Os Acromiale

An os acromiale is an accessory ossification center of the acromion that fails to fuse to the acromion proper by the age of 22 years. The os acromiale may articulate with the acromion by fibrous tissue, cartilage, periosteum, or synovium.

Depending on the location of its articulation with the acromion, an os acromiale may be classified as pre-, meso-, meta-, or basi-acromion (see figure).

An os acromiale can be seen in up to 15% of the population, is bilateral in 60% of cases, and may or may not be symptomatic. Most are meso or meta-acromions.

References

Steinbach LS. Chapter 4. In Chung CB and Steinbach LS. MRI of the Upper Extremity: Shoulder, Elbow, Wrist, and Hand. Lippincott Williams & Wilkins. 2010. p 250.