MRI KNEE JOINT ANATOMY

BY: DR NIKHIL BANSALRESIDENT RADIO-DIAGNOSIS

UNDER GUIDANCE OF:

DR ANAND VERMA HOD (RADIO-DIAGNOSIS)

MGMC&H

RADIOLOGICAL ANATOMY OF KNEE

JOINT

INTRODUCTION The knee joint is one of the

important weight-bearing joints of the human body

Complex and extensive movements are performed , involving numerous active and passive mechanisms.

Knee is more l ikely to be damaged than most other joints because it is subject to tremendous forces during vigorous activity. 

Therefore not surprising that the knee is frequently aff ected by traumatic and degenerative condit ions

PROTOCOL Field of view (FOV) --small 10

to 14 cm

A matrix of 256 x 256 is usually standard.

Dedicated knee coil is mandatory as it improves the signal to noise ratio

Patient Positioning Supine, with the leg in full extension. The knee is placed in 10 to 15° of external

rotation(esp for sagittal image)

Slice Thickness 3-4 mm sections are used for axial, coronal

and sagittal images of the knee. Adults: 4mm Children's: 3mm 3DFT(Fourier Transformation) Sub

centimeter

Imaging Planes and Pulse Sequences

Short echo time (TE) conventional spin echo (CSE) images generally provide the best contrast for anatomical evaluation

Proton-density images are probably the most sensitive for detection of meniscal tears.

FSE T2-weighted images have demonstrated high accuracy for detection of cartilage lesions.

3D Fourier transformation (3DFT) Imaging is becoming popular

-provides the highest resolution -with an acceptable S/N ratio -allowing image reconstruction in any

plane.

Knee protocol

Fast spin echo PD and T2w in the sagittal plane (meniscal, cartilage)

STIR sequence in the coronal plane(marrow)

T1W coronal images

T2W axial images

General anatomy Knee is the largest and more complex joint of the

body Complexity is the result of fusion of three joint - lateral t ib iofemoral jo int - medial t ib iofemoral jo int

- femoropatel lar jo int It is a compound synovial joint ,incorporating two

condylar joints between condyles of femur and tibia and one saddle joint between femur and patella.

ARTICULAR SURFACEFormed by – condyles of femur , patella and

condyles of tibia

X-Ray

Sartorius

INRACAPSULAR LIGAMENTS1. Anterior cruciate ligament2. Posterior cruciate ligament3. Medial meniscus4. Lateral meniscus5. Transverse ligament

Menisci: The menisci of the knee are two

semilunar, C-shaped fi brocart i laginous disks that s i t on the per ipheral margins of t ib ia l p lateau

Upper surfaces of both menisci are concave, and they art iculate with the convex femoral condyles.

Each meniscus has two ends which are attached to t ib ia, and two borders

(a)The outer border is thick , convex and fi xed to the fi brous capsule

(b) Inner border is thin concave and free.

Micro-anatomy: Type 1 Collagen

Red Zone: 1/3White Zone: 2/3

They measure ~3 to 5 mm in height at the periphery ~1 mm or less at the free edge.

MEDIAL MENISCUS

Medial meniscus is shaped more l ike a half-c irc le.(open “C”)

The width of the medial meniscus, in contrast to the lateral meniscus, gradual ly tapers from posterior(12mm) to anterior(6mm)

Peripheral margin of the medial meniscus is more fi rmly attached to the t ibial col lateral l igament.

MRI APPEARANCEANTERIOR & POSTERIOR HORNS- Best demonstrated on sagittal viewBODY of meniscus- Best seen on coronal images

Lateral meniscus

The lateral meniscus has the same width throughout, approximately 10 mm

Peripheral margin of the lateral meniscus is attached to the capsule except poster lateral , where the popl iteal tendon crosses it , and more posteriorly and central ly near the central attachment site, where the capsule does not extend anteriorly into the joint.

Anterior horn of lateral meniscus

The anterior and posterior horns of the lateral meniscus are about equal in size

Anterosuperiorly transverse l igament is attached to it .

Posterior horn of lateral meniscus

It differs from medial meniscus

its attachment to the capsule is interrupted by the popliteal tendon,

Superiorly it gives origin to ligament of wrisberg ( meniscofemoral ligament) which appear as round dot adjacent to superior aspect of the posterior horn

Discoid Meniscus

A discoid meniscus refers to a meniscus, almost always the lateral one, that is not C-shaped but disklike.

it covers most of the tibial plateau to varying degrees rather than just its periphery.

is usually seen in children and adolescents, in whom it may be asymptomatic and noted incidentally.

It is prone to tearing The prevalence of discoid lateral

meniscus (1.5%-15.5%) is greater than that of discoid medial meniscus

High-resolution coronal images allow better depiction of this enlarged meniscus.

A discoid meniscus is said to be present if three or more 5mm-thick contiguous sagittal images demonstrated continuity of the meniscus between the anterior and posterior horns.

Another criteria was height difference of 2mm on coronal image.

Lateral meniscus from the periphery to the notch

Normal lateral meniscus.

Discoid lateral meniscus

Pitfalls…

The posterior horns are seen on coronal views as flat bands that should not be confused with discoid menisci

NORMAL VARIATIONS AND PITFALLS 1. Wrisberg and Humphry Ligaments: The meniscofemoral ligaments of Wrisberg and Humphry originate from the superior aspect of the posterior horn of the lateral meniscus.

The Wrisberg ligament is located posterior to the posterior cruciate ligament and seen in 33% sagittal image.

The Humphry ligament is anterior to the posterior cruciate ligament

1 of these 2------ 70 % Both---------------6%

Ligament of Wrisberg

Ligament of Humphry

Popliteus Tendon

Popliteus tendon and its hiatus separate the lateral meniscus from the joint capsule.

Signal intensity from the popl iteus tendon sheath or fl uid within its hiatus could be mistaken for a meniscal tear on both sagittal and coronal images

T 1w show the popliteus tendon. as it courses medially and inferiorly in the more medial section.

(a) Image shows the tendon above the lateral meniscus.

(b) Image shows the tendon (arrow) has moved behind the meniscus.

(c) Image shows the tendon (arrow) is inferior to the meniscus.

Transverse Ligament

Connects the anterior horns of both menisci

The signal intensity produced from the loose connective t issue between the transverse l igament and the most medial part of the anterior horn of the lateral meniscus can be mistaken for a meniscal tear.

This error can be avoided by tracing the cross-section of the l igament through the infrapatel lar fat pad on more central MR imaging sections

Sagittal fat suppressed

Medial--lateral

CENTRAL STRUCTURES OF KNEE

Anterior Cruciate Ligament

Anatomy extends from its semicircular attachment at the lateral femoral condyle to the

anterior intercondylar region of the tibia. It is just posterior to the transverse

ligament and just anterior to the central attachment of the anterior horn of the lateral meniscus where some fibers mix.

The tibial attachment is larger than the femoral and fanlike in shape.

ligament measures approximately 4 X 1 cm

may consist of two or more distinct bundles separated by loose connective tissue and fat, more prominent at the mid- and distal portions.

MRI Appearance

ACL is best seen on sagittal oblique images with slices parallel to the cortex of the lateral femoral condyle.

ACL may appear as a solid low-signal-intensity band

Coronal image

ACL as a c fanlike structure adjacent to the horizontal segment of the PCL near the medial surface of the lateral femoral condyle

Proximally, the signal intensity is uniformly low, whereas distally it may be slightly increased.

ACL: Origin to insertion

Posterior Cruciate Ligament Anatomy The PCL arises at the lateral surface of the medial

femoral condyle and extends to the posterior surface of the intercondylar region below the level of articular surface of tibia.

It is wider and thicker than the ACL. Sagittal images best show the PCL; it appears as a

uniformly low-signal-intensity structure and arcuate in shape in routine MR imaging

It has a nearly horizontal takeoff at the femoral origin and then an abrupt descent at about 45 degrees to the tibia.

AXIAL SECTION SAGITTAL SECTION

Sagittal MR images of PCL

posterior cruciate ligament bows posteriorly In extension but is straight (taut) in flexion.

extended knee

50 degree flexed knee

MRIAxial Section

Tibial tuberosity

Saphenous nerve

Great saphenous vein

Medial gastrocnemiusLateral gastrocnemius

Soleus

TibiaTibialis anterior

Fibula

Patellar tendon

Lateral tibial condyle

Iliotibial tract

Medial tibial condyle

Sartorius tendon

Gracilis tendon

Semitendinosus tendonSemimembranosus tendon

Medial femoral condyle

Lateral femoral condyle

Infrapatellar fat pad Patellar tendon

Popliteus tendon

Sartorius muscle

Semimembranosus tendon

Semitendinosus tendon

Tibial nerve

Popliteal veinPopliteal artery

Lateral gastrocnemius

Joint capsule

Superior medial geniculate arterySuperior lateral geniculate artery

PatellaSynovial fluid

Quadriceps tendon

Semitendinosus tendonSemimembranosus muscle

Popliteal artery and vein

Biceps femoris

Femur Vastus medialis

Sartorius muscle

Suprapatellar bursa

Sagittal Section

Vastus medialis

Medial gastrocnemius

Sartorius

Vastus medialis

Medial femoral condyle

Medial meniscus

Tibia

Medialgastrocnemius

Gracilis tendon

Sartorius muscle

Vastus medialis

Medial femoral condyle

Medial meniscus

Tibia

Semitendinosus tendon

Medialgastrocnemiusmuscle

Gracilis tendon

Medial gastrocnemiustendon

Posterior horn of medial meniscus

Joint capsule

Anterior horn of medial meniscusSemimembranosustendon

Semitendinosustendon

Semimembranosusmuscle

Shaft of the tibia

Shaft of the femur

Infrapatellar fat pad

Patella

Oblique poplitealligament

Posterior cruciate ligament

Popliteus muscle

Posterior cruciateligament

Popliteal artery

Anterior cruciate ligament

Patellard tendon

Quadriceps tendon

Tibial nerve

Popliteal vein

Anterior cruciate ligament

Popliteal artery

Popliteus muscle

Posterior horn oflateral meniscus

Quadriceps tendon

Patella

Patellar tendon

Tibia

Femur

Popliteus muscle

Popliteus tendon

Posterior horn oflateral meniscus

Head of fibula

Anterior horn of lateral meniscus

Lateral femoral condyle

Commonperoneal nerve

Lateral head ofgastrocnemius muscle

Biceps femoris muscle

Tendon of the lateralhead of gastrocnemius

Common peronealnerve

Lateral meniscus

Vastus lateralis muscle

Superior tibiofibularjoint

Tibialis anterior muscle

Coronal Section

Biceps femoris tendon

Biceps femoris

Popliteal artery

Lateral head of gastrocnemius muscle

Head of fibula

Semimembranosusmuscle

Gracilis tendon

Semimembranosustendon

Medial head ofgastrocnemius muscle

Semitendinosustendon

Lateral superior geniculate artery

Sartoriusmuscle

Medial inferior geniculateartery

Popliteal artery

Popliteus muscle

Biceps femoris tendon

Lateral femoral condyleGreatsaphenousvein

Popliteus muscle

Lateral gastrocnemius tendon

Medial gastrocnemius tendon

Medial femoral condyle

Sartorius tendon

Gracilistendon

Posterior cruciate ligament

Lateral tibial plateau

Semimembranosus tendon

Medial tibial plateau

Great saphenous vein

Lateral meniscus

Head of the fibula

Anterior cruciate ligament

Lateral collateral ligament Medial collateralligament

Medial femoral condyle

Lateral femoral condyle

Popliteus tendon

Lateral intermuscularseptum

Anterior cruciate ligament

Lateral meniscus

Lateral intercondylar tubercleMedial intercondylar tubercle

Posteriorcruciate ligament

Vastus medialis muscle

Anterior cruciate ligament

Iliotibial band

Iliotibial band

Anterior horn ofmedial meniscus

Infrapatellar fat pad

Vastus lateralis tendon

Lateral retinaculum

Patella

Lateral retinaculum

Infrapatellar fat pad

Patellar tendon

Medial retinaculum

Quadriceps tendon