The shoulder capsule
Shoulder joint capsule and labrum · capsula articularis humeri
The loose sleeve and rim of cartilage that hold the ball of the shoulder in its socket.
What it does
The shoulder capsule is a loose, baggy sleeve around the joint, which lets the arm move freely. A rim of cartilage, the labrum, deepens the shallow socket, and thickened bands in the capsule tighten at the extremes of movement.
Surprising fact
The capsule is so loose that, with muscles relaxed, the ball of the humerus can be pulled a centimetre or more out of the socket.
Why it matters
In "frozen shoulder" this capsule becomes inflamed, thickened and tight, slowly limiting movement over months before gradually easing.
Nearby
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Sources
Drafted with AI help; awaiting a human fact-check against these sources.
Open in the 3D atlas · Suggest a correction · Not medical advice.
3D models: Z-Anatomy & BodyParts3D (CC BY-SA 4.0 / 2.1 JP). Card text CC BY 4.0.