The document summarizes the anatomy and function of the knee joint. It describes the articulating surfaces of the patella and femur, the muscles that act on the knee joint as flexors, extensors, and rotators, and how the angle of pull of the quadriceps femoris muscle is increased by the patella acting as a pulley. It also discusses the Q-angle and how increased or decreased angles can impact patellofemoral contact pressures.

2.  Articulation:
 Posterior surface of the patella
 Femoral sulcus or patellar surface of femur

3.  Triangular with apex
downwards
 divided by a vertical
ridge into medial and
lateral facets.
 a second vertical ridge
toward the medial
border separates the
medial facet from an
extreme medial
edge, known as the odd
facet of the patella

4.  The femoral sulcus has
a groove that
corresponds to the ridge
on the posterior patella
 it divides the sulcus into
medial and lateral
facets.
 The lateral facet of the
femoral sulcus is
slightly moreconvex
than the medial facet
and has a more highly
developed lip than does
the medial surface

5.  Changes with knee position
 Extension:only the inferior Pole is
in contact with the femur.
 along the inferior margin of both the
 medial and lateral facets of the
patella at 10 to 20 of knee flexion.
 At 45 degree covers middle of
patella and spreads outward to
cover the medial and lateral facet.
 At 90 superior pole
 beyond 90 the area of contact begins
to migrate inferiorly. smaller odd
facet makes contact with the medial
femoral condyle for the first time.
 At full flexion, the patella is lodged
in the intercondylar groove, and
contact is on the lateral and odd
facets, with the medial facet
completely out of contact.

6.  Muscles crossing knee are basically flexors or
extensors, and have additional function of
rotation/ abdn addn

7.  7 muscles flex the knee:
3Hamstrings:
the semimembranosus, semitendinosus, biceps
femoris(long and short heads)
sartorius
gracilis
popliteus
gastrocnemius muscles
Plantaris also flexes the knee when present

8. Other than short head of biceps femoris and
popliteus all other are two joint muscles, thus
their flexing ability depends on angle of the
other joint where it is attached.

9.  Rotation:
the popliteus, gracilis,
sartorius,
semimembranosus,
and semitendinosus
are also medial
rotators
Biceps femoris is a lateral
rotator

10.  Varus & valgus moment:
 The lateral muscles
 (biceps femoris, lateral head of the gastrocnemius,
 and the popliteus) are capable of producing valgus
moments
 Muscles on the medial side of
 the joint
(semimembranosus, semitendinosus, medial
 head of the gastrocnemius, sartorius, and gracilis)
can
 generate varus moments.

11.  Popliteus is known as the unlocking muscle
although without it also locking will take place.
 active assistance of the semimembranosus and
popliteus muscles ensures that tibio femoral
congruence is maximized throughout the range
of knee flexion by acting on menisci

12.  RF, VI pull upwards.
 pull of vastus lateralis
muscle is 35 degree
laterally, whereas the
pull of the vastus
medialis muscle is
40degree medially.
 The combined action
produces a force
directly upwards.

13.  the patella
 lengthens the MA of the
quadriceps by increasing
the
 distance of the patellar
tendon from the axis of
the knee joint. The
patella, as an
 anatomic pulley, deflects
the action line of the
quadriceps
 femoris muscle away from
the joint center, increasing
 the angle of pull

14.  at semi flexion, the patella is primarily responsible
for increasing the quadriceps angle of pull.
 In full knee flexion, the patella is fixed firmly
inside the intercondylar notch of the femur, which
reduces the pulley action of patella. Still the
quadriceps maintains a fairly large MA because
the rounded contour of the femoral condyles
deflects the muscle’s action line and because the
axis of rotation has shifted posteriorly into the
femoral condyle.

15. in the final stages of knee extension, patella’s
effect on the quadriceps’ MA is diminished but
the small improvement in joint torque
provided by the patella is important.
 because near end range extension, the
quadriceps is in a shortened position, which
reduces its ability to generate active tension.

16.  If there is substantial quadriceps weakness or if the
 patella has been removed because of trauma (a
procedure
 known as a patellectomy), the quadriceps may
 not be able to produce adequate torque to
complete
 the last 15degree of non–weight-bearing knee
extension.
 This is called as “quadriceps lag” or “extensor
lag.”

17.  The Q-angle (or "quadriceps
angle) is formed in the frontal
plane by two line segments:
from tibial tubercle to the
middle of the patella
 from the middle of the patella
to the ASIS
 The q-angle in adults is
typically 15 degrees. Increases
or decreases in the q-angles are
associated in cadaver models
with increased peak
patellofemoral contact
pressures (Huberti &
Hayes, 1984). Insall, Falvo, &
Wise (1976) implicated
increased q-angle, along with
patella alta, in a prospective
study of patellofemoral pain.

18.  Oblique fibers of
vastus medialis.
 Credited to locking of
knee joint and
terminal knee
extension.

19. Soleus and gmax can
produce knee
extension although
they do not have any
attachment in knee.