Knee Anatomy
Reza Omid, M.D.
Assistant Professor Orthopaedic Surgery
Shoulder & Elbow Reconstruction
Sports Medicine
Keck School of Medicine of USC
Bony Anatomy
Tibiofemoral joint
Patellofemoral joint
Femoral Condyles
– A–
Lateral Condyle
» Smaller radius of curvature
» Smaller in all dimensions
» Extends more anteriorly
– B – Medial Condyle
» Larger radius of curvature
» Extends more distally
– C – Intercondylar notch
Tibial Plateau
– D – Medial Plateau
» Greater surface area
» Concave
» Circular shape
– E – Intercondylar Eminence
– F – Lateral Plateau
» Smaller surface area
» Convex
» Oval shape
Patella
– Sesamoid bone in quadriceps
– Dividing central ridge
– Comprised of seven facets
» Medial and Lateral facets
divided into 3rds
» 7th facet is most medial (odd
facet)
– Medial half usually smaller
– Thick hyaline cartilage (5.5mm)
Femoral Sulcus
– Lateral wider and higher
– Both with sagittal convexity
Screw Home Mechanism
• Knee achieves terminal extension via the “screw
home mechanism
• The tibia externally rotates in relation to the
femur.
• When the knee needs to flex, the popliteus
contracts which causes internal rotation of the
tibia and in essence unlocking the knee and
allowing it to bend
Bony Alignment
Popliteal Artery
 Originates at the adductor hiatus and passes through the
popliteal fossa, then deep to the fibrous arch over the soleus
muscle
 Divides into the anterior and posterior tibial arteries at the
distal aspect of the popliteus muscle
Popliteal Artery
• The popliteal artery is 9mm
posterior to the posterior cortex
of the tibia at 90° of flexion and
even closer in extension.
• Place retractors biased to the
medial side when possible.
Skin Blood Flow
• If two longitudinal incisions are present, the
more lateral incision should be used (if
allows adequate exposure) because most of
blood supply comes in medially.
• The lateral skin edge is more hypoxic than
the medial skin edge so keep this in mind
when placing sutures.
Tibial Nerve
• Initially lateral to the
popliteal artery
• Crosses at midpoint to end
medial to the artery at soleus
arch
Common Peroneal Nerve
• Lateral aspect of the popliteal
space
• Medial and posterior to the
biceps femoris tendon
Infrapatellar Branch of
Saphenous
Patellofemoral Biomechanics
Joint Reactive Force
– In flexion, patella compressed
onto femur creating joint
reactive force
– Stair climbing – 3.5 X BW
– Deep bends – 7-8 X BW
Menisci
•
•
Primarily type I collagen with fibers arranged
obliquely, radially, and vertically
Outer 10% to 30% has blood supplied from the
perimeniscal capillary plexus off the superior and
inferior medial and lateral genicular arteries
Meniscus Function
Load Transmission
– 50% load transmitted in extension
– 85% load transmitted at 90 degrees flexion
– Resection of 15-34% increases pressure 350%
Secondary Stabilization
– Medial meniscus provides anterior restraint
» Especially in ACL deficient knee
Lateral Meniscus
•
•
•
•
•
Loose peripheral attachment allows
greater translation during motion
– Average excursions of the menisci with
knee flexion
» 5.2 mm for the medial
» 11 mm for the lateral
Bare area anterior to popliteus tendon
Two highly variable meniscofemoral
ligaments attach it to medial femoral
condyle:
Anterior – Humphrey
Posterior – Wrisberg’s
Ligaments
Tensile strengths of various knee
ligaments:
• MCL ~ 4400-5000N
• PCL ~2500-3000N
• ACL ~ 2200-2500N
• LCL ~750N
Anterior Cruciate Ligament
– 26-38 (33) mm in length
» ACL graft selection you aim for at least 100110mm graft length because it needs about
~33mm for the tibial tunnel, ~33mm for the
femoral tunnel and ~33 for the graft itself
– 11 mm in width
– Primary restraint
» Anterior translation of tibia (74-85%)
» Normal 3-5mm of translation
– Secondary restraint
» Internal rotation
» Varus/Valgus
» Hyperextension
Anterior Cruciate Ligament
Two bands
– Anteromedial band taut
in flexion
– Posterolateral band taut
in extension
Anterior Cruciate Ligament
Femoral Attachment
–
–
–
–
Posterior portion of medial surface of LFC
Oriented in line of axis of femur in extension
Footprint in shape of circular segment
Posterior convexity 4 mm anterior to articular
surface
– Surface area measures 16-24 x 11 mm
– Lateral to midline on AP view
– Posterosuperior on lateral view
Anterior Cruciate Ligament
Tibial Attachment
–
–
–
–
–
–
–
Anterolateral to medial spine
Insertion has oval shape
Sections attach to bone, AHLM, PHLM
15 mm posterior to anterior tibia
17-30 x 11 mm surface area
Just lateral to midline on AP
40% back on lateral view
Lateral Bifurcate Ridge
– Running perpendicular to the lateral
intercondylar ridge) seperates the origins
of the anteromedial and posterolaterla
bundles.
Lateral Intercondylear Ridge
• Resident’s ridge on the lateral
femoral condylar wall denotes
the lateral intercondylear ridge
and marks the most anterior
and superior extent of the
femoral origins of the ACL.
Anterior Cruciate Ligament
Blood Supply
– ACL completely ensheathed in fold of synovial membrane
– Although intraarticular, technically extrasynovial
– Main supply is middle geniculate with smaller contribution from both inferior
geniculates
Innervation
– Branches of tibial nerve
– Very few pain receptors in substance of ACL
Posterior Cruciate Ligament
– 38 mm in length
– 13 mm in width
– Narrowest diameter at
midsubstance
– Anterolateral band
» More robust, Taut in
flexion
– Posteromedial band
» Thinner, Taut in extension
Posterior Cruciate Ligament
Femoral Attachment
– Lateral surface MFC
– Shape of circular segment
– Distal margin 3 mm proximal to articular surface
Posterior Cruciate Ligament
Tibial Attachment
– Depression between tibial plateaus
– 1 cm distal to tibial articular surface
– Can have contributions to PHLM as well as meniscofemoral
ligaments
– Average width 13 mm
PCL Biomechanics
Function
– Primary restraint
» Posterior translation of tibia (90-95%)
» Greatest translation occurs at 75 degrees flexion
– Secondary restraint
» Varus/valgus
» External rotation
Medial Structures
Layer 1: Deep fascia and Sartorius
Layer 2: Superficial MCL, MPFL
Layer 3: Joint capsule, Deep MCL
Pes Anserinus
Medial Ligaments
• Superficial MCL (Medial Collateral Ligament)
• Originates on medial epicondyle
– avg: 3.2 mm proximal and 4.8 mm posterior to medial
epicondyle
• Tibial insertions (2) distal and proximal
– Proximal: anterior arm of the semimembranosus tendon
– Distal: broad-based, just anterior to the posteromedial crest
of the tibia, most located within the pesanserine bursa
• Posterior Oblique Ligament (POL)
• superficial, central (main component), and capsular arms
• Deep MCL
– Divided into meniscofemoral and meniscotibial ligaments
MCL
MCL Biomechanics
Stability – Most important
in flexion when posterior
structures relaxed
– Valgus rotation
– External rotation
– Medial/Lateral translation
Superficial MCL most
important for stability
(57-78%)
Sectioning Deep MCL
does not result in
instability if Superficial
MCL intact
Medial Patellofemoral Ligament
Runs transversely in Layer 2
Originates from adductor tubercle, femoral
epicondyle, and superficial MCL
Proximal fiber inserts on undersurface of
VMO and vastus intermedius
Distal fibers insert on superomedial patella
Width averages 1.3 cm
MPFL
MPFL Biomechanics
Soft tissue restraint of extensor
mechanism
Patella subluxes most easily at
20° knee flexion
MPFL resists patellar lateral
subluxation greatest in
extension
Primary stabilizer followed by
patellomeniscal, patellotibial,
and medial retinaculum
Lateral Structures
Layer 1
– IT band
– biceps tendon
–
–
–
–
–
–
–
Layer 2
Lateral retinaculum
patellofemoral ligaments
Layer 3
Joint capsule
LCL
arcuate ligament
fabellofibular ligament
popliteofibular ligament
Lateral Structures
 Layer 1
 IT band
 biceps tendon
 Layer 2
 Lateral retinaculum
 patellofemoral ligaments
 Layer 3
 Joint capsule
 LCL
 arcuate ligament
 fabellofibular ligament
 popliteofibular ligament
Iliotibial Band
Coalescence at greater trochanter of
tensor fascia lata, gluteus medius and
gluteus maximus
IT band continues distally to form the:
– IT tract
» Inserts distally on Gerdy’s tubercle and on
distal femur through intermuscular septum
– Iliopatellar band
» Inserts on lateral patella resisting medial
directed forces
IT Band Biomechanics
Functions
–
–
–
–
Stabilizes against varus opening
Knee extensor in extension
Knee flexor in flexion
External rotator of tibia in >40 flexion
Lateral
Collateral
Ligament
Arises in fovea slightly proximal (1.4 mm) and posterior
(3.1 mm) to lateral epicondyle
Attaches to V-shaped plateau of fibular head (8.2mm
distal to anterior edge)
Surrounded by biceps femoris tendon distally
Average length 59-71 mm
AP diameter 3.4 mm ML diameter 2.3 mm
LCL Origin
•
•
Posterior (4.6 mm) and proximal (1.3
mm) to the lateral femoral epicondyle
Posterior and superior to the insertion of
the poplitieus (18mm away from each
other)
LCL Biomechanics
Tightest in extension, 0-30 degrees
Becomes looser in flexion >30 degrees
Primary restraint to varus
Secondary restraint to ER and posterior translation
Posterolateral Corner
• FCL
• Popliteus tendon
• Popliteofibular lig
Posterolateral Corner
Static Stabilizers
(highly variable)
–
–
–
–
–
–
–
–
LCL
Fabellofibular ligament
Short lateral ligament
Popliteofibular ligament
Arcuate ligament
Posterolateral capsule
Posterior horn lateral meniscus
Lateral coronary ligament
Posterolateral Corner
Dynamic Stabilizers
– IT band
– Lateral gastrocnemius
– Biceps femoris
– Popliteus
Popliteus Complex
Dynamic
– Popliteus muscle
Static
– Popliteofibular ligament
– Popliteotibial fascicle
– Popliteomeniscal fascicle
Popliteus Muscle
•
•
Originates from
posteromedial
surface of proximal
tibia
Tendon passes in
hiatus of coronary
ligament, crosses
under LCL, inserts
on lateral femoral
condyle 3-5 mm
proximal to articular
surface
Popliteofibular ligament
Average length 42 mm
Descends from popliteus muscle (at
musculotendinous junction) to
posterosuperior fibular head
Composed of anterior and posterior
fascicle
Functions as pulley to the popliteus
Arcuate Ligament
Fibers oriented in various
directions
Y-shaped configuration over
popliteus
Medial limb terminates into
oblique popliteal ligament
Lateral limb invariable present,
and is less distinct
Fabellofibular vs
Short Lateral Ligament
Fabellofibular ligament
– Present when fabella present (8-16%)
– Courses from fabella to fibular head
Short lateral ligament
– Present when fabella absent
– Courses from lateral femur to fibular head
– Represents a homologue of the fabellofibular ligament