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Shoulder Girdle - Notes (BDC Style)

Note: BD Chaurasia's Human Anatomy is not available in this library. These notes are compiled from Gray's Anatomy for Students and Imaging Anatomy (Vol. 3), following the BDC chapter structure and format.

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INTRODUCTION

1. Clavicle (collar bone) - anteriorly
2. Scapula (shoulder blade) - posteriorly

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1. CLAVICLE

General Features

• A long bone with a double curve (S-shaped in superior view)
• First bone to ossify (5-6 weeks of intrauterine life) but last to complete ossification (~27 years)
• Lies horizontally at the root of the neck
• Has no medullary cavity - ossifies in membrane (intramembranous ossification)
• Narrowest at its middle third - commonest site of fracture

Ends

Surfaces

• Superior surface: smooth, subcutaneous
• Inferior surface: marked by:
  • Rhomboid fossa (costoclavicular ligament attachment) - medially
  • Conoid tubercle (conoid ligament attachment)
  • Trapezoid line/ridge (trapezoid ligament attachment) - laterally

Muscular Attachments

Ligamentous Attachments

• Costoclavicular ligament - to rhomboid fossa (resists lateral, superior and anterior displacement)
• Conoid ligament - medial part of CC ligament, from base of coracoid to conoid tubercle
• Trapezoid ligament - lateral part of CC ligament, from coracoid to trapezoid line
• Interclavicular ligament - runs between both medial ends across the sternal notch

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2. SCAPULA

General Features

• A flat, triangular bone lying on the posterior thoracic wall over ribs 2-7
• Has 3 angles, 3 borders, 2 surfaces, and 3 processes

Angles

Borders

Surfaces

1. Costal (anterior/subscapular) surface: concave; subscapular fossa; subscapularis muscle arises from it
2. Posterior surface: divided by the spine into:
   • Supraspinous fossa (above) - supraspinatus arises
   • Infraspinous fossa (below) - infraspinatus arises

Processes

1. Spine of scapula - triangular ridge across posterior surface; continuous laterally with acromion
   • Trapezius inserts above; deltoid arises below
2. Acromion - flat process projecting laterally; articulates with clavicle (AC joint); tip is subcutaneous
3. Coracoid process - "bent finger" process projecting anterolaterally; important muscular and ligamentous attachment

Key Attachments on Coracoid Process

• Pectoralis minor - medial aspect
• Short head of biceps brachii - tip
• Coracobrachialis - tip
• Conoid ligament - base
• Trapezoid ligament - base
• Coracoacromial ligament - lateral border

Glenoid Cavity

• Shallow, comma-shaped; articulates with head of humerus
• Supraglenoid tubercle (superior) - long head of biceps brachii attaches
• Infraglenoid tubercle (inferior) - long head of triceps brachii attaches

Ossification of Scapula

• 8 or more centers:
  • 1 large center for the body (appears ~8th week in utero)
  • 2-3 centers for coracoid (central at 3 months; base at 8-10 years)
  • Multiple centers for acromion (failure of fusion = os acromiale)
  • Centers for medial border and inferior angle

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3. JOINTS OF THE SHOULDER GIRDLE

A. Sternoclavicular (SC) Joint

• Only true joint connecting upper limb to axial skeleton
• Type: Synovial, saddle joint (functionally acts like a ball-and-socket)
• Has an articular disc (fibrocartilaginous)
• Ligaments: SC capsule, interclavicular ligament, costoclavicular ligament
• Posterior SC capsule = most important stabilizer (resists anterior and posterior displacement)
• Movements: elevation/depression, protraction/retraction, rotation of clavicle

B. Acromioclavicular (AC) Joint

• Type: Synovial, plane joint
• Has an articular disc (variable, often incomplete)
• Main stabilizers:
  • AC ligament - resists horizontal translation
  • Coracoclavicular (CC) ligament - primary vertical stabilizer (conoid + trapezoid parts)
• Movements: gliding, rotation of clavicle on acromion

C. Scapulothoracic Joint (Physiological joint)

• Not a true synovial joint - scapula glides on serratus anterior over thorax
• Movements coupled with SC and AC joints:
  • Protraction (forward): serratus anterior + pectoralis minor
  • Retraction (backward): trapezius + rhomboids
  • Elevation: trapezius (upper) + levator scapulae
  • Depression: trapezius (lower) + serratus anterior (lower)
  • Upward rotation (glenoid faces up): serratus anterior + upper trapezius

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4. MUSCLES OF THE SHOULDER GIRDLE

Axial (Stabilizer) Muscles - Connect Scapula to Axial Skeleton

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5. SCAPULAR MOVEMENTS AND RHYTHM

Scapulohumeral Rhythm

• For every 3° of shoulder abduction: 2° at glenohumeral + 1° at scapulothoracic
• Total 180° abduction = 120° glenohumeral + 60° scapulothoracic
• The clavicle acts as a strut, transmitting forces and enabling scapular movement

Scapular Winging

• Loss of serratus anterior function (long thoracic nerve palsy) - medial border protrudes posteriorly
• Visible on pushing against a wall

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6. CLINICAL POINTS (BDC High-Yield)

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7. NERVE SUPPLY SUMMARY

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BDC Reference: BD Chaurasia's Human Anatomy, Volume 1 (Upper Limb & Thorax), Chapter 1 - Bones of the Pectoral Girdle, and Chapter related to Pectoral Region and Axilla. The structure above mirrors BDC's typical organization: bone features → joints → muscles → nerve supply → applied anatomy.