AC Joint X-Ray Positioning: 3 Views (Weight-Bearing, Zanca & Alexander)

Why AC Joint Positioning Matters

The acromioclavicular (AC) joint is one of the most frequently injured joints in the shoulder girdle — think contact sports, falls onto the shoulder, or a direct blow. As a radiologic technologist, you'll image it regularly in the emergency department, and it's a classic topic on the ARRT exam.

Here's the catch: a standard shoulder series often misses or underestimates an AC joint injury. That's why dedicated AC joint projections exist — and why knowing the difference between the Pearson, Zanca, and Alexander methods matters for both patient care and your registry.

This guide covers the routine and supplemental projections for the AC joint, with centering points, CR angles, evaluation criteria, and the exam traps to avoid.

Anatomy of the AC Joint

The AC joint is the articulation between the acromial (lateral) end of the clavicle and the acromion process of the scapula.

• It's a synovial gliding (diarthrodial) joint, allowing slight movement to accommodate shoulder motion.
• AC ligaments (superior, inferior, anterior, posterior) reinforce the joint capsule.
• The coracoclavicular (CC) ligaments — conoid and trapezoid — connect the clavicle to the coracoid process and are the main suspensory support.
• The coracoid process projects anteriorly from the scapula, just inferior to the clavicle — it's your centering landmark for the Alexander method.

When the AC and CC ligaments are torn, the clavicle can displace superiorly, posteriorly, or inferiorly relative to the acromion. The weight-bearing AP view is what makes that displacement visible. Clark's Pocket Handbook for Radiographers covers the AC joint within its shoulder girdle projections; the direct positioning values in this article are sourced from the references listed below.

AP Bilateral (Pearson Method): The Routine Weight-Bearing View

The Pearson method is the classic bilateral AP projection of both AC joints — the workhorse of AC joint trauma evaluation. The key word is bilateral: both joints on one image for side-by-side comparison of the injured and uninjured sides.

Patient Position

• Upright, seated or standing. Recumbent positioning should be avoided because it can reduce or mask a dislocation — gravity is your ally here.
• Center the midline of the body to the midline of the IR.
• Shoulders in the same horizontal plane, weight distributed evenly on both feet.
• Arms relaxed at the sides.

The Two-Exposure Rule

You'll typically make two exposures:

1. Without weights — baseline anatomy
2. With weights attached to the wrists (commonly 5–10 lb; some protocols use 3–5 lb)

Central Ray and Technique

Evaluation Criteria

• Both AC joints entirely included on one image for side-by-side comparison
• AC joint space clearly demonstrated without superimposition
• No rotation — sternoclavicular joints symmetric and equidistant from the vertebral column; shoulders equidistant from the bucky
• Clavicles horizontal and level — no leaning or shoulder elevation
• Sharp cortical margins and soft tissue edges (no motion)
• Rt/Lt and weight markers clearly present

Zanca Method (AP Axial AC Joint)

The Zanca method is an AP axial projection that isolates the AC joint by eliminating overlying structures — specifically the scapular spine and acromion overlap.

Positioning and CR

• Patient upright, affected side against the IR (or supine per department protocol for trauma).
• Center the AC joint to the IR.
• CR: 10–15° cephalic angle, directed at the AC joint (commonly cited as 10°; some protocols use up to 15°).
• Soft tissue technique — roughly one-third to one-half the kVp of a standard AP shoulder, so the joint space isn't burned out.

Why the Cephalic Angle Works

Angling the beam cephalad projects the clavicle above the acromion, "unfolding" the joint so the distal clavicle and joint space are seen clearly — which a flat AP can obscure. This makes the Zanca view valuable for:

• Distal clavicle fractures
• Joint space narrowing and degenerative changes
• Small avulsion fragments
• Subtle separations

Evaluation Criteria

• AC joint and distal clavicle clearly demonstrated, free of superimposition
• Joint space visible with soft tissue technique
• No rotation or motion

Alexander Method (AP Axial, Supplemental)

The Alexander method is a supplemental AP axial projection of the affected AC joint, used when subtle subluxation or dislocation needs to be demonstrated by projecting the joint above the acromion.

Positioning and CR

• Patient upright, back against the grid.
• Center the affected AC joint to the IR; align the coracoid process with the center of the field.
• CR: 15° cephalic angle to the coracoid process — this projects the AC joint above the acromion.
• SID: 40 inches.
• Respiration: suspend.
• Exposure: slightly higher kVp than the standard AP to penetrate the shoulder girdle.

Evaluation Criteria

• Entire AC joint and distal clavicle visualized
• AC joint projected slightly above the acromion — no body rotation
• Sharp cortical outlines of the joint and clavicle
• Proper brightness and contrast to visualize the joint space

Additional and Adjunctive Views

Depending on the clinical question, the department may add:

• Axillary lateral — a cross-sectional view of the shoulder that can detect posterior displacement of the clavicle (associated with Rockwood Type IV injuries). This is an orthogonal view, valuable when the AP alone is inconclusive.
• AP unilateral AC joint — a single-joint AP when only one side is ordered, without the bilateral comparison.
• Clavicle series (AP + AP axial) — if the clinical question includes distal clavicle fracture, the clavicle series is the appropriate examination. See our clavicle X-ray positioning guide.

What You're Looking For: Rockwood Classification

The Rockwood classification (I–VI) is the standard system for grading AC joint injuries on plain radiographs. Knowing it helps you understand why certain views are ordered — and it's tested on the ARRT.

• Types I–II are typically managed conservatively (sling, rest, rehab).
• Type III is the clinical "gray area" — management depends on symptoms and activity level.
• Types IV–VI are surgical indications.

The coracoclavicular distance (between the clavicle and coracoid process) is measured bilaterally on the weight-bearing view — the injured side is compared to the uninjured side. The interpreting clinician makes the measurement and classification.

Projection Reference Table

Common Positioning Errors and How to Avoid Them

• Unequal weight distribution tilts one shoulder higher than the other — both shoulders must be level and the weight evenly distributed.
• Patient rotation makes one AC joint appear higher than the other. Check the sternoclavicular joints — they should be equidistant from the vertebral column.
• Off-centered CR misses one AC joint on the image. Center precisely at the level of the AC joints.
• Weights held in the hands instead of attached to the wrists — this activates shoulder muscles and can mask a separation. This is the classic student trap.
• Collimation too tight clips the distal clavicles or lateral scapulae; too loose adds unnecessary anatomy. About 1 inch above and below the AC joints is the common starting point.
• Recumbent positioning for a suspected separation — it can reduce the dislocation and hide the injury. Use the upright position whenever the patient can tolerate it.
• Wrong tube angle — the Zanca method needs the cephalic tilt (10–15°); a perpendicular beam on the Zanca setup won't clear the scapular spine.

Exposure, Collimation, and Patient Safety

• Technique: Use the department's validated extremity/shoulder girdle technique chart. The Zanca view intentionally uses a lower (soft tissue) kVp; the Alexander method uses slightly higher kVp. Fixed universal values are inappropriate — patient size, detector, and processing all vary.
• Collimation: Collimate tightly to include both AC joints, distal clavicles, and lateral scapulae; include soft tissue margins.
• Shielding: Current expert guidance recommends discontinuing routine gonadal/fetal contact shielding because it offers little benefit against internal scatter and can obscure anatomy or cause repeats. Follow facility policy; never place shielding in the field.
• Weights and safety: Weights are attached to the wrists — never handed to the patient to grip. Confirm the ordered weight amount, support the patient, and use fall precautions when upright.
• Trauma: Preserve splints unless removal is authorized, support the injured arm, and move the tube/detector rather than the injury. If the patient cannot stand, follow the approved supine or horizontal-beam modification and document the limitation.

Related Reading

• Clavicle X-Ray Positioning: 2 Views (AP & AP Axial) — the companion shoulder girdle examination for distal clavicle fractures
• Shoulder X-Ray Positioning: AP, Grashey, Y-View, and Axillary — the glenohumeral series and trauma views
• Scapula X-Ray Positioning — scapular AP and lateral views
• Trauma Radiography Principles — moving the tube, not the patient
• ARRT Exam Prep Tips — registry study strategies

Frequently Asked Questions

Why are AC joint views taken upright instead of supine?

Lying down can reduce or mask a dislocation — gravity helps demonstrate the separation when the patient is upright. Recumbent positioning is avoided for suspected AC joint injuries whenever the patient can tolerate standing or sitting.

Why are the weights attached to the wrists and not held in the hands?

Holding weights activates the shoulder muscles, which can pull the joint together and mask a ligamentous separation. Attaching the weights to the wrists lets gravity stress the joint without voluntary muscle contraction.

What is the Zanca view?

The Zanca view is an AP axial projection of the AC joint with a 10–15° cephalic tube angle, using a soft tissue technique (about one-third to one-half the kVp of an AP shoulder). The cephalic tilt projects the clavicle above the acromion, eliminating overlying structures and clearly demonstrating the joint.

What is the difference between the Zanca and Alexander methods?

Both are AP axial projections with a cephalic angle. The Zanca view centers on the AC joint with a 10–15° cephalic angle at a soft tissue technique and is the primary view for isolating the joint. The Alexander method centers on the coracoid process with a 15° cephalic angle and is a supplemental projection for demonstrating subtle subluxation by projecting the joint above the acromion.

How is a Rockwood Type III AC injury different from Type II?

In Type II, the AC ligament is ruptured but the coracoclavicular ligaments remain intact or only sprained, producing slight joint widening. In Type III, both the AC and CC ligaments are completely ruptured, producing 25–100% increase in the coracoclavicular distance with elevation of the clavicle.

Why is a 72-inch SID used for the bilateral AP AC joint view?

The longer SID reduces magnification and beam divergence, allowing both AC joints to be demonstrated on a single image for direct side-by-side comparison of the injured and uninjured sides.

Reviewed Sources

• University of Missouri Clinical Preceptor Reference Guide — Acromioclavicular (AC) Joints (Carla M. Allen, PhD, RT(R)(CT), 2025)
• RadTechPrepper — AC Joints AP (aligned to 2025 ARRT Content Specifications)
• Wheeless' Textbook of Orthopaedics — Zanca View (AC Joint View)
• Fresh Scientific — AC Joint X-Ray Guide
• Orthobullets — Acromioclavicular Joint Injury