Topics

Topic

design image
Superior acromioclavicular ligament

The superior acromioclavicular ligament (SACL) is a strong fibrous band that reinforces the superior part of the acromioclavicular (AC) joint capsule. It connects the superior surface of the lateral clavicle to the adjacent upper surface of the acromion process of the scapula, maintaining the integrity and stability of the AC joint.

It is one of the primary static stabilizers of the joint, working together with the inferior acromioclavicular ligament and the coracoclavicular ligaments (trapezoid and conoid parts). The SACL resists superior displacement of the clavicle and prevents horizontal translation during shoulder motion.

Synonyms

  • Superior AC ligament

  • Superior capsular ligament of the AC joint

  • Acromioclavicular joint superior reinforcement

Location and Structure

  • Type: Capsular ligament, part of the fibrous AC joint capsule.

  • Shape: Flat, rectangular band of dense fibrous tissue.

  • Orientation: Runs obliquely between the acromion and the clavicle, covering the superior aspect of the AC joint.

  • Continuity: Blends with the trapezius fascia and fibers of the deltoid aponeurosis, strengthening the superior joint capsule.

Attachments

  • Medial attachment: Superior surface of the lateral end of the clavicle.

  • Lateral attachment: Upper surface of the acromion process of the scapula.

  • Fibrous continuity: Merges posteriorly with the trapezius fascia and anteriorly with the deltoid fascia.

Relations

  • Superiorly: Trapezius muscle and deep fascia of shoulder region.

  • Inferiorly: Acromioclavicular joint capsule and intra-articular disc (if present).

  • Anteriorly: Deltoid muscle fibers.

  • Posteriorly: Fibers of trapezius and posterior joint capsule.

  • Deep to ligament: Acromioclavicular joint cavity, which may contain a fibrocartilaginous disc.

Nerve Supply

  • Supplied by lateral pectoral nerve and suprascapular nerve branches contributing to the AC joint innervation.

Function

  • Joint stabilization: Prevents superior and posterior displacement of the clavicle relative to the acromion.

  • Capsular reinforcement: Strengthens the superior aspect of the AC joint capsule.

  • Load distribution: Transfers load between clavicle and scapula during arm elevation and shoulder girdle movement.

  • Dynamic support: Works synergistically with deltoid and trapezius fascia to maintain AC joint congruity during motion.

Clinical Significance

  • Sprains and tears: Common in AC joint injuries (Rockwood types I–III). The ligament may be stretched, partially torn, or completely disrupted.

  • Shoulder separation: Complete rupture of superior AC ligament combined with coracoclavicular ligament injury leads to clavicular elevation and AC joint widening.

  • Degenerative changes: Chronic stress or repetitive overhead activity can cause thickening or calcification visible on imaging.

  • Post-traumatic instability: Leads to pain, prominence at distal clavicle, and impaired shoulder mechanics.

  • Imaging relevance: MRI and CT are essential for assessing AC joint integrity, ligament disruption, and post-surgical repair.

MRI Appearance

  • T1-weighted images:

    • Ligament: Low signal (dark linear band) between acromion and clavicle.

    • Adjacent fat planes: Bright signal outlining the ligament.

    • In acute injury: Discontinuity or irregular low-signal fibers with surrounding bright edema.

    • Chronic injury: Thinned or scarred ligament with intermediate signal intensity.

  • T2-weighted images:

    • Normal ligament: Low signal intensity against bright joint fluid or fat.

    • Acute sprain or tear: Bright hyperintense signal within or around ligament fibers due to edema or hemorrhage.

    • Chronic degeneration: Mild thickening, irregular margins, and heterogeneous intermediate signal.

    • Associated findings: AC joint effusion, periarticular edema, and coracoclavicular ligament involvement.

  • STIR:

    • Normal ligament: Dark, sharply defined.

    • Pathology: Bright hyperintense signal around disrupted or edematous ligament fibers.

    • Useful for detecting subtle sprains, capsular distension, or fluid tracking along the joint capsule.

  • Proton Density Fat-Saturated (PD FS):

    • Ligament: Normally dark continuous band.

    • Partial tears: Bright linear intraligamentous hyperintensity without complete discontinuity.

    • Complete tears: Full discontinuity with surrounding high-signal fluid and joint widening.

    • Excellent for assessing associated deltoid-trapezial fascia injury and mild instability.

  • T1 Fat-Sat Post-Contrast:

    • Normal ligament: Minimal or no enhancement.

    • Inflammatory or postoperative changes: Enhance peripherally or diffusely.

    • Chronic scar: Minimal enhancement; low-signal fibrotic appearance.

CT Appearance

Non-Contrast CT:

  • Ligament itself not directly visualized due to thinness, but AC joint capsule margins may be inferred.

  • Bony landmarks: Clear visualization of acromion and clavicle alignment.

  • Pathology:

    • Widened AC joint space in ligament rupture.

    • Small avulsion fragments from acromion or clavicle may be visible.

    • Chronic degeneration shows irregular cortical margins or ossification at ligament attachment sites.

MRI images

Superior acromioclavicular ligament axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Superior acromioclavicular ligament sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Superior acromioclavicular ligament coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000