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Regional Biomechanics
knee Joint
Kinematics
Kinetics
Pathomechanics
Biomechanics of the knee joint
1- Bony Structure
1- Femoral articulation: pulleyshaped, convex, longer
anteroposteriorly than
transversely.
- Shaft of the femur is not
vertical.
- Medial condyle 2/3 of an
inch longer than the lateral
2- Tibial Articulation: Concave
-medial tibial condyle is 50%
larger than the lateral
condyle
* All articular surfaces are
covered by cartilage with a
thickness of 3-4mm.
Tibiofemoral Joint
Tibiofemoral Angle
• The mechanical axis of LE (WB line)
passes from the center of the femur
to the superior surface of head of
talus (average 3 deg. with the
vertical).
• Frontal plane. Measured between
anatomical axes of femur and tibia.
• Normal value 170-175 laterally or
185-190 medially.
• Laterally: less than 170 “Genu valgum
or Knock-knee”
• more than 180 “Genu varum or bowleg”
• (A)
(A) Genu valgum
(B)
(b) Genu varum
The Q (quadriceps) angle
• Frontal view. Between a line
connecting between the ASIS
to the mid point of patella and
a line connecting the tibial
tubercle to the mid point of
patella.
• Normal value 15 deg.
• Greater in females than males
due to wider pelvis and
increases femoral anteversion.
2- Capsule of the Knee joint
• Reinforced
- Posterior: by muscles (popliteus,
gastrocnemius, and hamstring)
ligaments (oblique popliteal, and
arcuate popliteal ligament).
- Lateral & Medial: medial and
lateral patellar retinacular fibers,
collateral ligaments and iliotibial
band.
- Anterior: Quadriceps tendon,
patella and patellar ligament, .
3- Menisci of the knee joint
Fibro cartilaginous joint discs
Attach to intercondylar region of the tibia
Medial meniscus
• C- shaped and is attached to the medial
collateral ligament and to the
semimembranosus muscle. It is more firmly
attached and less movable so it is more torn
than the lateral meniscus.
• Lateral meniscus
• 4/5 of a ring, is much loose and mobile than
the medial meniscus
• The ante anterior horns of the two menisci are
linked by the transverse ligament.
Function Medial meniscus & Lateral meniscus
1- Distribute weight.
2- Increase the joint congruency.
3- Lubricate the articular cartilage.
4- Reduce friction between joint surface.
5- Shock absorber.
4- Ligaments of the knee joint
(1) Medial collateral ligament
• Position: Medial aspect of the
joint.
• Attachment: Med. Femoral
epicondyle and upper end of
tibia.
• Orientation: Inferior & Anterior.
• Function:
1- Resist valgus stress especially
when knee is extended.
2- Resist lateral rotation of tibia.
3- Restrict Ant. Displacement of tibia.
4- Resist Excessive Knee extension.
(2) Lateral collateral ligament
• Position: Lateral aspect.
• Attachment: Lat. Epicondyle. Head of fibula.
• Orientation: Inferior and Posterior.
• Function:
1- Resist varus stress.
2- Resist axial rotation.
3- Resist Post. Displacement of tibia.
4- Resist knee extension.
N.B: Both collateral ligaments are
relaxed at 20-30 flexion so it is
the position of immobilization
after injury.
(3) Posterior Capsular ligament
1)Oblique popliteal ligament.
• Position: Posteromedial aspect.
• Attachment: Med. Tibial condyle
central part of posterior
aspect of the joint capsule.
• Orientation: Upward and laterally.
• Function: 1-Check valgus stress. 2-Tight in full extension.
2)Arcuate popliteal ligament.
• Position: Posterolateral aspect.
• Attachment: Post, aspect of the head of fibula
epicondyle
• Orientation: upward and medially.
• Function: 1- Check varus stress.
2- Tight in full extension.
lat.
4- Anterior Cruciate Ligament
• Position: Intracapsular ligament.
• Attachment: Ant. Part of
intercondylar eminence post
part of inner aspect of lat.
Femoral condyle.
• Orientation: Posterior, Superior
and lateral.
• Function:
1- Prevent anterior displacement of
tibia 85%.
2- Limit full knee extension.
3- Resist varus and valgus stresses
(minor contribution).
4- Control medial rotation (axial) of
the tibia.
N.B: Injury to the ACL occurs when
the knee is flexed and the tibia
rotates in either direction.
5- Posterior Cruciate Ligament
• Position: Intracapsular Ligament.
• Attachment: Post. Part of intercondylar
eminence
Anterior part of inner
aspect of medial femoral condyle.
• Orientation: Ant. superior, and
medially.
• Function:
• Prevent posterior displacement of tibia
95%.
• Tight during full flexion.
• Resist varus and valgus stresses (minor
contribution).
Function of cruciate ligaments during knee
motion.
• Full extension: ACL is more vertical
& PCL is more horizontal.
• During hyperextension ACL is
stretched and PCL is relaxed.
• Full flexion: PCL raised up vertically
making 60 degrees with tibia and
become taut.
• Medial rotation: ACL wind around
PCL ( ACL stretches and PCL
relaxes).
• Lateral rotation: parallel “ACL relax
and PCL stretches”
6- iliotibial band
• Position: Anterolateral aspect of
the knee joint.
• Attachment: fascia of tensor
fascia lata, G. max, and G. med,
lateral tubercle of tibia.
• Orientation: two band one
downward and the other Anterior
and lateral to patella “Iliopatellar
band”.
• Function:
1- Tight regardless the position of
the hip or the knee.
2- Prevent post. Displacement of
femur when the tibia is fixed and
knee extended.
Stability of the knee joint
• Stability of the knee joint is provided by:
-Static stabilizers (joint capsule and powerful
ligaments)
• - Dynamic stabilizers (flexor and extensors
muscles)
Stability of the knee joint
• Close-packed position: Max Stability
Max. Extension and max. lateral rotation.
“Screw home mechanism”
• Loose-packed position: Min. Stability
Flexion position
Knee axis of motion
• The axis of knee motion passes horizontal
and oblique through the knee joint (lower
on the medial side). So full flexion is
accompanied by medial tibial rotation and
full extension is accompanied by lateral
tibial rotation .
• This axis moves through the ROM forming a
semicircle moving posteriorly and
superiorly on the femoral condyles with
increasing flexion (instantaneous axis of
rotation -IRA).
Surface motion of the knee joint during flexion
in CKC
During flexion:
- From full extension to 25º of flexion is
pure posterior rolling of the femoral
condyles on the tibia.
- After 25º rolling is accompanied by
anterior gliding to prevent posterior
dislocation of the femoral condyles
(facilitated by the ACL).
- At the end of the range of flexion the
femoral condyles glide without
rolling
Surface motion of the knee joint
during extension in CKC
• During extension:
• The first part of the extension range is
pure anterior rolling of the femoral
condyles on the tibia displacing them
back to the neutral position.
• After that anterior rolling is
accompanied with posterior gliding (
facilitated by the PCL).
Role of the menisci during
flexion and extension
• During flexion : the menisci move posteriorly: the MM
moves posteriorly by the semimembranosus while the
LM is drawn posteriorly by the popliteus
• During extension : the menisci are pulled anteriorly by
the meniscopatellar fibers. The posterior horn of the LM
is pulled anteriorly by tension in the meniscofemoral
ligament.
Role of Cruciate ligament
• During flexion:
ACL causes the femoral condyle to slide ant.
while the femur rolls posteriorly.
• During extension:
PCL causes the femoral condyle to slide post.
While the femur rolls anteriorly.
Load transmission through the knee joint
• Distal end of femur:
• (a)-Vertical lateral
trabeculae Ipsi(compression
force). Contra lateral
(tension force).
• (b)- Horizontal trabeculae :
join the two condyle.
• Distal end of tibia: the
similar set
Load transmission through the intact menisci
• Collagen in the menisci are
oriented in circumferential
direction.
• Load on the knee joint will
cause extruding force(which
pushes the menisci outward)
• This force is resisted by their
powerful attachment to the
tibia.
• In their resistance the menisci
transmit some of the load to
the tibia.
Load transmission through torn
menisci
• The meniscus become
redundant.
• During transmission of
load , the meniscus will
not be able to resist the
extruding forces so it will
open and loads will be
transmitted directly
between condyles.
• The load will be carried
by the cartilage . This will
increase the joint load
significantly.
Patellofemoral Joint
surface motion of the patella on the femur
• During flexion:
• The patella slides distally
between the femoral condyles
(travels twice its length(8cm).
• The patella moves also backward
or posteriorly.
• - Tilts medially (rotate around its
vertical axis).11° “Vertical
axis”(from 25 to130 flexion)
• The patella also rotate medially
around its Anteroposterior axis
(medial rotation).
• SO(during flexion: the patella
slides downward and moves
posteriorly and medially. In
addition it tilt and rotate
medially.
Patellofemoral Joint
surface motion of the patella on the femur
• During extension: the patella slides upward and moves
anteriorly away from the femoral condyles and laterally. In
addition it tilt and rotate laterally.
Function of the patella
• Improve mechanical efficiency
of the quadriceps muscle
through two mechanism:
1- Increase the moment arm.
2- Increase the angle of pull.
• Reduce friction between the
quadriceps tendon and femoral
condyles.
• Provide good cosmetic
appearance.
The mechanical effect of patella on the
moment arm through the ROM in addition
to the physiological effect
• In full knee flexion: the patella moves
downward and backward on the intercondylar
groove. So the moment arm of the quadriceps
decreases. This does not affect the torque
because of two reasons.
(1) –
the IAR moves posteriorly away from the line of
action of the quadriceps.
(2) –
The muscle at physiological advantage as it is
stretched (length- tension relationship).
The mechanical effect of patella on the moment arm
through the ROM in addition to the physiological
effect
• During knee extension: The patella moves
upward and forward on the intercondylar groove.
So the MA of the quadriceps lengthens
(
mechanical advantage). The maximum torque of
the quadriceps is produced at 60º because the
muscle shows both mechanical and physiological
advantaged.
• With continuous extension: the MA again begins
to diminish.
The mechanical effect of patella on the
moment arm through the ROM in addition
to the physiological effect
• At the last 15º of extension:
the
quadriceps at both mechanical disadvantage
(decrease MA) and physiological disadvantage
(decrease muscle length). A 60% increase in
force is required to complete the range.
Effect of removal of the patella:
• Removal of the patella decrease the
quadriceps torque up to 50%.
• N.B: Loss of patella has its most apparent
effect in the last stages of extension when
there is both mechanical and physiological
disadvantages especially if the muscle has to
work against the resistance of gravity.
Stability of the Patellofemoral joint
(mediolateral forces on the patella)
• During full extension and the quadriceps is relaxed:
the patella can be passively displaced medially or
laterally half the width of the patella (so it is used as
position for patellar mobilization).
• During active extension: the force of the patella is
determined by the pull of the quadriceps and the
patellar tendon. Since they do not lie in the same
action lines, the patella tends to be pulled laterally.
This may cause the patella to sublaxate or dislocate
laterally.
Mediolateral forces on the patella
• The patellar tendency towards lateral
dislocation is prevented by:
• (1)- the lateral lip of the patellar surface of the
intercondylar groove.
• (2)- The muscular pull of vastus medialis
longus and vastus medialis oblique (VMO)
muscles.
Risk factors for lateral patellar dislocation
Tightness of iliotibial band
Laxity of MCL
Increased Q angle
Increased genu valgum
Excessive hip anteversion
Excessive external tibial
torsion
Weakness of VMO
Shallow patellar track
Kinetics ( Patellofemoral JRF)
• During full flexion : the patella sinks and becomes
more in contact in the intercondylar groove. So
the compressive forces (JRF) increases.
• Between 90º- 70º of knee flexion: the quadriceps
tendon contacts the femoral condyles and
dissipates some of the PF compression.
• During full extension: the patella makes little or no
contact with the femur so the compressive forces
decreases. That is why straight leg raising is used
to improve the quadriceps strength in cases of PF
problems.
Patellofemoral joint reaction force values
JRF is ½ W at 15 knee
flexion.
JRF 7.8W at 130 knee
flexion.
JRF 3.3 W during
climbing stairs.
Calculation of PF joint reaction force
• R= 2T cos Ø/2
Pathomechanics of the knee joint
1- Bony abnormality: Genu varum (bow legs):
Tibiofemoral less than normal medially. Center of joint
displaces laterally leading to medial osteoarthritis.
Genu Valgum “Knock knees”: Tibiofemoral
greater than normal medially. Center of joint displaces medially
leading to lateral osteoarthritis
.
2-Meniscus injury
(A) twisting movement of the knee
(B) violent extension of the knee
3- Ligaments injury
1) anterior cruciate ligament
• Mechanism of injury: foot firmly planted and femur
vigorously externally rotated or translated
posteriorly. Another mechanism excessive hyper
extension of the knee.
• Following injury: hamstring spasm.
• Post surgical rehabilitation:
Exercise for hamstring and quadriceps to keep the
ratio of 0.7 : 1
Avoid OKC exercise for the first 3 months.
CKC exercises are the choice for early post operative
rehabilitation.
2) posterior cruciate ligament
• Mechanism of injury:
1- Falling over hyper flexed knee.
2- dash board injury.
• Rehabilitation program directed for
strengthening quadriceps to prevent posterior
displacement of tibia
4- Patellar dysfunction
1) Change of Q angle
2) Chondromalachia patella
3) Patellectomy:
- Reduce the torque of quadriceps by about 49%
- Internal moment arm of quadriceps reduce from 4.7
cm to 3.8 cm.
- Has no effect on the strength of quadriceps if the
knee fully flexed.
- Has effect at the last stage of knee extension.