rotation

LIGAMENTSLIGAMENTS

•Joint conformity

•Varus valgus stability

•Resists translation

•Joint conformity

•Varus valgus stability

•Resists translation

MENISCUSMENISCUS

IDEAL KNEEIDEAL KNEE

• Extends fully & achieves excellent stability

• Flexes beyond 110 & still retains stability

• Gliding and sliding occurs simultaneously

• Allows more rotation as knee flexes

• Articular contact maximum throughout range

• Extends fully & achieves excellent stability

• Flexes beyond 110 & still retains stability

• Gliding and sliding occurs simultaneously

• Allows more rotation as knee flexes

• Articular contact maximum throughout range

• Reduplicate the function of menisci

• Reduplicate the function of cruciates

• Achieve excellent ligament balance

• Have anatomic femur & tibial surface

• Reduplicate the function of menisci

• Reduplicate the function of cruciates

• Achieve excellent ligament balance

• Have anatomic femur & tibial surface

IDEAL KNEEIDEAL KNEE

RESTORATION OF MECHANICAL AXISRESTORATION OF MECHANICAL AXIS

RESTORATION OF MECHANICAL AXISRESTORATION OF MECHANICAL AXIS

Perpendicular to the Mechanical & Anatomical axis of the Tibia

Perpendicular to the Mechanical & Anatomical axis of the Tibia

BIOMECHANICS OF TKR

BIOMECHANICS OF TKR

Should none, one or both cruciate ligaments be sacrificed

Should none, one or both cruciate ligaments be sacrificed

ACL & PCL SACRIFICEDACL & PCL

SACRIFICED• Conforming

concave surface of tibia producing inherent stability

• Long term results from HSS still remains the gold standard

• Conforming concave surface of tibia producing inherent stability

• Long term results from HSS still remains the gold standard

• Limited knee motion• Tibial component

subluxated posteriorly• Stair climbing was

difficult

• Limited knee motion• Tibial component

subluxated posteriorly• Stair climbing was

difficult

TOTAL CONDYLAR DESIGNS




RETAIN THE PCLRETAIN THE PCL

• PCL roll back in flexion

• Roll back needs flat tibial surface

• PCL roll back in flexion

• Roll back needs flat tibial surface

ROLL BACK WITH PCLROLL BACK WITH PCL

More arc of motion Intact PCL prevents post

subluxation of tibia Stability is increased Decreased interface

stresses Shear forces are well

tolerated

More arc of motion Intact PCL prevents post

subluxation of tibia Stability is increased Decreased interface

stresses Shear forces are well

tolerated


• Proprioception is better

• Retention of PCL helps in

maintaining the joint line

• Proprioception is better

• Retention of PCL helps in

maintaining the joint line


Why surgeon sacrifices PCL?

Why surgeon sacrifices PCL?

• Minimum tibial resection • Easier surgical technique• Easier correction of

deformity

• Minimum tibial resection • Easier surgical technique• Easier correction of

deformity

PCL SUBSTITUTING KNEE


• Spine & Cam mechanism

• Produces roll back

• Prevents posterior subluxation

• Spine & Cam mechanism

• Produces roll back

• Prevents posterior subluxation

• Anterior tibial subluxation not prevented

• Does not substitute collaterals

• Posterior slope in tibia necessary

• Anterior tibial subluxation not prevented

• Does not substitute collaterals

• Posterior slope in tibia necessary






PCL SUBSTITUTING KNEE• Bad for valgus knee

• Wear of spine

• Bone loss

• Bad for valgus knee

• Wear of spine

• Bone loss

Can we substitute the PCL by ultra congruent insert ?

Can we substitute the PCL by ultra congruent insert ?

PCL SUBSTITUTING KNEEPCL SUBSTITUTING KNEE

PCL SUBSTITUTING KNEEPCL SUBSTITUTING KNEE• Patellectomy

• Old PCL injury

• Over release of PCL

• Inflammatory conditions ?

• Patellectomy

• Old PCL injury

• Over release of PCL

• Inflammatory conditions ?

MENISCAL BEARING KNEE

MENISCAL BEARING KNEE

• ACL, PCL retaining• PCL retaining

• ACL, PCL retaining• PCL retaining

ROTATING PLATFORM KNEE

ROTATING PLATFORM KNEE

• Cruciate sacrificing

• Spin off

• Undersurface wear

• Cruciate sacrificing

• Spin off

• Undersurface wear

FEMURFEMUR• Anatomic• Decrease

radius of curvature posteriorly

• Anatomic• Decrease

radius of curvature posteriorly

EXTERNAL ROTATION OF FEMUR






TIBIAL TRAYTIBIAL TRAY

• Concave conforming

• No rotation in extension

• Intercondylar eminence to prevent translocation

• Anterior Posterior margin equal height

• Concave conforming

• No rotation in extension

• Intercondylar eminence to prevent translocation

• Anterior Posterior margin equal height

•Anatomic•Anatomic

TIBIAL TRAYTIBIAL TRAY

PATELLAPATELLA

PATELLAPATELLA

Recent thoughts…Recent thoughts…• Adductor moment• Rotatory arthritis

of knee (RAK)• Does tibia really

slope posteriorly?

• Adductor moment• Rotatory arthritis

of knee (RAK)• Does tibia really

slope posteriorly?

Adductor MomentAdductor Moment

Rotatory Arthritis of KneeRotatory Arthritis of Knee

• Deformities in Knee are triplanar – frontal, saggital & coronal

• ACL ‘s role• Soft tissue involvement

• Deformities in Knee are triplanar – frontal, saggital & coronal

• ACL ‘s role• Soft tissue involvement

Posterior slope of tibiaPosterior slope of tibia

Health & Medicine

Biomech of Knee & tkr knee