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Extensors of the knee joint
They include quadriceps
femoris muscle:
a) Rectus femoris: with
straight and reflected
heads
...

c) Vastus medialis: medial to
rectus femoris
...


Rectus femoris

Vastus medialis
Vastus lateralis

- Don’t forget tensor fascia lata and
ilio-tibial band, they can also
extend the leg at the knee joint
...


Lateral view

Quadriceps femoris:
Origin:
2) Vastus medialis:
• Lower part of intertrochanteric line, spiral
line, medial lip of linea
aspera, and medial
supracondylar ridge
...


Posterior view

Quadriceps femoris:
Origin:

Vastus
intermedius

4) Vastus intermedius:
• Upper 2/3 of anterolateral
surface of the femur
...
It is
inserted into the base of
the patella, and continue
as ligamentum patellae to
be inserted into the tibial
tuberosity
...
B: on either sides of patellar
ligament, 2 fibrous expansions
descend from both vastus
medialis and vastus lateralis to
be attached to the capsule of
the knee joint supporting it
(patellar retinaculae)
...

Rectus femoris can flex the
thigh at the hip joint
...
):
•

Lower deep fibers of vastus
intermedius forms
articularis genu muscle
which tenses and pulls the
knee joint capsule
superiorly during knee
extension to protect it
from crushing between
femur and tibia
...

- Each head has its own branch from
the femoral nerve
...

b) Semitendinosus: its lower
part is like a tendon
...

In addition to:
Popliteus: short muscle
behind the knee joint)
- Don’t forget sartorius and
gracilis muscles, they can also
flex the leg at the knee joint
...


•

Short head: lower part of
lateral lip of linea aspera +
upper part of lateral
supracondylar ridge
...


Action:
•
•
•

Flexion of the leg at the
knee joint
...

Extension of the thigh at
the hip joint (long head
only)
...


Semitendinosus:
Origin:
•

Ischial tuberosity (with
long head of biceps
femoris)
...


Action:
•
•
•

Flexion of the leg at the
knee joint
...

Extension of the thigh at
the hip joint
...


- The muscles forming the pes
anserine tendon (SGS) act as guy
ropes stabilizing the pelvis on the
lower limb supporting it from
anterior, medial, and posterior
aspects
...


Insertion:
• Into a groove behind the
medial tibial condyle
...

Medial rotation of the
semi flexed leg at the
knee joint
...
It is used in
walking
...


Popliteus:
Origin:
•

Lateral aspect of the
lateral femoral condyle
(popliteal groove)
...


Action:
•
•

•

Flexion of the leg at the
knee joint
...

It is the un-locker of the
knee joint (see below)
...

- Popliteus is supplied by tibial nerve
...


Articular surfaces:
• Medial condyle of femur
with medial condyle of tibia
...

• Back of the patella with the
patellar surface of femur
...

• anteriorly, it is
deficient(incomplete), being
replaced by tendon of
quadriceps muscle, patella,
and the patellar ligament
...


Capsular ligaments:
1) Patellar ligament and
patellar retinaculae,
they support the joint
anteriorly
...

3) Fibular (lateral)
collateral ligament, it
supports the joint
laterally
...
):
4) Popliteal ligaments,
from the back of the
femur to both tibia and
fibula
...


Intra-capsular structures (2 menisci + 2 ligaments ) :
1) The medial and lateral menisci, a pair of semi-lunar
fibrocartilage pads lying between the femoral and tibial articular
surfaces
...

It passes upwards, backwards,
and laterally
...

Posterior cruciate ligament
(PCL): from posterior part of
intercondylar area of the tibia
to the medial femoral condyle
...
It prevents posterior
displacement of tibia
...
Now all
ligaments are tense while the
extensors are relaxed, and the
knee joint is locked
...


- What is the importance of
locking of the knee joint?



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