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Trapezoid Line

linea trapezoidea

The trapezoid line is a short, rough ridge on the underside of the outer clavicle, running forward and outward from the conoid tubercle. It marks the attachment of the trapezoid ligament, the flatter, more lateral part of the coracoclavicular ligament. Together the conoid tubercle and trapezoid line anchor the clavicle to the coracoid process below.

Anatomical Data

Structure & Landmarks

Articulations	No joint; attachment of the trapezoid part of the coracoclavicular ligament
Landmarks	Inferior surface of the lateral clavicle Extends anterolaterally from the conoid tubercle Trapezoid ligament attachment
Ossification	Part of the clavicle, which ossifies in membrane; the ridge develops with ligament pull.

Clinical Relevance

Clinical Notes

In anatomic coracoclavicular ligament reconstruction, a second tunnel or fixation point is placed at the trapezoid line to recreate the trapezoid ligament, which mainly resists compression and horizontal translation of the AC joint. Excising too much of the outer clavicle during distal clavicle resection can damage the trapezoid ligament attachment and cause instability. The line is visible on CT and helps surgeons judge how much bone can be safely removed.

Pathology

Common Injuries & Conditions

AC Joint Instability after Distal Clavicle Excision

Excessive removal of the outer clavicle can detach the trapezoid ligament from its line, leaving the clavicle unstable and painful.

Coracoclavicular Ligament Rupture

Tearing of the trapezoid and conoid ligaments in high-grade AC joint separations.

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