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Upper Extremities

Humerus

Anatomy & Pathology

Anatomy Overview

  • The humerus is the long bone of the upper arm, extending from the shoulder joint to the elbow joint.
    It articulates proximally with the scapula to form the glenohumeral (shoulder) joint, and distally with the radius and ulna to form the elbow joint.
    • Both are diarthrodial synovial joints—the shoulder is a ball-and-socket, and the elbow a hinge.
  • Proximal Humerus: Includes the head, anatomic neck, surgical neck, greater tubercle, lesser tubercle, and intertubercular groove (bicipital groove).
    • The head articulates with the glenoid cavity of the scapula.
    • The greater and lesser tubercles serve as attachment sites for rotator cuff muscles.
    • The surgical neck is a common fracture site due to its narrow diameter.
  • Humeral Shaft (Body): The body (shaft) is slightly anteriorly convex and serves as attachment for deltoid and brachialis muscles. Contains the deltoid tuberosity and radial groove (for the radial nerve and profunda brachii artery).
  • Distal Humerus: Includes the capitulum (lateral), trochlea (medial), medial and lateral epicondyles, coronoid fossa, radial fossa, and olecranon fossa.
    • These structures form the articular surface of the elbow with the radius and ulna.
    • The epicondyles serve as key positioning landmarks.
  • Scapular Landmarks (Articulating Structures):  The glenoid cavity, coracoid process, and acromion form the scapular components of the shoulder joint.
    • The glenoid cavity receives the humeral head; the acromion and coracoid process provide attachment for ligaments and muscles.

Common Pathologies

  • Fractures:
    • Surgical neck fractures – common in elderly patients from falls on an outstretched arm.
    • Greater or lesser tubercle fractures – often due to direct trauma or avulsion from rotator cuff tension.
    • Humeral shaft fractures – may injure the radial nerve (resulting in wrist drop).
      Exposure note: Increase kVp slightly (~5%) for thick-casted or post-reduction imaging.
  • Metastatic Lesions:  Secondary bone tumors frequently metastasize to the humerus; may appear osteolytic (bone loss) or osteoblastic (bone formation).  Exposure note: Adjust technique based on lesion type — decrease kVp for lytic, increase slightly for sclerotic.
  • Osteoporosis:  Decreased bone density leading to thinning of cortical bone; often incidental on trauma imaging. Exposure note: Decrease kVp (~5%) to enhance cortical contrast.
  • Osteolytic / Osteoblastic Lesions: Seen in metastases or primary bone tumors (e.g., osteosarcoma, chondrosarcoma).
    • Osteolytic lesions appear radiolucent due to bone destruction.
    • Osteoblastic lesions appear radiopaque due to new bone formation.

Routine Projections (ARRT- Required)

AP Humerus

CR Location & Positioning

  • SID: 40 inches (102 cm)
  • Patient position: Upright preferred (standing or seated) or supine if necessary. Place the back against the upright Bucky or table.
  • Adjustments: Abduct the arm slightly and supinate the hand. Align humeral epicondyles parallel with the IR plane so the shoulder and elbow are in the same horizontal plane.
  • CR (angle and centering): Perpendicular to mid-humerus, centered midway between shoulder and elbow.
  • Patient instructions: Suspend respiration during exposure.
  • Exposure: Use 70–85 kVp range. Collimate to include the entire humerus and both joints.

Evaluation Criteria

  • Coverage: Entire humerus including shoulder and elbow joints visible; 1 inch of forearm and entire shoulder joint included.
  • Rotation checks: Humeral epicondyles seen in profile; greater tubercle in profile laterally; lesser tubercle between humeral head and greater tubercle.
  • Motion checks: Sharp bony margins and trabecular detail indicate no motion.
  • Technique checks: Uniform brightness and contrast from proximal to distal; soft tissue and bone detail visible; no artifacts.
  • Clinical aim: Demonstrates humeral shaft and shoulder articulation for trauma, pathology, or degenerative evaluation.

Lateral Humerus

CR Location & Positioning

  • SID: 40 inches (102 cm)
  • Patient position: Upright or supine.
  • Adjustments: Flex the elbow 90 degrees and internally rotate the arm so the palm rests on the hip, placing epicondyles perpendicular to the IR.
  • CR (angle and centering): Perpendicular to mid-humerus, centered midway between shoulder and elbow.
  • Patient instructions: Suspend respiration.
  • Exposure: 70–85 kVp, same technique range as AP for comparison.

Evaluation Criteria

  • Coverage: Entire humerus including shoulder and elbow joints.
  • Rotation checks: Humeral epicondyles superimposed; lesser tubercle in profile medially; greater tubercle superimposed over humeral head.
  • Motion checks: Sharp humeral outline and trabecular pattern.
  • Technique checks: Even brightness and contrast; visible soft tissue and bony trabeculae.
  • Clinical aim: Demonstrates the entire humerus in a true lateral projection; used for trauma, dislocation, or alignment assessment.

Transthoracic Lateral Humerus (Lawrence Method)

CR Location & Positioning

  • SID: 40 inches (102 cm)
  • Patient position: Upright or supine lateral, affected arm against the upright Bucky. Raise the unaffected arm above the head to clear the humerus.
  • Adjustments: Ensure the midcoronal plane is perpendicular to the IR. If the patient cannot elevate the arm fully, angle the CR 10–15° cephalad.
  • CR (angle and centering): Perpendicular to the surgical neck (or angled 10–15° cephalad if limited mobility).
  • Patient instructions: Perform shallow breathing during exposure if possible; otherwise suspend respiration.
  • Exposure: Use a long exposure time (3–5 seconds) with low mA to blur ribs and lung markings.

Evaluation Criteria

  • Coverage: Proximal humerus and shoulder joint included; entire shaft if possible.
  • Rotation checks: Epicondyles superimposed; minimal rib superimposition over the humerus.
  • Motion checks: Ribs appear blurred with breathing technique; humerus remains sharply defined.
  • Technique checks: Adequate penetration through thorax; soft tissue and bone detail visible.
  • Clinical aim: Used when fracture or immobilization prevents conventional lateral positioning; demonstrates the proximal humerus without moving the injured limb.

Hows & Whys of Humerus Radiography

Anatomy

  • What structure articulates with the head of the humerus?
    The glenoid cavity of the scapula.
  • What bony landmark is a frequent fracture site on the humerus?
    The surgical neck.
  • Which tubercle serves as the insertion for the subscapularis muscle?
    The lesser tubercle.
  • Which depression receives the olecranon process during elbow extension?
    The olecranon fossa.

Positioning

  • Why must the hand be supinated for the AP projection?
    Supination aligns the humeral epicondyles parallel to the IR, ensuring a true AP without rotation.
  • Why is the elbow flexed 90° and the hand placed on the hip for the lateral projection?
    This internal rotation makes the epicondyles perpendicular to the IR and places the humerus in a true lateral position.
  • Why is the transthoracic lateral projection used for suspected fractures?
    It visualizes the proximal humerus without rotating or manipulating the injured arm.
  • Why must both the shoulder and elbow joints be included on AP and lateral images?
    To ensure accurate evaluation of alignment, possible fracture extension, and joint integrity.

Technique & Image Evaluation

  • How can you tell the humerus was properly positioned for the AP projection?
    The greater tubercle appears in profile laterally and the epicondyles are parallel to the IR.
  • How can you tell the humerus was properly positioned for the lateral projection?
    The lesser tubercle is seen in profile medially and the epicondyles are perfectly superimposed.
  • How can you confirm correct centering on the transthoracic lateral projection?
    The proximal humerus is clearly visible through the thorax at the level of the surgical neck.
  • How can you verify that a breathing technique was successful on the transthoracic lateral?
    The ribs appear blurred while the humeral cortex remains sharp, confirming motion of soft tissue only.
  • How can you tell that exposure technique was appropriate?
    Soft tissue and bony trabeculae are visible throughout; no clipped highlights or lost cortical definition.

Clinical Applications

  • When would the transthoracic lateral projection be preferred?
    When the patient has a suspected fracture or casted humerus that cannot be rotated.
  • Why is it critical to assess both proximal and distal joints on humerus projections?
    Fracture displacement or angulation may involve the shoulder or elbow, affecting surgical planning or reduction.

 

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Radiographic Procedures Review Guide Copyright © 2025 by Carla M. Allen and Taylor M. Otto is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, except where otherwise noted.

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