The infraspinatus bursa is a small fluid-lined sac near the back of the shoulder. It sits beneath the infraspinatus tendon and helps reduce friction as the tendon moves over nearby tissue.

Location

On the posterior side of the shoulder joint
Deep to the infraspinatus tendon
Close to the back of the glenohumeral joint capsule
Separate from the much larger subacromial-subdeltoid bursa in most people

Small shoulder bursae vary between people, and some may communicate with the joint. That makes their appearance less predictable than the major subacromial-subdeltoid bursa.

Function

The bursa provides a low-friction surface between the infraspinatus tendon and deeper structures. It supports smooth tendon movement when the arm rotates outward and during overhead activity.

Why It Matters

This bursa is not a common stand-alone diagnosis. Posterior shoulder pain is more often discussed in relation to the infraspinatus tendon, the joint, the labrum, or referred symptoms from the neck.

Fluid or irritation around a small bursa on imaging therefore needs to be interpreted alongside the examination and the rest of the scan. Its location alone cannot identify the source of pain.

Infraspinatus — the rotator cuff muscle directly above it
Glenohumeral joint capsule — the fibrous envelope deep to the tendon
Subacromial bursa — the larger and more clinically familiar shoulder bursa

References

Kennedy MS, Nicholson HD, Woodley SJ. “The morphology of the subacromial and related shoulder bursae: an anatomical and histological study.” Journal of Anatomy. 2022. https://pmc.ncbi.nlm.nih.gov/articles/PMC9005683/
Chang LR, Anand P, Varacallo M. “Anatomy, Shoulder and Upper Limb, Infraspinatus Muscle.” StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK513255/

Infraspinatus Bursa