KNEE
Dr. Michael P. Gillespie
KNEE: GENERAL CONSIDERATIONS
The knee consists of lateral and medial
compartments at the tibiofemoral joint and the
patellofemoral joint.
 Motion of the knee occurs in two planes:

Dr. Michael P. Gillespie
Flexion and extension
 Internal and external rotation

Two-thirds of the muscles that cross the knee
also cross either the ankle or the hip. This
creates a strong functional association within the
joints of the lower limb.
 Stability of the knee is based primarily on its
soft-tissue constraints rather than on its bony
configuration.

2
KNEE: BIOMECHANICAL
FUNCTIONS
During the swing phase of walking, the knee
flexes to shorten the functional length of the
lower limb, thereby providing clearance of the
foot from the ground.
 During the stance phase, the knee remains
slightly flexed allowing for shock absorption,
conservation of energy, and transmission of
forces through the lower limb.

Dr. Michael P. Gillespie
3
OSTEOLOGY
Dr. Michael P. Gillespie
4
BONES AND ARTICULATIONS OF
THE KNEE
Dr. Michael P. Gillespie
5
DISTAL FEMUR

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
Dr. Michael P. Gillespie

At the distal end of the femur are the large lateral
and medial condyles (Greek kondylos, knuckle).
Lateral and medial epicondyles project from each
condyle. These serve as attachment sites for the
collateral ligaments.
Intercondylar notch – passageway for the cruciate
ligaments.
Femoral condyles fuse anteriorly to form the
intercondylar (trochlear) groove. This groove
articulates with the patella.
Lateral and medial facets – formed from the sloping
sides of the intercondylar groove.
Lateral and Medial grooves are etched into the
cartilage that covers the femoral condyles and the
edge of the tibia articulates with these grooves.
6
OSTEOLOGIC FEATURES OF THE
DISTAL FEMUR
Lateral and medial condyles
 Lateral and medial epicondyles
 Intercondylar notch
 Intercondylar (trochlear) groove
 Lateral and medial facets (for the patella)
 Lateral and medial grooves (etched in the
cartilage of the femoral condyles)
 Popliteal surface

Dr. Michael P. Gillespie
7
PATELLA, ARTICULAR SURFACES
OF DISTAL FEMUR & PROXIMAL
TIBIA
Dr. Michael P. Gillespie
8
FIBULA
The fibular has no direct function at the knee;
however, it splints the lateral side of the tibia
and helps to maintain its alignment.
 The head of the fibula is an attachment for biceps
femoris and the lateral collateral ligament.
 Proximal and distal tibiofibular joints attach the
fibula to the tibia.

Dr. Michael P. Gillespie
9
PROXIMAL TIBIA
The proximal end of the Tibia flares into medial
and lateral condyles which articulate with the
femur.
 Tibial plateau – the superior surfaces of the
condyles.
 Intercondylar eminence – separates the articular
surfaces of the proximal tibia.
 Tibial tuberosity – anterior surface of the
proximal shaft of the tibia. Attachment point for
the quadriceps femoris, via the patellar tendon.
 Soleal line – posterior aspect of tibia.

Dr. Michael P. Gillespie
10
OSTEOLOGIC FEATURES OF THE
PROXIMAL TIBIA AND FIBULA

Proximal Fibula

Proximal Tibia






Medial and lateral condyles
Intercondylar eminence (with tubercles)
Anterior intercondylar area
Posterior intercondylar area
Tibial tuberosity
Soleal line
Dr. Michael P. Gillespie

Head
11
RIGHT DISTAL FEMUR, TIBIA, AND
FIBULA
Dr. Michael P. Gillespie
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LATERAL VIEW RIGHT KNEE
Dr. Michael P. Gillespie
13
PATELLA
The patella (Latin, “small plate”) is embedded
within the quadriceps tendon.
 The largest sesamoid bone in the body.
 Part of the posterior surface articulates with the
intercondylar groove of the femur.

Dr. Michael P. Gillespie
14
OSTEOLOGIC FEATURES OF THE
PATELLA
Base
 Apex
 Anterior surface
 Posterior articular surface
 Vertical ridge
 Lateral, medial, and “odd” facets

Dr. Michael P. Gillespie
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PATELLA
Dr. Michael P. Gillespie
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ARTHROLOGY
Dr. Michael P. Gillespie
17
GENERAL ANATOMIC AND
ALIGNMENT CONSIDERATIONS
The shaft of the femur angles slightly medial due
to the 125-degree angle of inclination of the
proximal femur.
 The proximal tibia is nearly horizontal.
 Consequently, the knee forms an angle of about
170 to 175 degrees on the lateral side. The
normal alignment is referred to as genu valgum.
 Excessive genu valgum – a lateral angle less than
170 degrees or “knock-knee”.
 Genu varum – a lateral angle that exceeds 180
degrees or “bow-leg”.

Dr. Michael P. Gillespie
18
FRONTAL PLANE DEVIATIONS
Dr. Michael P. Gillespie
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CAPSULE AND REINFORCING
LIGAMENTS
The fibrous capsule of the knee encloses the
medial and lateral compartments of the
tibiofemoral joint and patellofemoral joint.
 Five regions of the capsule


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Anterior capsule
Lateral capsule
Posterior capsule
Posterior-lateral capsule
Medial capsule
Dr. Michael P. Gillespie

20
LIGAMENTS, FASCIA, AND MUSCLES
THAT REINFORCE THE CAPSULE OF
THE KNEE
Connective Tissue
Reinforcement
Muscular-Tendinous
Reinforcement
Anterior
Patellar Tendon
Patellar retinacular fibers
Quadriceps
Lateral
Lateral collateral ligament
Lateral patellar retinacular
fibers
Iliotibial band
Biceps femoris
Tendon of the popliteus
Lateral head of gastrocnemius
Posterior
Oblique popliteal ligament
Arcuate popliteal ligament
Popliteus
Gastrocnemius
Hamstrings, especially the
tendon of semimembranosus
Posterior-Lateral
Arcuate popliteal ligament
Lateral collateral ligament
Tendon of popliteus
Medial
Medial patellar retinacular
fibers
Medial collateral ligament
Thickened fibers posteriormedially
Expansions from the tendon of
the semimembranosus
Tendons from sartorius, gracilis,
and semitendinosus
Dr. Michael P. Gillespie
Region of the
Capsule
21
ANTERIOR VIEW RIGHT KNEE:
MUSCLES & CONNECTIVE TISSUES
Dr. Michael P. Gillespie
22
LATERAL VIEW RIGHT KNEE:
MUSCLES & CONNECTIVE TISSUES
Dr. Michael P. Gillespie
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POSTERIOR VIEW RIGHT KNEE:
MUSCLES & CONNECTIVE TISSUES
Dr. Michael P. Gillespie
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MEDIAL VIEW RIGHT KNEE:
MUSCLES & CONNECTIVE TISSUES
Dr. Michael P. Gillespie
25
SYNOVIAL MEMBRANE, BURSAE,
AND FAT PADS
The internal surface of the capsule is lined with a
synovial membrane.
 The knee has as many as 14 bursae.
 These bursae form inter-tissue junctions
involving tendon, ligament, skin, bone, capsule,
and muscle.
 Some bursae are extensions of the synovila
membrane and others are formed external to the
capsule.
 Fat pads are often associated with the
suprapatellar and deep infrapatellar bursae.

Dr. Michael P. Gillespie
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EXAMPLES OF BURSAE AT VARIOUS
INTER-TISSUE JUNCTIONS
Examples
Ligament & Tendon
Bursa between lateral collateral ligament &
tendon of biceps femoris
Bursa between the medial collateral ligament and
tendons of pes anserinus (i.e. gracilis,
semitendinosus, sartorius)
Muscle & Capsule
Unnamed bursa between medial head of
gastrocnemius and medial side of the capsule
Bone & Skin
Subsutaneous prepatellar bursa between the
inferior border of the patella and the skin
Tendon & Bone
Semimembranosus bursa between the tendon of
the semimembranosus and the medial condyle of
the tibia
Bone & Muscle
Suprapatellar bursa between the femur and the
quadriceps femoris (largest of the knee)
Bone & Ligament
Deep infrapatellar bursa between the tibia and
patellar tendon
Dr. Michael P. Gillespie
Inter-tissue Junction
27
KNEE PLICAE


Superior or suprapatellar plica
 Inferior plica
 Medial plica (goes by about 20 names including alar ligament,
synovialis patellaris, and intra-articular medial band).

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

Plicae that are unusually large or thickened due to
irritation or trauma can cause knee pain.
Inflammation of the medial plica may be confused with
patellar tendonitis, torn medial meniscus, or patellofemoral
pain.
Treatment includes: rest, anti-inflammatory agents, PT,
and in severe cases arthroscopic resection.
Dr. Michael P. Gillespie

Plicae or synovial pleats appear as folds in the synovial
membrane.
Plicae may reinforce the synovial membrane of the knee.
Three most common plicae:
28
TIBIOFEMORAL JOINT
Articulation between the large convex femoral
condyles and the nearly flat and smaller tibial
condyles.
 The large articular surface area of the femoral
condyles permits extensive knee motion in the
sagittal plane.
 There is NOT a tight bony fit at this joint.
 Joint stability is provided by muscles, ligaments,
capsule, menisci, and body weight.

Dr. Michael P. Gillespie
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SUPERIOR SURFACE OF TIBIA
Dr. Michael P. Gillespie
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POSTERIOR VIEW: DEEP
STRUCTURES RIGHT KNEE
Dr. Michael P. Gillespie
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MENISCI: ANATOMIC
CONSIDERATIONS
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Dr. Michael P. Gillespie

The medial and lateral menisci are crescent-shaped,
fibrocartilaginous structures located within the knee
joint.
They transform the articular surfaces of the tibia into
shallow seats for the large femoral condyles.
Coronary (meniscotibial) ligaments anchor the
external edge of each meniscus.
The transverse ligament connects the menisci
anteriorly.
Several muscles have secondary attachments to the
menisci.
Blood supply to the menisci is greatest near the
peripheral border. The internal border is essentially
avascular.
32
MENISCI: FUNCTIONAL
CONSIDERATIONS

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Dr. Michael P. Gillespie

The menisci reduce compressive stress across the
tibiofemoral joint.
They stabilize the joint during motion, lubricate the
articular cartilage, provide proprioception, and help
guide the knee’s arthrokinematics.
Compression forces at the knee reach 2.5 to 3 times
the body weight when one is walking and over 4 times
the body weight when one ascends stairs.
The menisci nearly triple the area of joint contact,
thereby significantly reducing the pressure.
With every step, the menisci deform peripherally.
The compression force is absorbed as circumferential
tension (hoop stress).
33
MENISCI: COMMON MECHANISMS
OF INJURY




Dr. Michael P. Gillespie

Tears of the meniscus are the most common injury of
the knee.
Meniscal tears are often associated with a forceful,
axial rotation of the femoral condyles over a partially
flexed and weight-bearing knee.
The axial torsion within the compressed knee can
pinch and dislodge the meniscus.
A dislodged or folded flap of meniscus (often referred
to as a “bucket-handle tear”) can mechanically block
knee movement.
The medial meniscus is injured twice as frequently as
the lateral meniscus. Axial rotation with a valgus
stress to the knee can cause this.
34
OSTEOKINEMATICS AT THE
TIBIOFEMORAL JOINT

Two degrees of freedom:
Flexion & extension in the sagittal plane
 Provided the knee is slightly flexed, internal and
external rotation.

Dr. Michael P. Gillespie
35
TIBIOFEMORAL JOINT: FLEXION
AND EXTENSION




Dr. Michael P. Gillespie

The healthy knee moves from 130 to 150 degrees of
flexion to about 5 to 10 degrees beyond the 0-degree
(straight) position.
The axis of rotation for flexion and extension is not
fixed, but migrates within the femoral condyles.
The curved path of the axis is known as an “evolute”.
With maximal effort, internal torque varies across the
range of motion.
External devices attached to the knee rotate about a
fixed axis of rotation. A hinged orthosis can cause
rubbing or abrasion against the skin. Goniometric
measurements are more difficult. Place the device as
close as possible to the “average” axis of rotation.
36
SAGITTAL PLANE MOTION AT THE
KNEE
Dr. Michael P. Gillespie
37
“THE EVOLUTE”
Dr. Michael P. Gillespie
38
TIBIOFEMORAL JOINT: INTERNAL
AND EXTERNAL (AXIAL) ROTATION






External rotation of the knee is when the tibial tuberosity is
located lateral to the anterior distal femur.
 This does not stipulate whether the tibia or femur is the
moving bone.
Dr. Michael P. Gillespie

Internal and external rotation of the knee occurs about a
vertical or longitudinal axis of rotation.
This motion is called axial rotation.
The freedom of axial rotation increases with greater knee
flexion.
A knee flexed to 90 degrees can perform about 40 to 45
degrees of axial rotation.
External rotation generally exceeds internal rotation by a
ratio of nearly 2:1.
Once the knee is in full extension, axial rotation is
maximally restricted.
The naming of axial rotation is based on the position of the
tibial tuberosity relative to the anterior distal femur.

39
INTERNAL AND EXTERNAL (AXIAL)
ROTATION OF THE RIGHT KNEE
Dr. Michael P. Gillespie
40
ARTHROKINEMATICS AT THE
TIBIOFEMORAL JOINT: EXTENSION OF
THE KNEE

Tibial-on-femoral extension

Femoral-on-tibial extension
Standing up from a deep squat position.
 The femoral condyles simultaneously roll anterior
and slide posterior on the articular surface of the
tibia.

Dr. Michael P. Gillespie

The articular surface of the tibia rolls and slides
anteriorly on the femoral condyles.
41
ARTHROKINEMATICS OF KNEE
EXTENSION
Dr. Michael P. Gillespie
42
ARTHROKINEMATICS AT THE
TIBIOFEMORAL JOINT: “SCREW-HOME”
ROTATION KNEE
Locking the knee in full extension requires about
10 degrees of external rotation.
 It is referred to as “screw-home” rotation.
 It is a conjunct rotation. It is mechanically
linked to the flexion and extension kinematics
and cannot be performed independently.
 The combined external rotation and extension
maximizes the overall contact area. This
increases congruence and favors stability.

Dr. Michael P. Gillespie
43
“SCREW-HOME” LOCKING
MECHANISM
Dr. Michael P. Gillespie
44
ARTHROKINEMATICS AT THE
TIBIOFEMORAL JOINT: FLEXION OF THE
KNEE
For a knee that is fully extended to be unlocked,
it must first internally rotate slightly.
 This internal rotation is achieved by the
popliteus muscle.

Dr. Michael P. Gillespie
45
ARTHROKINEMATICS AT THE
TIBIOFEMORAL JOINT: INTERNAL AND
EXTERNAL (AXIAL) ROTATION OF THE
KNEE
The knee must be flexed to maximize
independent axial rotation between the tibia and
femur.
 The arthrokinematics involve a spin between the
menisci and the articular surfaces of the tibia
and femur.

Dr. Michael P. Gillespie
46
MEDIAL AND LATERAL
COLLATERAL LIGAMENTS:
ANATOMIC CONSIDERATIONS

The medial (tibial) collateral ligament (MCL)
A flat, broad structure that crosses the medial aspect
of the joint.
 Superficial part
 Deep part


The lateral (fibular) collateral ligament

A round, strong cord that runs nearly verticle
between the lateral epicondyle of the femur and the
head of the fibula


Attaches to the medial meniscus
Dr. Michael P. Gillespie

Does NOT attach to the lateral meniscus
The popliteus tendon crosses between these two
structures
47
MEDIAL AND LATERAL COLLATERAL
LIGAMENTS: FUNCTIONAL
CONSIDERATIONS
The function of the collateral ligaments is to limit
excessive knee motion within the frontal plane.
 The MCL provides resistance against valgus
(abduction) force.
 The lateral collateral ligament provides
resistance against varus (adduction) force.
 Produce a general stabilizing tension for the knee
throughout the sagittal plane range of motion.

Dr. Michael P. Gillespie
48
ANTERIOR & POSTERIOR CRUCIATE
LIGAMENTS: GENERAL
CONSIDERATIONS
Cruciate, meaning cross-shaped, describes the
spatial relation of the anterior and posterior
cruciate ligaments as they cross within the
intercondylar notch of the femur.
 The cruciate ligaments are intracapsular and
covered by extensive synovial lining.
 Together, they resist the extremes of all knee
movements.
 The provide most of the resistance to anterior
and posterior shear forces.
 They contain mechanoreceptors and contribute to
proprioceptive feedback.

Dr. Michael P. Gillespie
49
ANTERIOR CRUCIATE LIGAMENT:
ANATOMY AND FUNCTION
The anterior cruciate ligament (ACL) attaches
along an impression on the anterior intercondylar
area of the tibial plateau.
 It runs obliquely in a posterior, superior, and
lateral direction.
 The fibers become increasingly taut as the knee
approaches and reaches full extension.
 The quadriceps is referred to as an “ACL
antagonist” because contraction of the quadriceps
stretches (or antagonizes) most fibers of the ACL.

Dr. Michael P. Gillespie
50
ANTERIOR CRUCIATE LIGAMENT:
COMMON MECHANISMS OF INJURY
The ACL is the most frequently totally ruptured
ligament of the knee.
 Approximately half of all ACL injuries occur in
persons between the ages of 15 and 25.
 Landing from a jump
 Quickly and forcefully decelerating, cutting, or
pivoting over a single planted limb
 Hyperextension of the knee while the foot is
planted firmly on the ground

Dr. Michael P. Gillespie
51
POSTERIOR CRUCIATE LIGAMENT:
ANATOMY AND FUNCTION
The posterior cruciate ligament (PCL) attaches
from the posterior intercondylar area of the tibia
to the lateral side of the medial femoral condyle.
 The PCL is slightly thicker than the ACL.
 The “posterior drawer” test evaluates the
integrity of the PCL.
 The PCL limits the extent of anterior translation
of the femur relative to the fixed lower leg.

Dr. Michael P. Gillespie
52
POSTERIOR CRUCIATE LIGAMENT:
COMMON MECHANISMS OF INJURY
Most PCL injuries are associated with high
energy trauma such as an automobile accident or
contact sports.
 Falling over a fully flexed knee with the ankle
plantar flexed
 “Dashboard” injury – the knee of a passenger in
an automobile strikes the dashboard subsequent
to a front-end collision, driving the tibia posterior
relative to the femur.
 Often after a PCL injury the proximal tibia sags
posterior relative to the femur when the lower leg
is subjected to the pull of gravity.

Dr. Michael P. Gillespie
53
GENERAL FUNCTIONS OF
ANTERIOR & POSTERIOR CRUCIATE
LIGAMENTS
Provide multiple plane stability to the knee, most
notably in the sagittal plane
 Guide the natural arthrokinematics, especially
those related to the restraint of sliding motions
between the tibia and femur
 Contribute to the proprioception of the knee

Dr. Michael P. Gillespie
54
ANTERIOR & POSTERIOR CRUCIATE
LIGAMENTS
Dr. Michael P. Gillespie
55
MUSCLE CONTRACTION AND TENSION
CHANGES IN ANTERIOR CRUCIATE
LIGAMENTS / ANTERIOR DRAWER TEST
Dr. Michael P. Gillespie
56
KNEE FLEXION & POSTERIOR
CRUCIATE LIGAMENTS / POSTERIOR
DRAWER TEST
Dr. Michael P. Gillespie
57
TISSUES THAT PROVIDE PRIMARY &
SECONDARY RESTRAINT IN FRONTAL
PLANE
Varus Force
Primary Restraint
Medial collateral ligament,
especially superficial fibers
Lateral collateral ligament
Secondary Restraint
Posterior-medial capsule
(includes
semimembranosus tendon)
Anterior and posterior
cruciate ligaments
Joint contact laterally
Compression of the lateral
meniscus
Medial retinacular fibers
Pes anserinus (i.e. tendons
of the sartorius, gracilis,
and semitendinosus)
Gastrocnemius (medial
head)
Arcuate complex (includes
lateral collateral ligament,
posterior-lateral capsule,
popliteus tendon, and
arcuate popliteal ligament)
Iliotibial band
Biceps femoris tendon
Joint contact medially
Compression of the medial
meniscus
Anterior and posterior
cruciate ligaments
Gastrocnemius (lateral
head)
Dr. Michael P. Gillespie
Valgus Force
58
FUNCTIONS OF KNEE LIGAMENTS &
COMMON MECHANISMS OF INJURY
Function
Common Mechanism
of Injury
Medial collateral ligament
(and posterior-medial
capsule)
1.
2.
3.
Resists valgus (abduction)
Resists knee extension
Resists extremes of axial
rotation (especially knee
external rotation)
1.
Lateral collateral ligament
1.
2.
3.
Resists varus (adduction)
Resists knee extension
Resists extremes of axial
rotation
1.
1.
2.
Resists knee extension
Oblique popliteal ligament
resists knee external rotation
Posterior-lateral capsule
resists varus
1. Hyperextension or combined
hyperextension with external
rotation of the knee
Posterior capsule
3.
2.
2.
Valgus-producing force with
foot planted
Severe hyperextension of the
knee
Varus-producing force with
foot planted
Severe hyperextension of the
knee
Dr. Michael P. Gillespie
Structure
59
FUNCTIONS OF KNEE LIGAMENTS &
COMMON MECHANISMS OF INJURY
Function
Common Mechanism
of Injury
Anterior cruciate ligament
1.
1.
2.
Most fibers resist extension
(either excessive anterior
translation of the tibia,
posterior translation of the
femur, or a combination
thereof)
Resists extremes of varus,
valgus, and axial rotation
2.
3.
4.
Posterior cruciate ligament
1.
2.
Most fibers resist knee flexion
(either excessive posterior
translation of the tibia or
anterior translation of the
femur, or a combination
thereof)
Resists extremes of varus,
valgus, and axial rotation
Large valgus-producing force
the foot firmly planted
Large axial rotation torque
applied to the knee, with the
foot firmly planted
The above with strong
quadriceps contraction with
the knee in full or near-full
extension
Severe hyperextension of the
knee
1. Falling on a fully flexed knee
(with ankle fully plantar flexed)
such that the proximal tibia
first strikes the ground
2. Any event that causes a forceful
posterior translation of the tibia
(i.e. “dashboard” injury) or
anterior translation of the
femur
3. Large axial rotation or valgusvarus applied torque
4. Severe hyperextension of the
knee causing a large gapping of
posterior aspect of joint
Dr. Michael P. Gillespie
Structure
60
FEMORAL-ON_TIBIAL EXTENSION
WITH ELONGATION OF FIBERS
Dr. Michael P. Gillespie
61
PATELLOFEMORAL JOINT
The patellofemoral joint is the interface between
the articular side of the patella and the
intercondylar (trochlear) groove of the femur.
 The quadriceps muscle, the fit of the joint
surfaces, and passive restraint from retinacular
fibers and capsule all help to stabilize this joint.
 Abnormal kinematics of this joint can lead to
anterior knee pain and degeneration of the joint.
 As the knee flexes and extends, a sliding motion
occurs between the articular surfaces of the
patella and intercondylar groove.

Dr. Michael P. Gillespie
62
PATELLOFEMORAL JOINT
KINEMATICS
The patella typically dislocates laterally.
 There is an overall lateral line of force of the
quadriceps muscle.

Dr. Michael P. Gillespie
63
POINT OF MAXIMAL CONTACT OF
PATELLA ON FEMUR DURING
EXTENSION
Dr. Michael P. Gillespie
64
POINT OF MAXIMAL CONTACT OF
PATELLA ON FEMUR DURING
EXTENSION
Dr. Michael P. Gillespie
65
PATH OF CONTACT OF PATELLA ON
INTERCONDYLAR GROOVE
Dr. Michael P. Gillespie
66
MUSCLE AND JOINT INTERACTION
Dr. Michael P. Gillespie
67
INNERVATION OF THE MUSCLES
The quadriceps femoris is innervated by the
femoral nerve (one nerve for the knee’s sole
extensor group).
 The flexors and rotators are innervated by
several nerves from both the lumbar and sacral
plexus, but primarily the tibial portion of the
sciatic nerve.

Dr. Michael P. Gillespie
68
SENSORY INNERVATION OF THE
KNEE
Sensory innervation of the knee and associated
ligaments is supplied primarily by spinal nerve
roots from L3 to L5.
 The posterior tibial nerve is the largest afferent
supply of the knee.
 The obturator and femoral nerve also supply
some afferent innervation to the knee.

Dr. Michael P. Gillespie
69
MUSCULAR FUNCTION AT THE
KNEE

Muscles of the knee are described as two groups:
Knee extensors (quadriceps femoris)
 Knee flexor-rotators

Dr. Michael P. Gillespie
70
ACTIONS & INNERVATIONS OF
MUSCLES THAT CROSS THE KNEE
Action
Innervation
Plexus
Sartorius
Hip flexion,
external rotation,
and abduction
Knee flexion and
internal rotation
Femoral nerve
Lumbar
Gracilis
Hip flexion and
abduction
Knee flexion and
internal rotation
Obturator nerve
Lumbar
Femoral nerve
Lumbar
Quadriceps
Rectus Femoris
Vastus Group
Dr. Michael P. Gillespie
Muscle
Knee extension
and hip flexion
Knee extension
Popliteus
Knee flexion and
internal rotation
Tibial nerve
Sacral
Semimembranosus
Hip extension
Knee flexion and
internal rotation
Sciatic nerve (tibial
portion)
Sacral
71
ACTIONS & INNERVATIONS OF
MUSCLES THAT CROSS THE KNEE
Action
Innervation
Plexus
Semitendanosus
Hip extension
Knee flexion and
internal rotation
Sciatic nerve (tibial
portion)
Sacral
Biceps femoris
(short head)
Knee flexion and
external rotation
Sciatic nerve
(common fibular
portion)
Sacral
Biceps femoris (long
head)
Hip extension
Knee flexion and
external rotation
Sciatic nerve (tibial
portion)
Sacral
Gastrocnemius
Knee flexion
Ankle plantar
flexion
Tibial nerve
Sacral
Plantaris
Knee flexion
Ankle plantar
flexion
Tibial nerve
Sacral
Dr. Michael P. Gillespie
Muscle
72
EXTENSORS OF THE KNEE

Quadriceps femoris
Dr. Michael P. Gillespie
73
QUADRICEPS FEMORIS: ANATOMIC
CONSIDERATIONS

Quadriceps femoris
Rectus femoris
 Vastus lateralis
 Vastus medialis
 Vastus intermedius



Contraction of the vastus group produces about 80%
of the extension torque at the knee. They only extend
the knee.
Contraction of the rectus femoris produces about 20%
of the extension torque at the knee. The rectus
femoris muscle extends the knee and flexes the hip.
The inferior fibers of the vastus medialis exert an
oblique pull on the patella that help to stabilize it as
it tracks through the intercondylar groove.
Dr. Michael P. Gillespie

74
QUADRICEPS CROSS-SECTION
Dr. Michael P. Gillespie
75
QUADRICEPS FEMORIS:
FUNCTIONAL CONSIDERATIONS
The knee extensor muscles produce a torque that
is about two thirds greater than that produced by
the knee flexor muscles.
 Isometric activation – stabilizes and protects the
knee
 Eccentric activation – controls the rate of descent
of the body’s center of mass during sitting and
squatting. Provides shock absorption at the
knee.
 Concentric activation – accelerates the tibia or
femur toward knee extension. Used in raising
the body’s center of mass during uphill running,
jumping, or standing from a seated position.

Dr. Michael P. Gillespie
76
EXTERNAL TORQUE DEMANDS
AGAINST QUADRICEPS
During tibial-on-femoral knee extension, the
external moment arm of the weight of the lower
leg increases from 90 to 0 degrees of knee flexion.
 During femoral-on-tibial knee extension (as in
rising from a squat position), the external
moment arm of the upper body weight decreases
from 90 to o degrees of knee flexion.

Dr. Michael P. Gillespie
77
EXTERNAL (FLEXION) TORQUES
Dr. Michael P. Gillespie
78
QUADRICEPS WEAKNESS:
PATHOMECHANICS OF “EXTENSOR
LAG”
People with significant weakness of the
quadriceps often have difficulty completing the
full range of tibial-on-femoral extension of the
knee.
 They fail to produce the last 15 to 20 degrees of
extension.
 This is referred to as “extensor lag”.
 Swelling or effusion of the knee increases the
likelihood of an extensor lag.
 Swelling increases intra-articular pressure.
 Passive resistance from hamstring muscles can
also limit full knee extension.

Dr. Michael P. Gillespie
79
FUNCTIONAL ROLE OF THE
PATELLA
The patella acts as a “spacer” between the femur
and the quadriceps muscle, which increases the
internal moment arm of the knee extensor
mechanism.
 Torque is the product of force and its moment
arm.
 The patella augments the extension torque at the
knee.

Dr. Michael P. Gillespie
80
USE OF PATELLA TO INCREASE THE
INTERNAL MOMENT ARM
Dr. Michael P. Gillespie
81
PATELLOFEMORAL JOINT KINETICS

The patellofemoral joint is exposed to high
magnitudes of compression force.
The knee flexion angle influences the amount of
force experienced at the joint.
 Both the compression force and the area of
articular contact on the patellofemoral joint
increase with knee flexion, reaching a maximum
between 60 and 90 degrees.
Dr. Michael P. Gillespie
1.3 times body weight during walking on level
surfaces
 2.6 times body weight during performance of a
straight leg raise
 3.3 times body weight during climbing of stairs
 7.8 times body weight during deep knee bends


82
TWO INTERRELATED FACTORS
ASSOCIATED WITH JOINT
COMPRESSION FORCE ON THE
PATELLOFEMORAL JOINT
1. Force within the quadriceps muscle
 2. Knee flexion angle

Dr. Michael P. Gillespie
83
COMPRESSION FORCE WITHIN THE
PATELLOFEMORAL JOINT
Dr. Michael P. Gillespie
84
FACTORS AFFECTING THE TRACKING
OF THE PATELLA ACROSS THE
PATELLOFEMORAL JOINT
If the patellofemoral joint has less than optimal
congruity, it can lead to abnormal “tracking” of
the patella.
 The patellofemoral joint is then subjected to
higher joint contact stress, increasing the risk of
degenerative lesions and pain.
 This can lead to patellofemoral pain syndrome
and osteoarthritis.
 Excessive tension in the iliotibial band or lateral
patellar retinacular fibers can add to the natural
lateral pull of the patella.

Dr. Michael P. Gillespie
85
ROLE OF QUADRICEPS MUSCLE IN
PATELLAR TRACKING
As the knee is extending, the quadriceps muscle
pulls the patella superior, slightly lateral, and
slightly posterior in the intercondylar groove.
 Vastus lateralis has a larger cross sectional area
and force potential.
 The quadriceps angle (Q-angle) is a measure of
the lateral pull of the quadriceps.
 Q-angles average about 13 to 15 degrees.

Dr. Michael P. Gillespie
86
QUADRICEPS PULL & Q-ANGLE
Dr. Michael P. Gillespie
87
LOCAL FACTORS THAT NATURALLY
OPPOSE THE LATERAL PULL OF THE
QUADRICEPS ON THE PATELLA

Local factors
The lateral facet of the intercondylar groove is
normally steeper than the medial facet which blocks
or resists the approaching patella.
 The oblique fibers of the vastus medialis balance the
lateral pull.
 Medial patellar retinacular fibers are oriented in
medial-distal and medial directions (referred to as
the medial patellofemoral ligament). Often ruptured
after a complete lateral dislocation of the patella.

Dr. Michael P. Gillespie
88
LOCALLY PRODUCED FORCES
ACTING ON THE PATELLA
Dr. Michael P. Gillespie
89
GLOBAL FACTORS



Dr. Michael P. Gillespie

Factors that resist excessive valgus or the extremes of
axial rotation of the tibiofemoral joint favor optimal
tracking of the patellofemoral joint.
Excessive genu valgum can increase the Q-angle and
thereby increase the lateral bowstring force on the
patella. Increased valgus can occur from laxity or
injury to the MCL.
Weakness of the hip abductors (coxa vara) can allow
the hip the slant excessively medial, which in turn
places excessive stress on the medial structures of the
knee.
Excessive internal rotation of the knee, which is
related to excessive pronation of the subtalar joint
during walking.
90
BOWSTRING FORCE ON THE
PATELLA
Dr. Michael P. Gillespie
91
PATELLOFEMORAL PAIN
SYNDROME





Dr. Michael P. Gillespie

Patellofemoral pain syndrome (PFPS) is one of the
most common orthopedic conditions encountered in
sports medicine outpatient settings.
It accounts for about 30% of all knee disorders in
women and 20% in men.
Diffuse peripatellar or retropatellar pain with an
insidious onset.
Aggravated by squatting, climbing stairs, or sitting
with knees flexed for a prolonged period of time.
Pain or fear of repeated dislocations may be severe
enough to significantly limit activities.
Abnormal movement (tracking) and alignment of the
patella within the intercondylar groove.
92
CAUSES OF EXCESSIVE LATERAL
TRACKING OF THE PATELLA
Specific Examples
Bony Dysplasia
Dysplastic lateral facet of the intercondylar
groove of the femur (“shallow” groove)
Dysplastic or “high” patella (patella alta)
Excessive laxity in periarticular
connective tissue
Laxity of medial patellofemoral ligament
Laxity or attrition of medial collateral ligament
Laxity or reduced height of the medial
longitudinal arch of the foot (overpronation of the
subtalar joint)
Excessive stiffness or tightness
in periarticular connective tissue
and muscle
Increased tightness in the lateral patellar
retinacular fibers or iliotibial band
Increased tightness of the internal rotator or
adductor muscles of the hip
Dr. Michael P. Gillespie
Structural of Functional Cause
93
CAUSES OF EXCESSIVE LATERAL
TRACKING OF THE PATELLA
Specific Examples
Extremes of bony or joint
alignment
Coxa varus
Excessive anteversion of the femur
External tibial torsion
Large Q-angle
Excessive genu vlagum
Muscle weakness
Weakness or poor control of
•Hip external rotator and abductor muscles
•The vastus medialis (oblique fibers)
•The tibialis posterior muscle (related to
overpronation of the foot)
Dr. Michael P. Gillespie
Structural of Functional Cause
94
TREATMENT PRINCIPLES FOR
ABNORMAL TRACKING AND CHRONIC
DISLOCATION OF THE
PATELLOFEMORAL JOINT







Dr. Michael P. Gillespie

Reduce the magnitude of the lateral bowstring force
on the patella.
Strengthen hip abductor and external rotator
muscles.
Strengthen the oblique fibers of the vastus medialis.
Strengthen the medial longitudinal arch of the foot.
Stretch tight periarticular connective tissues of the
hip and knee.
Mobilize the patella.
Use a patellar brace or using a foot orthosis to reduce
excessive pronation of the foot.
Patellar taping to guide the patella’s tracking.
95
KNEE FLEXOR-ROTATOR MUSCLES

Hamstrings
 Sartorius
 Gracilis
 Popliteus


Dr. Michael P. Gillespie

With the exception of the gastrocnemius, all muscles
that cross posterior to the knee have the ability to flex
and to internally or externally rotate the knee.
Flexor-rotator group
The flexor-rotator group has three sources of
innervation
Femoral
 Obturator
 Sciatic

96
KNEE FLEXOR-ROTATOR MUSCLES:
FUNCTIONAL ANATOMY
The hamstring muscles have their proximal
attachment on the ischial tuberosity.
 The hamstrings extend the hip and flex the knee.
 In addition to flexing the knee, the medial
hamstrings (semimembranosus and
semitendanosus) internally rotate the knee.
 The biceps femoris flexes and externally rotates
the knee.
 The sartorius, gracilis, and semitendinosus
attach to the tibia using a common, broad sheet
of connective tissue known as the pes anserinus.
The “pes muscles” are internal rotators of the
knee.

Dr. Michael P. Gillespie
97
KNEE FLEXOR-ROTATOR MUSCLES:
GROUP ACTION
Dr. Michael P. Gillespie
98
KNEE AS A PIVOT POINT – AXIAL
ROTATION
Dr. Michael P. Gillespie
99
POPLITEUS MUSCLE “KEY TO THE
KNEE”
The popliteus muscle is an important internal
rotator and flexor of the knee joint.
 As the extended and locked knee prepares to flex,
the popliteus provides an important internal
rotation torque that helps to mechanically unlock
the knee.
 The popliteus has an oblique line of pull.
 This muscle has the most favorable leverage of
all of the knee flexor muscles to produce a
horizontal plane rotation torque on an extended
knee.

Dr. Michael P. Gillespie
100
CONTROL OF TIBIAL-ON-FEMORAL
OSTEOKINEMATICS
An important action of the flexor-rotator muscles
is to accelerate or decelerate the lower leg during
the swing phase of walking or running.
 Through eccentric action, the muscles help to
dampen the impact of full knee extension.
 They shorten the functional length of the lower
limb during the swing phase.

Dr. Michael P. Gillespie
101
CONTROL OF FEMORAL-ON-TIBIAL
OSTEOKINEMATICS
The muscular demand needed to control femoralon-tibial motions is generally larger and more
complex than that needed for most tibial-onfemoral knee motions.
 The sartorius may have to simultaneously control
up to five degrees of freedom (i.e. two at the knee
and three at the hip).

Dr. Michael P. Gillespie
102
ABNORMAL ALIGNMENT OF THE
KNEE: FRONTAL PLANE
In the frontal plane the knee is normally aligned
in about 5 to 10 degrees of valgus.
 Deviation from this alignment is referred to as
excessive genu valgum or genu varum.

Dr. Michael P. Gillespie
103
GENU VARUM WITH
UNICOMPARTMENTAL
OSTEOARTHRITIS OF THE KNEE
During walking across level terrain, the joint
reaction force at the knee is about 2.5 to 3 times
body weight.
 The ground reaction force passes just lateral to
the heel, then upward to the medial knee.
 In some individuals this asymmetric dynamic
loading can lead to excessive wear of the articular
cartilage and ultimately to medial
unicompartmental osteoarthritis.
 Thinning of the articular cartilage and meniscus
on the medial side can lead to genu varum, or a
bow-legged deformity, which will further increase
medial compartment loading.

Dr. Michael P. Gillespie
104
GENU VARUM (BOW-LEG)
Dr. Michael P. Gillespie
105
GENU VARUM (BOW-LEG) / HIGH
TIBIAL OSTEOTOMY
Dr. Michael P. Gillespie
106
EXCESSIVE GENU VALGUM
Several factors can lead to excessive genu valgum
or knock-knee.
 Previous injury, genetic predisposition, high body
mass index, and laxity of ligaments.
 Coxa vara or weak hip abductors can lead to genu
valgum.
 Excessive foot pronation
 Standing with a valgus deformity of
approximately 10 degrees greater than normal
directs most of the joint compression force to the
lateral joint compartment.
 This increased regional stress may lead to lateral
unicompartmental osteoarthritis.

Dr. Michael P. Gillespie
107
GENU VALGUM
Dr. Michael P. Gillespie
108
“WIND-SWEPT” DEFORMITY / GENU
VALGUM & GENU VARUM
Dr. Michael P. Gillespie
109
“WIND-SWEPT” DEFORMITY BEFORE
& AFTER KNEE REPLACEMENT
Dr. Michael P. Gillespie
110
SAGITTAL PLANE: GENU
RECURVATUM
Full extension with slight external rotation is the
knee’s close-packed, most stable position.
 The knee may be extended beyond neutral an
additional 5 to 10 degrees.
 Hyperextension beyond 10 degrees of neutral is
called genu recurvatum (Latin genu, knee, +
recurvare, to bend backward).
 Chronic, overpowering (net) knee extensor torque
eventually overstretches the posterior structures
of the knee.
 Due to poor postural control or neuromuscular
disease (i.e. polio). That causes spasticity and / or
paralysis of the knee flexors.

Dr. Michael P. Gillespie
111
GENU RECURVATUM
Dr. Michael P. Gillespie
112