Biomechanics of knee

Biomechanical roles of the knee joint complex

Arthrokinematics of the knee

Knee joint loading

Soft tissue mechanics

1. Biomechanicsofthekneejoint

2. Tableofcontents
•Biomechanicalrolesofthekneejoint
complex
•Arthrokinematicsoftheknee
•Kneejointloading
•Softtissuemechanics

3. Kneejointcomplex

4. Mainbiomechanicalrolesofthe
kneejointcomplex
•Toallowlocomotionwith
(a)minimumenergyrequirementsfromthe
muscles
(b)stability,accommodatingfordifferentterrains.
•Totransmit,absorbandredistributeforces
causedduringtheactivitiesofdailylife

5. Arthrokinematicsoftheknee

6. Kneejoint•Ginglymus(hinge)
•Arthodial(pivot,gliding)
•6degreesoffreedom
–3rotations
–3translations
Frontal axis
(varus-valgus
rotation)
Sagittalaxis
(flexion-
Extension)
Transverseaxis(interna-externalrtation)

7. Rotationandtranslationinkneejoint
•Rotation:
–flexion-extension:upto160degofflexion
(upto-5degflexion–hyperextension)
–varus-valgus:6-8deginextension
–internal-externalrotation:25-30deginflexion
•Translation:
–anterior-posterior:5–10mm
–compression:2–5mm
–medio-lateral:1-2mm

8. Centreofrotationforfemurmotionduring
flexion-extension
(sagittalview)
Rolling Sliding Purerotation
femur
tibia
IC

9. Femoralcondylesinflexion

10. Kneejointkinematicsinthesagittalplaneduringgait.
aExtension:contactislocatedcentrally.bEarlyflexion:posteriorrolling;contact
continuouslymovesposteriorly.cDeepflexion:femoralsliding;
contactislocatedposteriorly;the unlocking of the ACL prevents further femoral roll back.
(

11. Theirreduciblemechanismoftheknee(bonescutawaytoshow
cruciateligaments).
ACL
PCL

13. Screw-homeduringkneeextension
Duringthelast20degreesofkneeextension
anteriortibialglidepersistsonthe tibia'smedial
condylebecauseitsarticularsurfaceislongerinthat
dimensionthanthelateralcondyle's.
Prolongedanteriorglideonthemedialsideproduces
externaltibialrotation,the"screw-home"mechanism.
LATERAL

14. Functionalrangeofmotion(ROM)attheknee
•Activities
◆Normalgait/level surfaces
◆Stairclimbing
◆Sitting/risingfrom most
chairs
◆Sitting/risingfromtoiletseat
◆Advancedfunction
Knee flexion
60°
80°
90°
115º
>115°

15. Diagramsshowingthemeanmovement(mm)ineachmeniscusduringflexion
(shaded)andextension(hashed).ANT,anterior;POST,posterior;mme,mean
meniscalexcursion;P/A,ratioofposteriortoanteriormeniscaltranslationduring
flexion.
Extension
Flexion

16. Kneejointloading

17. Tibiofemoraljointactivities:
Flexion&compressiveload
BW=bodyweight
Front
•Cycling 60-100deg 1.2BW
•Walking 15 3.0
•Stairs 60 3.8
•Stairs 45 4.3
•Squat-rise 140 5.0
•Squat-down 140 5.6

18. VARUS NEUTRAL VALGUS

19. Functionofthepatella
•Largestsesamoidboneinthebody
•Location:embeddedinquadricepstendon
•Function:toincreasemechanicalleverageof
thequadriceps

20. Laterally-lateralretinaculum,vastuslateralism,iliotibialtract.
Medially-medialretinaculumandvastusmedialism.
Superior-Quadricepsviaquadriceps
tendon.
Inferior-Patellarligamentum
Forcesactingonthepatella:

21. Risingupfromachair.Assumingthat0.5BWistransferredthrougheachlegappliedatthe
foot,thenitslineofactionisapproximately200mmposteriortothejointcentre;also,thePT
lineofactionisapproximately35mmoffthejointcentre.MomentequilibriumrequiresPT×
35mm=0.5BW×200mm, which results in PT ≈ 3.0 BW. At 90°flexion it has been shown
that PT ≈ 70% Q, therefore Q ≈ 4.5 BW.Forceequilibriumrequiresthetriangleofforces
actingateachjointtobeclosed;thisresultsinjoint forces of PF ≈ 5.5 BW and TF ≈ 3.5 BW
(BW: body weight, PT: patellar tendon, Q: quadriceps muscle,PF:patellofemoral,TF:
tibiofemoral).

22. Patellofemoraljointreactionforces

23. Patellarcompressionforce
Activity
Walking
Force
850N
%Bodyweight
1/2xBW
Bike
Stairascend
Stairdescend
Jogging
850N
1500N
4000N
5000N
1/2xBW
3.3xBW5x
BW7xBW
Squatting 5000N 7xBW

24. Squat exercise stressful tothe knee complex, produces a
patellofemoral joint reactionforce7.6timesbodyweight.
Itone-halfofbodyweightduringnormalwalking,
increasinguptooverthreetimesbodyweightduring
stairclimbing.

25. Menisci
•Twofunctions:
–loadbearing
–stability
•also,jointlubrication
•preventcapsule,synovialimpingement
•shockabsorbers

26. Menisci

27. Diagramdemonstratestheimportanceofintactmeniscalentheses
fortheloaddistributionfunctionofthemeniscus.(A)Withintact
enthesistheload(thickarrows)istransmittedviathemenisciandarticular
cartilagethroughalargecontactarea(lefthandpicture,smallarrows).
Partoftheloadistransformedtohoopstresses(righthandpicture,long
arrows).(B)Whentheinsertionalligamentsaretransected,themenisci
willextrudefromthekneejointduringloading,andtheloadismainly
transmittedviaarticularcartilagethroughareducedcontactarea(small
arrows)

28. Load-bearingfunctionofthemenisci

29. Theload-bearingmodeofthemenisci.aSagittalsection:asthefemur
compressesthroughthemeniscusontothetibia,itpushesthemeniscusout
ofthejointcavity;themeniscusdeformstoconformwiththefemoralcondyle
andallowsforthecontacttobedistributedoveralargerarea.bTopview:
themeniscusincreasesitscircumferenceandmovesradiallyoutwardsand
posteriorlywithkneeflexion,followingtherollingandslidingofthefemoral
condylewithflexion.

30. KneeadductionmomentandCompressive
loadsduringgait

31. Thekneeadductionmomentisaresultofthemagnitudeof
thegroundreactionforce(GRF)timesthedistance(i.e.
momentarm)fromthecenterofrotation(GRF*LA).The
graphofthekneeadductionmomentduringagaitcycleina
patientwithkneeOAischaracterizedbyanincreaseinthepeak
andimpulse(theareaunderthecurve)ofthemoment.

33. Softtissuemechanics

35. Schematicrepresentationofthebiomechanical
musculoskeletalkneemodelusedtocalculatekneejoint
loadsandmuscleforces

37. (A)Kneecompressive,and(B)Hamstring,(C)Quadriceps,and(D)
Gastrocnemiusmuscleforcesofacompletestancephaseofatypical
participant.Note:1bodyweight=923.1N(94.1kg).

38. Force-lengthdiagrammofligamentsand
tendons
PatellarLigament

39. Figure1Schematicdiagramillustratingthesixdegreesofmotionofthehumankneejoint

40. Patellofemoraljointreactionforces

41. Abiomechanicalmodelforestimatingmomentsofforceathipandkneejointsin
thebarbellsquat

43. Ascending stairs
•Theactualdegreeofkneeflexionrequiredtoascendstairsis
determinednotonlybytheheightofthestep,butalsoby
theheightofthepatient.
•Forthestandard7"stepapproximately
65°offlexionwillberequired.
•Inclimbingstair,leverarmcanbereduced
byleaningforward.Also,instairclimbingthe
tibiaismaintainedrelativelyvertical,which
diminishestheanterior
subluxationpotentialofthefemuronthetibia.

44. Descendingstairs
•Instandardstep85°offlexionisrequired.
•Thetibiaissteeplyinclinedtowardthe
horizontal,bringingthetibialplateausinto
anobliqueorientation.
•Theforceofbodyweightwillnow
tendtosubluxthefemuranteriorly.
Thisanteriorsubluxationpotentialwillbe
resistedbythepatellofemoraljointreaction
force,andthetensionwhichdevelopsinthe
posteriorcruciateligament.

45. Kneejoint
•Kneeprovidesmobilityandsupport
duringdynamicandstaticactivities
•Supportduringweightbearing
•Mobilityduringnon-weightbearing
•Involvedwithalmostanyfunctional
activityofthelowerextremity

46. Thekneejointinthefrontalplane.aTheQ-angleisdefinedastheanglebetweenthelineofactionofthe
patellartendon,PTandthelineofactionoftheresultantquadricepsmuscles,Q.TheQ-angleeffect
resultsinalateralforceonthepatella,L.bThequadricepsmuscleforceresultsfromsummingdirection
andmagnitudeofthequadricepscomponentsactingonthepatella.Thelinesofactionofeach
componentlieonthefrontalplane,exceptfortheobliquusmuscles,whichdescribeananglewiththe
sagittalplaneaswell
8(RF:rectusfemoris,VI:vastusintermedius,VML:vastusmedialislongus,VMO:
vastusmedialisobliquus,VLL:vastuslateralislongus,VLO:vastuslateralisobliquus).

47. PatellofemoralJointActivities:
Flexion&Load
BW=bodyweight
•walking 10deg 0.5BW
•legraise 0 0.5
•stairs 60 3.3
•isometric 90 6.5
•squat 120 7.6
•jumping --- 20
•tendonrupture 90 25

49. Compressiveforceisadditionalforceat
patellofemoraljoint.
PFCompressiveForceFunction:
Stabilizespatellaintrochleagroove.
Patellaassures“some” compression infull
extension.
Patellofemoralcompressionwithkneeflexionduring
weightbearing,becauseofasflexionincreases,a
largeamountofquadricepstensionisrequiredto
preventthekneefrombucklingagainstgravity.

50. Q-angle

51. Themeanmovement(mm)ineachmeniscusduringflexiononaweight-bearing
knee.
Themeanmovement(mm)ineachmeniscusduringflexiononasittingnonweight-
bearingknee.

52. Figure2.Definitionofaxesusedinthestudy.Thetransepicondylarline,asdefinedin
thisstudy,isthelineformedbytheinsertionsofthelateral(LCL)andmedialcollateral
ligaments(MCL),respectively.

53. Patellofemoraljointreactionforces

58. Figure8.8b
SynovialJoints:Knee–
OtherSupportingStructures

59. KneeInjury

60. Patellaasa
pulley
•apulleychangesthe
directionofanapplied
force
•thepatellahelpsto
supporttheworkofthe
quadricepmuscles
duringthecontractionof
thequadricepthatallows
forextensionoftheknee

61. MusclesoftheLeg

62. Questions