Shoulder capsule !

The shoulder capsule is the loose sleeve that seals the ball-and-socket joint; its looseness lets the shoulder move more than any other joint.

Official name: Shoulder (glenohumeral) joint capsule

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What it is

The loose bag of tissue around the shoulder ball and socket; its thick parts are the glenohumeral ligaments.

What it does

Seals the joint and holds its fluid; its looseness lets the shoulder move more than any other joint.

Key facts

Attaches: Glenoid rim and labrum to the anatomical neck of the humerus (further down medially)
Function: Loose for range; reinforced by the glenohumeral ligaments and rotator cuff; axillary pouch below; thickens and shrinks in frozen shoulder; supplied by the axillary and suprascapular nerves and the circumflex humeral and suprascapular arteries

Relations

Above: Supraspinatus tendon, which blends with it; above that, the subacromial bursa and the coracoacromial arch
In front: Subscapularis tendon and the subscapular recess; the glenohumeral ligaments thicken it from the inside
Behind: Infraspinatus tendon and teres minor tendon, which blend with it
Below: The axillary recess; below it the axillary nerve and posterior circumflex humeral artery pass back through the quadrangular space
Contents: Humeral head and glenoid with the labrum; the long biceps tendon crosses inside the joint but stays outside the synovial membrane

How to find it

It cannot be felt as a structure. The joint line lies below and in front of the acromion; aspiration or injection uses a posterior entry below the posterolateral corner of the acromion, aiming at the coracoid, or an anterior entry lateral to the coracoid.

Examination

Passive external rotation with the elbow at the side: loss compared with the other side, with normal X-rays, points to frozen shoulder rather than a cuff tear (which keeps passive motion)
Apprehension and relocation tests: fear in abduction and external rotation that eases when the humeral head is pushed back suggests anterior capsulolabral laxity
Sulcus sign: downward pull on the arm opens a gap below the acromion, a sign of a lax inferior capsule (multidirectional instability)

On imaging

MR arthrography shows capsular volume, labral tears and capsular tears from the humerus (HAGL). In frozen shoulder MRI shows a thick capsule in the axillary recess and scarring in the rotator interval; ultrasound shows a thick coracohumeral ligament. Joint fluid tracks into the biceps sheath and subscapular recess.

Common problems

Frozen shoulder (adhesive capsulitis): the capsule becomes inflamed, thick and tight, so the shoulder hurts and stiffens.
Stretched or torn in a dislocation; a loose capsule lets the shoulder slip.
Frozen shoulder is more common in people with diabetes and thyroid disease.

How it is diagnosed

Loss of both active and passive motion, especially outward rotation, with normal X-rays. MRI may show a thick capsule.

Treatment

Gentle stretching, pain control and time: most frozen shoulders improve over months.
Steroid injection or hydrodilatation in the painful phase.
Arthroscopic capsular release or manipulation under anesthesia when stiffness persists.

Clinical notes

Anterior dislocation or its reduction can stretch the axillary nerve: numbness over the lateral deltoid (regimental badge area) and weak abduction, checked before and after reduction
A stretched capsule in recurrent instability is tightened by capsular shift or arthroscopic plication, usually with labral repair
Septic arthritis of the shoulder may be subtle in infants and older adults; aspiration of the joint settles the diagnosis
Frozen shoulder passes through freezing (painful), frozen (stiff) and thawing phases over months; options include physiotherapy, hydrodilatation and capsular release
Anterior dislocation squares off the shoulder (epaulette sign): the acromion juts out, the rounded deltoid contour is lost and the humeral head is felt below the coracoid

Anatomical variants

Sublabral foramen and Buford complex (no anterosuperior labrum, with a thick cord-like middle glenohumeral ligament): normal variants that can be mistaken for labral tears on MRI

Development

From week 6 the joint forms between the cartilage models of the humerus and scapula: the centre of the interzone breaks down into the cavity while the mesenchyme around it becomes the capsule; its thicker bands are the glenohumeral ligaments.

Test yourself

Think of the answer, then tap the question to see it.

What is the weakest part of the shoulder capsule, and what runs below it?

The inferior capsule (axillary pouch); most dislocations go anterior-inferior through it, and the axillary nerve runs just below.

What is the capsular pattern of the shoulder in frozen shoulder?

External rotation is lost most, then abduction, then internal rotation.

What closes the rotator interval of the shoulder capsule?

Capsule, the coracohumeral ligament and the superior glenohumeral ligament, between the supraspinatus and subscapularis tendons; it thickens early in frozen shoulder.

What is the sulcus sign of the shoulder capsule?

Downward pull on the arm opens a gap below the acromion, a sign of a lax inferior capsule (multidirectional instability).

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): capsula articularis articulationis glenohumeralis TA2 1536
Official Spanish (DeCS): Cápsula articular de la articulación glenohumeral
English (TA2): Shoulder (glenohumeral) joint capsule
Also called: shoulder joint capsule

Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb, Glenohumeral Joint; Anatomy, Shoulder and Upper Limb, Shoulder; 9.7 Development of Joints (OpenStax (Rice University), 2022) · adapted, CC BY 4.0; Anatomy of the Human Body (20th ed.): Development of the Joints (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain; Anatomía humana (4.ª ed.), tomo 1, cap. 55: Cintura escapular.

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Representative model, for educational purposes only.

Shoulder capsule highlighted on the Durgical 3D model