Upper Limb and Pectoral Girdle Study Notes

Upper Limb and Pectoral Girdle: Study Notes

• LO 8 (Learning Outcome): Describe the structure of the musculoskeletal system and its role in support, coordination and control of movements in the human body, employing appropriate anatomical terminology.
• Contents covered: appendicular skeleton, pectoral girdle, bones of the upper limb (arm, forearm, hand), and basic clinical aspects.

Appendicular Skeleton: overview and function

• Of the 206 bones in the skeleton, $206$ form the entire skeleton, while $126$ form the appendicular skeleton.
• Includes:
  • Bones of the shoulder or pectoral girdle connecting to the bones of the arm, forearm, wrist and hands.
  • Bones of the hip or pelvic girdle connecting to the bones of the thigh, leg, ankle and foot.
• Functions: movement/locomotion; attachment sites for muscles.
• General comparison: lower limb bones are thicker and stronger than upper limb bones due to weight-bearing and locomotor demands.

Bones of the upper limb and pectoral girdle (overview)

• Pectoral girdle: clavicle and scapula.
• Upper arm: humerus.
• Forearm: radius and ulna.
• Hand: 8 carpal bones in the wrist; 5 metacarpal bones in the palm; 14 phalanges in the fingers.
• Per side (one limb):
  • Clavicle: 1
  • Scapula: 1
  • Humerus: 1
  • Radius: 1
  • Ulna: 1
  • Carpal bones: 8
  • Metacarpals: 5
  • Phalanges: 14
• Per pair (both limbs): numbers double accordingly; e.g., carpal bones total 16, metacarpals total 10, phalanges total 28, etc.

Clavicle (Collarbone)

• Shape and position: S-shaped bone on top of the thorax.
• Articulations:
  • Acromial (lateral) end articulates with the scapula.
  • Sternal (medial) end articulates with the sternum.
• Relationships and function:
  • Joins the shoulder girdle to the axial skeleton.
  • Provides attachment sites for muscles and acts as a brace to hold the scapulae and arms laterally.
• Clinical note: Clavicles are easy to fracture and may heal with a lump; called a palpable deformity at the fracture site.
• Landmarks to know: Acromial end, Sternal end.

Scapula (Shoulder blade)

• Location and shape: Triangular flat bone on the dorsal aspect of the rib cage, typically between ribs 2 and 7.
• Borders: Superior, Medial (vertebral), Lateral (axillary).
• Angles: Superior, Lateral, Inferior.
• Key markings and features:
  • Supraspinous fossa and Infraspinous fossa.
  • Spine of the scapula.
  • Acromion process.
  • Coracoid process.
  • Suprascapular notch.
  • Glenoid cavity (glenoid fossa) – socket for the head of the humerus.
• Relationships:
  • Scapula is not directly attached to the axial skeleton, enabling a wide range of shoulder mobility.
  • The scapula forms part of the shoulder girdle and interacts with the clavicle at the acromioclavicular joint.

Humerus (Upper arm bone)

• The only bone of the arm; the longest bone of the upper limb.
• Articulations:
  • Proximally with the glenoid cavity of the scapula (shoulder joint).
  • Distally with the radius and ulna at the elbow.
• Proximal features:
  • Head (articulates with glenoid cavity).
  • Anatomical neck and Surgical neck (common fracture sites).
  • Greater and Lesser tubercles.
  • Intertubercular groove (bicipital groove).
  • Deltoid tuberosity (site of deltoid muscle attachment).
  • Radial groove (spiral groove) on the lateral aspect for radial nerve.
• Distal features:
  • Capitulum (lateral, articulates with head of radius).
  • Trochlea (medial, articulates with trochlear notch of ulna).
  • Medial and Lateral epicondyles.
  • Medial and Lateral supracondylar ridges.
  • Fossae: Medial and lateral epicondylar fossae; Coronoid, Olecranon fossae (articulation with ulna during flexion/extension).
• Clinical relevance:
  • Fractures commonly occur at the surgical neck, deltoid tuberosity, and distal humerus; anatomical landmarks important for nerve and muscle attachments (e.g., radial nerve spirals around the radial groove).

Forearm: Radius and Ulna

• Two parallel bones: Ulna (medial) and Radius (lateral in anatomical position).
• Proximal ends articulate with the humerus and with each other to form elbow joints; Distal radioulnar joint connects the two at the wrist.
• Interosseous membrane: fibrous sheet connecting the radius and ulna along their length, providing stability and sites for muscle attachment.

Ulna (Medial bone of the forearm)

• Key features:
  • Olecranon process and Coronoid process: grip the trochlea of the humerus to form the hinge elbow joint.
  • Trochlear notch (between olecranon and coronoid processes).
  • Radial notch: articulates with head of the radius.
  • Ulnar head: distal knob-like end.
  • Ulnar styloid process: ligament attachment site.
• Relationship: forms the major portion of the elbow joint with the humerus.

Radius (Lateral bone of the forearm)

• Key features:
  • Head: articulates with the capitulum of the humerus and the radial notch of the ulna.
  • Neck: narrow region just distal to the head.
  • Radial tuberosity: attachment site for the biceps brachii muscle.
  • Ulnar notch: articulates with the head of the ulna.
  • Radial styloid process: ligament attachment at the wrist.

Bones of the hand

Carpals (8 per hand; 16 total for both hands)

• Arrangement: short bones forming the wrist, arranged in two rows of four bones each, forming a bony crescent at the wrist.
• Proximal row (lateral to medial): Scaphoid, Lunate, Triquetrum, Pisiform.
• Distal row (lateral to medial): Trapezium, Trapezoid, Capitate, Hamate.
• Memory aid (example phrase): "Sally left the party to take Cindy home" to recall the order of carpal bones.
• Clinical note: Scaphoid is especially prone to fractures and may risk nonunion due to blood supply patterns.

Metacarpals (5 per hand; 10 total for both hands)

• Form the framework of the palm.
• Each metacarpal bone has a base (proximal), a shaft, and a head (distal) that forms knuckles when the fist is made.
• Numbered I to V from the thumb side to the little finger.

Phalanges (14 per hand; 28 total for both hands)

• Digits consist of:
  • Proximal phalanges (5)
  • Middle phalanges (4 in each hand; not present in the thumb)
  • Distal phalanges (5)
• The thumb (digit I) has only proximal and distal phalanges (no middle phalanx).

Joints and articulations (basic concepts across the upper limb)

• Shoulder girdle and joints allow a wide range of motion due to:
  • Scapula not being directly attached to the axial skeleton.
  • A shallow glenoid fossa providing limited bony constraint, enabling mobility.
• Elbow joint: hinges primarily between the ulna and humerus; radius participates in radioulnar joints.
• Wrist joints: radiocarpal joint between radius (and interposed interosseous membrane) and carpals; distal radioulnar joint between distal radius and ulna.

Clinical considerations and tests

• Suprascapular nerve entrapment (related to scapula region):
  • Can lead to atrophy of the supraspinatus and infraspinatus muscles, affecting shoulder abduction and external rotation.
  • Symptoms may include weakness and shoulder girdle discomfort; entrapment can occur around the suprascapular notch.
• Median nerve and carpal tunnel syndrome (hand/wrist):
  • Compression of median nerve within the carpal tunnel can cause numbness, tingling, or weakness in the hand.
  • Associated with carpal ligament integrity and tendinous structures of the forearm.
• Clinical examination tests for carpal tunnel and related structures:
  • Phalen maneuver: wrist flexion held for a period to elicit symptoms.
  • Tinel test: tapping over the median nerve at the wrist to reproduce tingling.
  • Manual carpal compression test: direct compression of carpal bones to elicit symptoms.
  • Hand elevation test: evaluating nerve/vascular function with elevated hands.
• Practical implications:
  • Early recognition of nerve entrapments and fractures is important for preventing long-term deficits.
  • Occupational and repetitive use factors can influence risk for carpal tunnel syndrome and rotator cuff issues.

Quick reference: key numbers and landmarks

• Skeleton counts:
  • Total bones: $206$
  • Appendicular skeleton bones: $126$
• Upper limb per limb (one side):
  • Clavicle: 1
  • Scapula: 1
  • Humerus: 1
  • Radius: 1
  • Ulna: 1
  • Carpals: 8
  • Metacarpals: 5
  • Phalanges: 14
• Carpal bones per hand: 8; Carpal bones total (both hands): 16.
• Phalanges per hand: 14; Phalanges total (both hands): 28.
• Metacarpals per hand: 5; Metacarpals total (both hands): 10.

Connections to foundational principles

• Structure dictates function: the architecture of the pectoral girdle (preferential mobility) contrasts with the rigidity of the pelvis to illustrate how different girdles optimize movement vs. stability.
• Attachments and leverage: muscle attachment sites (e.g., deltoid tuberosity, attachments at the epicondyles) explain movement mechanics and force transmission during limb activities.
• Neurovascular relationships: bone markings and grooves (e.g., radial groove, suprascapular notch) reflect the path of nerves and vessels; awareness aids clinical diagnosis of nerve injuries.

Practical implications for exams

• Be able to identify major bones and their landmarks on diagrams: clavicle ends, scapular spine, glenoid cavity, humeral head, tubercles, intertubercular groove, epicondyles, capitulum, trochlea, olecranon fossa, radial and ulna fossae.
• Describe the orientation and articulation of radius and ulna at the elbow and the wrist.
• Memorize the order of carpal bones in proximal-to-distal and lateral-to-medial sequences using the memory aid.
• Explain why the shoulder girdle allows wide ranges of motion and the clinical significance of its relative mobility.

Summary of major points

• The upper limb consists of the pectoral girdle (clavicle and scapula), the arm (humerus), the forearm (radius and ulna), and the hand (carpals, metacarpals, phalanges).
• The pectoral girdle provides upper-limb mobility and muscle attachment points, with the scapula not directly attached to the axial skeleton.
• Each bone has characteristic landmarks that articulate with adjacent bones and serve as muscle attachment points.
• The hand bones are organized into carpals (wrist), metacarpals (palm), and phalanges (fingers), with a specific order and arrangement important for joint function.
• Clinical anatomy emphasizes nerve pathways (e.g., suprascapular nerve, median nerve) and common entrapment syndromes (e.g., carpal tunnel) along with simple, reproducible clinical tests.