Background and indications: The subacromial bursa injection is a commonly performed procedure in orthopedic, musculoskeletal, and pain practices. Surface landmarks provide inadequate appreciation of anatomy, and the rate of inaccurately placed injections is between 13% and 71%.^{1, 2and 3} A surface anatomy-based (“blind”) subacromial injection is often targeted for the region just above the supraspinatus tendon. Unfortunately, the needle often enters superior aspect of the supraspinatus tendon, and the injectate must then rupture through the rotator cuff capsule with subsequent overflow of medications into the superior aspect of the rotator cuff and then spreading into bursa via a ruptured rotator cuff capsule.⁴ Therefore, ultrasound guidance is highly recommended to more accurately target the bursal space.

Anatomy: The subacromial bursa is a very narrow space that is noted just above the supraspinatus muscle. It is a self-contained thin-walled structure extending from the anterolateral aspect of the shoulder (subdeltoid) to the subacromial space and the supraspinatus area. This bursa is the largest in the human body and may accumulate up to 15 to 20 mL of fluid. However, the subacromial space is only a potential space, normally represented by two membranous surfaces separated by a thin film of lubricating fluid.