Hip X-Ray Positioning: AP, Frog-Leg Lateral, Cross-Table, and Dunn Methods

Why Hip X-Ray Positioning Matters

Hip X-rays are among the most commonly performed radiographic examinations in clinical practice. Whether the patient arrives from the emergency department with a suspected hip fracture after a fall, the orthopedic clinic with chronic hip pain, or the pediatric unit with developmental dysplasia of the hip (DDH), the radiologic technologist's ability to produce diagnostic-quality images directly affects patient management.

The hip joint is a ball-and-socket synovial joint that bears significant weight and undergoes tremendous stress throughout life. Osteoarthritis, avascular necrosis (AVN), femoral neck fractures, and developmental dysplasia represent just a fraction of the pathology that hip radiographs help diagnose. The ARRT registry exam consistently includes hip positioning questions — from the standard AP projection to specialized trauma views like the cross-table lateral and Dunn method.

This guide explains common hip projections and the safety decisions that surround them. Positioning terminology and detector sizes vary among departments; the examination order, local protocol, patient condition, and radiologist's direction take precedence. The clinical claims below are tied to the authoritative and peer-reviewed sources listed at the end rather than to an unverifiable textbook page.

Key Bony Anatomy of the Hip Joint

Before positioning the patient, you must understand the anatomy you are imaging. The hip joint consists of:

• Acetabulum — the cup-shaped socket formed by the fusion of the ilium, ischium, and pubis (the triradiate cartilage in children)
• Femoral head — the roughly spherical articular surface that meets the acetabulum; it is covered by articular cartilage except at the fovea
• Femoral neck — the narrow segment connecting the femoral head to the shaft and a common site of proximal femoral fracture
• Greater trochanter — the palpable bony prominence on the lateral proximal femur; attachment site for the gluteal muscles
• Lesser trochanter — the smaller medial prominence; the iliopsoas tendon inserts here

The femoral neck-shaft angle is commonly around 125° in adults, with normal variation by age and individual anatomy. Internal rotation in a non-trauma AP view places the femoral neck closer to parallel with the IR and reduces foreshortening.

AP Hip (Unilateral Anteroposterior Projection)

The AP hip is the most frequently requested hip projection. It is performed as a unilateral study when the clinical concern is limited to one hip (e.g., unilateral hip pain, suspected fracture after a fall on one side).

Positioning Steps

1. Patient position: Supine on the radiographic table with the midsagittal plane aligned to the midline
2. Leg rotation: For a non-trauma hip, internally rotate the entire limb 15–20° to place the femoral neck closer to parallel with the IR; the patella should face anterior. Do not internally rotate when fracture or dislocation is suspected unless specifically directed after clinical assessment
3. IR size and orientation: 24 × 30 cm (10 × 12 inch) IR, placed lengthwise (portrait orientation) centered at the hip joint. For larger patients, 35 × 43 cm (14 × 17 inch) may be necessary
4. Centering point: Central ray perpendicular to the IR, directed approximately 2.5–5 cm (1–2 inches) distal to the midpoint of a line between the ASIS and superior pubic symphysis on the side of interest. This surface landmark is approximate; adapt to habitus and the anatomy requested
5. SID: Use the department's calibrated hip/pelvis SID; 100–110 cm (40–44 inches) is common
6. Collimation: Include the proximal femur, hip joint, and lower iliac bone. Collimate closely to the skin margins
7. Respiration: Suspend respiration on expiration

Evaluation Criteria

• The femoral neck should be visualized without foreshortening (evidence of adequate internal rotation)
• The lesser trochanter should be not visible or barely visible (facing posteriorly)
• The acetabulum and femoral head should be well demonstrated
• The greater trochanter should be seen in profile laterally
• No motion blur; adequate penetration to visualize trabecular detail in the femoral head and neck
• No unintended pelvic rotation; on a sufficiently collimated image, pelvic landmarks should remain symmetric

AP Bilateral Hips

When the clinical question involves both hips (for example, bilateral symptoms or comparison), an AP pelvis commonly supplies the bilateral view. Departmental definitions of “AP bilateral hips” differ, so use the ordered coverage and local protocol rather than assuming the labels are universally interchangeable.

The requested clinical coverage matters: a pelvis examination must include the pelvic ring, whereas a hip examination must include the hip joint and adequate proximal femur. Do not crop required anatomy merely because similar positioning is used.

Frog-Leg Lateral (Modified Cleaves / Lauenstein Method)

The frog-leg lateral demonstrates the proximal femur in an oblique-lateral projection and is used only when hip movement is clinically acceptable. “Modified Cleaves,” “bilateral frog-leg,” and unilateral Lauenstein techniques are not perfectly interchangeable names; flexion, abduction, coverage, and centering must follow the requested departmental protocol.

Positioning Steps

1. Patient position: Supine on the radiographic table
2. Affected leg positioning: Flex the knee and flex and abduct the hip, commonly about 40–45° of abduction for a modified Cleaves-type view. Do not force a textbook angle: unilateral and bilateral variants differ, and motion must remain pain-free and permitted
3. IR size and orientation: 24 × 30 cm (10 × 12 inch), lengthwise, centered to the hip joint. For bilateral frog-leg lateral, use 35 × 43 cm crosswise
4. Centering point: For a unilateral view, use a perpendicular CR to the hip region, approximately 2.5–5 cm (1–2 inches) distal to the ASIS–pubic-symphysis midpoint on the side of interest; bilateral centering is on the midline according to the required coverage
5. SID: 100 cm (40 inches)
6. Respiration: Suspend on expiration

Evaluation Criteria

• Femoral head, neck, trochanters, acetabulum, and requested proximal femur are included
• The femoral neck is demonstrated without excessive foreshortening and the greater trochanter is substantially superimposed over the neck
• No motion; exposure permits cortical and trabecular assessment

When to AVOID the Frog-Leg Lateral

Do not force a frog-leg position when acute fracture, dislocation, or unstable SCFE is suspected. Flexion and abduction may:

• Displace a nondisplaced femoral neck fracture
• Convert a stable fracture to an unstable one
• Worsen an existing dislocation
• Cause severe pain and patient distress

In acute trauma, keep the affected limb undisturbed and use the ordered trauma lateral—commonly a horizontal-beam cross-table lateral—under the local protocol. If the unaffected limb cannot safely be elevated, consult the radiologist about an alternative such as a horizontal-beam lateral modification.

Cross-Table Lateral (Danelius-Miller Method)

The cross-table lateral (horizontal-beam or Danelius–Miller method) is commonly paired with an AP view in hip trauma because it can be obtained with no deliberate movement of the affected hip. It is not synonymous with every horizontal-beam lateral modification.

Positioning Steps

1. Patient position: Supine on the table or stretcher, with the affected hip as close to the center as possible
2. Unaffected leg: If safe, flex and elevate the unaffected hip and knee out of the beam. Support it securely without asking the patient to hold it. Leave the affected leg as found; do not lift or rotate it
3. IR placement: Place a suitably sized detector vertically at the lateral hip and align it parallel to the femoral neck (often with its top tilted away from the patient). Use a grid when required by thickness and protocol, ensuring grid/beam alignment
4. Central ray: Direct a horizontal beam from the medial side, perpendicular to the femoral neck and IR, centered approximately 2.5–5 cm (1–2 inches) distal to the ASIS–pubic-symphysis midpoint. The entry point is therefore in the proximal medial thigh, not at the skin-level ASIS–symphysis midpoint itself
5. SID: Use the protocol SID (commonly about 100 cm/40 inches) and maintain detector/beam alignment; bed clearance alone should not create an unvalidated geometry
6. Respiration: Suspend on expiration

Evaluation Criteria

• Femoral head, neck, trochanters, acetabulum, and required proximal femur are included
• No superimposition of the unaffected leg over the anatomy of interest
• The femoral neck is demonstrated laterally without avoidable foreshortening; the greater trochanter is superimposed over the neck
• Adequate penetration without motion

Dunn Views (45° and 90° Variations)

The Dunn view is a standardized non-trauma projection of the femoral head–neck junction. It is most often used to assess cam morphology/femoroacetabular impingement and quantify the alpha angle. It should not be confused with the modified Dunn procedure, which is an operation for SCFE, and it is not a routine acute-trauma view.

Positioning Steps

1. Patient position: Supine on the radiographic table
2. Hip positioning: Keep the femur neutrally rotated and use the specifically ordered variation:
   • 45° Dunn: 45° hip flexion and 20° abduction
   • 90° Dunn: 90° hip flexion and 20° abduction
3. IR: 24 × 30 cm (10 × 12 inch), lengthwise
4. Centering: CR perpendicular to the table, directed to the midpoint between the ASIS and pubic symphysis on the side of interest; bilateral variants center on the midline according to protocol
5. SID: 100 cm (40 inches)

Clinical Indications

Lauenstein / Frog-Leg Terminology in Pediatric Imaging

“Lowenstein” is a frequent misspelling of Lauenstein. The term is used inconsistently for unilateral or bilateral frog-leg-type lateral views; there is no universal separate “Lowenstein” view defined by 30–40° flexion. In children, perform only the exact view ordered and follow the pediatric protocol. A frog-leg view may help assess femoral-head shape, containment, or reducibility in selected children, but it is not automatically part of every DDH examination and must not be forced in an acutely painful hip or possible unstable SCFE.

Comparison Table of Hip Projections

Trauma Considerations for Hip Radiography

Hip fractures are serious injuries, particularly in older adults, and safe diagnostic imaging directly affects management. The radiologic technologist must prioritize fracture precautions over idealized routine positioning.

Key Safety Rules for Trauma Hip Exams

1. Minimal patient manipulation — Do not rotate the affected extremity if a fracture is suspected. The cross-table lateral allows you to image the hip without moving the injured leg
2. Safe transfer — Use the number of trained staff and transfer device required by the mobility assessment and local policy; do not prescribe a universal two-person maneuver
3. Document limitations — If trauma prevents routine positioning, record the limitation according to departmental practice; do not attempt 15–20° internal rotation
4. Pain management — Coordinate with the treating clinical team; radiologic technologists do not independently administer or time analgesia unless authorized within their scope and protocol

Portable Hip Technique

For patients who cannot be moved to the radiographic table:

• Move the patient as little as possible; use an approved detector-placement/transfer aid rather than forcing a detector beneath an injured hip
• Use a grid only when indicated by patient thickness and the validated technique chart, with careful grid alignment
• Select exposure factors from the equipment- and patient-specific technique chart; a short exposure time may reduce motion
• Portable AP and horizontal-beam lateral views may both be performed when ordered and feasible; “AP only” is not a universal rule

Geriatric Considerations

Elderly patients with hip fractures often present with:

• Osteoporotic bone — preserve trabecular detail by using the department's validated digital technique chart; do not apply a universal kVp reduction
• Limited cooperation due to pain, dementia, or delirium
• Thin soft tissues — may require lower mAs to prevent overexposure
• Skin fragility — handle patients gently to avoid skin tears

Pediatric Hip Considerations

Pediatric hip imaging requires special attention to technique, positioning adaptations, and radiation protection.

Developmental Dysplasia of the Hip (DDH)

• Younger than 4 weeks, risk factors/equivocal exam: ACR rates both ultrasound and radiography usually not appropriate as routine initial imaging; timing is clinically directed
• 4 weeks to 4 months: Ultrasound is usually appropriate for risk factors, equivocal examination, or positive physical findings; radiography is usually not appropriate
• 4–6 months: Pelvic radiography is usually appropriate and ultrasound may be appropriate
• Older than 6 months: Pelvic radiography is usually appropriate; ultrasound is usually not appropriate for initial DDH evaluation

These are modality recommendations, not a universal view set. The ACR DDH criteria specify pelvic radiography but do not mandate a frog-leg/Lauenstein view for every child. Follow the pediatric radiologist's requested projections.

Slipped Capital Femoral Epiphysis (SCFE)

SCFE can present with hip, thigh, or knee pain and may be subtle on AP imaging. AP pelvis plus a lateral view of both hips is commonly used because the opposite hip is also at risk. A frog-leg lateral may be used for a clinically stable presentation under the local pediatric protocol, but do not force flexion or abduction when the child cannot bear weight, has severe pain, or an unstable slip is possible. Keep the child non-weight-bearing and obtain urgent orthopedic/radiologist direction for a non-manipulative lateral. A radiographic Dunn view is not “essential” for SCFE and must not be confused with modified Dunn surgery.

Radiation Protection

• Use a size- and equipment-specific pediatric technique chart; no single kVp range applies to every child or system
• AAPM recommends discontinuing routine contact gonadal shielding because it can obscure anatomy, interfere with exposure control, and cause repeats; follow current law and institutional policy
• Collimate closely — limit exposure to the area of interest only

ARRT Practice Questions

Sources and Scope

Positioning dimensions are educational reference points, not exposure prescriptions or universal departmental protocols. No claim in this audit is attributed to Clark's because an exact edition-and-page source was not available for verification.

• ACR Appropriateness Criteria®: Acute Hip Pain (revised 2024) — initial radiography and next imaging after negative or indeterminate radiographs
• ACR Appropriateness Criteria®: Developmental Dysplasia of the Hip–Child — age- and scenario-specific ultrasound versus pelvic-radiography recommendations
• Sinha et al. Radiographic evaluation of the painful adolescent and young adult hip (JPOSNA, 2024) — 45° Dunn positioning (45° flexion, 20° abduction, neutral rotation), centering, and cam-morphology indication
• Clohisy et al. A systematic approach to the plain radiographic evaluation of the young adult hip (JBJS, 2008) — standardized AP and lateral evaluation and the need for technically adequate radiographs
• Millis. SCFE: clinical aspects, diagnosis, and classification (J Child Orthop, 2017) — biplanar imaging, AP pelvis/Lauenstein or frog lateral findings, and uncertainty of physeal stability
• AAPM Position Statement on Patient Gonadal and Fetal Shielding (PS 8-A) — current AAPM policy and evidence underlying discontinuation of routine contact shielding