The knee is a complex joint with three articulations that allow for six degrees of freedom of motion. Key structures that support the knee include the femur, tibia, patella, menisci, ACL, PCL, MCL, and LCL. The menisci act as shock absorbers and help with joint stability, while the ligaments limit various motions to prevent injury.

1. Anatomy of knee and
Biomechanics
Dr. Ajaya Regmi

2. Knee
• complex joint
• three independent
articulations:
1. between each sphere-like
condyle of femur and
corresponding but more
planar condylar surface of
tibia, with interposed
menisci,
2. third between the patella
and the patellar or trochlear
groove of the femur

3. • six degrees of freedom of motion:
• three rotations and three translations.
• Translations:
1. anteroposterior (5 to 10 mm),
2. compression/distraction (2 to 5 mm)
3. mediolateral (1 to 2 mm).

4. • Rotations:
1. Flexion-extension,
2. Varus-valgus,
3. Internal-external
rotation
• Normal flexion and
extension: 0° to 15° of
hyperextension to 130°
to 150° of flexion.
• IR/ ER: little or no
motion in full extension
to 20° to 30° with the
knee flexed

5. Femoral condyles
• Viewed from side:
1. Medial: more constant radius of curvature
2. Posteriorly: both have similar radii
3. Anteriorly: lateral rapidly attains longer radius and
appears to flatten out to greater degree than medial

7. Tibial plateau
• Medial:longer in sagittal
plane
• Both facets: slightly
concave in coronal plane,
• lateral facet has convexity
in sagittal plane, producing
a saddle shape
• Rounded femoral condyle
rests on a convex surface
of the tibia

8. Locking of knee
• tibia externally rotates
during last degrees of full
extension
• tibia rolls farther forward
on medial than lateral
• This is screw home
mechanism

9. Unlocking of knee
• With flexion process is
reversed
• Tibia internally rotates
relative to the femur
during first 10° to 20°.
• Popliteus contracts to
externally rotate femur to
unlock the knee on fixed
tiba while descending from
standing position

10. Femoral roll back
• By 10° to 15° on medial and
by 20° on lateral side, sliding
of femur begins relative to
the tibia
• Contact area between tibia
and femur moves rapidly
backward during the first 10°
to 20
• then slowly progresses
posterior to ride entirely on
the posterior horns of both
menisci at the extreme of
flexion

11. Patella
• largest sesamoid bone
• medial and lateral
facets. Each facet is
divided by faint
horizontal lines into
equal thirds
• Articular cartilage -
thickest in the body
(>1cm)

12. • condyles of distal
femur are separated
by shallow articular
depression: trochlea,
(5 to 6 mm in depth)
• Patellofemoral contact
is initiated at about 20
of flexion

13. • Contact area moves
proximally with increasing
flexion of the knee
• 7cm of excursion from
extension to full flexion

14. • increase the lever
arm of the extensor
mechanism around
the knee,
• improving the
efficiency of
quadriceps
contraction.

15. • Full extension: patella does not contact the
articular surface of the femur
• lies over an area of synovial tissue on anterior
shaft of femur immediately proximal to lateral
aspect of trochlear surface: supratrochlear
tubercle

16. Meniscus

17. • Crescent shaped
fibrocartilage
• Triangular in cross section
• Peripheral edges
– Convex ,thick, fixed &
– attached to inner surface of
the knee joint capsule &
– borders of tibial plateau by
coronary ligament

18. • Inner edges
– Concave , thin & free
• Inferior surface
– Flat
• Superior surface
– concave

19. • Medial meniscus
– C –shaped
– less mobile(medial capsule)
– Larger in diameter than LM
– Thinner in the periphery
– Narrower in the body
– Doesn’t attach to either
cruciate ligament
• Lateral meniscus
– Circular
– more mobile
– Smaller in diameter
– Thicker in periphery
– Wider in the body
– Attached to both cruciate
ligaments & posteriorly to
medial femoral condyle (lig.
of Humphry or Wrisberg)

20. • Medial
– Anterior horn : attached to
the tibia anterior to
intercondylar eminence & to
ACL
– Posterior horn : infront of
the attachment of PCL
posterior to intercondylar
eminence
• Lateral
– AH : to the tibia medially in
front of intercondylar
eminence
– PH : posterior aspect of
intercondylar eminence &
infront of posterior
attachment of MM

22. Meniscal healing & Repair
• Based on vascular supply
– Meniscus : 3 zones
• Red-red : fully within
the vascular area
• Red-white : at the
border of vascular area
• White-white : within
the avascular area

23. Functions of meniscus
• Stability to the knee joint
• Acts as a joint filler, compensating for incongruity
between femoral & tibial articulating surfaces
• Acts as a shock absorber
• Assist in nutrition of the articular cartilage by
distribution of the synovial fluid
• Prevents capsular & synovial impingement during
flexion-extension movement
• Assists & controls gliding & rolling motion of the
knee

24. ACL
• Intraarticular extrasynovial
• Anteromedial fibers - tight
in flexion - limits anterior
translation of tibia on
femur
• Posterolateral fibers - tight
in extension - limits
anterior translation plus
external rotation

25. Femoral and Tibial Attachments:
femoral
posteromedial corner of
medial aspect of lateral
femoral condyle in
intercondylar notch;
tibial
fossa in front of & lateral
to anterior spine
11 mm in width to 17 mm
in AP direction;

26. • Bl.supply - middle genicular a. (post) &
synovial vv (ant)
• Mechanoceptors with a proprioceptive role

27. PCL
• 2 bundles: posteromedial and
anterolateral
Function:
• Limits hyperextension
• Prevents post translation of
tibia on femur especially
during flexion

28. • origin:
antero-lateral aspect of medial femoral
condyle in the area of intercondylar notch;
much more anterior than that of ACL;
• insertion:
extra articular, but over back of tibial plateau,
approximately 1 cm distal to the joint line;

30. MCL
Superficial: lies deep to pes
anserinus
• proximal attachment: proximal
and posterior to medial
epicondyle
distal attachment: 2
• Soft tissue over the ant. Arm of
Semimembranosus
• Bone, 6 cm distal to joint

31. Deep
• Thickening of medial joint capsule
• Intimately associated with medial meniscus
• Menisco tibial and menisco femoral
component

32. LCL
Femoral attachment:
• Proximal and posterior to
lateral epicondyle
• Fibular head anterior to
midpoint of lateral aspect

35. Summary
• Knee is complex joint with 6 different
movements
• Bony articulation supported by meniscal and
multiple ligamentous structures