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

Fig. 8.7 Vertical longitudinal tear in the right knee. (A) A sagittal fatsuppressed proton-density image shows a peripheral vertical longitudinal tear (arrow) of the posterior horn of the medial meniscus. Note the e usion and Baker cyst. (B) A coronal fat-suppressed T2-weighted

image shows the vertical longitudinal tear (arrow), propagating parallel to the meniscal curvature. Note the tear of the posterior horn of the lateral meniscus (arrowhead) with an adjacent lateral tibial plateau bone bruise in this patient with an acute ACL tear.

Fig. 8.8 Bucket-handle tear in the right knee. (A) A sagittal fat-sup- pressed proton-density image shows a meniscal flap (arrow), arising from the medial meniscus and displaced inferior to the PCL (arrowhead), exhibiting the double-PCL sign. (B) A coronal fat-suppressed

T2-weighted image shows a centrally displaced meniscal flap (arrow) inferior to the PCL. Note the abnormal morphology of the nondisplaced medial meniscal remnant.

Fig. 8.9 Artist’s sketches illustrating a displaced bucket-han- dle tear of the medial meniscus in the axial plane (A) and from an anterior perspective (B).

function.18 Failure to address surgically the presence of a displaced meniscal flap or fragment represents a cause of persistent joint pain and dysfunction after arthroscopy.19 Unstable meniscal tears may exhibit central or peripheral flap displacement. A typical bucket-handle tear represents a vertical longitudinal tear with central displacement of meniscal tissue. If the medial meniscus is involved, the flap is displaced inferior to the PCL, creating the double-PCL

B

sign20 (Figs. 8.8 and 8.9). Bucket-handle tears of the lateral meniscus often exhibit anterior central displacement of a flap arising from the posterior horn of the meniscus (Fig. 8.10). Displaced bucket-handle tears are a common cause of locked knee in an athlete. Posterior central flap displacement may also occur with a flap arising from the posterior horn of the medial meniscus and the displaced meniscal tissue positioned in the recess between the distal PCL and

the medial meniscus (Fig. 8.11). Meniscal tissue may also displace peripherally into the recess between the capsule and the femoral condyle (Fig. 8.12) or between the capsule and the tibial plateau (Fig. 8.13). Although peripherally displaced tears are less likely than centrally displaced tears to result in locking, they tend to cause adjacent capsular inflammation and osseous stress reaction, contributing to pain related to the meniscal tear. Preoperative identification and

localization of the displaced meniscal flap with MRI contribute to a more expeditious operative procedure.10

The designation of a tear as complex, based on MRI findings, implies that the tear exhibits multiple vectors or that the meniscus appears macerated and fragmented. These tears are usually unstable and, if chronic, are associated with chondromalacia and osseous stress reaction, also identified on MRI.

A

Patella

Anterior bucket-handle fragment

Anterior horn of the lateral meniscus

Tibial tuberosity

Posterior bucket-handle fragment

PCL

Fig. 8.12 This coronal fat-suppressed T2-weighted image of the right knee shows the peripheral superior displacement of a large meniscal flap (arrow), arising from the medial meniscus and extending into the recess medial to the medial femoral condyle.

Fig. 8.13 This coronal fat-suppressed T2-weighted image of the right knee shows the peripheral inferior displacement of a meniscal flap (arrow), arising from the medial meniscus and extending into the recess medial to the medial tibial plateau. Note the adjacent osseous stress reaction (arrowhead) and pericapsular edema.

Fig. 8.16 This sagittal fat-suppressed proton-density image shows the pseudomass appearance (arrow) of an acute ACL tear.

that shows high signal on T2-weighted imaging and low signal on T1-weighted imaging (Fig. 8.16). With both acute and chronic ACL tears, the ligament may appear abnormal in angulation, typically because of inferior displacement of the proximal portion of the ligament. Acute tears of the ACL are

Table 8.3 Signs of an ACL Tear on MRI

Primary signs

•Nonvisualization of ligament

•Complete disruption of a ligament segment

•Abnormal signal within ligament on T2-weighted images

•Alteration of normal linear configuration of ligament

•Alteration of normal angulation of ligament

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

often accompanied by bone bruises involving the posterior aspect of the lateral tibial plateau, the anterolateral aspect of the lateral femoral condyle with impaction of the articular surface notch, and the posterior aspect of the medial tibial plateau (Fig. 8.17). The osseous contusions are related to

Fig. 8.17 Bone bruise pattern with ACL tear. (A) A sagittal fatsuppressed proton-density image shows a bone bruise (arrow) with osteochondral impaction involving the lateral femoral condyle and a bone bruise (arrowhead) involving the posterior aspect of the lateral

tibial plateau. (B) A coronal fat-suppressed T2-weighted image of the right knee shows bone bruises involving the posterior aspect of the lateral tibial plateau (arrowhead) and medial tibial plateau (arrow).

A

C

to a single high-energy event that might produce an acute ACL tear. Minimal to no instability is seen on physical examination. The MRI may show evidence of advanced degeneration of the ACL with thickening of the ligament and less increase in T2-weighted signal than that which is typically seen with an acute tear (Fig. 8.21). Such patients also often have similar PCL involvement.

B

Fig. 8.19 Lateral meniscal tear with ACL tear. Sagittal protondensity (A), sagittal fat-suppressed T2-weighted (B), and coronal fatsuppressed T2-weighted (C) images of the right knee show a peripheral tear of the posterior horn of the lateral meniscus (arrow on each), associated with the attachment of the meniscofemoral ligament. Note the proximal tibial bone bruises, typical for an acute ACL injury.

PCL Tears

The PCL is more robust and more consistently has lower signal on MRI than does the ACL. MRI is very sensitive for tears of the PCL because of its normal low signal (Fig. 8.22). Any increased signal within the PCL on T2-weighted images is suspicious for injury.29–31 The PCL can be torn partially, indicated by increased signal on T2 images with the ligament in continuity (Fig. 8.23), or completely, visualized as a loss of

Fig. 8.20 This coronal fat-suppressed T2-weighted image of the right knee shows a Segond fracture (arrow) of the lateral aspect of the lateral tibial plateau at the capsular attachment in a patient with an acute ACL tear.

Fig. 8.21 This sagittal fat-suppressed proton-density image shows advanced degeneration (marked thickening) of the ACL (arrow).

Fig. 8.22 This sagittal T2-weighted image shows a normal PCL. Note the absence of signal within the PCL.

Fig. 8.23 This sagittal T2-weighted image shows thickening and abnormal signal intensity of the PCL (arrow), corresponding to a tear.