Книги по МРТ КТ на английском языке / MRI for Orthopaedic Surgeons Khanna ed 2010

Fig. 2.31 An axial illustration of the left hip at the level of the femoroacetabular joint showing the anterior and posterior labrum, articular cartilage, and surrounding musculature.

Fig. 2.33 A coronal proton-density image of the right hip showing the suprafoveal aspect of the femoral head and acetabular dome.

iliopsoas inserts along the lesser trochanter. The ITB is identified laterally. The external iliac vessels are seen anterior to the anterior column of the acetabulum and medial to the iliopsoas muscle.

Coronal Images

The coronal plane is helpful for evaluating the weight-bearing, suprafoveal aspect of the femoral head and acetabular dome (Fig. 2.33), the trochanteric bursa, and the superior labrum (Fig. 2.34). The normal labrum appears as a triangular structure of low signal at the lateral (peripheral) margin of the acetabulum (Fig. 2.35). To view the anterior superior, superior, and posterior superior labrum, images should be examined successively from anterior to posterior. The inferior portion of the acetabulum is not covered by the labrum and contains the transverse ligament. The joint capsule and capsular ligaments surround the femoral neck and appear as a low signal intensity structure.

The trochanteric bursa, the iliopsoas tendon, and the distal insertions of the gluteus medius and minimus tendons onto the greater trochanter are well visualized in the coronal plane. The articular cartilage appears as an intermediate signal overlying the low signal cortical bone.

Sagittal Images

The sagittal images are helpful for evaluating the weightbearing portion of the femoral head and acetabular dome, as well as the anterior superior labrum (Fig. 2.36). Articular cartilage is also well evaluated in the sagittal plane. The entire course of the labrum should be evaluated from medial to lateral. The hip adductors are visualized in cross-section in the sagittal plane, which is helpful in localizing pathologic changes to specific muscles in this group. The origin of the reflected tendon of the rectus femoris muscle can be visualized at the anterior inferior iliac spine.

Sagittal images also visualize the following:

•Iliopsoas muscle (which runs anterior to the hip joint as it courses toward its insertion on the lesser trochanter)

•Iliofemoral ligament (at its insertion on the anterior labrum)

•Ischiofemoral ligament (located posterior to the iliofemoral ligament)

■Knee

Axial Images

Axial images are useful for examining the patellofemoral joint and the medial and lateral retinaculum, and for assessing tilt and subluxation (Fig. 2.37). The patellar cartilage surfaces also are well visualized in this plane, and plicae can be seen (Fig. 2.38). The suprapatellar bursa can be evaluated for knee e usions. The axial images can also be used to correlate quadriceps or patellar tendon anatomy seen on sagittal images, as well as collateral ligament anatomy seen on coronal images.

The ACL can be followed as it courses in an anteromedial direction through the intercondylar notch (Fig. 2.37A) to the surface of the tibia just lateral and slightly posterior to the anterior horn of the medial meniscus. The tibial insertion of the PCL is just medial to midline. This position can be verified on sagittal images because the PCL is in the same plane as the anterior and posterior horns of the medial meniscus.

The menisci can be visualized on axial images, although meniscal pathology is better evaluated in the sagittal and coronal planes. The transverse ligament usually can be seen running from the anterior horn of the medial meniscus to the lateral meniscus.

Ischial tuberosity

Fig. 2.35 A coronal illustration of the left hip showing the articular cartilage of the femoral head and acetabulum, the labrum, and the surrounding musculature.

Iliopsoas m.

Acetabular labrum

Sartorius m.

Adductor brevis m.

Rectus femoris m.

Obturator externus m.

Hamstring origin

Quadratus femoris m.

Fig. 2.36 A sagittal illustration of the left hip showing the articular cartilage, labrum, and surrounding musculature.

The MCL and LCL complex components are seen as low signal intensity structures. The popliteal neurovascular structures can be seen just posterior to the joint capsule and are surrounded by fat. The popliteus tendon and posterolateral complex structures can also be seen in this plane.

Coronal Images

The coronal images are best for evaluating the collateral ligaments and the posterolateral and posteromedial corner complexes (Fig. 2.39), but they should be viewed in conjunction with the axial and sagittal sequences to better understand the location in all three dimensions.

Posterolateral and Posteromedial Corners

This complex layer of tissues lies deep to the popliteal neurovascular structures (Fig. 2.40). The posterolateral corner is composed of the arcuate ligament, fabellofibular ligament, popliteofibular ligament, popliteal tendon, fibular collateral ligament, and biceps femoris tendon. The posteromedial ligament corner is composed of the posterior oblique ligament and the insertion of the semimembranosus tendon with its five extensions, including the oblique popliteal ligament.10 The fabella (variably present) can be seen as a circular structure superior to the most proximal aspect of the fibular head. The fabella frequently contains marrow and can be bright on T1-weighted sequences. Di erentiating the individual components of these two complexes is di - cult because they vary in consistency and are relatively thin. MR images acquired with thick sections may capture only

a small portion of the complexes. The intricacy of the posterolateral complex structures makes evaluation especially sensitive to artifact in this region, particularly from patient motion or limited technical quality of the scan.

Collateral Ligaments

The MCL, which runs from the medial femoral epicondyle to the proximal tibia, deep to the pes anserinus tendon, has deep and superficial components. The lateral side is composed of a multistructure tendon and ligament unit known as the LCL complex. It comprises the ITB, the fibular collateral ligament, and the biceps femoris tendon. The fibular collateral ligament (Fig. 2.40) extends from the lateral femoral epicondyle to the fibular head, anterior to the insertion of the biceps femoris tendon. The MCL and LCL are low signal intensity structures (Fig. 2.41). The ITB is seen on anterior coronal sections and inserts into Gerdy’s tubercle on the anterolateral proximal tibia.

ACL and PCL

The ACL, which can be visualized running just anterior to the PCL, fills up the lateral aspect of the intercondylar notch, whereas the PCL is located in the medial aspect of the notch. The ACL can be seen almost in its entirety, whereas the PCL is captured by successive sections through its substance as it courses posteriorly and inferiorly. It should be noted that although the ACL and PCL are more easily evaluated on sagittal images, these structures are also well visualized in the coronal plane (Fig. 2.41).

Sartorius Fibular tendon collateral

lig.

Greater Popliteus saphenous v. tendon

Biceps femoris m.

Biceps femoris tendon

Fig. 2.37 An axial T2-weighted image (A) and artist’s sketch (B) of the right knee at the level of the intercondylar notch showing the ACL and PCL.

Sagittal Images

Structures that are well visualized on sagittal images include the cruciate ligaments, menisci, articular cartilage, and extensor mechanism (Figs. 2.42 and 2.43). It is important to localize the images to the lateral or medial compartment. Medial or lateral compartment localization on sagittal images is guided by the presence of the fibular head and the convex lateral tibial condyle. Another clue to medial or lateral location is that the ACL is seen before the PCL when progressing from lateral to medial images. It may also be helpful to have a coronal image with localizer lines available as a reference guide while scrolling through the sagittal plane images.

ACL

The ACL is best evaluated on sagittal images but should be identified in all planes. The ligament runs obliquely from its origin on the posteromedial aspect of the lateral femoral condyle to its insertion site just lateral to the anterior horn of the medial meniscus. The ACL is composed of the anteromedial and posterolateral bundles. The ligament is intraarticular but extrasynovial. Because of this anatomic feature,

Fig. 2.38 An axial T2-weighted image of the right knee showing the patellofemoral joint, including the articular cartilage.

the ACL may have fatty as well as fluid signal interspersed between the fibers.

On 5-mm sagittal sections, the ACL is usually visualized on at least one section. However, 3-mm sections for SE imaging and 1- to 2-mm sections for gradient-echo imaging are preferable because they allow for better visualization of the ACL. Normally, the ligament takes a straight course and has low signal intensity. However, the normal ACL does have some variation in its signal pattern, and subtle regions of increased T2-weighted signal may be seen in the uninjured ACL. Compared with the PCL, the ACL is less well defined and has higher signal intensity. Appreciating this normal appearance will help prevent inappropriate interpretations of a normal ACL as an ACL strain or partial tear. In a normal ACL, there should be at least one identifiable dark fiber bundle, and the ACL often appears as one thick dark band. There should be a clear anterior edge to the ligament. The ACL should not show marked increased signal on T2-weighted imaging, but it may have minimally increased signal on T1-weighted images because of the presence of fatty tissue. The normal ACL should follow the contour of the intercondylar roof, and attachments should be well delineated. Again, clinicians should be aware of these characteristics to avoid misdiagnosing ACL injuries.11

Vastus

lateralis m. Vastus medialis m.

Plantaris m.

Lateral epicondyle

Fig. 2.39 A coronal T2-weighted image (A) and artist’s sketch (B) of the right knee at the level of the intercondylar notch showing the MCL and LCL. The femoral and tibial articular cartilage is well shown.

Semitendinosus m.

Medial femoral

condyle Semimembranosus tendon

Medial meniscus

(anterior horn)

Medial meniscus (posterior horn)

Gastrocnemius m. (medial head)

Fig. 2.42 A sagittal proton-density image (A) and artist’s sketch (B) of the knee showing the articular cartilage and the anterior and posterior horns of the medial meniscus.

PCL

The PCL attaches on the posterior proximal tibia, inferior to the tibial joint surface. In contrast to the straight course of the ACL, the PCL curves anteriorly to insert on the anterolateral aspect of the medial femoral condyle (Fig. 2.44) because the knee is always imaged in extension. The PCL is usually

seen on at least two images, even on examinations acquired with thick sections. The PCL usually appears as a thicker, darker, curved band compared with the ACL. When present, the ligaments of Humphry and Wrisberg (anterior and posterior meniscofemoral ligaments, which occur concurrently in 70% of knees12) can be seen adjacent to the PCL.