Anterolateral Ligament of Knee (ALL): Anatomy, Attachments, Relations, Function, Clinical Significance, MRI & CT Imaging

Topic

Anterolateral ligament of knee

The anterolateral ligament (ALL) of the knee is a distinct capsular structure located in the anterolateral aspect of the joint. It plays an important role in rotational stability, particularly in association with the anterior cruciate ligament (ACL). The ligament extends from the lateral femoral condyle to the anterolateral proximal tibia, with close attachment to the lateral meniscus.

The ALL has gained attention in recent years due to its association with persistent instability following ACL injury or reconstruction, and in the mechanism of the classic Segond fracture.

Synonyms

ALL of the knee
Capsular ligament of the anterolateral knee
Anterolateral capsular thickening

Origin and Insertion

Origin: Lateral femoral condyle, just proximal and posterior to the origin of the lateral collateral ligament (LCL)
Course: Fibers descend obliquely anteroinferiorly across the anterolateral knee joint
Insertion: Proximal tibia between Gerdy’s tubercle (iliotibial band attachment) and the fibular head, with additional fibers attaching to the lateral meniscus

Relations

Anteriorly: Overlapped by the iliotibial band
Posteriorly: Related to the lateral collateral ligament (LCL) and popliteus tendon
Superiorly: Originates from the lateral femoral condyle, near ACL origin
Inferiorly: Inserts on the proximal tibia near Gerdy’s tubercle and fibular head
Medially: Attached to the lateral meniscus (meniscocapsular connection)
Laterally: In close relation to subcutaneous tissue of the knee

Nerve Supply

Supplied by articular branches of the common peroneal nerve and femoral nerve (via genicular branches)

Arterial Supply

Genicular branches of the lateral inferior genicular artery and superior lateral genicular artery

Venous Drainage

Drains into the corresponding genicular veins → popliteal vein

Function

Provides rotational stability of the knee, especially during internal tibial rotation
Acts as a secondary stabilizer in ACL-deficient knees
Contributes to the control of the pivot shift phenomenon
Prevents excessive anterolateral translation of the tibia

Clinical Significance

ALL injuries frequently occur with ACL tears
Associated with Segond fracture (avulsion of its tibial attachment)
May contribute to persistent instability after ACL reconstruction
Important in sports injuries and pivoting activities (soccer, basketball, skiing)
Imaging recognition helps in surgical planning and reconstruction techniques

MRI Appearance

T1-weighted images:

Appears as a thin linear low-signal structure extending from femur to tibia
Surrounded by bright fat, which improves visualization

T2-weighted images:

Ligament normally appears as a low-signal band
Injury or tear appears as discontinuity, thickening, or high signal within the ligament

STIR (Short Tau Inversion Recovery):

Normal ALL remains low signal
Acute sprain or tear shows bright hyperintensity

Proton Density Fat-Saturated (PD FS):

Best sequence for visualization
Normal ALL appears as a low-signal band
Pathology (partial tear, sprain) appears with bright signal intensity

T1 Fat-Sat Post-Contrast:

Normal ligament shows minimal to no enhancement
Injured ligament may show enhancement at attachment sites (enthesitis) or with associated synovitis

CT Appearance

Non-Contrast CT:

ALL not directly visualized due to its thin fibrous nature
May be inferred if a Segond fracture (small avulsion fragment at tibial insertion) is present
Surrounding soft tissues provide indirect localization

Post-Contrast CT: