The Shoulder Region

What you will be able to do

Four joints, not one

When a patient says their shoulder will not lift, they are describing a failure somewhere in a system of four joints. Treating only the ball and socket misses three quarters of it.

Figure 1 · The four joints of the shoulder complex

The scapulothoracic entry is worth pausing on, because it is not a joint in the anatomical sense at all. There is no capsule and no cavity — the scapula simply slides on a bed of loose connective tissue over the ribs. But it contributes roughly a third of total arm elevation, so functionally it behaves like one, and it is entirely dependent on muscle.

The glenohumeral joint

Figure 2 · The glenohumeral joint

Illustration to be added

A coronal section through the shoulder. Label the head of the humerus, the glenoid fossa, the glenoid labrum deepening its rim, the joint cavity, the fibrous capsule with its inferior redundant fold shown lax with the arm at the side, the superior, middle and inferior glenohumeral ligaments on the anterior capsule, the coracohumeral ligament above, the tendon of the long head of biceps arching over the head and descending in the intertubercular groove, the subacromial bursa, the acromion, the coracoid process and the coracoacromial ligament forming the arch. Show clearly how little of the head the socket actually covers. Add a small companion panel from the front showing the subacromial space with supraspinatus passing through it. Bone warm ivory, cartilage pale blue, capsule and ligaments navy, tendon pale gold, bursa in a distinct tint.

A ball and socket joint between the head of the humerus and the glenoid fossa. The geometry is the whole story: the head is large and the socket is small, shallow and faces slightly forwards and upwards.

The rotator cuff

Figure 3 · The rotator cuff

Four muscles running from the scapula to the tubercles of the humerus, blending with the capsule as they go. Their names describe where they come from, so they are easier to remember than most muscle groups.

Their headline actions — rotation, and starting abduction — are not really what they are for. Their essential job is to hold the head of the humerus centred in the glenoid while the large muscles move the arm. Without that, deltoid contracting would simply drag the head upwards against the acromion instead of raising the arm.

The muscles that move the shoulder

Notice how few muscles produce lateral rotation compared with medial. Three against four, and the medial rotators include some of the largest muscles in the body. This imbalance is normal, and it is why lateral rotation is so often the movement that needs training.

The muscles that move the scapula

These are the ones students skip, and they are usually where the clinical problem is.

How the arm actually gets overhead

Figure 4 · How the joint and the scapula share the work

Raising the arm fully is not the glenohumeral joint working alone. The scapula rotates upwards to keep the socket underneath the head, and the clavicle rotates and elevates at both its ends to allow it. All four joints participate.

The proportion is worth knowing, because it converts directly into clinical reasoning. The scapula contributes about a third of total elevation. A patient whose scapula cannot rotate upwards has therefore already lost roughly a third of their range, before the shoulder joint itself is considered. The cuff tendons are squeezed for the rest of it.

The axilla

The pyramid-shaped space between the arm and the chest wall. It is not a structure in itself; it is a passage, and knowing its walls tells you what can be injured together.

The axillary lymph nodes drain the upper limb, the chest wall and most of the breast. That is why they are examined and often sampled in breast cancer. It is also why surgery there can leave a patient with a swollen arm and a stiff shoulder for you to treat.

Figure 5 · The axilla and the brachial plexus

Illustration to be added

Two panels. Panel one: a parasagittal view of the axilla showing its pyramidal shape, with the anterior wall (pectoralis major and minor), posterior wall (subscapularis, teres major, latissimus dorsi), medial wall (ribs and serratus anterior) and lateral wall (intertubercular groove) labelled, and the axillary artery, vein, lymph nodes and plexus cords within it. Panel two: the brachial plexus drawn as a clean schematic from roots C5 to T1, through the upper, middle and lower trunks, anterior and posterior divisions, lateral, posterior and medial cords, to the five terminal branches - musculocutaneous, axillary, radial, median and ulnar. Colour each root level differently and carry that colour through, so a single fibre can be traced from root to terminal nerve. Label the main branches leaving before the terminal ones, including long thoracic, dorsal scapular, suprascapular and thoracodorsal. Nerves in gold, artery red, vein blue, muscle brick.

What goes wrong here

Where students get this wrong

Treating the shoulder as one joint

It is four. A patient who cannot lift their arm may have a normal glenohumeral joint and a scapula that will not rotate.

Thinking the cuff exists to rotate the arm

Its real work is holding the head centred while other muscles move the limb. Rotation is almost a side effect.

Blaming the tendon before looking at the scapula

The subacromial space narrows when the scapula fails to rotate upwards. The tendon is often the victim rather than the cause.

Testing deltoid power to check the axillary nerve

Power testing is unreliable in a painful shoulder. Test sensation over the outer shoulder instead; it takes seconds and is far more informative.

Confusing loss of active and passive range

Active loss with preserved passive range suggests a muscular or tendon problem. Loss of both, in a pattern, suggests the capsule.

Forgetting the long head of biceps runs inside the joint

It is intra-articular, it helps depress the head, and it is a genuine and often missed source of anterior shoulder pain.

Check yourself

Ten questions on this chapter. Tap one to see the answer and the reasoning.

Quick review

Further reading

Reviewed by the Physiotherapist India Team. · Human Anatomy contents