Corpus: Acromion
Definition
The acromion is a bony projection of the scapula. It emerges from the spine of the scapula and forms the highest point of the shoulder blade.
Anatomy
The superior face of the acromion is roughened and serves as the origin for the deltoid muscle, as does the lateral edge of the acromion. Here, the bone lies directly subcutaneous and can be palpated as an anatomical reference point.
On the medial edge of the acromion, there is a small oval surface that forms the joint connection to the clavicle. This joint is referred to as the acromioclavicular joint.
The acromion is connected to the coracoid process via the coracoacromial ligament, thus forming the roof of the shoulder joint (fornix humeri).
The acromion, together with the clavicle, forms the bony basis of the shoulder.
Clinic
The shape of the acromion plays a role in subacromial impingement. According to Bigliani, four shapes are distinguished in the sagittal view, with Type 2 being the most common, featuring a concave underside parallel to the head of the humerus. Type 3 has a ventrally located, caudally directed enthesophyte, associated with a higher incidence of shoulder impingement.
A lateral downward slope of the acromion and a low-lying acromion are also risk factors for impingement. Normally, the underside of the acromion runs parallel to the lateral clavicle in the oblique coronal plane. Quantification in MRI is not advisable due to variable angulation and slice positioning.
The lateral extension of the acromion also plays a role.