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Elbow X-Ray Positioning: AP, Lateral, Oblique, and Radial Head Views

The elbow joint is one of the most complex joints in the body — a hinge-and-pivot articulation where three bones (humerus, radius, and ulna) meet. Imaging it requires precise positioning to demonstrate the joint space, surrounding bony architecture, and soft tissue without superimposition that could hide fractures or dislocations.

In this guide, you'll learn the common elbow projections — AP, lateral, and oblique views — plus Coyle trauma axiolateral variants. Because examination composition and exposure technique vary by department, protocol variants are labeled rather than presented as universal rules.

For other upper extremity positioning guides, check out our hand, wrist, and finger X-ray positioning guide and upper extremity positioning overview.

Anatomy of the Elbow Joint

The elbow joint is actually three articulations within one synovial capsule:

• Humeroulnar joint — trochlea of the humerus articulating with the trochlear notch of the ulna. This is the primary hinge (flexion-extension).
• Humeroradial joint — capitellum of the humerus articulating with the radial head. This also allows forearm rotation (pronation-supination).
• Proximal radioulnar joint — radial head articulating with the radial notch of the ulna. This permits forearm rotation.

Key bony landmarks for positioning:

Landmark	Location	Palpable?
Medial epicondyle	Medial prominence of distal humerus	Yes — the "funny bone" area
Lateral epicondyle	Lateral prominence of distal humerus	Yes — smaller than medial
Olecranon	Posterior prominence of proximal ulna	Yes — the "point" of the elbow
Radial head	Lateral, distal to lateral epicondyle	Yes — rotates with supination/pronation
Coronoid process	Anterior projection of proximal ulna	No — deep to soft tissue

The carrying angle is physiologic cubitus valgus: the forearm angles laterally relative to the humerus with the elbow extended and forearm supinated. Its magnitude varies with anatomy, age, sex, and measurement method; it should not be reduced to one universal “normal” range. Keep the entire limb in the same plane for the AP projection.

Standard Elbow Series — Overview

Protocol note: examination composition varies by institution and indication. AP and lateral are the usual orthogonal foundation; one or both obliques may be routine or added for the clinical question. ACR guidance supports radiography as initial imaging for acute elbow or forearm pain but does not prescribe the article's former “minimum three-view” rule. Follow the order and local protocol.

Projection	Primary Purpose
AP Elbow	Overall joint survey, joint space alignment, distal humerus, proximal forearm
Lateral Elbow	Fat pad sign (effusion), coronoid process, olecranon, anterior/posterior displacement
AP Medial (Internal) Oblique	Coronoid process in profile
AP Lateral (External) Oblique	Radial head and neck free of superimposition

Projection 1: AP Elbow

The AP elbow is the basic survey projection for the elbow joint. It demonstrates the distal humerus, proximal radius and ulna, and the elbow joint space.

Patient Position

• Patient seated alongside the table with the affected arm extended
• Elbow fully extended, palm facing upward (hand supinated)
• Shoulder, elbow, and wrist should be at the same horizontal level — the upper arm, elbow, and forearm should all be in contact with the tabletop
• If the patient cannot fully extend the elbow, do not force it; use the two-projection AP partial-flexion method described below

Central Ray

• Perpendicular (0°) to the IR
• Centering point: mid-elbow joint, approximately 2 cm (3/4 in) distal to the midpoint of the line between the humeral epicondyles

Technical Factors

Parameter	Value
IR size/orientation	18 × 24 cm or 24 × 30 cm, lengthwise as needed to include the required anatomy; follow local protocol
SID	100 cm (40 in)
Grid	Typically nongrid; use the department's thickness/equipment policy
Exposure	Use the validated technique chart for the detector, patient size, and required image quality; a universal kVp/mAs pair is not appropriate
Breathing	Suspend respiration
Patient shielding	Follow current facility policy; routine gonadal/fetal contact shielding is no longer recommended by major U.S. medical-physics guidance

Evaluation Criteria

• Elbow joint space demonstrated with expected partial superimposition at the articulations
• Medial and lateral epicondyles visible in profile on respective sides
• Radial head partially superimposed over the ulna (normal for AP)
• Olecranon partially superimposed by the distal humerus and seated in the olecranon fossa
• Adequate penetration through the epicondyles
• No rotation — the epicondyles should be symmetric, not tilted

Projection 2: Lateral Elbow

A true lateral elbow is essential for assessing alignment and the anterior and posterior fat pads. After trauma, a displaced fat pad is an indirect sign of joint effusion and may indicate an occult intra-articular fracture.

Patient Position

• Patient seated alongside the table
• Elbow flexed 90° for the routine lateral when tolerated; do not force flexion in trauma
• Hand in true lateral position (thumb pointing upward, forearm midway between pronation and supination)
• Medial aspect of the arm and forearm resting on the table
• Shoulder, elbow, and wrist should be at the same horizontal level

Central Ray

• Perpendicular (0°) to the IR
• Centering point: mid-elbow joint, approximately 2 cm (3/4 in) distal to the midpoint of the line between the epicondyles
• CR enters the medial aspect of the elbow and exits the lateral aspect

Technical Factors

Parameter	Value
IR size/orientation	18 × 24 cm or 24 × 30 cm, lengthwise as needed; follow local protocol
SID	100 cm (40 in)
Grid	Typically nongrid; follow local policy
Exposure	Use the validated local technique chart for the detector and patient
Breathing	Suspend respiration

The Fat Pad Sign (Sail Sign)

Fat-pad assessment requires a well-positioned lateral. The relevant appearances are:

• Anterior fat pad — may be visible normally as a thin lucency anterior to the distal humerus. Elevation or a convex “sail” configuration suggests joint effusion; no universal millimetre cutoff should be applied.
• Posterior fat pad — normally not visible because it lies in the olecranon fossa. Visibility indicates displacement by joint effusion. In acute trauma this substantially raises suspicion for occult intra-articular fracture, but other causes of effusion remain possible.

Evaluation Criteria

• Humeral condyles superimposed — the single most important check. If the medial and lateral epicondyles appear as separate structures, this is not a true lateral.
• Joint relationships demonstrated without avoidable rotation
• Trochlear notch of the ulna visible in profile
• Coronoid process projected anteriorly, partially superimposed by the radial head
• Olecranon process visible posteriorly
• Radial head superimposed over the coronoid process (normal for true lateral)
• Anterior fat pad assessed; posterior fat pad should not be visible in a normal elbow without effusion

Projection 3: AP Oblique — Medial (Internal) Rotation

This view brings the coronoid process into profile.

Patient Position

• Start from the AP position (elbow extended, hand supinated)
• Rotate the entire arm medially (internally) approximately 45°; do not achieve the oblique by rotating only the hand
• The medial aspect of the elbow becomes more parallel to the IR

Central Ray

• Perpendicular (0°) to the IR
• Centering: mid-elbow joint, approximately 2 cm distal to the midpoint of the line between the epicondyles

Evaluation Criteria

• Coronoid process projected free of superimposition, visible in profile on the ulnar side
• Medial epicondyle visible en face
• Trochlea and coronoid process demonstrated with the expected medial-oblique relationship

Projection 4: AP Oblique — Lateral (External) Rotation

This view brings the radial head and neck into profile — essential when radial head fracture is suspected.

Patient Position

• Start from the AP position (elbow extended, hand supinated)
• Rotate the entire arm laterally (externally) approximately 45°; keep the elbow extended and avoid twisting only the wrist
• The lateral aspect of the elbow becomes more parallel to the IR

Central Ray

• Perpendicular (0°) to the IR
• Centering: mid-elbow joint, approximately 2 cm distal to the midpoint of the line between the epicondyles

Evaluation Criteria

• Radial head and neck free of superimposition over the ulna
• Capitellum visible en face
• Radiocapitellar articulation demonstrated with minimal ulnar superimposition of the radial head and neck

Projection 5: Coyle Trauma Axiolateral Projections

The Coyle method has distinct radial-head and coronoid-process variants for a patient who cannot fully extend the elbow. It supplements, rather than automatically replaces, the projections required by the local trauma protocol.

Patient Position

• Radial-head variant: elbow flexed 90°, hand pronated, posterior arm and forearm supported on the IR
• Coronoid-process variant: elbow flexed approximately 80°, hand pronated
• Do not force the injured elbow to the specified angle; follow local trauma modifications if it cannot be tolerated

Central Ray

• Radial-head variant: angle 45° toward the shoulder, centered to the mid-elbow joint
• Coronoid-process variant: angle 45° away from the shoulder, centered to the mid-elbow joint
• The directional wording “toward/away from the shoulder” is preferred because “cephalad/caudad” can be ambiguous when the arm is placed on the table

Technical Factors

Parameter	Value
IR size	18 × 24 cm or 24 × 30 cm as needed; follow local protocol
SID	100 cm (40 in)
Grid	Typically nongrid; follow local policy
Exposure	Use the validated local technique chart
CR angle	45° toward shoulder (radial head) or 45° away (coronoid)

Evaluation Criteria

• Radial-head variant: radial head, neck, and capitellum demonstrated with reduced superimposition by the coronoid process
• Coronoid-process variant: coronoid process demonstrated in profile with reduced radial-head superimposition
• Collimation includes the elbow joint and relevant distal humerus/proximal forearm

Trauma Elbow Series — Modified Techniques

When the patient cannot extend the elbow (suspected fracture, dislocation, or severe pain):

AP in Flexion

• Keep the elbow in the safest position it can tolerate
• Two separate exposures:
  • Distal humerus — CR perpendicular to distal humerus, entering the posterior aspect
  • Proximal forearm — CR perpendicular to the proximal radius and ulna
• These are separate projections with different planes; do not describe them as a single reconstructed AP image

Cross-Table Lateral (Supine Patient)

• Patient supine or semi-recumbent
• Arm abducted and supported on a radiolucent pad
• IR placed vertically against the medial aspect of the elbow
• Horizontal CR perpendicular to and centered at the mid-elbow joint
• Adjust IR distance to include the entire elbow joint

Positioning Errors: Quick Reference

Error	Likely Cause	Correction
Joint relationship distorted (AP)	Elbow not fully extended, limb not in one plane, or CR off-center	If safe, align shoulder–elbow–wrist and center to the mid-elbow joint; otherwise use partial-flexion trauma views
Epicondyles not symmetric (AP)	Patient rotated	Both shoulders should be at same horizontal level
Condyles not superimposed (lateral)	Shoulder, elbow, and wrist not level or elbow rotated	Correct the whole-limb plane; thumb-up position alone does not guarantee a true lateral
Joint relationships distorted (lateral)	Flexion differs from the routine 90° position	If tolerated, use 90° flexion; never force an injured elbow
Coronoid process not in profile (medial oblique)	Incorrect whole-arm rotation	Rotate the entire arm approximately 45° medially
Olecranon cut off (lateral)	Collimation or centering too far anterior	Recentre to the mid-elbow joint and recollimate
Insufficient receptor exposure	Technique unsuitable for patient/detector	Use the department's validated technique chart; do not apply a universal kVp correction
Motion blur	Patient discomfort	Use immobilization; increase mA, decrease time
Radial head obscured (Coyle method)	Flexion, pronation, or CR direction incorrect	For the radial-head variant, use 90° flexion, pronation, and 45° toward the shoulder when tolerated
Fat pad sign obscured (lateral)	Overexposed or rotated lateral	Check technique and rotation

ARRT Content Review: Elbow Positioning

The current ARRT Radiography Content Specifications list AP, lateral, medial oblique, lateral oblique, AP partial-flexion, and Coyle trauma axial lateral elbow procedures. ARRT does not publish a guaranteed elbow question count or identify concepts that appear on every form. Review these content-specification-aligned facts:

1. AP elbow centering — mid-elbow joint, approximately 2 cm distal to the midpoint of the line between the epicondyles
2. Routine lateral elbow flexion — 90° when tolerated; trauma safety takes priority
3. Lateral evaluation check — humeral condyles must be superimposed — if they appear separate, the view is not a true lateral
4. Posterior fat pad — indicates joint effusion; after trauma it strongly suggests an occult intra-articular fracture but is not fracture-specific
5. Oblique views — medial (internal) 45° demonstrates the coronoid process; lateral (external) 45° demonstrates the radial head and neck
6. Coyle method — radial-head variant: 90° flexion, hand pronated, 45° toward the shoulder; coronoid variant: about 80° flexion, 45° away
7. Trauma protocol — never force extension; use the ordered local partial-flexion/horizontal-beam techniques
8. Examination composition — AP and lateral form the usual orthogonal foundation; oblique use varies by indication and local protocol
9. Pediatric differences — ossification centers appear at variable ages. CRITOE (Capitellum, Radial head, Internal/Trochlea, Olecranon, External epicondyle) is an approximate sequence, not a rigid age-dating rule.
10. IR and exposure — select receptor size and the validated technique chart to include the anatomy and match the patient/detector

Clinical Pearls: Tips from the Techs

• Palpate the epicondyles gently — use them to locate the joint, then center approximately 2 cm distal to their midpoint. In trauma, avoid unnecessary manipulation of a swollen or deformed elbow.
• Assess the whole limb for the lateral — thumb-up hand position helps, but a true lateral also requires the shoulder, elbow, and wrist at the same level with the humeral condyles superimposed.
• Use pediatric technique charts — do not apply one fixed kVp reduction to every child or detector. Collimate carefully and use the facility's age/size-appropriate chart. Assess the fat pads and alignment on the lateral.
• The "fat pad" needs a true lateral — if the elbow is rotated even slightly, the fat pads may not be visible or can be misinterpreted. Make the lateral elbow the most carefully positioned view of the series.
• Distinguish fat-pad appearances — a thin anterior fat pad may be normal; elevation or a convex sail shape and any visible posterior fat pad indicate effusion. In trauma, search carefully for an occult intra-articular fracture.
• Document your trauma technique — when using the cross-table lateral or flexed AP, note on the requisition that the patient could not extend the elbow. The radiologist needs this clinical context to properly interpret the images.

Summary

Projection	Patient Position	CR	Centering Point	Primary Purpose
AP Elbow	Elbow extended, hand supinated; partial-flexion variants for trauma	0° (perpendicular)	Mid-elbow joint, about 2 cm distal to epicondylar midpoint	Joint survey, alignment
Lateral Elbow	Elbow 90° flexed when tolerated, forearm in true lateral	0° (perpendicular)	Mid-elbow joint	Alignment and fat-pad assessment
AP Medial Oblique	Entire arm medially rotated about 45°	0° (perpendicular)	Mid-elbow joint	Coronoid process in profile
AP Lateral Oblique	Entire arm laterally rotated about 45°	0° (perpendicular)	Mid-elbow joint	Radial head, neck, and tuberosity
Coyle—radial head	Elbow 90° flexed, hand pronated	45° toward shoulder	Mid-elbow joint	Radial head/capitellum
Coyle—coronoid	Elbow about 80° flexed, hand pronated	45° away from shoulder	Mid-elbow joint	Coronoid process

Authoritative Sources Used for This Audit

• ACR Appropriateness Criteria®: Acute Elbow and Forearm Pain — radiography as initial imaging and next imaging when fracture remains suspected.
• ARRT Examination Content Specifications and the current Radiography Content Specifications PDF — named elbow positioning procedures; no projection-specific question-count guarantee.
• Skaggs DL, Mirzayan R. The posterior fat pad sign in association with occult fracture of the elbow in children. J Bone Joint Surg Am. 1999. — a prospective study found fracture in 76% of children with an isolated traumatic posterior fat-pad sign, supporting strong suspicion but not “always a fracture.”
• DeFroda SF, et al. Radiographic Evaluation of Common Pediatric Elbow Injuries. Orthopedic Reviews. 2017. — pediatric ossification variability, CRITOE, alignment, and fat-pad interpretation.
• AAPM Position Statement on Patient Gonadal and Fetal Shielding — rationale against routine contact shielding; facility policy still governs practice.