Elbow and Humerus Anatomy & Imaging

Overview

This lecture provides an in-depth review of the anatomy of the elbow and humerus, radiographic positioning techniques, common pathologies, and the evaluation criteria necessary for effective imaging of the upper arm and elbow region.

Humerus and Elbow Anatomy

• The humerus is the only bone in the upper arm, consisting of a body and two articular ends. The proximal end articulates with the shoulder girdle.
• The distal humeral condyle features the trochlea (medial) and capitulum (lateral), which articulate with the ulna and radius, respectively.
• Medial and lateral epicondyles are prominent, palpable landmarks serving as muscle attachment points.
• The anterior surface contains the coronoid fossa (for the coronoid process during flexion) and the radial fossa (for the radial head). The posterior surface has the olecranon fossa, which accommodates the olecranon process during extension.
• The proximal humerus includes a large, smooth head, the anatomical neck (just below the head), the surgical neck (a common fracture site), and the greater and lesser tubercles separated by the intertubercular groove.
• The elbow joint is formed by three articulations: humeroulnar, humeroradial, and proximal radioulnar joints, all within a common capsule. These allow for flexion, extension, supination, and pronation of the forearm.

Elbow Fat Pads and Imaging

• Three fat pads are associated with the elbow joint: anterior (coronoid and radial fat pads), posterior (within the olecranon fossa), and supinator fat pad.
• The anterior fat pad appears teardrop-shaped on imaging; the posterior fat pad is the largest and only visible when displaced by pathology.
• Visualization and displacement of fat pads are important indicators of elbow injury or pathology.
• For AP projections, the elbow should be fully extended and the hand supinated. The central ray (CR) must be perpendicular to the joint.
• Exposure factors should be optimized to visualize both bone and soft tissue, especially for assessing fat pad displacement.

Common Elbow Pathologies

• Elbow conditions include bone cysts (fluid-filled sacs), bursitis (inflammation of the bursa), dislocations, fractures, and various forms of arthritis (osteoarthritis and rheumatoid arthritis).
• Tumors such as chondrosarcoma and osteosarcoma can occur in the elbow region, requiring careful imaging.
• Common named fractures:
  • Bennett's fracture: base of the first metacarpal, often from axial loading.
  • Boxer's fracture: metacarpal neck, typically from punching.
  • Colles' fracture: distal radius with dorsal displacement, common in falls.
  • Smith's fracture: distal radius with palmar displacement.

Standard Radiographic Techniques

• AP Projection: Elbow extended, hand supinated, CR perpendicular to the elbow joint. Collimation should include 8 cm proximal and distal to the joint and 2.5 cm on each side. Evaluation includes clear side markers, joint centering, and visible bony detail.
• Lateral Projection: Elbow flexed 90°, humerus and forearm in the same plane, CR perpendicular to the joint. Look for superimposed epicondyles and visible fat pads.
• AP Oblique Medial Rotation: Arm extended, humeral epicondyles rotated 45° medially. Visualizes the coronoid process free of superimposition and elongates the medial epicondyle.
• AP Oblique Lateral Rotation: Arm extended, humeral epicondyles rotated 45° laterally. Visualizes the radial head and neck, and the olecranon process within the olecranon fossa.
• Acute Flexion (Jones Method): Used for fractures around the elbow; requires complete flexion. Both AP arm and PA forearm projections are made through superimposed bones.

Special Projections and Adaptations

• Coyle Method (Axiolateral Projection): For patients unable to fully extend the elbow, especially in trauma. Elbow flexed 90° for radial head imaging (CR angled 45° toward the shoulder), and 80° for coronoid process imaging (CR angled 45° away from the shoulder). Enhances visualization of the radial head or coronoid process.
• Distal Humerus/Proximal Forearm Imaging: When full extension is not possible, obtain two AP projections—one for the distal humerus and one for the proximal forearm. Position the patient to ensure the area of interest is parallel to the IR.
• PA Axial Projections: Used to visualize the ulnar sulcus and olecranon process. The arm is flexed, and the CR is angled (e.g., 20° toward the wrist for the olecranon process) to optimize visualization of specific structures.

Humerus Imaging Techniques

• AP Humerus: Patient upright or supine, arm slightly abducted, hand supinated, CR perpendicular to the mid-humerus. The entire humerus, including shoulder and elbow joints, should be visible.
• Lateral Humerus: Can be performed in lateromedial or mediolateral orientation. Arm flexed at 90°, epicondyles perpendicular to the IR. Confirms positioning of the humeral head and tubercles.
• Mediolateral/Lateromedial Projections: Adjust patient and arm position based on injury or patient condition. Ensure the humerus is aligned with the IR and the epicondyles are superimposed for a true lateral image.

Evaluation Criteria and Tips

• Always place the side marker clear of the anatomy of interest to avoid confusion.
• The elbow and shoulder joints should be included in the image, though slight distortion may occur due to beam divergence.
• In true lateral views, the humeral epicondyles should be superimposed; the lesser tubercle should be in profile medially, and the greater tubercle superimposed over the humeral head.
• Collimate as instructed (e.g., 8 cm proximal/distal to the elbow, 2.5 cm on the sides) to minimize radiation dose and maximize image quality.
• Review images for clarity, bony trabecular detail, and soft tissue visibility. Adjust positioning or exposure as needed for optimal diagnostic value.
• Use supports or sandbags to stabilize the arm, especially in cases of trauma or patient discomfort.

Key Terms & Definitions

• Trochlea: Medial distal humerus articulation with the ulna.
• Capitulum: Lateral distal humerus articulation with the radius.
• Epicondyle: Bony prominence on the distal humerus for muscle and ligament attachment.
• Fat Pad Sign: Radiographic indication of elbow effusion or injury, seen as displacement or visibility of fat pads.
• Coyle Method: Axiolateral trauma elbow imaging technique for visualizing the radial head or coronoid process when full extension is not possible.
• AP/Lateral Projections: Standard radiographic views showing the anatomy in anatomic or profile orientation.

Action Items / Next Steps

• Practice patient positioning for all standard and special elbow and humerus projections, including AP, lateral, oblique, and trauma techniques.
• Review and memorize evaluation criteria for each projection, focusing on image quality, anatomical detail, and common pathologies.
• Study referenced figures and diagrams to reinforce correct positioning and expected radiographic appearances.
• Familiarize yourself with the appearance and significance of fat pads and common fracture types on radiographs.
• Continue to refine technique and understanding of anatomy to improve diagnostic accuracy in upper extremity imaging.