Anatomy of bundles of ACL and PCL.

A) Anatomy of PCL:

The normal PCL (arrow) demonstrates homogeneously low signal and a smooth contour on sagittal images as depicted on this proton-density weighted sagittal image.

A coronal proton-density weighted image through the posterior intercondylar region demonstrates the posteromedial bundle attachment of the PCL (arrow) to the medial femoral condyle. The ligament of Wrisberg is also seen just superior to the PCL (small arrow). The ACL origin is depicted (asterisk).

A second coronal proton-density weighted image anterior to (6a) demonstrates the normal ovoid low-signal appearance of the PCL in the intercondylar notch. The ACL is also demonstrated (asterisk).

Mild intrasubstance increased signal is present in the proximal PCL (arrow) compatible with a mild interstitial partial tear. The distal portion of the PCL is not depicted because of slice angle, but on contiguous images the PCL over this level was intact.

A sagittal T2 weighted image demonstrates a tibial avulsion fracture (arrow) at the PCL attachment. The tibial fracture fragment (arrowhead) is mildly elevated. Although mildly lax, the PCL demonstrates normal signal with no evidence for ligamentous injury. Hemarthrosis is demonstrated by layered blood in the anterior joint space (small arrows).

A sagittal fat-suppressed proton-density weighted image demonstrates a proximal tear of the PCL near the femoral attachment (arrow). Hemorrhage and edema associated with a posteriorly disrupted capsule (arrowheads) are demonstrated deep to the medial gastronemius muscle. An anterior tibial bone bruise is also depicted (asterisk).

Sagittal image in same patient as (10a) demonstrates hemorrhage and edema of the posterolateral capsule and ligamentous structures, suggesting a posterolateral corner injury.

A coronal fat-suppressed proton-density weighted image of the same patient in (10a) and (11a) demonstrates abnormal hyperintensity at the PCL-bone interface (arrow). Edema within the fibular collateral ligament (short arrow) is compatible with a ligament sprain. Hemorrhage and edema are present along the posteromedial capsule and posterior oblique ligaments (arrowheads). The findings in (10a-12a) indicate a combined PCL injury with associated injury of the posterolateral corner.

Sagittal fat-suppressed proton-density weighted image demonstrates a lax and attenuated PCL (arrow) compatible with a chronic partial tear.

B) Graphic Anatomy:

This 3-D graphic representation of the knee in extension with the medial femoral condyle removed depicts laxity of the anteromedial bundle (red) and a taut posterolateral band (blue).

In flexion, the anteromedial band (red) becomes taut and the posterolateral band (blue) becomes lax.

A 3-D representation of the PCL bundles with the knee in flexion and the lateral femoral condyle removed depicts laxity of the posteromedial bundle (blue) and a taut anterolateral bundle (red).

The anterolateral bundle (red) becomes lax and the posteromedial bundle (blue) taut in extension.

During extension:
-AM of ACL and AL of PCL are lax while they are taut during flexion and vice versa.
During flexion:
-AM of ACL and AL of PCL are taut and vice versa.




C) MR Anatomy of ACL:

A fat-suppressed proton-density weighted sagittal image demonstrates the normal straight anterior margin of the ACL correlating with the anteromedial band. Note the normal striated appearance of the ACL.

The normal ACL is ovoid and of low signal on axial images at the mid-intercondylar level demonstrated on this axial T2-weighted FSE image. The regions of the anteromedial band (red) and the posterolateral band (blue) are indicated by the superimposed oval.

A fat-suppressed proton-density sagittal image demonstrates a poorly defined ACL with intrasubstance increased signal (arrows). The yellow lines indicate the area covered and the angle used in obtaining coronal oblique images to better demonstrate the ACL.

This T2-weighted coronal oblique view of the same knee as in illustration (8a) demonstrates a normal appearance of the ACL (arrows).

In another patient, the T2-weighted coronal oblique image depicts a high-grade partial tear of the proximal ACL. The anteromedial bundle fibers are completely disrupted at the femoral origin (arrowhead) and the posterolateral band fibers are lax (arrow).









Reference