Shoulder joint is the usual name for the glenohumeral joint, a synovial ball-and-socket joint connecting the upper arm bone to the shoulder blade. It lies at the outer shoulder, beneath the deltoid muscle. A synovial joint has a fluid-containing cavity between its joint surfaces, allowing them to move against one another.
Where is the shoulder joint located?
The joint lies where the rounded head of the humerus, the upper arm bone, meets the glenoid cavity of the scapula, the shoulder blade. The glenoid cavity is a shallow socket on the outer angle of the scapula. The humeral head faces towards the body, upwards and slightly backwards.
Above the joint are the acromion, a projecting part of the scapula, and the coracoacromial ligament, a fibrous band joining the acromion to the coracoid process. The coracoid process is the hook-like projection at the front of the scapula. Together, these structures form an arch above the humeral head.
The deltoid muscle covers the joint externally. The axillary nerve and posterior circumflex humeral vessels pass close to its lower and posterior aspects, near the surgical neck, the narrowed region below the upper end of the humerus.
What forms the shoulder joint surfaces?
The humeral head forms the ball, and the glenoid cavity forms the socket. Both surfaces are covered by articular cartilage, a smooth layer of hyaline cartilage that reduces friction and distributes load. Much of the humeral head lies beyond the shallow socket at any one position.
The glenoid labrum is a rim of fibrocartilage, a tough cartilage containing abundant collagen fibres, attached around the glenoid margin. It deepens the socket and provides attachment for the capsule and associated ligaments. It improves the fit between the surfaces without making the socket as deep as that of the hip.
What surrounds and stabilises the shoulder joint?
The articular capsule of glenohumeral joint encloses the joint and has an outer fibrous layer. This layer attaches around the glenoid margin and labrum, and around the anatomical neck of the humerus, the groove immediately bordering the humeral head. Inferiorly, its attachment extends towards the surgical neck. Its lower part is relatively loose, allowing the arm to rise.
A synovial membrane, the tissue producing lubricating synovial fluid, lines the inner capsule but does not cover the articular cartilage. The tendon of the long head of biceps passes through the capsule before entering the groove between the humeral tubercles, the bony prominences beside the head. A tendon connects muscle to its attachment; this tendon lies within the capsule but outside the synovial cavity.
The rotator cuff is a group of muscles whose tendons blend with the capsule: supraspinatus above, subscapularis in front, and infraspinatus and teres minor behind. They help hold the humeral head against the glenoid during movement. The lower capsule lacks the same direct cuff reinforcement.
Which ligaments support the shoulder joint?
Ligaments are strong bands of connective tissue joining bones and reinforcing joints. The glenohumeral ligaments are thickened regions of the front of the capsule; their tension changes with arm position.
| Structure | Position and main anatomical role |
|---|---|
| The superior glenohumeral ligament | Reinforces the upper anterior capsule and helps resist downward movement of the humeral head when the arm is by the side. |
| The middle glenohumeral ligament | Reinforces the anterior capsule and helps restrain forward movement of the humeral head in some arm positions. |
| The inferior glenohumeral ligament | Forms a lower capsular support that becomes particularly important when the arm is raised away from the body. |
| The coracohumeral ligament | Extends from the coracoid process towards the humeral tubercles and reinforces the upper capsule. |
| The transverse humeral ligament | Bridges the groove between the humeral tubercles and helps retain the long head of biceps tendon there. |
These passive supports work with active muscle tension. The joint therefore depends on both its surrounding connective tissues and coordinated muscle action for stability.
What movements does the shoulder joint allow?
Its ball-and-socket shape permits movement around several axes. The principal movements are:
- Flexion and extension: moving the arm forwards and backwards.
- Abduction and adduction: moving the arm away from and towards the side of the body.
- Medial and lateral rotation: turning the humerus inwards and outwards around its long axis.
- Circumduction: combining movements so that the arm describes a cone.
The whole shoulder region moves through more than the glenohumeral joint alone. The scapula also moves over the chest wall, while the clavicle, or collarbone, moves at its joints with the sternum and acromion. This coordinated movement positions the socket as the arm rises.
What are the shoulder joint's blood and nerve supplies?
Arterial supply reaches the joint through branches of the anterior circumflex humeral artery, posterior circumflex humeral artery and suprascapular artery. The circumflex scapular artery also contributes to the surrounding arterial network. Connections between these vessels provide routes for blood around the shoulder.
Articular branches, meaning branches supplying a joint, arise from the axillary, suprascapular and lateral pectoral nerves. They carry sensation from the capsule and information about joint position and movement.
How can you locate the shoulder joint in the 3D model?
The article concerns the shoulder joint as a whole; its anatomical name is the glenohumeral joint, which connects the humeral head to the glenoid cavity. This is distinct from the broader shoulder complex, which includes the clavicular joints and movement of the scapula against the chest wall.
In the 3D model next to the article, rotate and zoom towards the outer shoulder, then select the glenohumeral joint. You can hide or fade overlying structures and switch layers on and off to study its position relative to the humerus and scapula.