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Shoulder Joint

Articulatio humeri

For medical students2 min readUpdated 2026-10-10

The shoulder joint (articulatio humeri) is the most mobile articulation in the human body. It provides a massive range of motion for the upper extremity, but due to its structural features, it is inherently unstable and prone to injury.

ClassificationMultiaxial, ball-and-socket (spheroidal) joint.
Glenoid labrumFibrocartilaginous rim (*labrum glenoidale*) surrounding the glenoid cavity of the scapula.
Weak pointsThe joint capsule is thinnest inferiorly and beneath the coracoid process.
Articular harmonyFunctions in close synergy with the scapula and clavicle.

Articular Surfaces and Capsule

The articulation is formed by two main bony structures. On one side is the large, sphere-shaped head of the humerus. On the other side is the glenoid cavity (fossa glenoidalis) of the scapula. Because the surface area of the glenoid cavity is significantly smaller than the humeral head, its rim features a specialized fibrocartilaginous ring called the glenoid labrum (labrum glenoidale). This structure increases joint congruence and deepens the socket.

The joint capsule is exceptionally thin and loose. It originates along the margin of the glenoid labrum and attaches to the humerus, enclosing its anatomical neck. The capsule features anatomically predictable weak spots where it is least reinforced: specifically, the areas beneath the coracoid process and in the axillary region.

Ligamentous Apparatus and the Coracoacromial Arch

Despite its high mobility, the joint is reinforced by several critical ligaments that limit excessive displacement and stabilize the capsule:

Biomechanics and Accessory Structures

In terms of shape and biomechanics, this is a multiaxial ball-and-socket joint. This configuration permits movement in all possible spatial planes. However, the trade-off for this freedom of movement is pronounced joint instability.

To ensure smooth gliding and minimize tissue friction around the joint, several synovial bursae are present. The most significant among these are the subdeltoid and subscapular bursae.

In physiological movement, actions rarely occur in isolation within this joint alone. It exhibits a high degree of combined motion, working in close coordination with the scapula and clavicle to deliver the full functional capacity of the upper limb.

Mnemonic

Imagine a golf ball (head of the humerus) resting on a flat saucer (glenoid cavity). To keep the ball from rolling off immediately, a soft rubber ring is glued around the rim of the saucer (the glenoid labrum).

Frequently asked questions

Which muscles form the rotator cuff of the shoulder?

The rotator cuff is formed by four muscles whose tendons blend into the capsule of the shoulder joint:

  • Subscapularis muscle (m. subscapularis).
  • Teres minor muscle (m. teres minor).
  • Infraspinatus muscle (m. infraspinatus).
  • Supraspinatus muscle (m. supraspinatus).

Their primary function is dynamic stabilization of the shoulder joint and rotation of the humeral head.

What anatomical structures form the coracoacromial arch?

The coracoacromial arch is formed by three anatomical structures:

  • Acromion of the scapula.
  • Coracoid process of the scapula.
  • Coracoacromial ligament (lig. coracoacromiale).

The arch lies superior to the shoulder joint and prevents upward dislocation of the humeral head past the horizontal plane during abduction.

Which tendon passes directly inside the cavity of the shoulder joint?

The tendon of the long head of the biceps brachii (m. biceps brachii, caput longum) passes directly inside the shoulder joint cavity. It originates from the supraglenoid tubercle and superior labrum, traverses the joint cavity within the rotator interval, and enters the intertubercular sulcus on the anterior surface of the humeral head, tightly wrapped in a synovial sheath.

What specific types of movement are possible in the shoulder joint?

The shoulder joint is multiaxial (spheroidal), permitting movements around all three principal axes.

  • Flexion (flexio) — up to 180° and extension (extensio) — up to 45° (around the frontal axis).
  • Abduction (abductio) — up to 180° and adduction (adductio) (around the sagittal axis).
  • Internal rotation (rotatio interna) — up to 90° and external rotation (rotatio externa) — up to 90° (around the vertical axis).

The wide range of motion is due to the shape of the articular surfaces and the lax joint capsule.

Which synovial bursae are located around the shoulder joint?

Several synovial bursae are located around the shoulder joint to facilitate tendon and muscle gliding:

  • Subtendinous bursa of subscapularis (bursa subtendinea m. subscapularis) — located beneath the subscapularis tendon, frequently communicating with the joint cavity.
  • Subacromial bursa (bursa subacromialis) — situated beneath the acromion.
  • Subdeltoid bursa (bursa subdeltoidea) — lies superficial to the greater tubercle beneath the deltoid muscle.
  • Subcoracoid bursa (bursa m. coracobrachialis) — located superficial to the subscapular bursa.
Which arteries supply blood to the shoulder joint?

Blood supply to the shoulder joint is derived from a well-developed periarticular vascular network formed by branches of the axillary artery and thyrocervical trunk:

  • Anterior circumflex humeral artery (a. circumflexa humeri anterior).
  • Posterior circumflex humeral artery (a. circumflexa humeri posterior).
  • Deltoid branch of the thoracoacromial artery (r. deltoideus a. thoracoacromialis).
  • Suprascapular artery (a. suprascapularis) — contributes to the supply of the posterosuperior capsule.
Which nerves provide innervation to the shoulder joint capsule?

Innervation of the shoulder joint capsule is provided by branches of the brachial plexus in accordance with Hilton's law:

  • Axillary nerve (n. axillaris) — principal source, innervating the lateral and inferior regions.
  • Suprascapular nerve (n. suprascapularis) — innervates the posterosuperior capsule.
  • Lateral pectoral nerve (n. pectoralis lateralis) — innervates the anterior capsule.
  • Subscapular nerve (n. subscapularis) — innervates the anteroinferior capsule.
To which anatomical structures does the capsule of the shoulder joint attach?

The shoulder joint capsule attaches to the scapula and humerus, creating a capacious cavity.

  • On the scapula — it attaches along the bony margin of the glenoid cavity and the rim of the glenoid labrum (labrum glenoidale).
  • On the humerus — superiorly it attaches to the anatomical neck (collum anatomicum), leaving the greater and lesser tubercles outside the joint cavity. Inferiorly and medially, the attachment line extends significantly lower, reaching the level of the surgical neck (collum chirurgicum), forming the axillary recess (recessus axillaris).
What type of joint is the articulatio humeri?

It is a multiaxial ball-and-socket (spheroidal) joint.

What structures form the coracoacromial arch?

The coracoacromial arch is formed by the coracoacromial ligament (lig. coracoacromiale), which spans above the joint between scapular processes.

Where are the weak points of the shoulder joint capsule located?

They are located inferiorly and beneath the coracoid process.

What is the function of the glenoid labrum?

The glenoid labrum (labrum glenoidale) rings the glenoid cavity of the scapula, deepening it and increasing the surface area of contact with the humeral head.

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