What is type 2 acromion?

Type II Acromion:

- There is an osseous connection between the acromion and the coracoid process, through which the supraspinatus muscle passes.

- The coracoacromial ligament ossifies into a bony arch above the supraspinatus tendon.

- The base of the osseous connection is broad, and the osseous connection narrows at its distal extent, through which the supraspinatus tendon passes.

- Osseous union between acromion and coracoid

- Prevalence: 1-6% of population

- Associated with acromioclavicular degenerative disease: 85% of cases

- Associated with rotator cuff issues: 25-50% of cases

- May be asymptomatic OR may cause pain due to impingement of supraspinatus tendon

Imaging Findings:

- On transaxial images, a bony bridge with a broad base will be seen in the interval between the acromion and the coracoid process, usually without evidence of degenerative disease in the surrounding structures.

- On coronal images, a “hooked beak” appearance is often created by this osseous bridge, especially when the acromion also curves superiorly.

- Rarely, a fibrous connection may be seen at the coracoacromial interval, which may create confusion in interpreting this variant as a Type I acromion.

- Note: the distal extent of the osseous bridge may be the only point where a supraspinatus tendon passes, potentially creating a point of impingement of the tendon.