MRI of ligaments. Ligament biomechanics Spine Shoulder Elbow Hand/wrist Pelvis/hip Knee Foot/ankle

Transcription

1 MRI of ligaments Chang Ho Kang M.D. Korea University Anam Hospital Spine Shoulder Elbow Hand/wrist Pelvis/hip Knee Foot/ankle Introduction Ligament Fibrous connective tissue Attaches bone to bone Holds structures together and provides stability Shorter and wider More elastic collagen Less longitudinally organized (more interweaving) fibers Tendon Fibrous connective tissue Attaches muscle to bone Serves to move the bone or structure Ligament anatomy Less regular histological and sonographical appearance Ligament biomechanics Non-linear load extension curve Affected by: 1. Orientation of the load 2. Temperature 3. Rate at which load is applied 4. Warming up Once a load exceeds a certain point, the ligament or tendon becomes permanently deformed and this is when a failure occurs Ligaments and tendons rupture at the weakest point. The most vulnerable location depends on the age of the patient Ligament 1

2 MRI vs US US Imaging of choice for superficial ligaments Best spatial resolution Dynamic examination Comparison with normal side MRI Imaging of choice for deep lying or intraarticular ligaments Best contrast resolution Associated soft tissue and bone abnormalities MRI technique Ligaments are best visualized where the imaging plane is identical to the plane of the ligament. This requires defined positioning and a defined imaging plane. (FS-)T2-weighted or PD-weighted SE sequence allows the best evaluation of an (acute) ligament injury. Normal ligament on MRI Complete continuity Hypointense or no signal Straight course Uniform width Exceptions Normal ligament on MRI Uniform or gradual increases in signal intensity over anatomical prominences may be a normal finding, and represents mild chondroid metaplasia as an adaptive change at compression sites. Fibrocartilaginous To the epiphyses or apophyses or carpal/tarsal bones Dense fibrous connective tissue Uncalcified fibrocartilage Calcified fibrocartilage Bone Entheses Fibrous To the metaphyses or diaphyses Superficial layer connects directly with periosteum Deeper layers anchor to bone via Sharpey s fibres 2

3 Entheses Entheses are regions where tendons, ligaments, or joint capsules are connected to bone. Many features of entheses are adapted to disperse stress and accommodate compressive and shear forces at, or near, boundaries between tendons or ligaments and bone. Conventional clinical magnetic resonance (MR) imaging has not been helpful in demonstrating the key tissues present in normal entheses. Ultrashort echo time (UTE) pulse sequences can identify the specific tissue components of entheses and differentiate cortical bone, calcified fibrocartilage, uncalcified fibrocartilage, and fibrous connective tissue. Magic angle effect Magic angle effect When the fibers of highly ordered, linear, collagen-rich tissues such as tendons or ligaments are shifted from 0 to B0 to 55 to B0 (the magic angle), dipolar interactions are decreased and their T2s are often considerably increased and result in detectable signal with conventional sequences. A less obvious change is seen with fibrocartilage because of the wider range of directions of its fibers. Ligament injury Sprain severity Grade I Sprain: overstretching or slight tearing of the ligaments with no joint instability Most patients can walk without crutches, but may not be able to jog or jump Grade II Sprain: partial tearing of the ligament. has some difficulty putting weight on the affected joint and experiences some loss of function x-ray or MRI may be needed. Grade III Sprain: complete tear or rupture a ligament. unable to put weight on the joint. x-ray is usually taken to rule out a broken bone. often requires immobilization and possibly surgery. Ligament injury Acute ligament injury Partial tear 1. Periligamentous signal alteration 2. Intraligamentous signal alteration 3. Ligament thickening 3

4 Acute ligament injury Complete tear 1. Completely interrupted contour 2. Stump change 3. Stump defect Acute ligament injury Partial or complete tear 1. Thinning 2. Elongation, undulating contour 3. Partially interrupted contour Ligament injury Localization 1. Intermediate 2. Close to the origin or insertion 3. Directly at the bony insertion 4. Bony avulsion injury Cortical avulsion can be missed on MRI. Chronic ligament injury Normal MRI of a healing injury: 1. Slight thickening 2. Slight signal increase Chronic insufficiency: 1. Very narrow ligament 2. Elongated ligament 3. Persisting ligament stumps or absence Knee Anterior cruciate ligament Prevent: 1. Excessive anterior translation of the tibia 2. Internal or external rotation of the tibia on the femur Anteromedial bundle + posterolateral bundle 4

5 Anterior cruciate ligament Normal appearance: somewhat variable 1. Solid dark band 2. Multiple linear fiber bundles 3. Anterior dark band +three or four fiber bundles Anterior cruciate ligament Optimally visualized by obtaining images parallel to its course in a sagittal oblique plane Anterior cruciate ligament 3D imaging Oblique coronal (ACL view) ACL tear Mechanism: sudden deceleration, hyperextension, and tibial torsion Full-thickness tear: MRI-sensitivity (94.4%)/specificity (94.3%), Direct/indirect signs: Indirect sign Bone contusion sign Deep sulcus sign Segond fracture Kissing contusion Anterior drawer sign Buckling of PCL Acute hemarthrosis 5

6 Knee at 3.0T Knee at 3.0T PD TSE, ST 2mm PD TSE, ST 3mm Recent meta-analysis 3.0T (1) 3.0T (2) ACL tear Complete tear Sensitivity 94.4% 100% 100% Specificity 94.3% 100% 97.9% 1. Clinical Radiology 2008; 63: Skeletal Radiol 2005; 34: ACL tear Partial tear: MRI-sensitivity (40 75%)/specificity (62 89%) 1. Absence of findings of complete ACL tear 2. Abnormal high T2 intrasubstance signal, but with residual low signal fibers present 3. Curved course or bowing of the ACL Chronic tear: 1. Residual fibers with low angulation 2. Variable sized discontinuous fragments without significant edema 3. Non-visualization of ACL ACL tear Chronic tear: 1. Residual fibers with low angulation 2. Variable sized discontinuous fragments without significant edema 3. Non-visualization of ACL Associated abnormalities: ACL tear + MCL tear + Meniscal tears Diagnosis? No trauma Celery stalk Posterior cruciate ligament Primary restraint to posterior tibial translation at 30 and 90 degrees Secondary restraint to IR, varus-valgus instability forces Twice as strong as ACL Anterolateral bundle+posteromedial bundle 6

7 Posterior cruciate ligament Normal posterior cruciate ligament is a dark, low signal intensity band that follows a curved or sigmoid course. PCL injury Direct blow to Anterior tibia Hyperextension injury Dashboard injury Fall onto a flexed knee with foot in plantar flexion PCL tear Less reliable physical examination Accuracy of MRI: 99% for PCL, 93% for ACL (Fischer, et al. JBJS 1991) PCL tear Complete tear Partial tear Peel-off injury PCL tear Meniscofemoral ligaments Chronic PCL Tears: Servant, et al. Knee 2004 MRI was performed on 10 knees with a clinical and arthroscopic diagnosis of a PCL injury sustained at least 6 months previously. Seven experienced musculoskeletal radiologists Accuracy in diagnosing a PCL injury was 57% (40-80%). MFL (amfl + pmfl) Humphrey + Wrisberg A. Amis et al. Knee Surg Sports Traumatol Arthrosc (2006) 7

8 Collateral ligaments Medial collateral ligament Extends from the medial epicondyle of the femur to the medial condyle of the tibia At its midpoint, its fibers are attached to the medial meniscus, Lateral collateral ligament Extends inferiorly from lateral epicondyle of femur to lateral surface of the fibular head Conjoined tendon with biceps tendon Medial supporting structures Superficial (I) : crural fascia Middle (II) : superficial MCL Deep (III) : true capsule of joint (deep MCL) De Maeseneer et al. Radiographics 2000 MCL injury More commonly injured than the lateral ligament complex Complete tears of MCL are usually treated nonoperatively unless ACL or some other major supporting structure is torn. Grade I/II/III Diffuse thickening of the medial collateral ligament may be seen with a chronic tear or with medial compartment osteoarthritis. MCL tear Grade I, II, III Lateral supporting structures Diffuse thickening of the medial collateral ligament may be seen with medial compartment osteoarthritis. 8

9 LCL injury LCL: Restrain varus angulation at the knee and external rotation of the tibia Lateral ligament disruption is usually part of a severe knee injury that includes disruption of the posterior or the anterior cruciate ligaments. Posterolateral corner Failure to identify an injury of the posterolateral corner of the knee may lead to knee instability and subsequent failure of cruciate ligament reconstruction. J Bone Joint Surg Am. 2007;89:2-14. Josephine Lee et al.skeletal Radiol 2003 AJR 2003; 180: Posterolateral corner on MRI Ankle Lateral complex 1. Anterior talofibular ligament 2. Posterior talofibular ligament 3. Calcaneofibular ligament 9

10 Medial complex Superficial portion 1. Tibionavicular ligament 2. Tibiospring ligament 3. Tibiocalcaneal ligament 4. Spring ligament Deep portion 1. Deep posterior tibiotalar ligament 2. Deep anterior tibiotalar ligament Syndesmotic complex 1. Interosseous ligament 2. Anterior tibiofibular ligament 3. Posterior tibiofibular ligament 4. Transverse tibiofibular ligament 5. Posterior intermalleolar ligament (56% in cadaveric study) Ligament injury Low ankle sprain: Injury to the collateral ligaments High ankle sprain: Injury to the syndesmotic ligaments Grade I/Grade II/Grade III Indications of MR imaging: 1. Athletes in whom primary ligamentous surgical repair is contemplated 2. Patients with a history of chronic ankle instability Ligament injury Injury to the ankle ligaments usually occurs in a certain order, depending the degree of supination. 1. Anterior talofibular ligament 2. Calcaneofibular ligament 3. Sinus tarsi ligaments 4. Posterior talofibular ligament Isolated injury to the distal syndesmosis and the medial ligament complex only rarely occur without a fracture. 10

11 Grade I or II Grade III Case 16 세남자 농구하다가발목을접질렸음. Case 24 세남자 10 년전부터반복되는 ankle sprain Conclusion MRI is the imaging modality of choice in evaluating ligamentous injuries. By optimizing examination technique and understanding the normal anatomy of the ligaments and their pathologic appearances, it is possible to achieve a high degree of sensitivity and specificity with MRI in diagnosing, grading, and localizing ligament injuries. 11