MRI KNEE.pptx

imaging

1. MR Imaging Anatomy of the Knee with emphasis on internal derangements Presenter Dr.Vishwanath Patil PG Resident Moderator Dr. Anupama C Senior Resident

2. IMAGING PROTOCOLS/TECHNICAL FACTORS The use of a dedicated knee coil is mandatory for a quality study because it improves the signal to noise ratio. Using a small field of view (FOV) :10 to 14 cm greatly improves the spatial resolution and facilitates optimal assessment of the small anatomical structures of the knee. Matrix of 256 × 256 is usually standard

3. Patient Positioning Supine position with leg in full extension . The knee is placed in 10 to 15° of external rotation to realign the anterior cruciate ligament parallel with the sagittal imaging plane . This is typically the position of the knee in the relaxed state. Only one knee can be imaged at a time. Slice Thickness 4mm sections are used for axial, coronal and sagittal images of the knee. When needed, submillimeter resolution can be obtained with three dimensional Fourier transformation (3D FT) volume protocols. In children, 3 mm slices allow optimal medial to lateral joint coverage in the sagittal plane and anterior to posterior coverage in the

4. KNEE ANATOMY HINGE TYPE OF JOINT Three articulating compartments Patello-femoral joint. Medial femoro-tibial. Lateral femoro-tibial.

5. KNEE ANATOMY

6. ANATOMY AND IMAGING FINDING MENISCI CENTRAL STRUCTURES OF KNEE ANTERIOR CRUCIATE LIGAMENT POSTERIOR CRUCIATE LIGAMENT MEDIAL STRUCTURES OF KNEE POSTERO-MEDIAL STRUCTURES OF KNEE POSTERO-LATERAL STRUCTURES OF KNEE POSTERIOR STRUCTURES OF KNEE ANTERIOR STRUCTURES OF KNEE ARTICULAR CARTILAGE

7. MENISCI The menisci are C-shaped fibrocartilaginous structures situated within the knee joint between the femoral condyles and the tibial plateau. Periphery of the menisci are thick and convex and Attach to the inside of the joint capsule, while tapering towards the intercondylar notch The accuracy of MR imaging of meniscal tears is greater than 90 percent in most series and the negative predictive value approaches 100 percent

8. ANATOMY AND MRI APPEARANCE C-shaped structures that are conventionally described as having three segments a. Anterior horn b. Body c. Posterior horn. Each meniscus measures approximately 5 mm in height along its periphery and tapers to a thin inner edge (a triangular shape in cross section) Surfaces – superior and inferior articular surfaces During arthroscopy – Superior articular surface and inferior surface to some extent visualized . However NON VISUALIZATION of outer nonarticular capsular surface MRI appearance Low signal in all MR pulse sequence(fibrocartilage nature) Best seen in T1WI PD and GRE

9. MEDIAL MENISCUS Semi-circular 🡪 posterior horn is wider compared to anterior horn More open C-shaped (compared to lateral meniscus = more circular). Normally on MRI anterior horn 🡪 1/3 to 1/2 of Posterior horn (sagittal section). Bow-tie shape of medial meniscus 🡪two most peripheral sagittal slices 🡪 when 3-4mm slice thickness acquired. Attachments: Medial femoral condyle and tibial plateau by coronary ligament (deep fibers of MCL – meniscofemoral and meniscotibial) Attached to joint capsule in peripheral circumference . Making it less mobile 🡪 more prone for injury .

10. LATERAL MENISCUS Tight C-shaped ( more circular ) Anterior horn = posterior horn in width Loosely attached to joint capsule; posterolateral= popliteus tendon courses through intra-articular tunnel ; meniscus has no attachment to LCL 🡪more mobile🡪 less likely to injure compared to medial meniscus. Meniscofemoral ligament(part of coronary ligament)🡪 From posterior horn🡪 2 bundles 🡪 either side of PCL 🡪 attached to inner margin of medial femoral condyle : Anterior – ligament of Humphry Posterior – Ligament of Wrisberg. (Either one – 70%; Both – 5%)

11. MENISCI - VARIANTS DISCOID MENISCUS Dysplastic meniscus 🡪 more of disc than C shaped. MC in lateral meniscus (3%) Enlarged meniscus Asymmetry of anterior and posterior horns Sagittal image🡪 4-5mm thickness 🡪 continuous meniscus or bow tie appearance in 3 or more consecutive slices (normally seen only in 2 sections) Coronal 🡪 distance between the free margin and the periphery of the body >1.5cm / extension of apex towards or into the intercondylar notch . Incidental ; But more prone to cystic degeneration 🡪 subsequent tears very likely MENISCUS FLOUNCE( BUCKLED MENISCUS) MC in medial meniscus Sagittal image🡪 The free edge of middle segment of the medial meniscus becomes slacked and folded , undulating or buckled appearance Meniscal tear can mimic similar appearance MENISCAL OSSICLE Embryonic variant / sequelae to trauma Small focus of ossification MC in Posterior horn of medial meniscus . Asymptomatic; Mechanical pain PITFALL: Confused with loose body.

12. MENISCAL TEAR Rotation of femur against fixed tibia during flexion and extension. MR imaging criteria for diagnosing a tear Meniscal distortion in the absence of prior surgery or Increased intrasubstance signal intensity unequivocally contacting the articular surface. (Seen on two or more images, fulfilling the “two-slice-touch” rule) MR grading of meniscal tear based on their configuration and relation to articular surface : GRADE 1 : Non-articular focal or globular intrasubstance increased signal (early mucinous degeneration) 🡪 also in asymptomatic athletes. GRADE 2 : Intrasubstance linear increased signal extending to capsular periphery of meniscus ; NON-INVOLVEMENT of articular meniscal surface . GRACE 3 : Extension into at least one articular surface . General Morphology Medial meniscus: Anterior horn – 6mm Posterior horn- 12mm Lateral meniscus: Anterior and posterior horn : 10mm Focal step like configuration and wedge defect (NOTCH sign) 🡪 only sign of some tear. If a smaller than normal meniscus is encountered 🡪look for displaced fragment

13. MR grading of meniscal tear

14. Horizontal tear Runs parallel to tibial plateau Involves either articular surfaces /central free edge Dividing the meniscus into superior and inferior halves

15. Horizontal tear

16. Longitudinal Tear Run perpendicular to the tibial plateau and parallel to the long axis of the meniscus Divide the meniscus into central and peripheral halves Doesn't involve free edge

17. Longitudinal Tear

18. Radial Tear Runs perpendicular to both the tibial plateau and the long axis of the meniscus Transects the longitudinal collagen bundles as it extends from the free edge toward the periphery Involves free edge

19. Radial Tear

20. Bucket-Handle Tear Longitudinal tear with central migration of the inner “handle” fragment MM >> LM Signs: Absent bow tie, Fragment within the intercondylar notch, Double PCL, Double anterior horn or flipped meniscus, and Disproportionally small posterior horn

21. Bucket-Handle Tear

22. MR imaging signs of a bucket-handle tear A- absent bow –tie B- Fragment within the interchondylar notch C- double PCL D- double anterior horn + diminutive posterior horn

23. MENISCAL IMAGING: CHALLENGES Numerous imaging pitfalls and artifacts that may simulate a tear and lead to an erroneous diagnosis. These are especially common in the posterior horn of the lateral meniscus. TRANSVERSE INTERMENISCAL LIGAMENT Attachment of the transverse ligament to anterior horn of medial or lateral menisci🡪 misdiagnosis for a tear( sagittal images) Overcome: Follow the ligament in successive images🡪 continuous with the normal ligament and seen coursing through the infrapatellar fat.(FIG) MENISCOFEMORAL LIGAMENT Ligament of Humphrey and Wrisberg 🡪 attached to the posterior horn of the lateral meniscus🡪 mistaken for a tear. POPLITEUS TENDON Junction of posterior horn and body of lateral meniscus , the popliteus tendon usually has small amount of fluid around the sheath🡪 mistaken for a tear. MAGIC ANGLE EFFECT Posterior horn of lateral meniscus attached to the posterior intercondylar notch🡪 slightly angled ( 55 degree or the magic angle) between the meniscus and the static magnetic field on short TE🡪 appear as high SI artefact . Solution : use a long TE sequence -> disappearance of the magic angle effect. PULSATION ARTEFACT FROM POPLITEAL ARTERY Phase artefacts from popliteal artery 🡪 misdiagnose as tear in the posterior horn of lateral meniscus. avoided by recognizing the alternating lines of increased and decreased signal propagating across the entire image at that level.

24. CENTRAL STRUCTURES OF THE KNEE ANTERIOR CRUCIATE LIGAMENT

25. ANTERIOR CRUCIATE LIGAMENT The ACL courses from the posteromedial aspect of the lateral femoral condyle to insert anterolateral to the anterior tibial spine.

26. ANTERIOR CRUCIATE LIGAMENT The normal ACL has a fan-shaped striated appearance on both T1-weighted and T2-weighted sequences whereas, in contrast, the PCL appears homogeneously hypointense on all sequences . Fascicles of ACL divided into 2 longitudinal fibres bundles Anteromedial bundle(ABM): longer and stronger Posterolateral bundle: shorter

27. ACL INJURY Mechanism: External rotation of femur on a fixed tibia with valgus force. MRI appearance An increased signal intensity within the ACL on proton density and T2W images indicates an acute or subacute injury. A cloud like or amorphous mass of increased signal intensity may be evident within the ligament reflecting edema or hemorrhage.

28. ACL INJURY When the ligament is either absent ( “empty notch sign” in coronal or discontinuous. An irregular or wavy contour with disruption of fibers🡪 suggest a complete ACL tear. An abnormal course of the ACL can be identified by Blumensaat’s angle , which is the angle between the roof of the intercondylar notch and the line of the ACL , the apex of which normally points posteriorly ; in ACL rupture, the apex points anteriorly.

29. ACL Injury Indirect signs of ACL injury i. Buckling (abnormal high arc) of the posterior cruciate ligament giving rise to a “ question mark” configuration. ii. Uncovered lateral meniscus sign : A vertical line drawn tangentially to the most posterior margin of the lateral tibial plateau intersects any part of the posterior horn of the lateral meniscus 🡪indicates anterior displacement of tibia III. Anterior tibial subluxation : If the distance between two parallel lines drawn tangential to the posterior lateral femoral condyle and posterior lateral tibial plateau is more than 5 mm it is a sensitive ancillary sign of complete ACL tear iv . Lateral notch sign in which the deep lateral femoral notch exceeds 2 mm in depth v. Bone bruises/contusions in the midportion of the lateral femoral condyle and posterior portion of the lateral tibial plateau . 🡪” kissing contusions ” 🡪microfractures that occur when the ACL ruptures.

30. ACL Injury vii. Avulsion fracture of the lateral tibial rim ( Segond fracture) is also suggestive of ACL tear. viii. Joint effusion/hemarthrosis is a common finding associated with ACL ix. A tibial spine avulsion is an uncommon but specific finding for ACL injury.

31. Posterior Cruciate Ligament The PCL has a broad origin along the mid aspect of the medial femoral condyle and tapers as it inserts along the posterior mid tibia approximately 1 cm below the joint line.

32. Posterior Cruciate Ligament PCL injury: MR findings of PCL injury are anatomic disruption Increased signal intensity in the ligament Thickening of the PCL ligament (7mm or more) Grading: Grade I : Intraligamentous edema and hemorrhage and appears as foci of increased signal in a ligament with otherwise intact borders. Grade II : Partial tears. Grade III : Complete tears.

33. MEDIAL FEMORO-TIBIAL JOINT STABILIZERS Deep & superficial portions of medial collateral ligament. Medial tendons (sar, gra, semiten, semimem) Deep crural fascia of vastus medialis. Further posteriorly deep portions of medial collateral ligament with contributing fibers of semimembranosus tendon & synovial sheath form posterior oblique ligament – major stabilizer of postero-medial knee.

34. MEDIAL FEMORO-TIBIAL JOINT STABILIZERS semimembranosus muscle is the largest of the posteromedial muscles . semitendinosus tendon can be seen immediately posterior to it. Smaller sartorius muscle is seen more medially with the gracilis tendon interposed. The vastus medialis muscle is draped over the medial femoral condyle.

35. MCL Injury Twisting injuries cause a large number of MCL injuries. Grade 1 injury : A slight contour irregularity or thickening of the ligament may be seen but there is no discontinuity of its fibers. Grade 2 : Discontinuity of some fibers may be evident. Grade 3 : Frank discontinuity of all its fibers. Conventional radiograph can predict MCL injury Pellegrini–Stieda disease or calcification around the medial femoral condyle represents chronic partial or complete tears of the MCL The reverse Segond fracture : an avulsion fracture of medial tibial plateau at the attachment of the deep fibers of the MCL 🡪 associated with PCL disruption and peripheral medial meniscal tear.

36. LATERAL FEMORO-TIBIAL JOINT STABILIZERS ANTEROLATERAL JOINT IS STABILIZED BY – joint capsule & ilio-tibial tract. POSTERO-LATERAL JOINT IS STABILIZED BY – arcuate ligament complex. Fibular (lateral) collateral ligament (FCL), Biceps femoris tendon, Popliteus muscle and tendon, Popliteal fibular and popliteal meniscal ligaments, oblique Popliteal, arcuate, and fabellofibular ligaments, and Lateral gastrocnemius muscle.

37. LATERAL FEMORO-TIBIAL JOINT STABILIZERS

38. POSTEROLATERAL CORNER OF THE KNEE MRI: LCL is best visualized in entirety in the coronal planes Low signal intensity structures on all sequences and nearly uniform in thickness. Contour changes, such as thickening and irregularity, are more typical of subacute or old injuries. Complete tears with discontinuity and retraction of the fibers may produce a ribbon-like deformity of the LCL Most complete ruptures involve the conjoined tendon and may produce a small avulsion of the styloid process of the fibular head(marrow edema in the proximal fibula)

39. POSTEROLATERAL CORNER OF THE KNEE A direct varus force to the knee produces injuries to the posterolateral corner. Acute injuries of the popliteus muscle most commonly involve the myotendinous junction , whereas avulsion injuries of fibular insertion are less common. Complete tears of the poplitealtendon🡪 enlargement of the muscle belly and the retracted tendon terminates abruptly.

40. POSTERIOR STRUCTURES OF THE KNEE Gastrocnemius , soleus , and plantaris muscles The gastrocnemius: Two heads from the posterior surface of the medial and lateral femoral condyles . The tendons of the gastrocnemius along with the soleus tendon form the Achilles tendon .

41. POSTERIOR STRUCTURES OF THE KNEE Acute injuries of the proximal gastrocnemius include interstitial edema of the myotendinous junction and surrounding soft tissues. Occasionally, an intramuscular hematoma forms a space occupying mass in the muscle. A complete rupture of the gastrocnemius head is associated with retraction of the muscle belly .

42. ANTERIOR STRUCTURES OF THE KNEE Includes Quadriceps tendon ,patellar tendon, the medial and lateral patellar retinacula. The medial and lateral patellar retinacula are extensions of the vastus medialis and lateralis respectively and contribute to passive stabilization of the patella.

43. ANTERIOR STRUCTURES OF THE KNEE The layers of the quadriceps tendon can be visualized best in sagittal plane on MRI as uniform low signal intensity bands with intervening higher signal intensity fat separating each layer. Discontinuity of any of the tendinous layers is consistent with partial tears often involving the rectus femoris component .

44. ANTERIOR STRUCTURES OF THE KNEE The patellar tendon also has homogeneous low signal intensity appearance except for small occasional triangular areas of intermediate signal intensity directly below the patella and adjacent to the tibial tuberosity . The normal thickness of the tendon does not exceed 7 mm in its proximal part . A large collection of adipose tissue, the infrapatellar fat pad of Hoffa, rests just posterior to the patellar tendon. The patellar tendon ruptures less frequently than the quadriceps tendon .

45. ANTERIOR STRUCTURES OF THE KNEE Acute Patellar Tendon Disruption This most commonly occurs near the patellar attachment and is best seen on sagittal MR images as discontinuity of the patellar ligament with buckling of the tendon, retraction of the patella , and fluid signal in the intervening gap.