Pectoral Girdle and Upper Limb Anatomy

Definition and Function:
- The pectoral girdle, also referred to as the shoulder girdle, serves to join the arms to the trunk of the body.
- It consists of two main elements:
- Clavicle: An S-shaped bone that connects the arm to the body.
- Scapula: A broad, flat bone that forms the back part of the shoulder.
Joints:
- Acromioclavicular Joint: The joint connecting the acromion of the scapula to the clavicle.
- Sternoclavicular Joint: The junction where the clavicle articulates medially with the sternum and laterally with the scapula.
- This joint is significant as the clavicle is the only bone of the pectoral girdle that articulates with the axial skeleton.
- Glenohumeral Joint: The shoulder joint, formed by the articulation of the scapula with the humerus.
Injuries:
- Injuries to the acromioclavicular joint are commonly known as a “separated shoulder.”

Anatomical Features of the Clavicle:
- Sternal End: Shaped like a hammer head; when positioned, the bone curves away from the body anteriorly.
- Acromial End: Flattened end of the clavicle.
- Conoid Tubercle: Located near the acromial end, for muscle attachment.
Views:
- Superior View: Appears smooth.
- Inferior View: Marked by grooves and ridges for muscle attachments.
Functionality: The clavicle acts as a brace; it is often thickened in individuals engaged in heavy manual labor.
Fracture Statistics: It is noted as the most commonly fractured bone in the human body, primarily due to its superficial location being vulnerable especially during falls.

Shape and Structure:
- Described as a triangular plate that posteriorly overlies ribs 2 to 7.
- Composed of three sides: superior, medial, and lateral borders, with both superior and inferior angles.
Major Features:
- Subscapular Fossa: A concave, anterior surface of the scapula.
- Spine of the Scapula: A transverse ridge along the posterior surface.
- Supraspinous Fossa: Indentation located superior to the spine.
- Infraspinous Fossa: Broad surface located inferior to the spine.
Lateral Angle Features:
- Acromion: A plate-like extension of the spine that articulates with the clavicle, serving as the sole point of attachment for the scapula with the upper limb and thereby, the skeleton.
- Coracoid Process: Shaped like a bent finger, serves for muscle attachments, including the biceps brachii.
- Glenoid Cavity: A shallow socket for articulation with the head of the humerus, critical for forming the glenohumeral joint.

Divisions of the Upper Limb: The upper limb is organized into four regions totaling 30 bones:
- Brachium (Arm Proper):
- Extends from shoulder to elbow,
- Contains one bone: the humerus.
- Antebrachium (Forearm):
- Extends from elbow to wrist,
- Contains two bones: radius and ulna.
- Carpus (Wrist): Framework of bones in the wrist area.
- Manus (Hand): The collection of bones forming the hand.

Proximal End:
- Features a hemispherical head that articulates with the glenoid cavity of the scapula.
- Contains an anatomical neck, greater and lesser tubercles, and deltoid tuberosity.
- Has an intertubercular sulcus for the biceps tendon.
- Contains a surgical neck, important for medical reference.
Distal End:
- Capitulum: A rounded end that articulates with the radius head.
- Trochlea: A structure that articulates with the ulna.
- Epicondyles (Lateral and Medial): Bony projections for muscle attachments.
- Fossae:
- Olecranon Fossa: Holds the olecranon process of the ulna.
- Coronoid Fossa: Located at the anterior aspect of the distal humerus.
- Radial Fossa: Similar to coronoid but for the radius.

Characteristics:
- Head: Disc-shaped to facilitate rotation during forearm movements like pronation and supination.
- Superior Surface: Articulates with the capitulum of the humerus.
- Radial Tuberosity: For the biceps muscle attachment.
- Styloid Process: A prominent bony point at the wrist, serves as a boundary for the wrist's lateral side.

Main Features:
- Trochlear Notch: Articulates with the trochlea of the humerus.
- Olecranon Process: The elbow's bony prominence.
- Coronoid Process: Forms the inferior lip of the trochlear notch.
- Styloid Process: Located at the distal end, serves as wrist boundary.
- Head of Ulna: Terminal end of ulna.
Interosseous Membrane: A ligament connecting the radius and ulna, evenly distributing forces borne between these bones.

Olecranon Process: The upper end of the ulna forming the elbow's point.
Trochlear Notch: Engages with the trochlea of the humerus for smooth elbow movements.
Coronoid Process: Contributes to the structure when the elbow is flexed by fitting into the coronoid fossa of the humerus.

Arrangement:
- Two rows of four bones each:
- Proximal Row: Scaphoid, lunate, triquetrum, and pisiform (arranged lateral to medial).
  - Pisiform: A sesamoid bone which develops between ages 9 to 12 within the tendon of the flexor carpi ulnaris muscle.
- Distal Row: Trapezium, trapezoid, capitate, and hamate (also arranged lateral to medial).
Mnemonic for Remembering:
- “Stop Letting The People Touch The Cadaver’s Hand” helps recall the carpal bones.
- Trapezium: Noted as being near the thumb.

Hands Features:
- Metacarpal Bones: Articulate with the distal ends of carpal bones and proximal phalanges; identified with Roman numerals I-V, starting from the lateral side of the hand.
- Phalanges:
- Total Phalanges per Hand: 14
- Pollex (Thumb): Contains 2 phalanges (proximal and distal).
- Other Fingers: Each has 3 phalanges (proximal, middle, and distal).
Metacarpal Heads: When making a fist, these form the knuckles of the hand.
Views of the Hand:
- Anterior (ventral) view showcases pisiform and hook of hamate.
- Posterior (dorsal) view does not display the pisiform nor the hook of hamate due to different anatomical orientation.