Fig 5.

(A) Masson trichrome stain of a coronal acromion section. The red deltoid muscle becomes tendon, which inserts onto the endplate (blue) through a zone of fibrocartilage. The bone of the acromion appears as red. The deltoid origin (white arrow) occupies 100% of the lateral wall of the acromion. The superior band of collagen (black arrow) is part of the same fibrocartilaginous structure that covers the lateral wall of the acromion. (B) Low-intensity signal (white arrow) on proton density-weighted coronal MRI corresponds to this band of collagen, which is seen arising from the superior acromion and continuing beyond the lateral border of the deltoid.