The document summarizes the biomechanics of the knee joint, including its components, degrees of freedom, and ligaments. It describes the tibiofemoral and patellofemoral joints. It discusses genu valgum and genu varum conditions. It covers the menisci, stability provided by the capsule and ligaments, and knee joint kinematics including flexion/extension, medial/lateral rotation, and abduction/adduction. It also describes the screw home mechanism, locking and unlocking of the knee, and role of muscles and ligaments in knee biomechanics.

1. BIOMECHANICS OF KNEE JOINT
MODERATOR- DR LN MEENA SIR
PRESENTED BY- DR VASU SRIVASTAVA
DEPARTMENT OF ORTHOPAEDICS ,PIMS
UMARDA, UDAIPUR

2. KNEE JOINT-
1.Tibiofemoral component
2.Patellofemoral component

4. TIBIOFEMORAL COMPONANT/JOINT-
•It is a double condyloid joint
•Has 3 degree of freedom-
sagittal plane- flexion/ extension
transverse plane- medial rotation/ lateral rotation
frontal plane- abduction/ adduction

5. TIBIOFEMORAL JOINT IS COMPOSED OF-
• DISTAL FEMUR-
from lateral and medial side it is convex shape
Medial condyle is larger than the lateral condyle
• PROXIMAL TIBIA-
It has medial condyle or platue and lateral condyle or platue
Medial condyle is larger than the lateral condyle
Lateral condyle is projected anteriorly
In between the condyle there is intercondyler tubercle
The tibial condyles are slightly concave to 5-7 degree ,inclined inferiorly

7. GENU VALGUM AND GENU VARUM
• LONGITUDINAL AXIS- LINE PARALLEL TO THE LONG BONE FROM THE CENTRE.
• MECHANICAL AXIS- LINE JOINING FROM THE CENTRE OF HEAD OF FEMUR TO
KNEE JOINT TO CENTRE OF CALCANEUM.
• IT IS A WEIGHT BEARING LINE
• So the angle formed between the longitudinal axis and the mechanical axis is
known as the physiological valgus angle ,which is normally 5-7 degree.
• Both these axis further forms a medial tibiofemoral angle, which is normally
185 degree.
• So, if there is increase in this medial tibio femoral angle to >185 degree ,it is
known as genu valgum.
• And if medial tibio-femoral angle is <185 degree ,it is known as genu varum

9. Genu valgum
• increases in compressive force in
the lateral compartment and
tensile force in the medial
compartment.
• Leads to joint laxity in the lateral
compartment.
• Knock knee.
• Adduction movement increases in
the knee
Genu varum
• Increase in the compressive force
in the medial compartment of joint
and tensile force in the lateral
compartment
• Leads to bow knees

10. • In the single leg stance –the weight bearing axis from the centre is
shifted to medial side,
• So the compressive force is more towards the medial condyle of
tibiofemoral component , so this is the reason that there is much
more chance of osteoarthritic changes in the medial condyle side.

11. Menisci of knee joint
• Cushions of the knee joint.
• Made of fibrocartilage tissue
• Disc shape.
• Medial meniscus is semi-lunar shape
• Lateral meniscus is circular in shape
• Each meniscus has anterior horn or anterior end and
posterior horn or posterior end.
• There is no meniscus over the intercondylar
tubercle.
• Thick periphery and thin centrally
• Lateral meniscus is shorter than the medial meniscus
• Function- increases the articular area.
increase joint congruency
increase joint stability
shock absorber
Distribute weight bearing force

14. STABILITY OF KNEE JOINT
• Stability of the knee joint depends upon the-
1.capsule
2.collateral ligaments
3.cruciate ligaments
4.various muscles associated with the knee joint movements

15. CAPSULE OF KNEE JOINT

17. THE CAPSULE HAS 2 LAYERS-
1. SUPERFICIAL LAYER 2. DEEP LAYER
SUPERFICIAL LAYER/ FIBROUS LAYER
• Provide passive stability
• Has extensor retinaculum
medial patellar retinaculum
lateral patellar retinaculum
Includes 6 ligaments-
1.Medial patella femoral ligament
2.Lateral patellofemoral ligament
3.Medial patello meniscus ligament
4.Lateral patello meniscus ligament
5. Medial patello tibial ligament
6. Lateral patello tibial ligament
DEEP LAYER / SYNOVIAL LAYER
• Related to medial and lateral femoral
condyle and intercondylar area.
• Some time associated with PLICA
syndrome-
• PLICA – at the time of gestation, some
part of patella do not get fuse ,which
causes irritation in the superior,
medial and lateral side of the patella.
• Most common is medial patella PLICA
• Syndrome can also occur on trauma
/fall.
• It is a reminant of synovial membrane

19. COLLATERAL LIGAMENT
Medial collateral ligament
• Arise from adductor tubercle
• Has 2 fibers-
Superficial or anterior fiber-
insertion is just distal to pes
anserinus
Deep or posterior fiber- insertion is
proximal surface of shaft of tibia
and is attached to capsule
• Function-
1.restricting the valgus force.
2.restricting the ACL while flexion
and prevents excessive lateral
rotation of tibia.
Lateral collateral ligament
• A/K as fibular collateral ligament
• Origin- lateral femoral epicondyle
• Insertion- head of fibula
• Not attached to capsule
• Function-
Restricting the varus force

21. Lateral
collateral
ligament

22. ANTERIOR CRUCIATE LIGAMENT
ORIGIN- postero-medial aspect of lateral femoral condyle
Insertion- medial tubercle of the spine
• Fibers of ACL are inferiorly, medially and anteriorly.
• Has 2 bundles of fibers-
1.antero-medial bundle
2.postero-lateral bundle
• Function-
1.resist the anterior translation of tibia on femur.
• Role of antero-medial bundle- during flexion, the anteromedial bundle get tight and
prevents the anterior translation of tibia on femur.
• Role of postero-lateral bundle- during extension, the postero-lateral bundle get tight and
prevents the anterior translation of tibia on femur.
Least amount of anterior translation during extension because postero-lateral bundle is
very strong.
• In 30 degree of flexion there is max. anterior translation of tibia.
2. prevents hyper-extension of knee by postero-lateral bundle.
3. help in providing rotational stability i.e medial/ lateral rotation or varus/valgus

24. MUSCLES ASSOCIATED WITH ANT. CRUCIATE LIGAMENT-
1. Quadricep muscle- extension. So anterior translation is prevented
by posterolateral bundle of ACL.
2. GASTROCNEMUS- prevent anterior translation
3. Hamstring and soleus- associated with posterior translation

26. POSTERIOR CRUCIATE LIGAMENT
• Arise from the anteromedial aspect of medial femoral condyle and attached to
the posterior horn of both menisci or 1cm distal to joint line in tibial platue.
• Direction of fiber- inferiorly and posteriorly
• Posterior cruciate ligament is shorter than ant. Cruciate ligament but the
surface area of post. Cruciate ligament is 150% more than ant. Cruciate
ligament.
Bundles of post. Cruciate ligament-
1. anterolateral bundle- a)weak during extension
b)on flexion (80-90degree) maximum tightness in post.
Cruciate ligament.
2. Posteromedial bundle- a)tight during extension
b) on flexion ,the posteromedial bundle get tightness.

28. FUNCTIONS OF POS. CRUCIATE LIGAMENT-
1) restriction to posterior translation of tibia on femur
2) provide valgus and varus stability
3) tibial rotational stability by postero medial bundle
Role of muscles in post. Cruciate ligament-
1) popletius – it helps in posterior translation of tibia if post. Cruciate ligament
is absent.
2) hamstrings- even though it is a knee flexor, but prevents the posterior
translation of tibia.
3) gastrocnemius – increase the strain on post. Cruciate ligament at more than
40 degree of flexion.

29. KNEE JOINT KINAMATICS
KNEE JOINT HAS FOLLOWING MOVEMENTS-
1)Flexion and extension
2)medial rotation and lateral rotation
3)abduction and addiction

30. 1) Flexion and extension -
• It is the principle motion of knee complex
• Movement occurs in transcondylar axis. but in knee trans-epicondylar is not constant,it
changes with the movement.
Can have 2 catogery motion
1)fixed tibia, only femur is in movement state
2)fixed femur, only tibia is in movement state
(when tibia is fixed and only femur is in movement state ,eg- down squatting position) ,
During flexion
so, femur is going for flexion ,the arthrokinamatic movement the femur rolls posteriorly
and slide or glide anteriorly.
so, at 0-25 degree of flexion ,there is only posterior rolling function and at more then 25
degree of flexion, the femur motion is accompanied by both the anterior sliding motion
and post. rolling motion.
During extension-
During extension the femur is showing anterior rolling and slide posteriorly
-after 25 degree of extension ,sliding starts, so also known as pure spin movement.

33. During extension- anterior rolling and
slide posteriorly
During flexion- rolling posteriorly
and gliding/sliding anteriorly

34. 2) fixed femur, only tibia is in movement state(eg. standing squatting position)
Tibia flexion- tibial cavity is concave i.e concave on convex
Movement- posterior rolling and sliding/gliding posteriorly
Posterior cruciate ligament is helpful in preventing posterior rolling from
dislocation.
On tibial extension- anterior rolling and anterior gliding/sliding

35. Role of Ante. Cruciate ligament and posterior
cruciate ligament in knee flexion and extension
1. when flexion increases, ACL get stretched out and prevent the ant. Translation
of tibia and help from dislocating.
2. on extension ,PCL get stretched and prevent posterior translation

36. Role of menisci in flexion and extension movement
• Menisci is wedge shape i.e thin from the centre and
thick from the pheriphery ,so it helps in uphill
movement of femur.
• During flexion the shear force transmit anteriorly.
• During extension ,the shear force transmit
posteriorly

41. 2. Medial and lateral rotation of knee joint
• Occurs in transverse plane and longitudinal axis.
• Longitudinal axis passes through medial tibial condyle or medial tibial
intercondyloid tubercle. So the movement around the pivot is in medial
tibial condyle or med. Tibial intercondyloid tubercle and movement in
lateral condyle will be more.
(Pivot or axis through which the movement take place will be restricted ,so
medial condyle will have less rotation.)
So,
lateral rotation- medial condyle will go anteriorly and lateral condyle will go
posteriorly.
medial rotation- the lateral tibial condyle will have arc more anteriorly and
medial tibial condyle les movement posteriorly

42. SCREW HOME MECHANISM
• Screw home mechanism (SHM) of knee joint is a critical mechanism that play
an important role in terminal extension of the knee.
• There is an observable rotation of the knee during flexion and extension.
• This rotation is important for healthy movement of the knee.
• During the last 30 degrees of knee extension, the tibia (open chain) or femur
(closed chain) must externally or internally rotate, respectively, about 10
degrees.
• This slight rotation is due to inequality of the articular surface of femur
condyles.
• Rotation must occur to achieve full extension and then flexion from full
extension

44. • The "screw-home" mechanism is considered to be a key element to
knee stability for standing upright. The tibia rotates internally during
the swing phase and externally during the stance phase.
• External rotation occurs during the terminal degrees of knee
extension and results in tightening of both cruciate ligaments, which
locks the knee.
• The tibia is then in the position of maximal stability with respect to
the femur.
• Last 30 degrees of Extension causes a Medial rotation of Femur on
Tibia will keep joint in closed packed position. The Knee is Unlocked
by Lateral rotation of Femur.
• In open Kinematic chain Tibia laterally rotates on Femur during last 5
degrees of Extension to produce LOCKING. Unlocking by Medial
rotation

46. Role of menisci and ligaments on medial and lateral
rotation-
ROLE OF MENISCI-
• On medial rotation of tibia on femur- lateral menisci move anteriorly due to
shape.
• On lateral rotation of tibia on femur – medial menisci move posteriorly
ROLE OF LIGAMENTS-
• As in flexion to extension –most of the ligaments get lax or loose, so they do
not restrict the movement, but in med/lat. rotation the ligaments causes
restriction of movements.
Upto 0-90 degree flexion- max. value of medial and lateral rotation.
Upto 0-20 degree - lateral rotation and upto 0- 15 degree –medial rotation.
• So, lateral rotation is more than the medial rotation in flexion position.
So, upto 0-90 degree –medial/lat. rotation increases and 90-130 degree-
med/lat. rotation decreases

47. 3.Abduction and adduction of knee
ABDUCTION – VALGUS MOVEMENT ADDUCTION- VARUS MOVEMENT
occurs in frontal plane i.e AP AXIS movements
5-8 degree of abduction or adduction are possible in extension, as the
ligaments are very tough
13-20 degree of movement of abduction / adduction are possible in flexion.
In abduction- tibia is going outward ,so joint is associated with valgus force
and increase in compression in the lateral compartment of condyle
In adduction – tibia is coming inwards ,causing varus force , and increase in
compression in medial compartment of condyle.

48. LOCKING AND UNLOCKING OF KNEE
• One of the most imp. topic in knee biomechanics
• Comes under coupled motion
• Coupled motion- motion that occurs in one axis and that motion occurs in
association with another axis.eg.- a motion occurring in x axis and associated
with y axis.
• IMPORTANCE-
• As medial condyle of femur is slightly distal than the lateral condyle ,so this
distal association creates a physiological association with the tibia creating a
physiological valgus.
• Normally tibia is a bit laterally, on flexion of tibia, the tibia comes bit midline of
the body. So, knee flexion is accompanied by varus and abduction movement
and extension is linked to valgus and adduction.
• Flexion occurs in sagittal axis and varus / valgus occurs in frontal axis,so there is
involvement of 2 axis, that’s why knee has coupled motion.

49. Coupled motion in knee joint
FLEXION / EXTENSION ACCOMPANIED BY LATERAL AND MEDIAL ROTATION
• This motion occurs in last 30 degree of flexion to extension of tibia (fixed femur),
leads to lateral rotation of tibia.
Medial tibial condyle having rolling and ant. Gliding -
the medial tibial condyle of tibia has greater degree of surface area, so associated
with rolling and ant. Gliding and associated with lateral rotation on medial side and
the lateral condyle act as PIVOT, so this is known as screw hole mechanism,
where lateral condyle act as a screw and medial condyle side rotating and gliding.
• This complete process is known as locking of knee or automatic
rotation or terminal rotation or screw home mechanism.

52. UNLOCKING OF KNEE-
• On flexion of tibia (with fixed femur)- the knee has slight medial rotation i.e
flexion accompanied by medial rotation.
• Popliteus muscle is directly related to unlocking and locking because of its
action.
The popliteus assists in knee flexion. Its function is dependent on whether the
lower extremity is in a weight-bearing or non-weight-bearing state; it is considered
the primary internal rotator of the tibia in the non-weight-bearing state.
• "Locking" the knee occurs with extension during weight-bearing. This describes
the femur medially rotating on the tibia, allowing for full extension without
muscular expenditure.
• When "unlocking" the knee, the popliteus contracts causing flexion and lateral
rotation of the femur on the tibia. This is why some refer to the popliteus as the
"key" to the locked knee

53. Screw home mechanism in non weight bearing
• LOCKING-
- extension is combined with lateral rotation
-flexion is combined with medial rotation
here tibia is fixed on moving femur so, at last 30 degree of extension from flexion
,small lateral condyle of tibia will have rolling and gliding posteriorly or opposite
direction.
So ,rolling upward and gliding posteriorly and medial rotation of femur

54. Screw home mechanism in weight bearing-
Tibia is fixed and femur is rotating (in extension ,while standing from
squatting position)
Extension is combined with medial rotation of femur
Flexion is combined with lateral rotation of femur