Shoulder Girdle Anatomy and Projections

Shoulder Girdle Overview

  • The shoulder girdle consists of three key bones:
    • Clavicle
    • Scapula
    • Humerus

Proximal Humerus Anatomy

  • Important features of the proximal humerus:
    • Greater Tubercle (Tuberosity): Lateral projection providing attachment for rotator cuff muscles.
    • Lesser Tubercle (Tuberosity): Smaller, anterior projection for muscle attachment.
    • Intertubular Groove (Bicipital Groove): Located between the tubercles; allows passage of the biceps tendon.
    • Head: Rounded end of the humerus fitting into the glenoid cavity of the scapula.
    • Anatomic Neck: Constriction below the head, not typically a site of fracture.
    • Surgical Neck: Common site for humeral fractures.
    • Deltoid Tuberosity: Roughened area on the lateral surface for attachment of the deltoid muscle.
    • Body (Shaft): Long midsection of the humerus.

Clavicle Anatomy

  • Acromial Extremity: Lateral end of clavicle, articulates with acromion of scapula.
  • Sternal Extremity: Medial end, articulates with the manubrium of the sternum.
  • Joints Involved:
    • Acromioclavicular Joint: Between the acromion and clavicle.
    • Sternoclavicular Joint: Between the sternum and clavicle.

Scapula Structure

  • Three major borders:
    • Superior Border
    • Medial (Vertebral) Border
    • Lateral (Axillary) Border
  • Scapulohumeral (Glenohumeral) Joint: Joint formed by the scapula and humerus.

Views of the Scapula

  • Anterior View:
    • Key features include:
    • Coracoid process
    • Glenoid cavity
    • Subscapular fossa
  • Posterior View:
    • Includes:
    • Supraspinous fossa
    • Infraspinous fossa
    • Acromion
  • Lateral View:
    • Important for understanding relationships between acromion and coracoid processes.

Joints of the Shoulder Girdle

  • Types of Joints:
    • Sternoclavicular Joint: Plane or gliding joint.
    • Acromioclavicular Joint: Also a plane or gliding joint.
    • Scapulohumeral Joint: Spheroidal or ball-and-socket joint, allows for greater range of motion.

Movement Types of Joints of Shoulder Girdle

  • Scapulohumeral Joint: Greater freedom of movement due to its structure.
  • Sternoclavicular & Acromioclavicular Joints: Allow slight gliding movements.

Humerus Projections

  • AP Proximal Humerus (External Rotation):

    • Shows the greater tubercle in lateral profile, lesser tubercle anteriorly.

  • Lateral Proximal Humerus (Internal Rotation):

    • Displays greater tubercle anteriorly, lesser tubercle medially.

  • Oblique Proximal Humerus (Neutral Rotation):

    • Positioned at a 45° angle to the image receptor; not showing tubercles clearly.

Evaluation Criteria for Humerus Projections

  • For each projection, ensure:
    • Entire humerus is included in the image.
    • Tubercle positioning is correct (greater tubercle lateral for external rotation, etc.).
    • Epicondyles are in appropriate alignment relative to the film/cassette.

Special Shoulder Projections

  • Inferosuperior Axial Projection (Lawrence Method):
    • CR angled 25° to 30° toward the axilla.
  • PA Transaxillary Projection (Hobbs Modification):
    • Used for non-traumatic imaging of the shoulder.
  • Neer Method: Outlet view of the shoulder, emphasizes the supraspinatus outlet to assess rotator cuff pathology.

Clavicle Projections

  • AP Clavicle:
    • CR perpendicular to midclavicle.
    • For AP axial, angles between 15° to 30°.

Evaluation Criteria for Clavicle Projections

  • Verify entire clavicle is shown, optimal exposure factors are met, correct markers visible, and collimation is appropriate.

Scapular Projections

  • Scapula AP: Breathing technique may be optional; CR directed to mid-scapula.
  • Scapular Y Lateral: 2 inches below the top of the shoulder.

Quiz Questions/Answers (Sample)

  1. Which of the following humeral structures is most distal?
    • Answer: Surgical neck
  2. What is another term for the mid area of the costal surface of the scapula?
    • Answer: Subscapular fossa
  3. Which projection demonstrates the Hill-Sachs defect best?
    • Answer: Inferosuperior axial projection with exaggerated external rotation.
  • Ensure understanding of body rotations necessary for oblique projections (e.g., Grashey 35° to 45°).

Radiation Protection and Technical Factors

  • Use shielding for radiosensitive areas and employ collimation to limit exposure.
  • Recommended technical factors for shoulder girdle include kVp range, grid requirements, and short exposure times for optimal imaging results.