Knee biomechanics

Knee joint biomechanics

1. BIOMECHANICS

THE KNEE COMPLEX

2. KNEE JOINT

3. INTRODUCTION

FUNCTIONS OF KNEE ARE:

Provide mobility

Support body during Dynamic & Static
activities.

In closed K chain it works with hip & ankle
joints to support body wt. in static erect
posture.

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

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

4. ARTICULATIONS

Knee complex composed of 2
articulations within a single
capsule:

The tibiofemoral joint

The patellofemoral joint

5. 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.

6. FEMORAL ARTICULAR SURFACE

= Medial & Lateral femoral condyles
forms proximal articular surface.

= Patellar groove.

Knee Joint

7. 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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9. 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.

10. MENISCI

USES.

Increases joint congruence.
Distribute weight bearing forces.
Reduces friction between joints.
Serve as shock absorbers.

11. MENISCI

ATTATCHMENTS:

.Both Men. are attached to,
Intercondylar tubercles of tibia.
Tibial condyle via coronary lig.
Patella via patellomeniscal & patellofemoral ligs.
Transverse lig.

ACL.

.Med. Men. attached to,

= MCL.

= Semitendinous muscle.

3.Lat. Men. attached to,

= Ant. & Post. menisco femoral ligs.

. PCL.

= Popliteus muscle.

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12. MENISCI

OTHER FACTS

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Meniscal complex is well established in 8 weeks old
embryo.

Well vascularised in 1° 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:
Joint position.

Movt. Direction.

Movt. Velocity.

Tissue formation.

13. TF ALLIGNMENT & WEIGHT
BEARING FORCES

Anatomical or LEE TE axis of
femur is oblique falling medially &
inferiorly.

Anatomical axis of tibia is almost . . .
vertical. Alignment and Weight Bearing
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.) itis Genu
Varum or Bow Legs.

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14. 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.

15. 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
Be en lat. From patella to collateral ligs. And tibial
condyles

16. Te. os

at (al body
pateltar (synovial) bursa
Patella
Subcutaneous prepatellar be
_—Articular cavity

_— Synovial membrane

— subcutaneous infrapatella Hn

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Sagittal section
eral to midline of knee)

17. 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.

18. 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.

e Lateral TF compartment.

19. 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.

20. 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.
Superior/Suprapatellar plica is located between suprapatellar
bursa and knee joint.

Medial/ Mediopatellar ale 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.

21. KNEE JOINT LIGAMENTS

The knee ligaments are credited with
restricting and controlling:

1. Excessive knee motion

2. Varus and valgus stresses at knee

3. Anterior and posterior displacement of
tibia beneath femur

4. Medial and lateral rotation of tibia
beneath femur

5. Stabilization in anteroposterior
displacements and rotations of tibia
known as rotary stabilization.

22. Anterior
Cruciate

Lateral
Collateral
Ligament

Medial
Collateral
Ligament

23. Stabilizing Ligaments
* MCL:

» Flat, broad ligament located on
the inside of the knee

» Prevents a valgus stress on the
knee.

» Part of it attaches to the Medial
Meniscus.

24. Stabilizing Ligaments
* LCL:

» Cordlike ligament located on
the outside of the knee.

» Prevents a varus stress on
the knee.

25. Knee - Cruciate and Collateral Ligament:
Right Knee in Flexion

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Knee - Cruciate and Collateral Ligaments
Right Knee in Extension

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26. 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

27. 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

28. Posterior Cruciate Ligament

= Two bundles

+ Anteromedial, taut in
flexion

+ Posterolateral, taut in
extension
= Orientation prevents
posterior motion of tibia

= PCL larger & stronger
than ACL

29. 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

30. 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

31. 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

32. ARTHROKINEMATICS
flexion/extension

Athrokinematics

Femur rolling &
gliding at 25°
Anterior glide is due
to

Tension of ACL

The menisci
Extension is reverse
roll, spin and glide
Tension of PCL
menisci

Knee Motion

33. LOCKING AND UNLOCKING

DURING KNEE
EXTENSION PU Een
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 ANTERIOR

on the medial side
00

produces external tibial
rotation, the "screw- oO
home" mechanism. MEDIAL \ +

34. LOCKING AND UNLOCKING

DURING KNEE FLEXION
When the knee begins to flex from ANTERIOR
a position of full extension,
posterior tibial
on the longer medial condyle. 0
Between 0 deg. extension and 20 Ó
deg. of st posterior glide on MEDIAL
the medial side produces relative
tibial internal rotation, a reversal
of the screw-home mechanism.
opliteus is the muscle that

unlocks' the knee at the beginning ANTERIOR
of flexion of the fully extended
knee. As the extended and locked

MEDIAL

le begins first

repares to flex (when

ining 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 ANTERIOR
femur on a fixed tibia, unlocking

the knee requires that the femur
ER on the fixed tibia. Ÿ () 0
MEDIAL

35. Clinical test for sc

+ Helfet test

- Patient sits with knee flexed at 90 deg and leg
hanging free

- Medial and lateral borders of patella are
marked on skin

- Tibial tuberosity and midline of patella are
designated

- Rotation of knee may be as large as % of width of
patella in normal knee

- Deranged knee may not rotate during e:

36. 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

37. 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

38. Knee Muscles

=» Knee Extension

e Rectus Femoris
eVastus Medialis
eVastus Lateralis
e Vastus Intermedius

39. Rectus Femoris

= Two-jointed, bipennate

ACTIONS

= May contribute to lateral
rotation and abduction of hip

= Extends knee and flexes hip

EFFECTS OF WEAKNESS

= Decreases knee extension
strength

EFFECTS OF TIGHTNESS Rectus —|

= Limits knee flexion range of
motion (ROM) with hip
extended Vastus

= Hip abduction reduces stretch Bis
of rectus femoris.

Tensor fasciae

femoris Al

Vastus
medialis

40. Vastus Medialis

= Consists of longitudinal (vastus ps
medialis longus I) and (reflected)
oblique (vastus medialis oblique

[VMO]) portions

ACTIONS

= Knee extension

= Patellar stabilization

= Active with other heads
throughout knee extension ee .

EFFECTS OF WEAKNESS N

= 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

lateralis

41. = Largest head of quadriceps
in many individuals

ACTIONS

= Knee extension

EFFECTS OF WEAKNESS

= Significant weakness in
knee extension

EFFECTS OF TIGHTNESS
= Decreased knee flexion
ROM

astus —
= May contribute to lateralis
patellofemoral dysfunction

42. = Unipennate and deep Rectus
ACTIONS (rates)
= Extends knee and pulls
capsule proximally
EFFECTS OF WEAKNESS
= Significant loss of knee
extension strength 15-
40% of PCSA \ /
EFFECTS OF TIGHTNESS \ YI! due
= Decreased knee flexion meals Wy Longus (VML)
ROM regardless of hip ' Oblique (VMO)
position y

43. Knee Muscles

= Knee Flexion—
e Biceps Femoris
e Semitendinosous
e Semimembranosus
e Gastrocnemius
e Plantaris

44. Hamstrings

ACTIONS

EFFECTS OF WEAKNESS

EFFECTS OF TIGHTNESS

Knee flexion

Active knee flexion without

rotation requires simultaneous

contraction of medial and lateral

hamstrings.

Contribute to knee joint stability

Hap extension throughout ROM of
hip

May also adduct and rotate hip

Knee flexion weakness

Larger impairment may be Snes
weakness of hip extension.

Semitendinosus

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

Semimembranosus -

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

48. Popliteus

ACTIONS

= Small muscle

= Increased activity with
combined knee flexion and
medial rotation of tibia

= Medially rotates knee

= Adds stability to tibiofemoral
joint

EFFECTS OF WEAKNESS

= Difficult to determine

= Injured with extensive
posterolateral ligamentous
structures

EFFECTS OF TIGHTNESS

= Difficult to discern but would

contribute to knee flexion
contractures

49. MEDIAL ROTATORS OF THE
KNEE

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

50. Sartorius

= Strap muscle with very long
muscle fibers

ACTIONS

= Hip flexion with large moment
arms to also abdu
laterally rotate hip

= Knee flexion

= Inactive with isolated medial
rotation of knee

EFFECTS OF WEAKNESS

= Isolated weakness may have
little effect

EFFECTS OF TIGHTNESS

= Small effect but may
contribute to flexion
contracture

51. Gracilis

ACTIONS

= Medial rotation and
flexion of knee

= Adduction of hip

EFFECTS OF
WEAKNESS

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

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

a They effectively
stabilize the medial
aspect of the
knee.

53. LATERAL ROTATORS OF THE
KNEE
= Tensor fasciae

latae with lateral
hamstrings

54. 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 lim

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

55. 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 I

tendon and lengthening

the lever arm of the quad

muscle force

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

56. PATELLAR MOVEMENTS

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

condyles to full flexion [ 7
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 Flexion up to 90 deg

In flexion , pig patella slides + |
distally on the femoral Cor -

flexion > 90 deg

57. PMJ STABILITY

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

Transverse group of
stabilizers

Longitudinal group of
stabilizers

In aso 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 forces

Pull of VL is 12-15° lateral
on long axis of femur

Pull of VM is 15-18° medial
with 50-55° pulling of VMO

58. 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.

59. 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)

60. 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

Magnitude of active or
passive pull of quadriceps
Angle of knee flexion

Ay satel) flexion: 50% of

Increase flexion, increased
muscle activity up to 3.3xBW
Mechanical advantage is the
biggest between 30-70deg
flexion