MRI KNEE MRI KNEE ORTHOPEDIC APPROACH ORTHOPEDIC APPROACH

PROF. Dr. : Ahmed M. El-Saeed

MD Ain Shams University

MRI kneeMRI kneeUses non ionizing radiation created by placing patients in strong

magnetic field (30.000 times stronger than earth`s m.f.)

Has no demonstrated adverse biological effects

Depends on Hydrogen atom (single proton)When hydrogen proton is placed in magnetic

field it align its own m.f. to the direction of external m.f. = steady state

In this steady state radio frequency (RF) pulse is applied ----- excites the magnetized proton in the field ----- proton change its alignment with MF

When RF pulse is turned off ---- tendency of the proton to give up this energy to restore its alignment in MF before RFP

As proton do so emits RF signals of its own-- through a receiver coil or antenna these signals used to generate images

The rate at which proton returns to their equilibrium positions is regulated by two constants :

T1= spin-lattic relaxation time T2= spin-spin relaxation timeT1=results from interaction of the

hydrogen nucleus with its molecular environment

T2 =reflects local MF strength surrounding each individual proton

T1&T2 are property of tissue and will vary for different tissues

T1 images have the advantage of being obtainable in relatively short periods while providing good anatomic details

T2 images are excellent for lesion detection because almost all pathologic processes prolong T2

By varying timing of application of RF pulses (TR=repetition time) and timing of acquisition of the returning signals (TE=echo time) an imaging sequence can accentuate T1 (short TR & TE) or T2 (long TR&TE)

Fat and bone marrow give bright signals (abundant in H2)

Cortical bone, ligaments, tendon and air appear black (little H2 )

Cartilage, spinal canal and muscles are in the gray scale (intermediate H2)

Fat suppression technique for intense fat signals

Parameters used for MRI knee :

FOV=12-16cm Slice thickness =3-4mm

planes =Sagittal for menisci and cruciates

=Coronal for collateral ligaments

=Axial for patellofemoral jointContraindications :

absolute= IC aneurysm clips, internal ear devices, pacemakers, defibrillators and metallic eye.

Relative= Cardiac valves, Middle ear devices and Penile prostheses

FOV < 12cmFOV < 12cm

Anatomy of the kneeAnatomy of the knee The coil

surrounds knee while imaging

meniscimenisci Different cuts of

different sites of the meniscus

A B C

A

B

C

Meniscal Anatomy

SAGITTAL VIEW

Meniscal AnatomyMeniscal Anatomy(CORONAL VIEW)(CORONAL VIEW)

Lateral meniscusLateral meniscus

Sagittal plane

lateral meniscus =bow tie appearance

LAT. MENISCUSLAT. MENISCUSSaSagittal plane gittal plane equal size meniscusequal size meniscus

DISCOID L. MENISCUS

1 2 3

Arrangement of ligamentsArrangement of ligaments

MM LM

PCL

ACL

Coronal anatomyCoronal anatomy MCL

First meniscus to be seen is MM

Iliotibial band

Medial collateral ligamentMedial collateral ligament

Lateral knee structuresLateral knee structures

BICEPS TENDONBICEPS TENDON

Posterior Coronal sectionPosterior Coronal section

Most posterior of the coronal plane the PCL

Lateral=biceps , LCL

Note MM still seen (larger) than LM

Intercondylar notchIntercondylar notch Change of femoral

shape Indistinct posterior

border is seen Sharp roof of notch

is seen

PCL PCL

(convex shape, just medial to post horn MM )(convex shape, just medial to post horn MM )

ACLACL (entire lig(entire lig. Is seen in one or two adjacent 4mm slices). Is seen in one or two adjacent 4mm slices)

Grading of meniscal signal= Grading of meniscal signal= G1G1

G1= signal changes not extended to surface

(cut sec—gray)

Grading of meniscal signal=Grading of meniscal signal=G2G2

G2= linear signals common with capsular margin

cut--linear discoloration due to inter substance deg.

Cut section

Grading of meniscal signal= Grading of meniscal signal= G3G3

G3= signals extend to articular surface

cut--M tears through surface

MenisciMenisciMeniscal tears ch.ch.

1) abnormal signal within a meniscus extending to an articular surface

2) alteration in shape and position of meniscus

G3

Torn Medial MeniscusTorn Medial Meniscus1) Abnormal signal1) Abnormal signal

MM tear extending to under surface of mm

Flap tear Flap tear 2) 2) Alteration in shapeAlteration in shape

Bucket handle tear

small post. Segment displaced M. in notch

Bucket handle tearBucket handle tear

Menisco-capsular separationMenisco-capsular separation

Med M. cystMed M. cyst

MENISCUS ?

MENISCUS ?

GRADING ?GRADING ?

WHERE IS MM?WHERE IS MM?

ACL TEARACL TEAR1-ill-defined mass

2-Loss of continuity

3-retraction of torn ends

4-signals within ligament

ACL TEAR ACL TEAR (Signals within lig)(Signals within lig)

ACL

Secondary signs ACL tearSecondary signs ACL tear

Bone fragment

Tibial shift forward on femur

Chronic ACL tearChronic ACL tear

ACL attaches to PCLHorizontal ACL

ACL FOLLOW-UPACL FOLLOW-UP

PCL TEARPCL TEAR

Retracted ends

MCL injuryMCL injury

MCLMCL

Osteochondritis dissicansOsteochondritis dissicans

OCDOCD

Extensor systemExtensor system

Synovial HerniaSynovial Hernia

Sometimes Fractures!!!Sometimes Fractures!!!

ARTICULAR CARTILAGEARTICULAR CARTILAGE

LOOSE BODYLOOSE BODY

Gstrocenimius muscleGstrocenimius muscle

BURSA ?BURSA ?