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Shoulder joint
The most mobile joint in the body, and the one that trades stability for that range.
Latin name: Articulatio humeri. In plain English, the ball and socket at the top of the arm. It is filed here under joints, tendons and fascia.
Reference information, not a diagnosis. Where a symptom is described below, it is there so you can describe your own more precisely to a clinician — not so you can name what you have.
Where it is
The socket is shallow — a small, slightly hollowed oval on the outer angle of the shoulder blade, covering only about a third of the humeral head. A rim of fibrocartilage, the glenoid labrum, deepens it a little. The capsule around the joint is loose enough to allow the huge range of movement the shoulder has, and the thickened bands within it, the glenohumeral ligaments, only really tighten at the extremes.
Above the joint sits the coracoacromial arch, formed by the acromion, the coracoid process and the ligament between them. The supraspinatus tendon and the subacromial bursa run through the space beneath it. Stability therefore comes not from bone but from the rotator cuff muscles, the labrum, the capsule, and the coordinated movement of the shoulder blade.
| Feature | Detail |
|---|---|
| Type | Synovial ball-and-socket joint |
| Bones | Head of the humerus against the glenoid fossa of the scapula, deepened by the glenoid labrum |
| Key ligaments | Superior, middle and inferior glenohumeral ligaments, the coracohumeral ligament, and the coracoacromial arch above |
| Main movements | Flexion, extension, abduction, adduction, internal and external rotation, and circumduction |
What it does
Raising the arm overhead is not one movement but two joints working together. As the arm elevates, the shoulder blade rotates on the rib cage so the socket faces upward, and the conventional description of that partnership is roughly two degrees at the glenohumeral joint for every one at the scapula through most of the range. Lose the scapular part and the arm jams well short of vertical.
The price of mobility is instability. The shoulder is the most commonly dislocated large joint, usually forward and downward, and once the labrum and capsule have been damaged the risk of it happening again is high, particularly in younger people. That is a genuinely important reason a first dislocation deserves proper follow-up rather than a shrug.
Movements that load it
| Exercise | Category | Muscles the exercise library lists |
|---|---|---|
| Bench press | Strength | Chest, triceps, front shoulder |
| Overhead press | Strength | Shoulders, triceps, core |
| Pull-ups | Strength | Lats, biceps, mid-back, grip |
| Dips | Strength | Triceps, chest, front shoulder |
| Swimming, freestyle | Cardio | Whole body, heart, lungs |
Pressing, pulling and carrying all load the joint, and the cuff has to work in all of them. Loading through a full range, including overhead, generally builds a more robust shoulder than avoiding overhead work — provided range comes first and load second. If overhead positions hurt, the useful question is whether the shoulder blade is rotating, not whether to abandon the movement forever.
Keeping its range
Range work matters more here than stretching. Slow controlled circles, wall slides, and reaching overhead with the ribs down all maintain the movement the joint needs. Avoid pushing hard into an end range that hurts: the shoulder capsule reacts badly to being forced, and a stiff, painful shoulder is more often an irritated capsule than a short muscle.
When it goes wrong
| Problem | What it typically feels like | Usual setting |
|---|---|---|
| Anterior dislocation | Sudden severe pain with the arm held away from the body and an obvious change in shoulder contour | A fall on an outstretched arm or a forced external rotation; needs immediate medical care |
| Frozen shoulder | Progressive loss of movement in all directions, especially external rotation, with pain that often precedes the stiffness | Adhesive capsulitis; more common in people with diabetes, and it typically runs a long course |
| Acromioclavicular joint injury | Pain right on top of the shoulder at the end of the collarbone, worse reaching across the body | A fall directly onto the point of the shoulder |
A shoulder that has visibly changed shape after an injury, that cannot be moved at all, or that is accompanied by numbness or a cold hand needs emergency care. Progressive stiffness in all directions is worth having examined rather than stretching harder.
Nothing on this page is a treatment plan. If a problem is limiting what you do, is not improving, or is getting worse, the right next step is an assessment by a doctor or a physiotherapist who can examine you.
Sources: descriptive anatomy from Gray's Anatomy of the Human Body, 20th US edition (1918), which is in the public domain; Latin names follow Terminologia Anatomica, published by the Federative International Programme for Anatomical Terminology. Nerve root levels are the conventional ranges taught from those sources and vary between individuals and between textbooks. Exercise cross-links use the TempoLife exercise library. Checked 2026-09-06.
Frequently asked questions
Why is the shoulder dislocated so easily?
Because the socket is shallow and the capsule is loose, which is exactly what gives the joint its range. Stability depends on soft tissue rather than on bony containment.
What is scapulohumeral rhythm?
The coordinated contribution of the shoulder blade to raising the arm. Conventionally described as about two degrees of movement at the ball-and-socket joint for each degree at the shoulder blade, though the ratio varies through the range and between people.
Does frozen shoulder get better on its own?
It typically follows a long course over many months and most people regain much of their movement, but the timeline is measured in seasons rather than weeks. It is a diagnosis worth confirming with a clinician, because several other things cause a stiff shoulder.
Nearby in this reference
Knee joint
The hinge between thigh and shin
Hip joint
The ball and socket where the leg meets the pelvis
Lumbar spine
The five vertebrae of the lower back
Achilles tendon
The thick cord at the back of the ankle
Plantar fascia
The thick band along the sole of the foot
Deltoid
The cap of the shoulder
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