General Overview – Upper Appendicular Skeleton

Introduction

The upper appendicular skeleton comprises the bones and joints of the pectoral girdle and upper limb. This region is essential for a wide range of movements and functions, including manipulation, locomotion, and support.

• Pectoral Girdle: Consists of the clavicle (collar bone) and scapula (shoulder blade).

• Upper Limb: Includes the humerus (arm), radius and ulna (forearm), carpals (wrist bones), metacarpals (hand bones), and phalanges (finger bones).

Key Regional Terms: Arm (brachium), forearm (antebrachium), wrist (carpus), hand (manus), and fingers (digits).

Pectoral Girdle

Clavicle and Scapula

The pectoral girdle connects the upper limb to the axial skeleton and provides attachment points for muscles that move the shoulder and arm.

• Clavicle: S-shaped bone that acts as a strut to keep the upper limb away from the thorax, allowing for maximum range of motion.

• Scapula: Flat, triangular bone located on the posterior thoracic wall. It provides attachment for several muscles and forms part of the shoulder joint.

Joints of the Pectoral Girdle:

• Sternoclavicular Joint: Synovial, modified gliding joint with some ball & socket and saddle properties. Allows elevation, depression, protraction, and retraction of the clavicle.

• Acromioclavicular Joint: Synovial, gliding joint between the acromion of the scapula and the clavicle.

• Scapulothoracic Joint: Not a true anatomical joint, but a functional ("muscular" or "imaginary") joint where the scapula glides over the thoracic wall.

Shoulder Joint (Glenohumeral Joint)

Anatomy and Function

The glenohumeral joint is a synovial ball-and-socket joint formed between the head of the humerus and the glenoid cavity of the scapula. It is highly mobile but relatively unstable, relying on muscles, ligaments, and the glenoid labrum for stability.

• Ligaments: Glenohumeral ligaments, coracohumeral ligament, and the coracoacromial ligament (forms a protective arch over the joint).

• Labrum: Fibrocartilaginous rim that deepens the glenoid cavity and increases joint stability.

• Movements: Flexion, extension, abduction, adduction, medial and lateral rotation, and circumduction.

Example: Raising the arm overhead involves abduction at the glenohumeral joint, with stabilization from the rotator cuff muscles.

Arm, Forearm, and Elbow Joint

Humerus, Radius, and Ulna

The arm contains the humerus, while the forearm consists of the radius and ulna. The elbow joint complex allows for flexion, extension, and rotation of the forearm.

• Humerus: Proximal features include the head, anatomical neck, greater and lesser tubercles, and intertubercular groove. Distal features include the medial and lateral epicondyles, trochlea, and capitulum.

• Ulna: Medial bone of the forearm, forms the major articulation with the humerus at the elbow (humeroulnar joint).

• Radius: Lateral bone of the forearm, rotates around the ulna during pronation and supination.

Elbow Joint Complex:

• Humeroulnar Joint: Synovial hinge joint allowing flexion and extension.

• Humeroradial Joint: Also contributes to flexion and extension.

• Proximal and Distal Radioulnar Joints: Synovial pivot joints allowing pronation and supination of the forearm.

Example: Turning a doorknob involves supination and pronation at the radioulnar joints.

Hand: Carpals, Metacarpals, and Phalanges

Structure and Function

The hand consists of the wrist (carpals), palm (metacarpals), and fingers (phalanges). These bones allow for complex movements and dexterity.

• Carpals: Eight short bones arranged in two rows. The proximal row articulates with the radius and ulna, forming the wrist joint.

• Metacarpals: Five bones forming the palm of the hand.

• Phalanges: Fourteen bones forming the fingers (three per finger, two in the thumb).

Carpal Bones (Lateral to Medial):

Articulation: The scaphoid and lunate articulate with the radius at the wrist joint.

Joints of the Hand:

• Radiocarpal Joint: Main wrist joint (condyloid type), allows flexion, extension, abduction, and adduction.

• Carpometacarpal Joints: Gliding joints, except for the thumb (saddle joint for greater mobility).

• Metacarpophalangeal Joints: Condyloid joints ("knuckles"), allow flexion, extension, abduction, and adduction.

• Interphalangeal Joints: Hinge joints, allow flexion and extension.

Example: Opposition of the thumb is enabled by the saddle-shaped first carpometacarpal joint.

Movements and Functional Anatomy

Key Movements

• Scapular Movements: Elevation, depression, protraction, retraction, upward and downward rotation at the scapulothoracic joint.

• Shoulder Movements: Flexion, extension, abduction, adduction, medial and lateral rotation, circumduction at the glenohumeral joint.

• Elbow Movements: Flexion and extension at the humeroulnar joint; pronation and supination at the radioulnar joints.

• Wrist and Hand Movements: Flexion, extension, abduction, adduction, opposition, and reposition.

Etymology of Key Terms

Understanding Anatomical Vocabulary

• Brach- (G): Arm

• Ante- (L): Before, preceding (as in antebrachium = forearm)

• Sterno- (G): Breast/breastbone

• Humerus (L): Shoulder (bone that moves the shoulder)

• Ulna (L): Elbow (bone that moves at the elbow)

• Radius (L): Ray, wheel-spoke (bone that rotates around the ulna)

• Carp- (G): Wrist

• Meta- (G): With, after, between, change

• Phalanx (G): Finger bone

Example: The term trapezium (carpal bone) comes from the Greek for "table," reflecting its shape.

Summary Table: Joints of the Upper Limb

Additional info:

• Details on muscle attachments and innervation are typically covered in subsequent lectures.

• The role of the flexor retinaculum is to hold tendons in place at the wrist, preventing bowstringing during flexion.

• Mnemonic for carpal bones (lateral to medial, proximal to distal): "Some Lovers Try Positions That They Can't Handle" (Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate).