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Humerus X-Ray Positioning: AP, Lateral, and Transthoracic Views

The humerus is the long bone of the upper arm, extending from the shoulder to the elbow. It's one of the most commonly imaged long bones in the emergency department — humeral fractures account for 4–5% of all fractures, and they come in many forms: surgical neck fractures (the most common), mid-shaft fractures, and supracondylar fractures in children.

As a radiologic technologist, you need to know the standard humerus series inside and out. The ARRT exam frequently tests humerus positioning, and in clinical practice, you'll encounter everything from ambulatory outpatients to trauma patients who cannot move their arm.

This guide covers the AP, lateral, and transthoracic lateral (Lawrence method) views, plus a trauma modification for patients with limited mobility.

Anatomy of the Humerus

Before positioning, make sure you can identify these key landmarks — they're all ARRT exam material:

Structure	Clinical Notes
Head	Articulates with the glenoid cavity of the scapula
Anatomic neck	Just below the head; fracture here is less common
Surgical neck	Most common fracture site — distal to the anatomic neck, narrow cross-section
Greater tubercle	Lateral aspect; insertion for supraspinatus, infraspinatus, teres minor
Lesser tubercle	Medial/anterior aspect; insertion for subscapularis
Shaft (diaphysis)	Long cylindrical body, mid-centering point for all standard projections
Medial and lateral epicondyles	Distal landmarks used to assess rotation on AP and lateral views
Trochlea	Medial distal articulation at the elbow
Capitulum	Lateral distal articulation at the elbow
Olecranon fossa	Posterior depression that receives the olecranon during elbow extension

AP Humerus

The AP projection is the standard first view in the humerus series. It demonstrates the humerus in its natural anatomical position and is the primary trauma screening view.

Patient Positioning

• Position: Upright preferred (standing or seated) with the patient's back against the upright Bucky. Supine is acceptable if the patient cannot stand.
• Arm: Abduct the affected arm slightly away from the body. Supinate the hand (palm facing forward) — this externally rotates the humerus, aligning the epicondyles parallel with the IR plane.
• IR: 35 × 43 cm (14 × 17 inches), portrait orientation. The IR must be large enough to include both the shoulder and elbow joints.

Technical Factors

Parameter	AP Humerus
Projection	Anteroposterior (AP)
CR	Perpendicular to mid-humerus shaft
Centering point	Midway between shoulder and elbow
SID	100–102 cm (40 inches)
IR size	35 × 43 cm (14 × 17"), portrait
kVp	60–85 (department-dependent)
Grid	Yes
Respiration	Suspend

Evaluation Criteria

• Coverage: Entire humerus from shoulder joint to elbow joint, plus approximately 2.5 cm (1 inch) of forearm
• Rotation: Medial and lateral epicondyles seen in profile; greater tubercle visualized on the lateral aspect of the humeral head; lesser tubercle seen between humeral head and greater tubercle
• Motion: Sharp bony margins and trabecular detail — no motion blur
• Technique: Uniform brightness from proximal to distal humerus; adequate penetration through both joints

Lateral Humerus

The lateral projection is the second standard view, obtained 90° from the AP. It's typically a PA projection with the patient rotated toward the detector.

Patient Positioning

• Position: Upright preferred. The patient stands facing the detector with the affected side closest to the upright Bucky.
• Rotation: Rotate the patient so the lateral aspect of the shoulder, arm, and elbow are all in contact with the Bucky.
• Arm: Flex the elbow 90° and internally rotate the arm. Place the patient's hand on their hip or ASIS (anterior superior iliac spine) to maintain position.
• Result: The epicondyles are now perpendicular to the IR, producing a true lateral projection.

Technical Factors

Parameter	Lateral Humerus
Projection	PA (lateromedial)
CR	Perpendicular to mid-humerus shaft
Centering point	Midway between shoulder and elbow
SID	100–102 cm (40 inches)
IR size	35 × 43 cm (14 × 17"), portrait
kVp	60–85 (same range as AP for comparison)
Grid	Yes
Respiration	Suspend

Evaluation Criteria

• Coverage: Entire humerus including both shoulder and elbow joints
• Rotation: Epicondyles superimposed; lesser tubercle seen in profile medially; greater tubercle superimposed over the humeral head
• Motion: Sharp humeral outline and trabecular pattern
• Technique: Even brightness and contrast throughout; scapula appears in Y-shaped lateral position

Transthoracic Lateral Humerus (Lawrence Method)

When a patient has a suspected fracture or cast that prevents abduction and rotation of the arm, the transthoracic lateral (also called the Lawrence method) is your go-to alternative. It visualizes the proximal humerus through the thorax without moving the injured limb.

When to Use

• Suspected humeral fracture with gross deformity
• Patient cannot abduct or rotate the arm
• Post-surgical or casted arm that cannot be manipulated
• Non-ambulatory or trauma patients on a stretcher

Patient Positioning

• Erect method: Patient stands or sits in a true lateral position with the affected side against the upright Bucky. The unaffected arm is raised above the head to clear the humerus.
• Recumbent method: Patient lies on the affected side on the table. A cross-table (horizontal beam) technique is used. Raise the unaffected arm above the head.
• Adjustment: Move the affected arm slightly anteriorly to avoid superimposition of the humerus on the thoracic spine.

Technical Factors

Parameter	Transthoracic Lateral
Projection	Transthoracic lateral
CR	Perpendicular to surgical neck (or 10–15° cephalad if limited mobility)
Centering point	Surgical neck of humerus
SID	100 cm
IR size	35 × 43 cm (14 × 17"), portrait
kVp	Higher than standard (penetrate thorax)
Grid	Yes
Respiration	Shallow breathing during exposure (3–5 seconds)

The Breathing Technique

The key to a successful transthoracic lateral is blurring the ribs with motion. Instruct the patient to take shallow, gentle breaths during the exposure. Use a longer exposure time (3–5 seconds) with a lower mA setting. The ribs and lung markings will blur while the humerus remains sharp because it moves less during respiration.

Evaluation Criteria

• Coverage: Proximal humerus and shoulder joint clearly visible through the thorax; entire shaft if possible
• Rotation: Epicondyles superimposed (confirming lateral position)
• Motion: Ribs appear blurred (breathing technique was effective); humeral cortex remains sharply defined
• Technique: Adequate penetration through the thorax; soft tissue and bone detail visible

Horizontal Beam Lateral (Trauma Modification)

For patients who cannot abduct the arm at all — for example, a severe mid-shaft fracture secured to the body — the horizontal beam lateral provides a true lateral without moving the injured limb.

Technique

1. Place the IR between the patient's body and the distal humerus, advancing it into the axilla
2. Use a horizontal (cross-table) beam directed perpendicular to the mid-humerus shaft
3. The patient remains supine or semirecumbent

This projection is 90° from the AP and serves as the lateral component when conventional lateral positioning is impossible due to trauma or immobilization.

Positioning Summary Table

View	Patient Position	CR Centering	Key Rotation Check	Best For
AP Humerus	Back to Bucky, arm abducted, hand supinated	Mid-humerus shaft	Epicondyles parallel; greater tubercle lateral	Standard first view; trauma screening
Lateral Humerus	Facing Bucky, affected side against it, hand on hip	Mid-humerus shaft	Epicondyles superimposed; lesser tubercle medial	Standard second view; 90° from AP
Transthoracic Lateral	True lateral, affected side against Bucky, unaffected arm up	Surgical neck	Epicondyles superimposed; ribs blurred	When arm cannot be moved
Horizontal Beam Lateral	Supine, IR in axilla	Mid-humerus shaft	Cross-table technique; 90° from AP	Severe trauma; immobile arm

Common Positioning Errors

Insufficient Joint Coverage

The most common mistake in humerus radiography is failing to include one or both joints. Always check that the shoulder and elbow joints are both visible on the image. If either joint is cut off, the study may need a repeat. This is why the 14 × 17 inch IR is mandatory — a smaller IR simply won't cover both joints.

Rotation on AP

If the epicondyles are not in profile, the humerus is rotated. Check: are both epicondyles visible symmetrically? If not, the arm was not fully supinated (external rotation was incomplete).

Rotation on Lateral

If the epicondyles are not superimposed, the lateral is oblique. Make sure the elbow is flexed a full 90° and the hand is resting on the hip/ASIS to achieve the necessary internal rotation.

Poor Transthoracic Technique

Common issues: ribs not blurred (breathing technique failed or exposure too short), humerus overlapped by spine (patient not in true lateral, or arm not moved anteriorly), underexposure (kVp too low to penetrate the thorax).

ARRT High-Yield Facts

Fact	Details
Most common fracture site	Surgical neck of the humerus
IR size requirement	14 × 17 inches (35 × 43 cm) to include both joints
AP rotation check	Epicondyles parallel to IR; greater tubercle lateral
Lateral rotation check	Epicondyles superimposed; lesser tubercle medial
Lateral arm position	Elbow flexed 90°, hand on hip (internal rotation)
Transthoracic indication	Patient cannot abduct/rotate arm; Lawrence method
Transthoracic respiration	Shallow breathing (3–5 sec exposure) to blur ribs
AP arm position	Hand supinated (external rotation) for epicondyles parallel

Related Articles

• Shoulder X-Ray Positioning Guide — AP, Grashey, Y-view, and axillary shoulder projections with centering points
• Elbow X-Ray Positioning Guide — AP, lateral, oblique, and Coyle method for radial head fractures
• Upper Extremity Positioning Guide — Hand, wrist, and elbow projections
• Trauma Radiography Principles — Modified techniques for non-ambulatory and trauma patients
• X-Ray Modality Page — Complete list of radiographic procedures