2. KNEE BIOMECHANICS
The knee joint complex is extremely elaborate and includes
three articulating surfaces, which form two distinct joints
contained within a single joint capsule: the patellofemoral and
tibiofemoral joint
Given the frequency of knee injuries and the intricate nature of
this joint complex, clinicians caring for knee injuries must have
an extensive knowledge base
Participating bones –
o Femur
o Tibia
o Patella
Knee complex
Tibio-femoral joint
Patello-femoral joint
Tibio-femoral/Knee joint
Ginglymus – (Hinge)
A freely moving joint in which the bones are so articulated as to allow
extensive movement in one plane.
Arthodial – (Gliding)
6 degrees of freedom
o 3 Rotations
o 3 Translations
Knee degree of freedom
Rotations
o Flex/Ext – 150 – 1400
o Varus/Valgus – 60 – 80 in extension
o Int/ext rotation – 250 – 300 in flexion
Translations
3. o AP 5 - 10mm
o Compression/Distraction 2 - 5mm
o Medial/Lateral 1-2mm
Double condyloid knee joint is also referred to as Medial & Lateral
Compartments of the knee.
Double condyloid joint with 30 freedom of Angular
(Rotatory) motion.
o Flexion/Extension –
Plane – Sagittal plane
Axis – Coronal axis
o Medial/lateral (int/ext) rotation –
Plane – Transverse plane
Axis – Longitudinal axis
o Abduction/Adduction –
Plane – Frontal plane
Axis – Antero-posterior axis.
Femur is proximal articular surface of the knee joint with
large medial & lateral condyles.
Because of obliquity of shaft, the femoral condyles do not
lie immediately below the femoral head but are slightly
medial to it.
The medial condyle extend further distally, so that, despite
the angulation of the femur’s shaft, the distal end of
the femur remains essentially horizontal.
In sagittal plane - Condyles have a convex shape
In the frontal plane - Slight convexity
The lateral femoral condyle
o Shifted anteriorly in relation to medial
o Articular surface is shorter
4. o Inferiorly, the lateral condyle appears to be longer
Two condyles are separated –
o Inferiorly by Intercondylar notch
o Anteriorly by an asymmetrical, shallow groove called
the Patellar Groove or Surface
Tibial articulating surface
Asymmetrical medial & lateral tibial condyles constitute the distal
articular surface of knee joint.
Medial tibial plateau is longer in AP direction than lateral
The lateral tibial articular cartilage is thicker than the medial side.
Tibial plateau slopes posteriorly approx 70 to 100
Medial & lateral tibial condyles are separated by two bony spines
called the Intercondylar Tubercles
The tibial plateaus are predominantly flat, but convexity at anterior &
posterior margins
Because of this lack of bony stability, accessory joint structures
(menisci) are necessary to improve joint congruency.
Menisci of knee joint
2 asymmetrical fibro cartilaginous joint disk called Menisci are located on
tibial plateau.
The medial meniscus is a semicircle & the lateral is 4/5 of a ring (Williams,
PL, 1995).
9
5. Both menisci are –
o Open towards intercondylar area
o Thick peripherally
o Thin centrally forming cavities for femoral condyle
By increasing congruence, menisci play in reducing friction
between the joint segment & serve as shock absorber.
Meniscal attachment
Common attachment of medial & lateral –
o Intercondylar tubercles of the tibia
o Tibial condyle via coronary ligaments
o Patella via patellomeniscal or patellofemoral ligament
o Transverse ligament between two menisci
o Anterior cruciate ligament (ACL)
Unique attachment of medial menisci –
o Medial collateral ligament (MCL)
o Semitendinous muscle
Unique attachment of lateral menisci –
o Anterior & posterior meniscofemoral
ligament
o Posterior cruciate ligament (PCL)
o Popliteus muscle
Young children whose menisci have ample of blood supply have low
incidence of injury
In adult, only the peripheral vascularized region is capable of inflammation,
repair & remodeling following a tearing injury.
Menisci are well innervated with free nerve ending & 3 mechanoreceptors
(Ruffine corpuscle, Pacinian corpuscle & Golgi tendon organs)
TF alignment & weight bearing force
The anatomic/ longitudinal axis –
o Femur – Oblique, directed inferiorly & medially
o Tibia – Directed vertically
o The femoral & tibial longitudinal axis form an angle medially at
the knee joint of 1850 – 1900, i.e. 50 – 100 creating Physiological
Valgus at knee
6. In bilateral static stance – equal weight distribution on medial & lateral
condyle
Deviation in normal force distribution –
o TF angle > 1900 – Genu Valgum – compress lateral condyle
o TF angle < 1800 – Genu Varum – compress medial condyle
Compressive force in dynamic knee joint
o 2 – 3 time body weight in normal gait
o 5 – 6 time body weight in activities (like – Running, Stair Climbing etc.)
Knee joint capsule
Joint capsule enclose – TF & PF is large lax
Outer portion – firmly attached to the inferior aspect of femur & superior
portion of tibia.
Posterior attachment
o Proximally to posterior margins of the femoral condyles and
intercondylar notch.
o Distally to posterior tibial condyle.
Anterior attachment
o Superiorly – Patella, tendon of quadriceps muscles
o Inferiorly patellar tendon complete the anterior portion of the joint
capsule.
The antero-medial & antero-lateral portions of the capsule, are often
separately identified as the medial and lateral patellar retinaculae or
together as the extensor retinaculum.
The joint capsule is reinforced medially, laterally & posteriorly by capsular
ligaments.
Extensor retinaculum
2 layers – superficial & deeper
Deeper layer –
o Connecting the capsule anteriorly to menisci & tibia via coronary
ligament (known as patellomeniscal or patellotibial band)
Superficial layer –
o Mixed with vastus medialis & lateralis muscle & distal continue to
posterior femoral condyle (patellofemoral ligament)
7. Synovial lining
The intricacy of fibrous layer capsule is surpassed by its
synovial lining except posteriorly.
Synovium adheres to anterior aspect & side to the ACL &
PCL.
Embryologically, the synovial lining of the knee joint
capsule is divided by septa into 3 separate compartment –
o Superior patellofemoral compartment
o 2 separate medial & lateral tibiofemoral
compartment
Ligament of knee joint
Collateral ligament
o Medial collateral ligament (MCL)
o Lateral collateral ligament (LCL)
Cruciate ligament
o Anterior cruciate ligament (ACL)
o Posterior cruciate ligament (PCL)
Posterior capsular ligament
Meniscofemoral ligament
Iliotibial band
8. MCL
Attachment –
o Origin – medial aspect of medial femoral condyle
o Insertion – proximal tibia
Function –
o Resist valgus stress force (specially in extended knee)
o Check lateral rotation of tibia
o Also restrain anterior displacement of tibia when ACL is absent.
LCL
Attachment –
o Origin – lateral femoral condyle
o Insertion – posteriorly to head of fibula
Function –
o Resist varus stress force across the knee
o Check combined lateral rotation with
posterior displacement of tibia in
conjunction with tendon of popliteal
muscle.
Cruciate ligament
Cruciate = “Resembling a cross” in Latin.
Located within the joint capsule & are therefore called Intracapsular
Ligaments.
Cruciate ligament provide stability in sagittal plane
The ACL & PCL are centrally located within the capsule but lie
outside the synovial cavity.
ACL
Attachment –
o Origin – from anterior surface the tibia in the intercondylar area
just medial to medial meniscus.
o It spans the knee laterally to PCL & runs in a superior & posterior
direction
o Insertion – to posteriorly on lateral condyle of femur
ACL is divided into 2 bands –
o Antero-medial band (AMB)
o Postero-lateral band (PLB)
Function of acl
Primarily –
o Check femur from being displaced posteriorly on the tibia
o Conversely, the tibia from being displaced anteriorly on femur.
PCL
ACL
9. It tightens during extension, preventing excessive hyperextension of the
knee.
ACL carried 87% of load when anterior translatory force was applied to tibia
with extended knee.
Check tibial medial rotation by twisting around PCL
ACL injury is common when knee is in flexed & tibia rotated in either
direction
PCL
Attachment –
* Origin – from posterior tibia in intercondylar area and runs in a superior
and anterior direction on medial side of ACL.
* Insertion - to anterior femur on the medial condyle
PCL is divided into 2 bands –
* Antero-medial band (AMB)
*Postero-lateral band (PLB)
Function of pcl
Primarily –
* Check femur from being displaced anteriorly on the tibia or
*Tibia from being displaced posteriorly on femur.
It tightens during flexion & is injured much less frequently than ACL.
PCL carry 93% of load when posterior translatory force was applied to
tibia with extended knee.
PCL play a role in both restraining & producing rotation of the tibia.
Summary of ACL & PCL attachments –
o ACL – Runs from anterior tibia to posterior femur
o PCL – Runs from posterior tibia to anterior femur
Posterior capsular ligament
Oblique popliteal ligament
Posterior oblique ligament
Arcuate ligament:
o Arcuate ligament lateral branch
o Arcuate ligament medial branch
Oblique popliteal ligament
Attachment –
o Origin – The central part of posterior aspect of
the joint capsule
o Insertion - Posterior medial tibial condyle
Function –
10. o Reinforces posteromedial knee joint capsule obliquely on a lateral-to-
medial diagonal from proximal to distal
Posterior oblique ligament
Attachment –
o Origin – Near the proximal origin of the MCL and adductor tubercle
o Insertion – Posteromedial tibia, posterior capsule & posteromedial
aspect of the medial meniscus
Function –
o Reinforces the posteromedial knee joint capsule obliquely on a
medial-to-lateral diagonal from proximal to distal
Arcuate Ligament
Lateral Branch Medial branch
Distal
Attachment
From posterior aspect of the head of the fibula
Proximal
Attachment
To tendon of popliteus muscle
& posterior capsule
Into oblique popliteal lig on
medial side of joint
Function
Reinforces the postero-lateral knee joint capsule obliquely on a medial
to lateral from proximal to distal
11. Meniscofemoral ligament (MFl)
There are 2 portions of MFL, at least one in 91% of
knees & 30% knee having both.
MFL are not true ligaments because they attach
bone to meniscus, rather than bone to bone.
Attachment –
o Origin – Both originate from posterior horn
of lateral meniscus
o Insertion – to lateral aspect of medial
femoral condyle
The “Ligament of Humphry” or “Antero-MFL” is the
ligament run anterior to PCL on tibia
The “Ligament of Wrisberg” or “Postero-MFL” is the
ligament run posterior to PCL, also known as “3rd Cruciate
Ligament of Robert”
Function –
o They may assist PCL in restraining posterior tibial translation
o Also assist popliteus muscle by checking tibial lateral rotation
Bursa associated with knee
Pre-patellar bursa –
o Located between the skin & anterior surface of
patella
o They allows free movement of skin over patella
during knee flexion & extension
Subcutaneous bursa –
o Located between patellar ligament & overlying
skin
Deep infra-patellar bursa –
o Located between patellar ligament & tibial
tuberosity
o Helps in reducing friction between the patellar
ligament & tibial tuberosity
Function of knee joint
Osteokinemetic of knee joint –
o Primary motions –
Flexion / Extension
Medial / Lateral Rotation
o Secondary motions –
Antero-posterior displacement of femur or tibia
Abduction / Adduction through valgus or varus force
12. Flexion & extension
Axis – no fixed axis but move through ROM (frontal axis)
Plan – sagittal plan
ROM of flexion / extension –
* Flexion – 1300 – 1400
* Extension – 50 – 100 (Consider normal, beyond this termed as
Genurecurvatum)
In close kinematic chain (OKC) – flexion / extension range is limited by ankle
range.
Medial / lateral rotation
Axis – Longitudinal / Vertical axis
Plan – Transvers plan
ROM at 900 knee flexion –
* Lateral rotation – 00 – 400
* Medial rotation – 00 – 300
TF CKC Flexion
Early 00 - 250 knee flexion –
o Posterior rolling of femoral condyles on the tibia
As flexion continues –
o Posterior Rolling accompanied by simultaneous
Anterior glide of femur
o Create a pure Spin of femur on the posterior tibia
TF CKC extension
Extension from flexion is a reversal of flexion motion.
Early extension –
o Anterior rolling of femoral condyles on tibial plateau
As extension continues –
o Anterior Rolling accompanied by simultaneous Posterior glide of
femur
o Produce a pure Spin of femoral condyles on tibial plateau
Tf ock flexion / extension
When tibia is flexed on a fixed femur –
o The tibia performed Both Posterior Rolling & Gliding on relatively
fixed femoral condyles.
o When tibia is Extended on a fixed femur –
o The tibia performed Both Anterior Rolling & Gliding on relatively fixed
femoral condyles.
13. Locking & unlocking (screw home mechanism)
Locking of knee joint
CKC femoral extension from 300 flexion –
* Larger medial femoral condyle continue rolling & gliding posteriorly
when smaller lateral side stopped.
* These result in medial rotation of femur on tibia, seen in last 50 of
extension.
* The medial rotation of femur at final stage of extension is not
voluntary or produce by muscular force, which is referred as
“Automatic” or “Terminal Rotation”.
* The rotation within the joint bring the joint into a closed packed or
Locked position.
* The consequences of automatic rotation is also known as
“Locking Mechanism” or “Screw Home Mechanism”.
OKC – lateral rotation of tibia on fixed femur
Unlocking of knee joint
To initiate flexion, knee must be unlocked.
A flexion force will automatically result in lateral rotation of femur
* Because the larger medial condyle will move before the shorter
lateral condyle.
* Popliteus is the primary muscle to unlocked the knee.
Role of Cruciate Ligaments
in Flexion/Extension
TF CKC Flexion: ACL Control
At full extension –
o Angle of ACL inclination greatest
o Anterior directed component force will
eventually Restrain Posterior Femoral
Roll
As TF flexion increases –
o Angle of ACL inclination decreases
o Anterior directed component force increases sufficient enough to
produce Anterior Femoral Slide
14. Hyperextension Impact on ACL
End ROM extension brings the mid-substance of the ACL in contact with
the femoral intercondylar shelf (notch of Grant)
This contact point acts as a fulcrum to tension load the ACL
TF CKC Flexion: PCL Control
Angle Of PCL Inclination is greatest at full flexion.
Anterior directed component force will eventually Restrain Posterior
Femoral Roll
TF CKC Extension: PCL Control
As TF extension increases –
o Angle Of PCL Inclination decreases
o Posterior directed component force increases sufficient
enough to Produce Posterior Femoral Slide
TF OKC Extension Arthrokinematics sagittal plan
ž Extension –
— Meniscal migrate Anteriorly –
○ Because of meniso-patellar
ligament
TF OKC flexion Arthrokinematics sagittal plan
Flexion – Menisci migrate posteriorly because of
* Semimembranosis attachment to medial meniscus
* Popliteus attachment to lateral meniscus
Knee axial rotation
Menisco-patellar
Ligaments
15. Axial rotation of knee arthrokinemetic
Axis – vertical axis
Plan – transvers plan
ROM – Maximum range is available at 90 of knee flexion.
The magnitude rotation diminishes as the knee approaches
both full extension and full flexion.
Medial condyle acts as pivot point while the lateral condyles
move through a greater arc of motion, regardless of
direction of rotation.
rotation of tibia
During Tibial lateral rotation on the femur –
o Medial tibial condyle moves slightly anteriorly on the relatively fixed
medial femoral condyle, whereas lateral tibial condyle moves a larger
distance posteriorly.
During tibial medial rotation –
o Medial tibial condyle moves only slightly posteriorly, whereas the
lateral condyle moves anteriorly through a larger arc of motion.
During both medial and lateral rotation –
o The menisci reduce friction & distribute femoral condyle force created
on the tibial condyle without restricting the motion.
o Meniscus also maintain the relationship of tibia & femoral condyles
just as they did in flexion and extension.
Valgus (Abduction)/Varus (Adduction)
Axis – Antero-posterior axis
Plan – Frontal plane
ROM –
o 8 at full extension
o 13 with 20 of knee flexion.
Excessive frontal plane motion could indicate ligamentous insufficiency
16. Patello-femoral joint (pfj)
pFj function
It work primarily as an anatomical pulley
It reduce friction between quadriceps tendon & femoral condyle.
The ability of patella to perform its function without restricting knee
motion depends on its mobility.
PFJ articulating surface
The triangular shape patella is a largest sesamoid bone in body is a least
congruent joint too.
Posterior surface is divided by a vertical ridge into medial & lateral
patellar facets.
The ridge is located slightly towards the medial facet making smaller
medial facet
The medial & lateral facet are flat & slightly convex side to side & top to
bottom.
At least 30% of patella have 2nd ridge separating medial facet from the
extreme medial edge known as Odd Facet of Patella.
Femoral articulating surface
Patella articulate in femur with intercondylar groove or
femoral sulcus on anterior surface of distal femur.
Femoral surface are concave side to side & convex top to
bottom but lateral facet is more convex then medial
surface.
PFJ congruence
The vertical position of patella in femoral sulcus is related to length of
patellar tendon, approximately 1:1 is (referred to as Insall-Salvati index)
An excessive long tendon produce an abnormally high position of patella
on femoral sulcus known as patella alta.
17. In neutral or extended knee, the patella has little or no contact with
the femoral sulcus beneath.
At 100 – 200 of flexion – contact with inferior margin of medial &
lateral facet.
By 900 of flexion – all portion of patella contact with femur except
the odd facet.
Beyond 900 of flexion – medial condyle inter the intercondylar notch
& odd facet achieves contact for the first time.
At 1350 of flexion – contact is on lateral & odd facet with medial
facet completely out of contact.
Patello femoral joint stabilizer
Medial-lateral PFJ stability
PFJ is under permanent control of 2 restraining mechanism across each other
at right angel.
o Transvers group of stabilizer
o Longitudinal group of stabilizer
Transvers stabilizer –
o Medial & lateral retinaculum
o Vastus Medialis & Lateralis
o The lateral PF ligament contributes 53% of total force when in full
extension of knee.
Medial-lateral positioning of patella / patellar tracking
When the knee is fully extended & relax, the patella should be able to
passively displaced medially or laterally not more then one half of patella.
Imbalance in passive tension or change in line of pull of dynamic
structures will substantially influence the patella.
Abnormal force may influence the excursion of patella even in its more
secure location within intercondylar notch in flexion.
Medial & lateral force on patella
Since the action line of quadriceps & patellar ligament do not co-inside,
patella tend to pulled slightly laterally & increase compression on lateral
patellar facets.
Larger force on patella may cause it to subluxation or dislocate off the
lateral lip of femur.
Genu valgum increase the obliquity of femur & oblique the pull of
quadriceps.
18. Femoral anteversion & tibial torsion creates an increased obliquity in
patella predisposing to excessive lateral pressure or to subluxation or
dislocation.
Excessive tension in lateral retinaculum (or weakness of VMO) may cause
the patella to tilt laterally.
Insufficient height of lateral lips of femoral sulcus may create patellar
subluxation or fully dislocation, even with relatively small lateral force.
Muscles of knee & its function
Muscles of the Knee
Area One-joint Muscle Two-joint Muscle
Anterior
Vastus Lateralis Rectus Femoris
vastus Medialis
Vastus Intermedialis
Posterior Biceps Femoris
(Short)
Biceps Femoris (Long)
Semimembranosus
Semitendinosus
Sartorius
Gracilis
Gastrocnemius
Lateral Tensor Fascia Latae
Muscles of Posterior Knee
Knee Flexors Semimembranosus, Semitendinosus, Biceps Femoris
(Long & Short Heads), Sartorius, Gracilis, Popliteus &
Gastrocnemius Muscles
Flex + Tibial Medial Rotators Popliteus, Gracilis, Sartorius, Semimembranosus &
Semitendinosus Muscles
Flex + Tibial Lateral Rotator Biceps Femoris
Flex + Abductor Biceps Femoris, Lateral Head Gastrocnemius &
Popliteus
Flex + Adductor Semimembranosus, Semitendinosus, Medial Head
Gastrocnemius, Sartorius & Gracilis
19. Anterior knee muscles :
quadriceps :
The Quadriceps are a group of four muscles that sit on the anterior or front
aspect of the thigh.
They are the Vastus Medialis, Intermedius and Lateralis and finally
the Rectus Femoris.
The Quadriceps attach to the front of the tibia and originate at the top of
the femur.
The exception to this rule is the Rectus Femoris which actually crosses the
hip joint and originates on the pelvis.
1-Rectus Femoris
Origin: Straight head: from the anterior inferior iliac spine
Reflected head: on a curved line along the upper part of the acetabulum
at the ilium
Insertion: The quadriceps tendon along with the three vasti muscles,
enveloping the patella then by the patellar ligament into the tibial
tuberosity.
Action: Extension of the leg at the knee
Innervation: Posterior division of the femoral nerve (L3 – 4)
2-Vastus Lateralis
Origin: Upper aspect of the intertrochanteric line, base of the greater
trochanter and onto its anterior surface, from the proximal portion of
the lateral lip of the linea aspera, lateral intermuscular septum
Insertion: Into the lateral side of the quadriceps tendon, joining with
rectus femoris and the other vasti muscles, enveloping the patella,
then by the patellar ligament into the tibial tuberosity.
Action: Extension of the leg at the knee
Innervation: Posterior division of the femoral nerve (L3 – 4)
3-Vastus Medialis
Origin: Lower part of the intertrochanteric line, along the spiral line to
the medial lip of the linea aspera and the medial intermuscular septum
and the aponeurosis of adductor magnus.
Insertion: Into the medial side of the quadriceps tendon joining with
the rectus femoris and the other vasti muscles, enveloping the patella,
then by the patellar ligament into the tibial tuberosity
Action: Extension of the leg at the knee
Innervation: Posterior division of the femoral nerve (L3 – 4)
20. 4-Vastus Intermedius Anatomy
Origin: Anterior and lateral aspects of the upper two-thirds of the femoral
shaft and the lower part of the lateral intermuscular septum of the femur.
Insertion: Into the quadriceps tendon along with rectus femoris and the
other vasti muscles, enveloping the patella, then by the patellar ligament
into the tibial tuberosity.
Action: Extension of the leg at the knee
Innervation: Posterior division of the femoral nerve (L3 – 4)
Posterior knee muscles
hamistring
The muscles in the posterior compartment of the thigh are
collectively known as the hamstrings. They consist of the biceps
femoris, semitendinosus and semimembranosus – as a group they
act to extend at the hip, and flex at the knee. They are innervated by
the sciatic nerve (L4-S3) as it descends through the thigh.
The hamstrings form prominent tendons medially and laterally at the
back of the knee. This explains the phrase ‘hamstringing the enemy’
– whereby these tendons are cut.
Muscles in the Posterior Compartment
1-Biceps Femoris.
Like the biceps brachii in the arm, the biceps femoris muscle has two heads –
a long head and a short head.
It is the most lateral of the muscles in the posterior thigh – the common
tendon of the two heads can be felt laterally at the posterior knee.
Attachments: The long head originates from the ischial tuberosity of the pelvis.
The short head originates from the linea aspera on posterior surface of the femur.
Together, the heads form a tendon, which inserts into the head of the fibula.
Actions: Main action is flexion at the knee. It also extends the leg at the hip, and
laterally rotates at the hip and knee.
Innervation: Long head innervated by the tibial part of the sciatic nerve, whereas
the short head is innervated by the common fibular part of the sciatic nerve.
2-Semitendinosus
The semitendinosus is a largely tendinous muscle. It lies medially to the
biceps femoris, and covers the majority of the semimembranosus.
Attachments: It originates from the ischial tuberosity of the pelvis, and attaches
to the medial surface of the tibia.
Actions: Flexion of the leg at the knee joint. Extension of thigh at the hip. Medially
rotates the thigh at the hip joint and the leg at the knee joint.
21. Innervation: Tibial part of the sciatic nerve.
3-Semimembranosus
The semimembranosus muscle is flattened and broad. It is located
underneath the the semitendinosus.
Attachments: It originates from the ischial tuberosity, but does so
more superiorly than the semitendinosus and biceps femoris. It attaches to the
medial tibial condyle.
Actions: Flexion of the leg at the knee joint. Extension of thigh at the hip. Medially
rotates the thigh at the hip joint and the leg at the knee joint.
Innervation: Tibial part of the sciatic nerve.
Popliteus Muscle
Origin: The lateral surface of the lateral condyle of the
femur.
Insertion: Medial 2/3rds of the triangular area above the
soleal line on the posterior surface of the tibia.
Action: Internal rotation of the knee; Assists with flexion of
the leg at the knee
Innervation: Tibial nerve (L4, 5, S1)
