Shoulder and Arm Bones Anatomy

Shoulder and Arm Bones

• The shoulder girdle is formed by the scapula (shoulder blade) and clavicle (collarbone), connecting to the humerus (upper arm bone).
• The scapula is a flat, triangular bone, located posteriorly in the shoulder region.
• The clavicle is a long, S-shaped bone, connecting the scapula to the sternum (breastbone).
• The humerus is a long bone extending from the shoulder joint to the elbow joint. It has a head that articulates with the glenoid cavity of the scapula.
• The humerus has a prominent deltoid tuberosity for deltoid muscle attachment.
• Key bony landmarks of the arm include the medial and lateral epicondyles on the distal humerus, crucial for muscle attachment. The forearm is composed of the radius and ulna bones.

Typical Bone Structure

• Bones consist of compact bone (dense outer layer) and spongy bone (porous inner layer).
• Compact bone provides strength and support.
• Spongy bone provides lightweight structure and houses bone marrow.
• Bone contains osteocytes, osteoblasts (bone-forming cells), and osteoclasts (bone-resorbing cells).

Clavicle

• The clavicle acts as a brace for the shoulder girdle.
• It transmits forces from the upper limb to the axial skeleton.
• It supports and positions the scapula.
• Its S-shape allows it to withstand stress and compression.

Shoulder Joints

• The shoulder joint (glenohumeral joint) is a ball-and-socket joint between the humerus head and the glenoid cavity of the scapula.
• This allows for extensive shoulder motion (flexion, extension, abduction, adduction, rotation, circumduction).
• The glenohumeral joint's shallow glenoid cavity makes it inherently unstable, relying on soft tissues for stability.
• The acromioclavicular joint connects the acromion of the scapula to the clavicle.
• The sternoclavicular joint connects the clavicle to the sternum.

Shoulder Ligaments

• Shoulder stability is maintained by glenohumeral ligaments (superior, middle, inferior), reinforcing the joint capsule.
• The coracohumeral ligament strengthens the anterior aspect of the joint.
• The transverse humeral ligament secures the tendon of the long head of the biceps.
• These ligaments restrict excessive movement and prevent dislocation.

Head and Neck Blood Supply

• The head and neck receive blood from common carotid arteries.
• Subclavian arteries, branching from the aortic arch, supply the upper limb and neck.
• Veins parallel arteries, returning blood to the heart.
• Internal and external carotid arteries supply structures like the brain, face, and neck muscles.
• Jugular veins carry deoxygenated blood back to the heart.
• Arterial branches serve specific organs. Vertebral arteries ascend through cervical vertebrae transverse processes, supplying the posterior brain.
• Venous drainage mirrors arterial patterns.