Coraco-acromial ligament

At a glance

English

Coraco-acromial ligament

Latin (TA2)

Ligamentum coracoacromiale

System

Ligament

Region

Upper limb

Side

Paired, left and right

About the coraco-acromial ligament

Unlike most ligaments, the coraco-acromial ligament does not cross a joint: both its ends are on the same bone, the scapula. It is a strong, flat, triangular band stretched between the coracoid process in front and the acromion behind, and with these two bony processes it forms the coraco-acromial arch, a roof over the head of the humerus.

The narrow apex of the triangle is fixed to the tip of the acromion, just in front of the facet for the clavicle. Its broad base is spread along the whole lateral edge of the coracoid process. Some descriptions divide it into two thicker marginal bands, one reaching the tip and one the base of the coracoid, with a thinner sheet between them that join at the acromion. When pectoralis minor reaches the shoulder capsule instead of stopping at the coracoid, its tendon slips between these bands and the middle sheet is then missing.

Above the ligament lie the clavicle and the deep surface of deltoid. Below it is the supraspinatus tendon, separated from it by the subacromial (subdeltoid) bursa, which lets the tendon glide beneath the arch as the arm moves. From its lateral border a dense fibrous layer continues under deltoid over the tendons of supraspinatus and infraspinatus.

The arch prevents the head of the humerus from being pushed upwards out of the shallow glenoid cavity and protects the rotator cuff from direct blows. It also explains much shoulder pain. When the space under the arch narrows, through a hooked acromion, bony spurs or a thickened ligament, the supraspinatus tendon and bursa are squeezed during elevation of the arm, giving subacromial impingement. Surgeons may trim the acromion and release or recess the ligament to enlarge the space, though in large rotator cuff tears it is usually preserved, as it is then the last check on upward escape of the humeral head.

Attachments and function

Attaches from

The tip of the acromion, just in front of its clavicular facet.

Attaches to

The outer edge of the coracoid process along its full length.

Function

Completes the coraco-acromial arch over the humeral head, resisting its upward displacement and protecting the rotator cuff.

Nerve supply

Branches of the suprascapular and lateral pectoral nerves.

Blood supply

The acromial branch of the thoraco-acromial artery.