Axiolateral hip CR direction: enters medially at the groin, cassette is lateral

When you use the axiolateral hip (and why it matters)

The axiolateral hip projection (also called the Danelius-Miller method) is a trauma positioning technique. It shows the femoral neck in profile, which is critical for detecting and assessing femoral neck fractures. The key difference from other hip projections is that the patient’s affected leg does not move.

In acute trauma, a patient with a suspected hip fracture cannot abduct or rotate the hip. The frog-leg lateral (which requires external rotation and abduction) is contraindicated because it causes severe pain and can displace a fracture. The axiolateral is designed for exactly this situation: the patient lies supine, the affected leg stays relaxed and in place, and the technologist brings the x-ray tube and cassette to the patient instead.

This is why the axiolateral is so common in trauma radiography, emergency departments, and portable (bedside) exams. It works when the patient cannot cooperate with positioning.

The Danelius-Miller setup, step by step

Here’s how the axiolateral hip is positioned:

1. Patient position: Supine on the x-ray table or stretcher. The affected hip is the side of interest.
2. Unaffected leg: Flexed at the knee and elevated out of the beam path. The knee is usually propped up on a pillow or the tech’s arm to keep it high enough.
3. Affected leg: Stays neutral and relaxed. No rotation, no abduction. Just as it would be if the patient were lying still.
4. Cassette placement: Placed on edge against the lateral side of the affected hip. The cassette is vertical and in contact with the greater trochanter and hip joint. It is parallel to the femoral neck.
5. CR direction: Enters horizontally from the medial side (the groin). The tube head comes in from underneath or from the side, aiming perpendicular to the femoral neck. The horizontal beam is critical for trauma because it allows the exam to happen without moving the patient off the stretcher.

The geometry is simple once you picture it: the cassette is on the lateral side, the tube is coming from the medial side, and the beam travels from medial to lateral across the hip joint.

Why CR enters medially (the femoral neck geometry)

The femoral neck is the narrow portion of bone between the femoral head and the femoral shaft. It runs at an angle, roughly from the medial (groin) side to the lateral (outer hip) side, and slightly anterior to the posterior shaft.

To show the femoral neck in true profile (without foreshortening or distortion), the CR must be perpendicular to the long axis of the neck. If the neck runs medial-to-lateral at a certain angle, the CR must match that angle.

The axiolateral does this by positioning the CR horizontally and aiming it perpendicular to the neck’s plane. Since the cassette is on the lateral side, the beam must come from the medial side. The medial approach also has a practical advantage in trauma: the medial side (groin) is usually accessible and pain-free; the lateral side (where the fracture often is) is protected.

This is why reversing the direction (putting the cassette medial and the CR lateral) produces a wrong image: you are imaging the hip from the opposite side, which distorts the femoral neck angle and can make fractures hard to see or invisible.

Common positioning errors that cause repeats

Here are the mistakes radiographers make on axiolateral hip exams:

Error 1: Reversing CR and cassette sides. This is the critical reversal the ARRT tests. If the cassette is placed medially and the CR comes from the lateral side, the geometry is flipped. The femoral neck projects distorted. This results in a repeat exam.

Error 2: Allowing the unaffected leg to remain in the beam. If the elevated leg drops back into the primary beam or into the collimated field, it superimposes over the hip joint and obscures the femoral neck. Elevate the unaffected leg high enough and keep the tech out of the way.

Error 3: Rotating the affected hip. If the affected leg is abducted or externally rotated (which defeats the purpose of the trauma technique), the femoral neck will not be in profile. The patient may move involuntarily due to pain. Use gentle positioning, explain the procedure, and be ready to proceed quickly.

Error 4: Non-horizontal beam. If the beam is angled instead of truly horizontal, the femoral neck will be foreshortened. Always confirm the tube is level before firing.

Error 5: Cassette not parallel to the femoral neck. If the cassette is placed flat against the hip instead of tilted to align with the neck’s obliquity, the image will be distorted. In true lateral hip exams (frog-leg), slight patient rotation can angle the cassette. In axiolateral, the cassette angle should match the neck’s plane. This is why portable axiolateral exams sometimes include a small degree of tube or patient rotation.

Why this matters on the ARRT

The Procedures section of the ARRT Radiography Boards tests hip positioning across three question types:

1. Direction questions: “For the axiolateral hip, the CR enters from the…?” Answer: medial side, horizontal, perpendicular to the femoral neck.

2. Indication questions: “The axiolateral hip is used when…?” Answer: the patient cannot abduct or rotate the hip due to pain or trauma.

3. Comparison questions: “How does the axiolateral differ from the frog-leg lateral?” Answer: axiolateral is used in trauma (leg stays in place, CR horizontal from medial); frog-leg requires abduction and external rotation (not possible in acute fracture).

The critical reversal (cassette medial instead of lateral, or CR lateral instead of medial) shows up in image-quality and repeats questions. If you can say “medial CR entry, lateral cassette” without hesitation, you will answer these questions correctly.

For a broader look at trauma positioning and when portable exams are indicated, see our chapter on trauma and adaptive positioning. For other lower-extremity projections and how they differ (AP hip, lateral hip, frog-leg), the lower extremity chapter covers the full range.

Quick reference table

Element	Specification
CR entry side	Medial (from groin side, unaffected side)
CR direction	Horizontal, perpendicular to femoral neck axis
Cassette side	Lateral (against affected hip)
Cassette angle	Parallel to femoral neck
Unaffected leg	Flexed and elevated out of beam path
Affected leg	Neutral, relaxed, no rotation
Patient position	Supine
Indication	Femoral neck fracture, trauma, patient cannot rotate
kVp range	70-80 kVp (portable technique)
mAs range	10-20 mAs (protocol-dependent)
SID	40 inches (portable) or 36-40 inches (stationary table)

ARRT exam tip

If you only memorize one thing from this page: for the axiolateral hip, the CR enters medially from the groin, and the cassette is lateral against the affected hip. This is the opposite of intuition if you’re thinking “cassette where the injury is,” but the geometry of the femoral neck requires the medial approach. Test questions often ask “CR enters from the [medial/lateral] side?” or show a reversed image and ask “what’s wrong?” Knowing the rule by anatomy (femoral neck angle requires perpendicular medial approach) helps you get it right and remember it under pressure.

For students building an ARRT prep plan, our Curriculum walks through trauma positioning in the Procedures domain, with free practice questions in every category and a full lower-extremity chapter covering all hip and leg projections.