Trapezoid ligament

At a glance

English

Trapezoid ligament

Latin (TA2)

Ligamentum trapezoideum

System

Ligament

Region

Upper limb

Side

Paired, left and right

About the trapezoid ligament

The coracoclavicular ligament holds the outer end of the clavicle down onto the coracoid process of the scapula. It has two parts, named for their shapes: the cone-shaped conoid ligament behind and medially, and the trapezoid ligament in front and laterally.

The trapezoid ligament is broad, thin and roughly quadrilateral. Its lower edge is anchored along a strip on top of the coracoid, close to its root. From there it rises obliquely, at an angle to the vertical, to the trapezoid line, a rough oblique ridge on the underside of the clavicle that runs forwards and laterally from the conoid tubercle. Its front border is free, while its back border is joined to the conoid ligament. Where the two meet they form an angle that projects backwards, and a bursa or some fat often sits between them. Subclavius and deltoid lie in front of the ligament and trapezius behind.

Its fibres run more horizontally than those of the conoid, and its function differs accordingly. The conoid mainly stops the clavicle lifting off the scapula, while the trapezoid resists the scapula being driven medially under the clavicle, which would otherwise crush the acromioclavicular joint when a force is applied to the side of the shoulder. Both parts also transmit some of the weight of the limb from the scapula to the clavicle and allow the scapula to rotate on the clavicle during arm elevation.

In acromioclavicular injuries the trapezoid and conoid usually tear together once the force exceeds what the acromioclavicular ligament can withstand, and the lateral clavicle then sits high above the acromion. Anatomical reconstructions recreate both bands separately, placing a tunnel at the trapezoid line as well as one at the conoid tubercle.

Attachments and function

Attaches from

A strip on top of the coracoid process, close to its root.

Attaches to

The trapezoid line on the inferior surface of the lateral part of the clavicle.

Function

Resists medial displacement of the scapula beneath the clavicle, helps carry the weight of the limb and allows scapular rotation on the clavicle.

Nerve supply

Twigs of the suprascapular and lateral pectoral nerves.

Blood supply

Branches of the suprascapular and thoraco-acromial arteries.