The knee joint is made up of four bones - the femur, tibia, patella, and fibula - that interact in the tibiofemoral and patellofemoral joints. These joints allow flexion and extension as well as other movements while providing load transfer through the lower limb. The tibiofemoral joint is responsible for rotations and translations through mechanisms like the screw home mechanism. The patellofemoral joint experiences forces that vary with knee flexion and extension angles. Both joints have varying centers of rotation that allow for smooth movement and avoid impingement.

1. Dr. Chhavi SinghTomar
Asst. Prof./Vice –Principal
NIMSCollege of Physiotherapy &
OccupationalTherapy
Nims University

2. The knee is a mechanism of three joints and
Four bones - the femur, tibia, patella and
fibula
Interact in separate joints - the tibiofemoral &
patellofemoral
The function of these joints is to allow certain
movements, restrict others, and to provide load
transfer through the lower limb.

3. Tibiofemoral joint
rotations
translations
screw home mechanism
Axial & rotational alignment of knee
Patello femoral joint
Joint forces

4. Rotations
› Flexion/extension-0 to
1350
› varus valgus - 6-8o in
extension
› Int/ext rotation - 25 – 300
in flexion
Translations
› AP 5 - 10mm
› comp/dist 2 - 5mm
› medio-lateral 1-2mm

6. flexion axis varies in a helical fashion in a normal
knee, with an average of 2 mm of posterior
translation of the medial femoral condyle on the tibia
during flexion compared with 21 mm of translation
of the lateral femoral condyle.
Relevance :posterior roll back
› as the knee flexes, the instant center of rotation on
the femur moves posteriorly

7. flexion axis as varying in a helical fashion

8. allows for increased knee
flexion by avoiding
impingement

9. the external rotation of the tibia on
the femur during extension and
internal rotation of the tibia during
knee flexion.
cause
› medial tibial plateau articular
surface is longer than lateral
tibial plateau(Medially based
pivoting of the knee.)
relevance
› "locks" knee decreasing the
work performed by the
quadriceps while standing

10. mechanical axis of the lower limb is defined as the
line drawn on a standing long leg antero posterior
radiograph from the center of the femoral head to
the center of the talar dome
anatomical axes of the femur and the tibia form a
valgus angle of 6 2 degrees.
the tibial articular surface is in approximately 3 0of
varus with respect to the mechanical axis, and the
femoral articular surface is in 90 of valgus.

12. "sliding" articulation
› patella moves 7cm caudally
during full flexion
maximum contact between
femur and patella is at 45
degrees of flexion
The primary function of the
patella is to increase the lever
arm of the extensor mechanism
around the knee, improving
the efficiency of quadriceps
contraction.

13. The quadriceps and patellar tendons insert anteriorly
on the patella, with the thickness of the patella
displacing their respective force vectors away from the
center of rotation of the knee .
This displacement or lengthening of the extensor lever
arm changes throughout the arc of knee motion.
the extensor lever arm is greatest at 20 degrees of
flexion, and the quadriceps force required for knee
extension increases significantly in the last 20 degrees
of extension

14. The length of the lever arm varies
as a function of the geometry of
the trochlea, the varying
patellofemoral contact areas, and
the varying center of rotation of
the knee.

15. passive restraints to lateral
subluxation
› medial patellofemoral
ligament
primary passive restraint to
lateral translation in 20
degrees of flexion
60% of total restraining force
› medial patellomeniscal
ligament
13% of total restraining force
› lateral retinaculum
10% of total restraining force
dynamic restraint
› quadriceps muscles

16. The angle between the extended
anatomical axis of the femur &
the line between the center of the
patella & the tibial tubercle
normal Q angle
› in flexion
males
13 degrees
females
18 degrees
› in extension
8 degrees

17. Limbs with larger Q angles have a
greater tendency for lateral patellar
subluxation.
Because the patella does not contact the trochlea in
early flexion, lateral subluxation of the patella in
this range is resisted primarily by the vastus
medialis obliquus fibers.

18. Position
Standing on both feet
Swing phase
u/l stance phase
Jogging
force acting on joint
- equal to body wt
- 1/2 x b.wt
– 2-4 x b.wt
– 6x b.wt

19. Walking
› 0.3 x body weight
Ascending Stairs
› 2.5 x body weight
Descending Stairs
› 3.5 x body weight
Squatting
› 7 x body weight

20. Prevent anterior tibial
displacement on femur
Secondarily, prevents
hyperextension, varus & valgus
stresses
 Least stress on ACLbetween 30-60
degrees offlexion
 Anteromedial
bundle tight in
flexion & extension
 Posterior lateral
bundle tight
only in extension

21. Primary stabilizer of the knee against posterior
movement of the tibia on the femur
resists rotation, esp.internal rotation of tibia on
femur
Two bundles
Anterolateral, taut in flexion
Posteromedial, taut in extension