MOB TCD

Anatomy of Anterior Cruciate Ligament

Professor Emeritus Moira O’Brien

FRCPI, FFSEM, FFSEM (UK), FTCD

Trinity College

Dublin

• 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

Anatomy of Knee Joint MOB TCD

• 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

Knee Joint MOB TCD

Close-Packed

• Stable position• Surfaces fit together • Ligaments taut• Spiral twist• Screw home articular surface

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

MOB TCD

Articular Surfaces

• The femoral articular surfaces are the medial 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

ACL

MOB TCD

• 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

Articular Surfaces MOB TCD

medial

Femoral Condyles

• The radius of the condyles' curvature isin 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

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

ligamentDomzalski et al., 2010; Shelbourne et al.,1998; Griffin et al., 2006

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

MOB TCD

• 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

Tibial Superior Articular Surface MOB TCD

• 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

anterior

ACL

lateral meniscus

PCL

Tibial Superior Articular Surface 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)

MOB TCD

• 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

Patella MOB TCD

Capsular Ligaments

• Quadriceps • Retinacular fibres• Patellar tendon• Coronary ligaments• Medial and lateral ligaments• Posterior oblique ligament

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

MOB TCD

• ACL repair with patellar tendon may result in fibrosis of fat pad and pain

• Delays rehabilitation• Inflammation of IFP may be process

leading to fibrosisMurakami et al., 1995

Infrapatellar Fat Pad (IFP) MOB TCD

Anterior and Posterior Cruciates

• Anatomically named by their tibial attachments

• Clinically, femoral attachments are called the origin

• 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

anterior

lateral

oblique popliteal ligaments

ACL

MOB TCD

Anterior Cruciate Ligaments

anterior

ACL

ACL

MOB TCD

Cruciate Ligaments

• ACL average length 31-38 mm• ± 10 mm width and ± 5 mm thickOdenstein, 1985; Girgis, 1975

• PCL average length 28-38 mm• PCL is 13 mm wide• Cruciates have a constant length ratio• ACL : PCl of 5:3Girgis et al., 1975

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

MOB TCD

• 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

• Passes upwards and laterally to the posterior aspect of medial surface of lateral femoral condyle

ACL

lateral

Anterior Cruciate Ligaments MOB TCD

Tibial Attachment

• Tibial attachment is in a fossa in front of and lateral to anterior spine

• 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 attachment

• Larger tibial than femoral attachment• Shape of the attachment to tibia variesAmis,1991

ACL

Medial

PCL Posterior meniscofemoral

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

MOB TCD

• 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

Femoral Attachment 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

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

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 stabilityO’Brien, 1992

MOB TCD

Posterolateral Bundle

• 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

posterolateral

anteromedial

MOB TCD

• 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

Posterolateral Bundle 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

MOB TCD

Anterior Cruciate Ligaments

• Tibial attachment is in antero-posterior 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

MOB TCD

ACL in Extension and 45°

O’Brien, 1992

MOB TCD

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

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

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 stabiliserHunziker et al., 1992

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

MOB TCD

Posterior Cruciate

• Anatomically the fibres pass anteriorly, medially and proximally

• It is attached on the antero-inferior 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

• .

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

MOB TCD

Blood Supply ofAnterior 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

Blood Supply of Cruciates MOB TCD

• 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

Blood Supply of Posteriro Cruciate Ligaments (PCL)

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

MOB TCD

• Posterior articular branch of tibial nerve

• Fat pad• Supplies cruciates • Synovial lining of cruciates • Mechanoreceptors and pain

sensitiveKennedy et al., Freeman & Wyke, 1967

Nerve Supply of IFP 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

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

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

MOB TCD

• 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

Extension MOB TCD

• 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

Flexion 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

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

MOB TCD

Anatomy of the Menisci

• 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

anterior

MOB TCD

• 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

Anatomy of the Menisci MOB TCD

• 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

Anatomy of the Menisci MOB TCD

Menisco-femoral Ligaments 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

MOB TCD

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

• 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

Medial Collateral Ligament (MCL) or Tibial Collateral Ligament

MOB TCD

• 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

Medial Collateral Ligament (MCL) MOB TCD

MOB TCD

Thank you MOB TCD

“BMJ Publishing Group Limited (“BMJ Group”) 2012. All rights reserved.”