Appendicular Skeleton and Bone Structure

Definition: The appendicular skeleton includes 126 bones.
Components:
- Pectoral Girdle: 2 scapulas, 2 clavicles connecting upper limbs to the axial skeleton.
- Pelvic Girdle: 2 hip bones connecting lower limbs to the axial skeleton.
- Total of 106 bones in wrists, hands, ankles, and feet.
Structure Breakdown:
- Pectoral Girdle:
- 4 bones:
  - 2 clavicles
  - 2 scapulas
- Upper Limb:
- 60 bones (majority in the wrists and hands):
  - 2 humerus
  - 2 radius
  - 2 ulna
  - 16 carpals
  - 10 metacarpals
  - 28 phalanges
- Pelvic Girdle:
- 2 bones (hips):
- Lower Limb:
- 60 bones (majority in the ankles and feet):
  - 2 femur
  - 2 patella
  - 2 tibia
  - 2 fibula
  - 14 tarsals
  - 10 metatarsals
  - 28 phalanges

Definition: A long bone with a curvy shape.
Articulations:
- Medial: Articulates with the manubrium of the sternum.
- Lateral: Articulates with the acromion of the scapula.
Joint: The sternoclavicular joint is the only direct connection between the axial skeleton and the pectoral girdle.

Definition: A flat bone with a complex shape.
Structure:
- Borders: Superior, medial, and lateral borders.
- Spine: Contains a spine that becomes acromion at its lateral tip.
Joint:
- Acromioclavicular Joint: The acromion of the scapula articulates with the clavicle.
Muscle Attachments:
- Acromion: Attachment point for trapezius and deltoid muscles.
- Coracoid Process: Anterior part, attachment for short head of the biceps brachii and pectoralis minor muscles.
Glenoid Cavity:
- Location: Lateral border, articulates with the humerus.
- Supraglenoid Tubercle: Superior to glenoid cavity, attachment for long head of biceps brachii muscle.
- Infraglenoid Tubercle: Inferior to glenoid cavity, attachment for long head of triceps brachii muscle.
Movement:
- Skeletal muscles move the scapulae, which glide over the rib cage (scapulothoracic joint).
- Muscles involved: Trapezius major and minor, rhomboids, levator scapula, serratus anterior, and pectoralis minor.

Mobility: The scapula is more mobile than the clavicle, capable of gliding for:
- Retraction & Protraction: Moving forward and backward.
- Elevation & Depression: Moving upward and downward.
Limitations: The sternoclavicular joint restricts movement of the scapula.

Definition: Formed by the scapula and humerus.
Functions: Stabilizes the shoulder joint and provides a base for arm movement.
Mobility: The glenohumeral joint is the most mobile joint in the body, allowing for:
- Flexion & Extension
- Abduction & Adduction
- Medial & Lateral Rotation
- Circumduction

Structure: Includes the humerus, radius, ulna, carpal bones, and the metacarpals and phalanges of the hand.

Description: The bone in the upper arm with a round head that articulates with the scapula.
Features:
- Greater Tubercle: On the lateral surface, insertion site for supraspinatus, infraspinatus, and teres minor muscles.
- Lesser Tubercle: On the anterior medial surface, insertion site for subscapularis muscle.
- Intertubercular Sulcus: Separates greater and lesser tubercles, tendon of long head of biceps brachii travels through.
- Anatomical Neck: Constriction between head and tubercles. Fractures typically occur at the surgical neck.
- Deltoid Tuberosity: On the lateral shaft, insertion site for deltoid muscle.
Distal Epiphysis:
- Medial Trochlea: Articulates with trochlear notch of the ulna.
- Coronoid Fossa: Articulates with coronoid process of ulna when elbow flexed.
- Olecranon Fossa: Articulates with olecranon of ulna when elbow extended.
- Capitulum: Lateral side, articulates with head of the radius.
- Epicondyles: Meant for attachment of muscles; easily palpable at the elbow.
- Ulnar Nerve: Crosses medial epicondyle, impacting sensitivity when struck.

Structure: Forearm contains two bones, radius (lateral) and ulna (medial).
Interosseous Membrane: Fibrous CT sheet connecting radius and ulna, site for muscle attachment.

Features:
- Proximal Epiphysis includes the Coronoid Process, Trochlear Notch, and Olecranon.
- Trochlear notch cups the trochlea of the humerus; olecranon fits the olecranon fossa when elbow extends.
- Articulates with the radius at proximal and distal radioulnar joints.
- Distal Epiphysis does not directly articulate with wrist bones; separated by fibrocartilage.

Features:
- Proximal Epiphysis with circular head articulating with lateral capitulum of the humerus.
- Rotation: Medial rotation leads to thumb crossing the ulna (pronation); lateral rotation brings the radius parallel to the ulna (supination).
- Distal end articulates with carpal bones of the wrist.

Structure: Comprised of three sets of bones:
- 8 Carpals (wrist bones)
- 5 Metacarpals (hand/palm bones)
- 14 Phalanges (finger bones)
Carpals: Short bones forming two rows, permit limited movements and articulate with distal radius and metacarpals.
Metacarpals: Long bones in the palm, numbered I to V from the thumb.
Phalanges: Each hand contains 3 groups: proximal (5), middle (4), distal (5); the thumb lacks a middle phalanx.

Components: Pelvic girdle consists of two hip bones; the pelvis includes the girdle, sacrum, and coccyx.
Functions:
- Support for the body while standing.
- Protects pelvic cavity organs and fetus in pregnant women.
- Attachment sites for muscles of buttocks and thighs.

Formed by fusion of three bones: ilium, pubis, ischium.
Acetabulum: Hip socket formed by all three bones, Obturator Foramen: A hole formed between pubis and ischium, covered by CT.

Features:
- Iliac crest: Superior part; ASIS (anterior superior iliac spine).
- Fossa: The iliac fossa supports abdominal organs.
Articulation: With sacrum at sacroiliac joints.
Sciatic notch: Nerve exit point from pelvis.