Anterior Cruciate Ligament
The knee should be positioned with 10°–15° of external rotation to bring the anterior cruciate ligament (ACL) into the sagittal plane. Alternatively, the same effect can be achieved by tilting of the imaging plane (sagittal oblique orientation). Specific
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3.1 Technique and Method The knee should be positioned with 10°–15° of external rotation to bring the anterior cruciate ligament (ACL) into the sagittal plane. Alternatively, the same effect can be achieved by tilting of the imaging plane (sagittal oblique orientation). Specific queries regarding the area of the ACL may require a slice thickness of 3 mm. Sagittal (oblique), coronal, and axial imaging planes. Sagittal sections provide the best overview while coronal and axial projections may yield useful additional information, especially in inconclusive cases. Also helpful are 3D acquisitions with reconstruction of the area of interest and direct 3D visualization of the ACL (higher spatial resolution but poorer image contrast).
3.2 Anatomy The ACL is a 3–4 cm long band of parallel fibers that extends from the medial side of the anterior tibial plateau to the most posterior aspect of the medial surface of the lateral femoral condyle. Anatomic measurements have shown that the center of the tibial attachment is situated at 41–43% of the greatest sagittal diameter of the tibial plateau (0% anteriorly, 100% posteriorly); see Diagram 1a, p. 59. Using the quadrant method according to Bernard and Hertel (1996), the center of the femoral attachment of the ACL as seen from the side lies in the distal lower corner of the uppermost posterior quadrant, which is at 25% of the greatest posterior condyle diameter measured along Blumensaat’s line (0% posteriorly, 100% anteriorly) and at 25% of the height of the femoral condyle measured perpendicular to this line (0% superiorly, 100% inferiorly); see Diagram 1b, p. 59. The diameter of the ACL is smaller in its midportion than at its attachments (trumpet-shaped conP. Teller et al., MRI Atlas of Orthopedics and Traumatology of the Knee © Springer-Verlag Berlin Heidelberg 2003
figuration). The course of the ACL is straight in nearly full knee extension and slightly curved when the joint is flexed. In extension, its anterior fibers run parallel to Blumensaat’s line. Hyperlaxity of the knee joint may be associated with physiologic diversion of the anterior ACL fibers around the anterior edge of the intercondylar notch. Depending on the extension and configuration of the infrapatellar plica (mucous ligament), there is variable covering of the ACL by synovium or structures of the plica.
3.3 Normal MRI Appearance Well-defined contour, straight course, delineation of individual fiber bundles. Mainly of intermediate signal intensity when the fibers are fanned, decreasing intensity with more compact bundling of fibers. High-signal-intensity areas correspond to synovium and/or fatty tissue (Figs. 3.1–3.5).
3.4 Pathomechanism The ACL can undergo partial or complete rupture, either alone or in conjunction with injury to other ligaments of the knee. Isolated ACL rupture is most commonly caused by extension/hyperextension with internal rotation as well as deceleration during active quadriceps muscle contraction. Combined injuries are induced by excessive flexing rotation (e.g.“unhappy triad” co
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