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Upper Extremities

19 Elbow

Anatomy & Pathology

Anatomy Overview
The elbow joint is a complex synovial hinge joint formed by articulations among three bones:

  • Humerus (distal): includes the capitulum (lateral), trochlea (medial), medial and lateral epicondyles, coronoid and olecranon fossae.
  • Ulna (medial forearm): includes the olecranon and coronoid processes, trochlear notch, and radial notch.
  • Radius (lateral forearm): includes the radial head, neck, and tuberosity.

Associated fat pads—anterior, posterior, and supinator—are radiographically significant indicators of joint effusion or occult fracture.

Common Pathology

  • Fractures: radial head/neck, olecranon, coronoid process, distal humerus, supracondylar fractures in pediatrics.
  • Joint injuries: dislocations or subluxations, especially radial head dislocations.
  • Pathologic signs: visible posterior fat pad = effusion or occult fracture.
  • Degenerative change: osteoarthritis or rheumatoid involvement of the humeroulnar articulation.

Projections

Elbow – AP Projection

CR Location & Positioning

  • SID: 40 inches (102 cm)
  • Patient position: Seated at table, shoulder, elbow, and wrist in the same plane (entire limb parallel to tabletop).
  • Adjustments: Fully extend the elbow, supinate the hand so the forearm is true AP. Lean laterally if needed until humeral epicondyles and anterior surface of elbow are parallel to IR.
  • CR: Perpendicular to the elbow joint; centered midway between epicondyles.
  • Pt. Instructions: Suspend breathing; remain still.
  • Exposure: Moderate kVp (60–70) with adequate contrast to visualize both bony and soft-tissue detail; ensure soft-tissue visibility for fat-pad evaluation.

Evaluation Criteria

  • Coverage: Distal humerus, proximal forearm, and open elbow joint centered to CR.
  • Rotation checks: Epicondyles seen in profile (no rotation); radial head, neck, and tuberosity slightly superimposed over proximal ulna; open humeroradial and humeroulnar joint spaces.
  • Motion checks: Sharp cortical margins and visible trabecular pattern confirm no motion.
  • Technique checks: Even exposure across both bone densities; soft tissue and fat pads visible; no artifacts.
  • Clinical aim: Evaluate for fracture/dislocation alignment, joint space narrowing, or pathology indicated by fat-pad displacement.

Elbow – Lateral Projection (Lateromedial)

CR Location & Positioning

  • SID: 40 inches (102 cm)
  • Patient position: Seated with shoulder, elbow, and wrist in same horizontal plane.
  • Adjustments: Flex elbow 90°; forearm and humerus resting on same plane; hand in true lateral position (thumb up). Ensure epicondyles perpendicular to IR. Elevate wrist slightly if forearm is muscular to maintain true lateral alignment.
  • CR: Perpendicular to the elbow joint; centered midway between epicondyles.
  • Pt. Instructions: Suspend breathing; remain still.
  • Exposure: Moderate kVp emphasizing soft-tissue detail to visualize fat pads; exposure must allow differentiation of anterior and posterior fat pads.

Evaluation Criteria

  • Coverage: Distal humerus and proximal forearm fully included with elbow flexed 90°.
  • Rotation checks:
    • Epicondyles superimposed
    • Radial head partially superimposing coronoid process
    • Olecranon process in profile
    • Radial tuberosity facing anteriorly
  • Motion checks: Crisp cortical outlines; soft tissue not blurred.
  • Technique checks: Visualization of anterior and supinator fat pads (posterior should not be visible unless pathology present); proper contrast for soft-tissue assessment.
  • Clinical aim: Demonstrate alignment, displacement, effusion, or occult fractures.

Elbow – AP Oblique Projection (Medial Rotation)

CR Location & Positioning

  • SID: 40 inches (102 cm)
  • Patient position: Seated at table with arm extended and in contact with tabletop.
  • Adjustments: From AP, pronate hand and medially rotate the arm until anterior surface of elbow forms a 45° angle to IR.
  • CR: Perpendicular to the elbow joint, midway between epicondyles.
  • Pt. Instructions: Hold still; suspend breathing.
  • Exposure: Standard kVp range; adjust for forearm thickness; maintain uniform contrast.

Evaluation Criteria

  • Coverage: Distal humerus and proximal forearm with open elbow joint centered to CR.
  • Rotation checks:
    • Coronoid process in profile
    • Elongated medial epicondyle
    • Ulna partially superimposed by radial head and neck
    • Olecranon process within its fossa
  • Motion checks: Sharp bone edges, no motion blur.
  • Technique checks: Appropriate brightness/contrast to differentiate coronoid and surrounding structures.
  • Clinical aim: Evaluate coronoid process and trochlear articulation; assess for fractures or osteophyte formation on the ulna.

Elbow – AP Oblique Projection (Lateral Rotation)

CR Location & Positioning

  • SID: 40 inches (102 cm)
  • Patient position: Seated at table, arm extended and supinated.
  • Adjustments: From AP, laterally rotate hand and arm until posterior surface of elbow is 45° to IR; first and second digits contact table.
  • CR: Perpendicular to the elbow joint, centered midway between epicondyles.
  • Pt. Instructions: Suspend breathing; remain still.
  • Exposure: Similar to AP; optimize contrast for visualization of radial head and capitulum.

Evaluation Criteria

  • Coverage: Distal humerus and proximal forearm with open elbow joint.
  • Rotation checks:
    • Radial head, neck, and tuberosity free of superimposition by ulna
    • Elongated lateral epicondyle
    • Capitulum in profile
  • Motion checks: Sharp bone and soft-tissue margins.
  • Technique checks: Appropriate brightness and contrast across joint; no artifacts.
  • Clinical aim: Demonstrate radial head and capitulum relationships; identify radial head or neck fractures.

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Hows & Whys of Elbow Radiography

Anatomy

  • Which bone articulates most directly with the humerus at the elbow?
    The ulna articulates with the trochlea of the humerus to form the primary hinge motion of the elbow.
  • Which structure of the radius articulates with the humerus?
    The radial head articulates with the capitulum of the humerus.
  • What type of joint is the elbow?
    A synovial hinge joint permitting flexion and extension.
  • What type of joint is the proximal radioulnar articulation?
    A pivot joint allowing pronation and supination of the forearm.
  • What radiographic sign can indicate an occult elbow fracture?
    Visualization of the posterior fat pad on a lateral projection.

Positioning

  • Why must the shoulder, elbow, and wrist be in the same plane for the AP projection?
    To prevent joint distortion and ensure the elbow joint is open and properly centered.
  • Why is the hand supinated for the AP projection?
    Supination prevents the radius and ulna from crossing, giving a true AP view.
  • Why is the elbow flexed 90° for the lateral projection?
    It shows the olecranon process in profile and keeps the posterior fat pad depressed, avoiding false indications of pathology.
  • Why is the hand placed in true lateral with thumb up for the lateral projection?
    This ensures the forearm is in a true lateral position, producing superimposed epicondyles.
  • Why is the arm rotated medially for the medial oblique projection?
    To visualize the coronoid process free of superimposition and profile the trochlea.
  • Why is the arm rotated laterally for the lateral oblique projection?
    To separate the radial head, neck, and tuberosity from the ulna for clearer evaluation.

Technique & Image Evaluation

  • How can you tell that the AP elbow is correctly positioned?
    Epicondyles appear in profile and the joint space is open, confirming the limb was in the same plane.
  • How can you tell that the AP projection was not truly supinated?
    The radius crosses over the ulna proximally, indicating pronation.
  • How can you tell the lateral projection is correctly positioned?
    Epicondyles are superimposed, the radial head overlaps the coronoid process, and the olecranon is in profile.
  • How can you confirm correct medial oblique positioning?
    The coronoid process is seen in profile with the trochlea; the medial epicondyle appears elongated.
  • How can you confirm correct lateral oblique positioning?
    The radial head and neck are completely free of ulnar superimposition and the lateral epicondyle appears elongated.
  • How can you tell if motion occurred?
    Loss of cortical sharpness or soft-tissue definition, especially at the fat pads.
  • How can you tell exposure factors were appropriate?
    Bony cortices and fat pads visible without overexposure; consistent brightness across both humeral and forearm portions.

Clinical Applications

  • Which projection best demonstrates the radial head and neck?
    The AP lateral oblique projection.
  • Which projection best demonstrates the coronoid process in profile?
    The AP medial oblique projection.
  • Why are fat pads important diagnostically?
    Displacement of the posterior fat pad or distortion of the anterior fat pad suggests joint effusion or occult fracture.
  • Which projection provides the best assessment of anterior or posterior fracture displacement?
    The lateral projection.
  • Why is it important to visualize both distal humerus and proximal forearm on each elbow image?
    To ensure alignment and exclude combined injuries involving the humerus or radius/ulna.

 

License

Radiographic Procedures Review Guide Copyright © 2025 by Carla M. Allen and Taylor M. Otto. All Rights Reserved.