Acl ligamnet anatomy

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ACL anterior cruciate ligament anatomy bundles attachments

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Anterior Cruciate Ligament (ACL) Anatomy

Overview

The ACL is an intra-articular but extrasynovial ligament - it sits inside the knee joint capsule but is wrapped in its own synovial sheath. It runs in an anteromedial direction from the femur to the tibia.

Length: 22-41 mm (variable)
Width: 7-12 mm (consistently narrowest at the midsubstance)

Two-Bundle Structure

The ACL is made up of two distinct fiber bundles, named according to their tibial insertion:

Feature	Anteromedial (AM) Bundle	Posterolateral (PL) Bundle
Length	~38 mm	~20 mm
Femoral origin	Superior and anterior portion of the lateral femoral condyle attachment (9:30-11:30 o'clock)	Posterior and inferior portion (8:30-10 o'clock)
Tibial insertion	Anteromedial part of the intercondylar fossa	Posterolateral part of the intercondylar fossa
Tension in extension	Relatively lax	Taut
Tension in flexion	Taut (especially beyond 45°)	Becomes lax
Primary function	Resists anterior tibial translation during flexion	Resists anterior translation in extension + rotational control

The two bundles are sometimes separated by a bony ridge called the lateral bifurcate ridge on the femur.

ACL two-bundle anatomy - right knee, anterior view showing AM and PL bundles, lateral femoral condyle, and medial tibial plateau

Femoral Attachment

Located on the posteromedial edge of the lateral femoral condyle, posterior to the lateral intercondylar ridge (also called the Resident's Ridge)
The attachment is oval in shape
The AM bundle arises from the superior and anterior aspect
The PL bundle arises from the posterior and inferior aspect

Using the clock-face convention (based on the posterior outlet of the femoral intercondylar notch):

AM bundle: 9:30 to 11:30
PL bundle: 8:30 to 10:00
Distance between the two bundle centers: 8-10 mm

Tibial Attachment

Located on the tibial plateau in the anterior intercondylar fossa, between the medial and lateral tibial spines
Positioned anterolateral to the medial tibial spine
The tibial footprint is ~120% larger than the femoral footprint
Some fibers pass deep to the transverse meniscal ligament
Some fibers merge with the anterior horn of the lateral meniscus

Course and Orientation

As the two bundles pass through the intercondylar notch, they lie behind each other (not side by side), giving the ACL an oval cross-section. The ligament twists slightly as it courses from femur to tibia in an anterior and medial direction.

Blood Supply and Innervation

Primary blood supply comes from the middle genicular artery (a branch of the popliteal artery), which penetrates the posterior capsule and travels within the synovial sheath
Nerve supply includes fibers from the posterior articular nerve (branch of the tibial nerve), carrying both pain fibers and mechanoreceptors (Ruffini endings, Pacinian corpuscles) important for proprioception

Functional Summary

Function	Bundle Responsible
Primary resistance to anterior tibial translation	Both (AM dominant in flexion, PL in extension)
Rotational stability / screw-home mechanism	Primarily PL bundle
Hyperextension prevention	PL bundle
Stability beyond 45° flexion	AM bundle (dominant)

Sources: Rockwood and Green's Fractures in Adults, 10th ed. 2025, p. 3058 | THIEME Atlas of Anatomy: General Anatomy and Musculoskeletal System, p. 473

Create a visual poster showing ACL anatomy with bundle locations

Generating Image

Medical education poster titled "ACL Anatomy" showing the anterior cruciate ligament of the knee. The poster includes: (1) a large central anatomical diagram of the right knee joint opened anteriorly showing the two ACL bundles - the Anteromedial (AM) bundle colored in teal/blue and the Posterolateral (PL) bundle colored in orange/gold, both running from the lateral femoral condyle down to the tibial plateau; (2) a top inset showing the femoral attachment with clock-face positions labeled - AM bundle at 9:30-11:30, PL bundle at 8:30-10:00, with the lateral intercondylar ridge (Resident's Ridge) and bifurcate ridge labeled; (3) a bottom inset showing the tibial footprint on the tibial plateau with AM and PL bundle insertion zones labeled, noting the tibial footprint is 120% larger than the femoral; (4) a side panel with a comparison table showing AM vs PL bundle properties: length (38mm vs 20mm), tension in flexion vs extension, and function; (5) labels pointing to key structures: lateral femoral condyle, medial tibial spine, lateral tibial spine, transverse meniscal ligament, lateral meniscus, medial meniscus; (6) clean white background, professional medical illustration style with clear labels, bold title, color-coded legend for AM (teal) and PL (orange) bundles

Here's your ACL anatomy poster. It covers:

Central knee diagram with the AM bundle (teal) and PL bundle (orange) clearly distinguished
Femoral attachment inset with clock-face positions (AM: 9:30-11:30, PL: 8:30-10:00) and the Resident's Ridge / bifurcate ridge landmarks
Tibial footprint inset showing the larger tibial insertion zone in the anterior intercondylar fossa
AM vs PL comparison with length, tension behavior, and functional roles
Key surrounding structures labeled (menisci, tibial spines, transverse meniscal ligament)

Let me know if you'd like any section expanded, a different orientation (e.g., sagittal view), or a version focused on a specific aspect like the tibial footprint or bundle biomechanics.

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