Trapezoid Ligament: Anatomy, Function, Relations, Imaging

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Trapezoid ligament

The trapezoid ligament is the lateral and anterior portion of the coracoclavicular ligament complex, which stabilizes the acromioclavicular (AC) joint by connecting the clavicle to the coracoid process of the scapula. It lies anterolateral to the conoid ligament, together forming a strong suspensory complex that anchors the clavicle to the scapula and maintains vertical stability of the shoulder girdle.

The trapezoid ligament is broad, flat, and quadrilateral in shape. It resists compression and shearing forces that would otherwise displace the clavicle medially or superiorly. It plays a crucial biomechanical role in maintaining the normal alignment and coordinated motion of the clavicle and scapula during upper limb movement.

Synonyms

Lateral coracoclavicular ligament
Anterior division of the coracoclavicular ligament

Location and Structure

Position: Lateral and anterior to the conoid ligament, forming part of the coracoclavicular ligament complex.
Shape: Broad, flat, quadrilateral band of dense connective tissue.
Orientation: Runs superolaterally from the coracoid process of the scapula to the clavicle.
Texture: Dense fibrous collagenous structure with a slightly oblique orientation to the coronal plane.

Attachments

Inferior attachment: Upper surface of the coracoid process of the scapula, near its lateral border.
Superior attachment: Trapezoid line on the inferior surface of the clavicle, approximately 2–3 cm from its lateral end.
The ligament fibers pass superolaterally and slightly anteriorly, forming a firm connection between the scapula and clavicle.

Relations

Superiorly: Subclavius muscle and clavicular attachments of the deltoid and trapezius.
Inferiorly: Coracoid process and attachments of the pectoralis minor.
Medially: Conoid ligament (the medial component of the coracoclavicular ligament).
Laterally: Acromioclavicular joint capsule.
Anteriorly: Clavipectoral fascia and pectoralis minor tendon.
Posteriorly: Supraspinatus and coracoclavicular bursa (when present).

Nerve Supply

Sensory innervation from lateral pectoral nerve and supraclavicular nerves, via periosteal and capsular branches.

Function

Primary stabilizer: Prevents excessive superior displacement of the clavicle relative to the scapula.
Suspensory support: Contributes to maintaining the vertical stability of the shoulder girdle.
Force transmission: Transfers mechanical loads between the clavicle and scapula during elevation and rotation.
Dynamic function: Works with the conoid ligament to control the scapuloclavicular motion arc during shoulder abduction and flexion.

Clinical Significance

Injury: Frequently involved in acromioclavicular (AC) joint separations; partial or complete rupture leads to clavicular elevation and instability.
Grading: Lesions form part of Rockwood classification of AC joint injuries (Type II–VI).
Degeneration: Chronic stress may cause ligament thickening, calcification, or ossification.
Surgical importance: Reconstruction or augmentation often required in coracoclavicular ligament repair procedures.
Imaging relevance: MRI and CT crucial in evaluating partial tears, complete ruptures, and post-surgical repair integrity.

MRI Appearance

T1-weighted images:
- Normal ligament: Low signal (dark band) extending from the coracoid to the clavicle.
- Marrow of clavicle/scapula: Bright signal due to fatty content.
- Surrounding fat planes: High signal intensity outlining ligament margins.
- Tear: Focal or complete discontinuity with interposed bright signal from hemorrhage or edema.
T2-weighted images:
- Normal ligament: Low signal (dark linear band).
- Acute tear: Bright hyperintense signal due to fluid or hemorrhage within or around ligament.
- Partial tear: Thickened ligament with central or marginal high signal intensity.
- Chronic injury: Irregular, thinned, or wavy fibers with intermediate signal intensity.
STIR:
- Normal ligament: Low signal structure with sharp margins.
- Acute pathology: Bright hyperintense periligamentous edema or hemorrhage.
- Excellent for differentiating acute sprain vs chronic scarring.
Proton Density Fat-Saturated (PD FS):
- Normal: Thin, dark band between coracoid and clavicle.
- Tear: Bright signal interruption with adjacent soft-tissue edema.
- Chronic degeneration: Diffuse thickening with irregular signal.
- Ideal for postoperative assessment and subtle partial disruptions.
T1 Fat-Sat Post-Contrast:
- Normal ligament: Minimal enhancement.
- Inflammation or healing tissue: Mild to moderate enhancement along fibers.
- Postoperative repair: Granulation or scar tissue shows rim or diffuse enhancement.

CT Appearance

Non-Contrast CT:

Ligament: Appears as a thin soft-tissue density band extending between the coracoid process and clavicle.
Coracoid and clavicle cortices: Sharp, high-attenuation margins.
Acute tear: Poor definition or discontinuity of ligament density; possible widening of coracoclavicular interval.
Chronic changes: Calcification or ossification along ligament fibers.

MRI image

CT image

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