Anterior cruciate ligament

Anterior cruciate ligament (ACL) is one of the two cruciate ligaments that stabilise the knee joint

The ACL arises from the anteromedial aspect of the intercondylar area on the tibial plateau and passes upwards and backwards to attach to the posteromedial aspect of the lateral femoral condyle. 

Like the posterior cruciate ligament, the ACL is intracapsular but extrasynovial.

The ACL consists of two components 4:

  1. anteromedial bundle (AMB)
    • attaches to roof of intercondylar notch
  2. posterolateral bundle (PLB)
    • more vertically orientated, and slightly shorter
    • attaches to wall of intercondylar notch

The ACL functions to prevent posterior translation of the femur on the tibia (or anterior displacement of the tibia) during flexion-extension of the knee. The AMB is responsible for the posterior translation of the femur at 30 degrees flexion, and the PLB resists hyperextension and prevents posterior translation of the femur in extension 1, 2

MRI

Unlike other ligaments or tendons, the ACL normally as a heterogeneous appearance and the AMB and PLB are defined by surrounding high-intensity structures 1

The ACL Blumensaat line angle is normally ≤15º. It is calculated by drawing a line parallel to the roof of the intercondylar notch of the femur (Blumensaat's line) and one parallel to the distal portion of the ACL. The angle is calculated at the intersection of these two lines. An angle of >15º indicates an abnormal course and probable ACL tear 3.

Lower limb anatomy
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Article information

rID: 23201
Section: Anatomy
Synonyms or Alternate Spellings:
  • ACL
  • Anterior cruciate ligament (ACL)
  • ACL Blumensaat's line angle

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Cases and figures

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    Case 1: normal cruciate ligaments (MRI)
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