Region of shoulder joint

The shoulder joint region corresponds to the area of the thoracic limb that surrounds the scapulohumeral joint, the junction between the glenoid cavity of the scapula and the head of the humerus. It forms the transition point between the scapular girdle and the arm.

Anatomically, this region includes the articular bone structures (glenoid cavity, humeral head), the joint capsule reinforced by the glenohumeral ligaments, the periarticular muscles (supraspinatus, infraspinatus, subscapularis), the proximal portions of the biceps brachii and triceps brachii, the nerves arising from the brachial plexus (suprascapular, axillary, and subscapular nerves), and the vessels of the scapular and brachial regions.

Functionally, this joint allows primarily flexion and extension movements, with degrees of rotation and abduction varying among species:

• Carnivores (dog, cat): a very mobile joint; stability relies mainly on periarticular muscles (absence of collateral ligaments).

• Horse and ruminants: a more stable joint, with movements mostly limited to flexion-extension; characterized by a substantial muscle mass around the scapula.

• Humans: a much more mobile joint, a true ball-and-socket articulation due to a different scapular morphology and the presence of a functional clavicle.