This document provides an overview of MRI of the knee, including general principles of MRI, anatomy of the knee, and signs of an ACL tear on MRI. It discusses how MRI works using magnets and radiofrequency signals without radiation. Key anatomy described includes the meniscus, ligaments like the ACL and PCL, and imaging planes like axial, sagittal, and coronal. Signs of an ACL tear seen on MRI include nonvisualization of the ligament, abnormal signal or configuration, and secondary signs like bone bruising and meniscal tears.

1. MRI of KNEE
Pembimbing:
DR. dr. Edi Mustamsir, Sp.OT (K)
Penyaji:
Joko Santoso

2. MRI of KNEE
 PRINCIPLES of MRI
 ANATOMY OF KNEE

3. General principles of MRI
1. MRI is similar to CT in that images are produced by reconstruction of a data set.
2. MRI does not use radiation or have the tissue damaging properties of radiation-based imaging
modalities.
3. MRI uses a strong magnet that generates a magnetic field in which protons line up like compasses.
Multiple coils send and/or receive radiofrequency (RF) signals.
4. The strength of the magnet is expressed in tesla(T) units. The stronger the magnet, the higher the
intrinsic signal-to-noise ratio, which can improve imaging speed and resolution.
5. Contrast on MRI can be manipulated by changing the pulse sequence parameters. Two important
parameters are the repetition time (TR) and the echo time (TE). The most common pulse sequences
are T1-weighted and T2-weighted sequences. The T1-weighted sequence uses a short TR and short
TE; the T2-weighted sequence uses a long TR and long TE. Different structures are identified more
easily on each sequence

4. PRINCIPLES of MRI

6.  In most cases, fat has a high signal (bright) on T1-weighted images and
fluid has a high signal on T2-weighted images.
 Structures with little water or fat, such as cortical bone, tendons, and
ligaments, are hypointense (dark) in all types of sequences.
 Fat suppression also can be achieved by using a short tau inversion
recovery (STIR) sequence. These fat-suppression techniques can be useful
in the detection of edema in both bone marrow and soft tissue and
therefore play an important role in the imaging of trauma and neoplasms.

11. BASIC MRI

12. BASIC MRI

13. Magnetic resonance arthrography
Magnetic resonance arthrography
Commonly used to augment MRI to diagnose soft-tissue conditions.
Two techniques
 Direct—A dilute gadolinium-containing solution is percutaneously injected
into the joint.
 Indirect—Gadolinium is administered intravenously and allowed to travel
through the vascular system to the region of interest.

14. Advantages of MRI
1. Provides superior images of soft tissues such as ligaments, tendons,
fibrocartilage, cartilage, muscle, bone marrow, and fat
2. Provides tomographic images of the object of interest
3. Can be more effective than CT at detecting changes in intensity within the
bone marrow to diagnose osteomyelitis, malignancy, contusions, occult
fractures, and stress fractures
4. MRI contrast (gadolinium) is safer than iodine based media.
5. No radiation to patient

15. Disadvantages of MRI
1. Prone to large and severe types of artifact
a. Metal screws, pellets, prostheses, and foreign bodies can produce significant artifact,
obscuring anatomic structures.
b. Metal suppression sequences can be used, but with loss of resolution.
2. Patient motion can cause significant artifact.
3. Imaging time is much longer than with CT.
4. Sedation often is needed for pediatric patients younger than 7 years.

16. Dangers associated with MRI
1. Because of the strong magnet in the machine, extreme caution is needed when any person (patient,
physician, nurse, technician) enters the room. Electrical appliances such as pacemakers and
mechanical pumps can malfunction.
2. Metal objects brought into the scanner can turn into dangerous projectiles.
3. Metal foreign bodies within the eye or brain can migrate and cause blindness and brain damage. To
avoid this, plain radiographs or CT scans of the skull can be obtained prior to MRI.
4. Patients with metal implants in their joints or body can undergo MRI if the implant is secured
in bone or is stable, but discussion with the physician and technician before the scan is important to
avoid a potentially disastrous outcome.
5. MRI is contraindicated in patients with implanted objects such as pacemakers, cochlear implants,
and some stents and filters because these devices can malfunction in the magnetic field. It is
important to determine which devices can be scanned with MRI and at what field strength.

17. Considerations in pregnant women
1. Although MRI does not use radiation, the effect of RF and magnetic field
on the fetus is unknown.
2. It is usually recommended that a pregnant
woman not undergo MRI.

18. ANATOMY

19. ANATOMY

20. ANATOMY

22. ANATOMY of MENISCUS

34. Anatomy of Knee Ligament
1. The stability of the knee joint is provided by bony articulations as well as dynamic and static soft
tissue stabilizers.
2. The four major ligamentous stabilizers of the knee are the anterior cruciate ligament (ACL), the
posterior cruciate ligament (PCL), the medial collateral ligament (MCL), and the lateral collateral
ligament (LCL).
3. The posterolateral corner (PLC) and posteromedial corner (PMC) as well as the medial and lateral
menisci confer additional stability to the knee.
4. The PLC is made up of the LCL, the iliotibial band, the popliteofibular ligament, and the popliteus
tendon.

42. Signs of an ACL Tear on MRI
Primary signs
 Nonvisualization of ligament
 Complete disruption of a ligament segment
 Abnormal signal within ligament on T2-weigheted images
 Alteration of normal linear configuration of ligament
 Alteration of normal angulation of ligament

43. Signs of an ACL Tear on MRI
Secondary signs
 Bone contusion (posterolateral and posteromedial tibia, lateral condyle of
femur)
 Deepening of lateral femoral condyle notch or sulcus
 Anterior translation of tibia > 5 mm from posterior margin of femoral condyle
 Buckling of the PCL (decreased angle of the PCL)
 Segond fracture
 Meniscal tear
 Posterior horn medial meniscus and tear of the lateral meniscus at the
meniscofemoral ligament attachment
 Posterior displacement of posterior horn of lateral meniscus

50. AXIAL SECTION

75. SAGITTAL SECTION

98. CORONAL SECTION

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