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2. MOB TCD
Anatomy of Anterior Cruciate Ligament
Professor Emeritus Moira O’Brien
FRCPI, FFSEM, FFSEM (UK), FTCD
Trinity College
Dublin

3. MOB TCD
Anatomy of Knee Joint
• The knee joint is the largest joint in
the body
• One of the most frequently injured
• Synovial condylar joint
• Knee has six degrees of freedom,
three translations and three rotations
• Flexion and extension occur
between femur and menisci
• Rolling occurs above the meniscus,
• Rotation between menisci and tibia
• Gliding below the meniscus

4. MOB TCD
Knee Joint
• The mechanism of the injury is an
important factor in determining
which structure is damaged
• Injury to the anterior cruciate
ligament occurs in both contact
and non contact sports
• Females are more at risk
particularly gymnastics, skiing,
soccer volleyball and basketball
• A rapid effusion into a joint after
an injury is a haemarthrosis and,
in 75% of cases, is due to rupture
of the anterior cruciate ligament

5. MOB TCD
Close-Packed
•
•
•
•
•
Stable position
Surfaces fit together
Ligaments taut
Spiral twist
Screw home articular surface

6. MOB TCD
Least-Packed
• Joint more likely to be injured
least-packed
• Capsule slackest
• Joint held in this
• Position when injured
• Knee in 20°flexion

7. MOB TCD
Articular Surfaces
• The femoral articular
surfaces are the medial
ACL
and lateral femoral
condyles
• The medial condyle has
a longer articular surface
• The superior aspect of
the medial and lateral
tibial condyles
• The posterior aspect of
the patella

8. MOB TCD
Articular Surfaces
• Two condyles are separated behind
by the intercondylar notch
• Joined in front by the trochlear
surface for the patella
• Femoral condyles are eccentrically
curved
• Medial is of more constant width. It
is narrow, longer and more curved
• Lateral condyle is broad and straight and diverges
slightly distally and posteriorly, wider in front than at
the back
Last, 1984
medial

9. MOB TCD
Femoral Condyles
• The radius of the condyles' curvature is
in the saggital plane,
• Becomes smaller toward the back
• This diminishing radius produces a
series of involute midpoints (i.e. located
on a spiral)
• The resulting series of transverse axes,
permit the sliding and rolling motion in the flexing knee
• While ensuring the collateral ligaments are sufficiently lax
to permit the rotation associated with the curvature of the
medial condyle about a vertical axis
Platzer, 2004

10. MOB TCD
Intercondylar Notch
• Intercondylar notch is a
continuation of the trochlea
• Varies in shape and size
• Female knee, intercondylar
notch and ACL tend to be smaller
• The mean notch width was
13.9 +/- 2.2 mm for women and
15.9 +/- 2.5 mm for men,
average is 17 mm
• Narrow notch more likely to tear
the anterior cruciate ligament
Domzalski et al., 2010; Shelbourne et al.,1998; Griffin et al.,
2006

11. MOB TCD
Tibial Superior Articular Surface
• The medial facet, oval in shape,
is slightly concave from side to
side, and from before backward
• The lateral, nearly circular, is
concave from side to side
• But slightly convex from before
backward, especially at its
posterior part
• Where it is prolonged on to the
posterior surface for a short
distance
medial

12. MOB TCD
Tibial Superior Articular Surface
• The central portions of these
facets articulate with the
condyles of the femur
• Their peripheral portions
support the menisci of the
knee-joint
• The intercondylar eminence is
between the articular facets
• Nearer the posterior than the
anterior aspect of the bone

13. MOB TCD
Tibial Superior Articular Surface
PCL
• In front and behind the
intercondylar eminence are
rough depressions for the
attachment of the anterior
and posterior cruciate
ligaments and the menisci
• The shape of the cruciate
attachments vary
lateral
meniscus
ACL
anterior

14. MOB TCD
Patella
• Sesamoid bone
• Thickest articular cartilage
in body
• Smaller medial facet
• Q angle
• Controlled by vastus medialis obliquus
(VMO) and vastus lateralis obliquus
(VLO)

15. MOB TCD
Patella
• The vastus medialis wastes within
24 hours after an effusion of the
knee
• If the oblique fibers of the vastus
medialis are wasted
• The patella tends to sublux laterally
when the knee is extended
• This results in retro patellar pain

16. MOB TCD
Capsular Ligaments
•
•
•
•
•
•
Quadriceps
Retinacular fibres
Patellar tendon
Coronary ligaments
Medial and lateral ligaments
Posterior oblique ligament

17. MOB TCD
Infrapatellar Fat Pad (IFP)
•
•
•
•
Posteriorly
Covered by synovial membrane
Forms alar folds
Blood supply of fat is by the inferior
genicular arteries
• Also supply the lower part of the ACL from
network of synovial membrane of fat pad
• Centre of fat pad has a limited blood
supply
• Lateral arthroscopic approach to avoid
injury
Williams & Warick, 1980; Eriksson et al., 1980; Kohn et al., 1995

18. MOB TCD
Infrapatellar Fat Pad (IFP)
• ACL repair with patellar tendon may
result in fibrosis of fat pad and pain
• Delays rehabilitation
• Inflammation of IFP may be process
leading to fibrosis
Murakami et al., 1995

19. MOB TCD
Anterior and Posterior Cruciates
oblique popliteal
ligaments
• Anatomically named by their
tibial attachments
• Clinically, femoral attachments
are called the origin
lateral
• Cruciates are intracapsular
but extrasynovial
• Cross in the sagittal plane
• Covered by synovial membrane on
anterior and on both sides which is
reflected from capsule, i.e. oblique
popliteal ligament
• Bursa between them on lateral aspect
ACL
anterior

20. MOB TCD
Anterior Cruciate Ligaments
ACL
ACL
anterior

21. MOB TCD
Cruciate Ligaments
• ACL average length 31-38 mm
• ± 10 mm width and ± 5 mm thick
Odenstein, 1985; Girgis, 1975
•
•
•
•
PCL average length 28-38 mm
PCL is 13 mm wide
Cruciates have a constant length ratio
ACL : PCl of 5:3
Girgis et al., 1975

22. MOB TCD
Anterior Cruciate Ligaments
• Three dimensional fan shaped
• Multiple non-parallel interlacing
collagenous fascicles
• Made up of multiple collagen fascicles;
surrounded by an
endotendineum
• Microspically: interlacing fibrils
(150 to 250 nm in diameter)
• Grouped into fibers (1 to 20 µm in
diameter) synovial membrane envelope
Jackson et al., 1993

23. MOB TCD
Anterior Cruciate Ligaments
• Anterior cruciate is attached
to anterior aspect of the
superior surface of the tibia
• Behind the anterior horn of
medial meniscus and in front
of the anterior horn of the
lateral meniscus
lateral
• Passes upwards and laterally
to the posterior aspect of
medial surface of lateral
femoral condyle
ACL

24. MOB TCD
Tibial Attachment
• Tibial attachment is in a fossa in front
•
•
•
•
of and lateral to anterior spine
Medial
Attachment is a wide area from 11
mm in width to 17 mm in AP direction
Some anterior fibers go forward to
level of transverse meniscal
ligament; into the interspinous area
of the tibia; forming a foot-like
PCL
attachment
Larger tibial than femoral attachment
Shape of the attachment to tibia
varies
Amis,1991
Posterior
meniscofemoral
ACL

25. MOB TCD
Femoral Attachment
• ACL attached to a fossa on the
posteromedial corner of medial
aspect of lateral femoral condyle in
the intercondylar notch
• Femoral attachment of ACL is well
posterior to longitudinal axis of the
femoral shaft.
• Femoral attachment is in the form
of a segmented circle
• Anterior border is straight, posterior
border convex
Arnoczky et al 1983

26. MOB TCD
Femoral Attachment
• Attachment is actually an
interdigitation of collagen fibers
and rigid bone, through a
transitional zone of
fibrocartilage and mineralized
fibrocartilage
• Attachment lies on a line which
forms a 40°angle with the long
axis of the femur
Muller, 1982; Frazer, 1975

27. MOB TCD
ACL Bundles
• The ACL consists of a smaller
anteromedial and a larger
posterolateral bundle, which twists
on itself from full flexion to
extension
• The posterolateral bundle is larger
and longest in extension and
resists hyperextension
• The taut ACL is the axis for medial
rotation of the femur, during the
locking mechanism of the knee in
extension
Hunziker et al.,1992
ACL

28. MOB TCD
Anteromedial Bundle of ACL
• Anteromedial bundle attached to
the medial aspect of the
intercondylar eminence of the
tibia
• Anteromedial fibres have the
most proximal femoral
attachment
• Anteromedial bundle is longest
and tight in flexion
• Femoral insertion of the
anteromedial bundle is the
centre of rotation of ACL
Arnoczky et al 1993
antero medial
bundle

29. MOB TCD
Anteromedial Bundle
• Anteromedial bundle has an isometric
•
•
•
•
•
behaviour
Tightens in flexion, while the postero
lateral bundle relaxes in flexion
Is more prone to injury with the knee in
flexion
Anteromedial band is primary check
against anterior translation of tibia on femur
When anterior drawer test is performed in usual manner
with knee flexed
Contributes to anteromedial stability
O’Brien, 1992

30. MOB TCD
Posterolateral Bundle
posterolateral
• Posterolateral is attached just lateral to
•
•
•
•
•
midline of the intercondylar eminence
Fibres are most inferior on femur, most
posterior on tibia
The bulkier posterolateral bundle is not
isometric
ACL bundles are vertical and parallel in
extension
Posterolateral bundle is tight in extension
Both bundles of ACL are horizontal at 90°flexion
Arnoczky, 1983
anteromedial

31. MOB TCD
Posterolateral Bundle
• Oblique position of the
posterolateral bundle
provides more rotational
control than is provided by
the anteromedial bundle,
which is in a more axial
position
• Hyperextension and internal
rotation place the
posterolateral bundle at
greater risk for injury

32. MOB TCD
Posterolateral Bundle
• It limits anterior translation,
hyperextension, and rotation
during flexion
• Femoral insertion site of the
postero lateral bundle moves
anteriorly
• Both bundles are crossed
• Posterolateral bundle loosens
in flexion

33. MOB TCD
Anterior Cruciate Ligaments
• Tibial attachment is in anteroposterior axis of tibia
• Femoral attachment is in
longitudinal axis of femur
• Forms 40°with its long axis
• 90°twist of fibres from
• Extension to flexion

34. MOB TCD
ACL in Extension and 45°
O’Brien, 1992

35. Anterior Cruciate Ligaments
• The anterior cruciates limit extension
and prevent hyperextension
• The anterior cruciate ligament is most
at risk during forced external rotation
of the femur on a fixed tibia with the
knee in full extension
Stanish et al., 1996
• During isometric quadriceps
contraction
• ACL strain at 30°of knee flexion is significantly higher
than at 90°
• Tension in ACL is least at 40°to 50°of knee flexion
Hunziker et al., 1992; Covey, 2001

36. MOB TCD
Anterior and Posterior Cruciate
• ACL
• Provides 86% of restraint to
anterior displacement
• PCL
• Provides 94% of restraint to
posterior displacement
• Hyperextension of the knee
develops much higher forces in
ACL than in the PCL

37. MOB TCD
Posterior Cruciate
• PCL is the strongest ligament of
knee
• It tends to be shorter
• More vertical
• Less oblique
• Twice as strong as ACL
• Closely applied to the centre of
rotation of knee
• It is the principle stabiliser
Hunziker et al., 1992

38. MOB TCD
Attachment of the PCL
• The tibial attachment of the
PCL was on the sloping
posterior portion of the tibial
intercondylar area
• Extended 11.5-17.3 mm
distal to the tibial plateau
• Anterior to tibial articular
margin
• Blends with periosteum and
capsule
Javadpour & O’ Brien, 1992

39. MOB TCD
Posterior Cruciate
• Anatomically the fibres pass
anteriorly, medially and
proximally
• It is attached on the anteroinferior part of the lateral
surface of the medial femoral
condyle
• The area for the PCL is larger
than the ACL
• It expands, more on the apex
of the intercondylar notch than
on the inner wall
Frazer 1965; Hunziker et al.,1992

40. MOB TCD
Cruciates Microscopic
• Collagen fibrils 150-200 µm in
diameter
• Fibres 1-20 µm in diameter
• A subfascicular unit from100-250
µm
• 3 to 20 subfascicular units form
collagen fasciculus, 250 µm to
several millimetres
Hunziker et al.,1992

41. Blood Supply of
Anterior Cruciate Ligaments
• Middle genicular enters upper third
and is the major blood supply via
synovium
• Inferior medial genicular and
Inferior lateral genicular arteries
supply via infrapatellar fat pad
• Bony attachments do not provide a
significant source of blood to distal
or proximal ligaments
Arnoczky 1987
MOB TCD

42. MOB TCD
Blood Supply of Cruciates

43. Blood Supply of
Posteriro Cruciate Ligaments (PCL)
• PCL is supplied by four branches
• Distributed fairly evenly over its course
• Main is middle genicular artery enters
upper third of PCL
• Synovium surrounding PCL also
supplies PCL
• Contributions inferior medial, inferior lateral genicular
arteries via infrapatellar fat pad
• Periligamentous and intra-ligamentous plexus
• Sub cortical vascular network at bony attachments
• Very little from bony attachment
Sick & Koritke, 1960; Arnoczky, 1987
MOB TCD

44. MOB TCD
Nerve Supply of Cruciates
•
•
•
•
Branches of tibial nerve
Middle genicular nerve
Obturator nerve (post division)
Branches of the tibial nerve enter
via the femoral attachment of
each ligament
• Nerve fibres are found with the
vessels in the intravascular
spaces
• Mechanoreceptors
• Proprioceptive action

45. MOB TCD
Nerve Supply of IFP
• Posterior articular branch of
tibial nerve
• Fat pad
• Supplies cruciates
• Synovial lining of cruciates
• Mechanoreceptors and pain
sensitive
Kennedy et al., Freeman & Wyke, 1967

46. MOB TCD
Mechanoreceptors
• Three types, found near the femoral
attachment
• Around periphery
• Superficially, but well below the
synovial lining
• Where maximum bending occurs
• Ruffini endings, paccinian corpuscles
• Ones resemble golgi tendon organs, running parallel to
the long axis of the ligament
• Proprioceptive function
• Posterior division of obturator nerve

47. MOB TCD
Sensory Reflex
• Sensory information from the ACL
assists in providing dynamic
stability
• Strain of ACL results in reflex
contraction of the hamstrings
• Protects ACL from excessive
loading by pulling the tibia
posteriorly
• Rapid loading ACL may rupture
before it can react

48. MOB TCD
Extension Screw Home
• Contraction of the quadriceps results in
extension
• The anterior cruciate becomes taut
• And medial rotation of the femur occurs
around the taut anterior cruciate to
accommodate the longer surface of the
medial condyle
• During extension the ACL lies in a smaller anterolateral
notch in the main intercondylar notch
• It can be kinked or torn here during hyperextension,
particularly if there is violent hyperextension and internal
rotation

49. MOB TCD
Extension
• The anterior horns of the
menisci block further movement
of the femoral condyles
• The posterior portion of the
capsule and the collateral
ligaments are also tight: this is
the close-packed position of the
joint

50. MOB TCD
Flexion
• Popliteus laterally rotates the
femur to unlock the knee
• So flexion can occur
• Then the hamstrings flex the knee
• The axis around which the motion
takes place is not a fixed one, but
shifts forward during extension
and backward during flexion
popliteus

51. MOB TCD
Screw-Home in Extension
• The effect of the screw-home
is to transform the leg into a
rigid unit, sufficiently stable for
the quadriceps to relax
• Little muscular effort is then
needed to maintain the
standing posture
• The screw-home action is due
to the inability of the central
ligaments to increase in length

52. MOB TCD
Screw-Home in Extension
• The screw-home does not
occur in the absence of the
controlling ligaments
• If the anterior cruciate and
postero-lateral complex are
missing, the lateral condyle is
not drawn forwards, resulting
in a positive pivot shift test
• Which is the abnormal
displacement of the lateral
tibial condyle on the femur

53. MOB TCD
Anatomy of the Menisci
anterior
• Menisci are made of fibro
cartilage
• Wedge shaped on cross
section
• Medial is comma shaped with
the wide portion posteriorly
• Lateral is smaller, two horns
closer together round
• They are intracapsular and
intra synovial

54. MOB TCD
Anatomy of the Menisci
• Anterior to posterior
• Medial, anterior horn is
attached to the intercondylar
area in front of the ACL and
the anterior horn of the lateral
meniscus
• Posterior horn of lateral,
posterior horn of medial and
PCL
• Medial is more fixed
• Lateral more mobile
anterior

55. MOB TCD
Anatomy of the Menisci
• Medial is attached to the deep
portion of medial collateral
ligament
• Lateral is separated from lateral
ligament by the inferolateral
genicular vessels and nerve and
the popliteus
• The popliteus, is also attached to
the lateral meniscus
• Posterior horn gives origin to
meniscofemoral ligaments

56. MOB TCD
Menisco-femoral Ligaments

57. MOB TCD
Coronary Ligament
• Connects the periphery of the
menisci to the tibia
• They are the portion of the
capsule that is stressed in rotary
movements of the knee

58. Medial Collateral Ligament (MCL)
or Tibial Collateral Ligament
• Is attached superiorly to the
•
•
medial epicondyle of the femur.
It blends with the capsule
Attached to the upper third of
the tibia, as far down as the
tibial tuberosity
MOB TCD

59. Medial Collateral Ligament (MCL)
or Tibial Collateral Ligament
• It has a superficial and deep
•
•
•
portion
The deep portion, which is
short, fuses with the capsule
and is attached to the medial
meniscus
A bursa usually separates the
two parts
The anterior part tightens during
the first 70–105°of flexion
MOB TCD

60. MOB TCD
Medial Collateral Ligament (MCL)
• Medial ligament, tightens in
•
•
•
•
extension
And at the extremes of medial and
lateral rotation
A valgus stress will put a strain on
the ligament
If gapping occurs when the knee
is extended, this is due to a tear of
posterior medial part of capsule
If gapping only occurs at 15º
flexion, this is due to tear of
medial ligament

61. MOB TCD

62. MOB TCD
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