Shoulder Joint Anatomy: Bones, Muscles, Movement, & Injuries

The shoulder joint, also known as the glenohumeral joint, is a ball-and-socket type synovial joint that allows a wide range of motion in the upper limb. Here’s a breakdown of its key features:

🦴 Bones Involved

1. Humerus – the upper arm bone; its head forms the "ball."
2. Scapula (shoulder blade) – contains the glenoid cavity, which forms the "socket."
3. Clavicle (collarbone) – indirectly involved, connecting the shoulder to the axial skeleton via the acromioclavicular and sternoclavicular joints.

🦾 Movements Allowed

Because it is a ball-and-socket joint, it allows:

• Flexion and Extension
• Abduction and Adduction
• Medial (internal) and Lateral (external) Rotation
• Circumduction (circular movement)

💪 Muscles Involved

Key muscles acting on the shoulder joint include:

• Rotator Cuff Muscles:
  • Supraspinatus
  • Infraspinatus
  • Teres minor
  • Subscapularis
• Deltoid
• Pectoralis major
• Latissimus dorsi
• Teres major
• Biceps brachii (long head helps stabilize the joint)

🔩 Stability Features

The shoulder joint is highly mobile but relatively unstable. Stability is provided by:

• Rotator cuff muscles (dynamic stabilizers)
• Glenoid labrum (fibrocartilage rim deepening the socket)
• Joint capsule and ligaments (static stabilizers)
• Coracoacromial arch (bony and ligamentous roof over the joint)

🧑‍⚕️ Clinical Significance

• Dislocations: Common due to high mobility (usually anterior dislocation).
• Rotator cuff injuries: Especially in athletes and older adults.
• Impingement syndrome: Soft tissues pinched during movement.
• Frozen shoulder (adhesive capsulitis): Painful stiffness due to inflammation.