The Blumensaat line, also known as the intercondylar line, is a key anatomical landmark on the femoral condyle used to evaluate the anterior cruciate ligament (ACL). It is a line corresponding to the roof of the intercondylar fossa of the femur as seen on a lateral knee X-ray or MRI.
Significance of the Blumensaat Line for an Intact ACL:
● Orientation: In a healthy, intact knee, the normal ACL fibers appear steeper and parallel to the Blumensaat line on a sagittal MRI or X-ray.
● Angle: The angle between an intact ACL and the Blumensaat line is typically less than 15 degrees.
● Positioning: The normal femoral attachment of the ACL is on the posterior part of the medial surface of the lateral femoral condyle, with the center of its footprint located in a consistent position relative to the Blumensaat line.
Signs of an Injured ACL in Relation to the Line:
● Abnormal Orientation: An ACL tear is indicated if the angle between the ligament and the Blumensaat line increases (typically >15 degrees), appearing less steep or "flattened".
● Discontinuity: The line can help highlight a lack of continuity in the ACL fibers if they do not reach their normal attachment point in the intercondylar notch.
● Empty Notch Sign: In cases of avulsion at the femoral attachment, fluid signal may be visible at the site where the ACL should insert in the intercondylar notch, which borders the Blumensaat line region.