The pelvic ring is one of the most complex anatomical structures in the body, serving as the critical weight-bearing bridge between the axial skeleton and the lower extremities. For radiologic technologists, mastering pelvis X-ray positioning is not just about producing diagnostic images — it is about recognizing when a patient has sustained life-threatening pelvic trauma and adapting the imaging approach accordingly.
Pelvic fractures are uncommon but potentially life-threatening because major bleeding may arise from fractured bone surfaces and injured venous or arterial structures. In trauma care, an AP pelvis radiograph may be obtained rapidly as an adjunct to the primary survey when it will affect immediate management; stable patients proceeding directly to contrast-enhanced trauma CT may follow a different local algorithm. It is inaccurate to describe a fixed chest–pelvis–lateral-cervical-spine series as a universal current ATLS requirement.
This guide covers commonly used AP pelvis, inlet, outlet, and Judet (oblique) projections. ARRT's radiography content specifications list AP pelvis, axial anterior pelvic bones (inlet/outlet), and posterior-oblique acetabulum (Judet), but they do not publish or guarantee the frequency of individual questions. Departmental protocols and the radiologist's request govern the examination performed.
Know the directions and your program's stated protocol. Inlet uses a caudad CR (toward the feet); outlet uses a cephalad CR (toward the head). A 40°/40° convention is common in US positioning instruction, while accredited institutional protocols also use 30–35° inlet and 35° outlet, and specialty literature describes broader patient-dependent ranges. Do not blend angle and entry-point instructions from different protocols.
The anteroposterior (AP) projection is the usual initial overview of the pelvis. Additional radiographs, CT, MRI, or other imaging depend on the clinical question; a single AP image neither excludes all pelvic/hip fractures nor characterizes every pelvic disorder.
The patient is placed supine with the midsagittal plane aligned to the detector midline and the arms clear of the field. For a routine nontraumatic AP pelvis, internally rotate both lower limbs approximately 15–20° to place the femoral necks closer to parallel with the detector; support the feet without constriction. Do not internally rotate either limb when fracture or dislocation is suspected, unless specifically directed by an appropriate clinician. Keep painful limbs as found and use a horizontal-beam approach when required.
A 14 × 17 inch (35 × 43 cm) detector is commonly placed crosswise, adjusted for habitus so the iliac crests and proximal femora through the lesser trochanters are included. Direct the CR perpendicular to the midsagittal plane, midway between the ASIS level and the pubic symphysis—commonly described as about 2 inches (5 cm) inferior to the ASIS level and approximately at the greater-trochanter level. Use the department's standard SID (commonly 40–44 inches/100–115 cm), collimate to the required anatomy, and suspend respiration for the exposure.
Technique charts are equipment-, detector-, SID-, grid-, and habitus-specific; fixed kVp/mAs values are not safely transferable between systems. Select the validated pelvis technique and the AEC chamber(s) specified by the manufacturer and department, position accurately over active chambers, and check the exposure index against the detector's target range. Use a grid when body-part thickness and local protocol require one (commonly for adult pelvis), not simply because the patient is an adult. Tight collimation and avoiding repeats are central dose controls. Routine gonadal or fetal contact shielding is no longer recommended by AAPM and ASRT because it can obscure anatomy, prompt repeats, and interfere with AEC while providing little or no benefit; follow current law and institutional policy.
Why 15–20° internal rotation? In routine nontraumatic imaging it reduces femoral-neck foreshortening and usually makes the lesser trochanters less prominent. This positioning improvement does not exclude an occult fracture. When clinical suspicion persists despite negative or indeterminate radiographs, ACR rates noncontrast MRI or noncontrast CT as appropriate next imaging; MRI remains necessary when concern persists after a negative or equivocal CT.
The AP inlet projection demonstrates the pelvic brim and helps assess anterior-posterior and rotational displacement of pelvic-ring disruptions. It may supplement the AP pelvis and CT when requested for pelvic-ring assessment.
The patient remains supine and unrotated. Do not internally rotate the limbs when fracture or dislocation is suspected. Suspend respiration. The following is the common 40° teaching convention; use it as a complete protocol rather than combining it with another source's entry point:
A properly positioned inlet view projects the pelvic brim as an oval ring — imagine looking down into a bowl. This en face view of the pelvic inlet allows the radiologist to directly visualize any inward or outward displacement of the pelvic ring segments. The sacral ala, sacroiliac joints, and the anterior sacral foramina should be well demonstrated. In patients with pelvic ring disruption, this view provides critical information about rotational and translational instability that guides surgical management decisions.
The AP outlet projection complements the inlet by helping assess superior-inferior (vertical) displacement and by elongating the sacrum and rami. It contributes to fracture characterization but does not by itself determine classification, stability, or need for fixation.
Again the patient remains supine and unrotated; do not manipulate injured limbs. Suspend respiration. Using the common 40° teaching convention:
On a properly positioned outlet view, the pubic and ischial rami are demonstrated and the sacrum is elongated, helping assess vertical displacement and sacral/pelvic-ring injury. It is particularly valuable for evaluating:
Inlet = caudad, demonstrating pelvic-brim configuration and AP/rotational displacement. Outlet = cephalad, elongating the sacrum and demonstrating vertical displacement. The paired views supplement—not replace—CT when cross-sectional characterization of significant pelvic trauma is required.
Named after the French surgeon Robert Judet, Judet views are paired approximately 45° posterior oblique projections for the acetabulum. They can complement the AP pelvis for suspected acetabular fracture; CT is commonly required to define complex fracture anatomy and aid treatment planning.
The acetabulum is formed by three bones: the ilium (superior), ischium (posteroinferior), and pubis (anteroinferior). The acetabular columns (anterior and posterior) and the quadrilateral surface are critical structures that must be evaluated when planning surgical fixation.
This view profiles the anterior column and the posterior wall of the acetabulum.
What it shows: The affected obturator foramen is profiled; the anterior column and posterior wall are assessed. A radiographic fracture finding does not by itself determine the need for fixation—management depends on fracture pattern, displacement, hip congruity/stability, patient factors, and usually CT assessment.
This view profiles the posterior column and the anterior wall of the acetabulum.
What it shows: The affected iliac wing is profiled; the posterior column and anterior wall are assessed. Neurologic status is a clinical assessment and cannot be inferred from this projection alone.
| View | CR Angle | Patient Position | Best For | IR Size |
|---|---|---|---|---|
| AP Pelvis | Perpendicular (0°) | Supine; legs IR 15–20° only if no suspected fracture/dislocation | Initial overview | Commonly 14×17" crosswise |
| AP Inlet | Caudad; commonly 30–40° per protocol | Supine, unrotated | AP/rotational pelvic-ring displacement | Commonly 14×17" crosswise |
| AP Outlet | Cephalad; commonly 30–45° per protocol | Supine, unrotated | Vertical displacement; elongated sacrum/rami | Commonly 14×17" crosswise |
| Obturator Oblique (Judet I) | Perpendicular | ~45° affected side up/farther from detector | Anterior column and posterior wall | Protocol-dependent coverage |
| Iliac Oblique (Judet II) | Perpendicular | ~45° affected side down/closer to detector | Posterior column and anterior wall | Protocol-dependent coverage |
Pelvic trauma patients present unique challenges. These patients are often hypotensive, may be in a cervical collar, and are frequently unable to cooperate with positioning. The technologist must balance image quality with speed and patient safety.
There is no universal three-view trauma pelvis series. Imaging follows the trauma team's pathway and the clinical question. An AP pelvis may provide rapid information in a hemodynamically unstable patient when it will change immediate treatment; stable major-trauma patients often proceed to CT. Inlet/outlet or Judet views are selective examinations and should be attempted only when the patient can be positioned safely and the images add information not already supplied by CT or other imaging.
For portable pelvis radiography, leave the patient on the stretcher when movement is unsafe and use its detector tray if available. Coordinate any detector placement or log-roll with the trauma team; do not reach beneath or move an unstable patient independently. Use the validated portable technique, SID, grid strategy, and scatter-control method. Merely increasing SID to 50–60 inches does not create an air gap: an air-gap technique requires deliberate object-to-detector separation and entails magnification and technique changes.
Do not attempt internal rotation when a fracture or dislocation is suspected. Image with the limbs as found unless the responsible clinician directs otherwise. Do not remove a pelvic binder, repeat pelvic stability testing, or reposition an unstable patient without authorization. Record positioning limitations and communicate them according to local policy.
Pediatric pelvic anatomy includes age-dependent open physes, apophyses, and synchondroses—such as the triradiate cartilage and ischiopubic synchondrosis—that must not be mistaken for injury. Use a pediatric technique chart based on patient size and the installed detector rather than a broad fixed kVp/mAs range; avoid an adult grid when thickness and protocol do not require it, collimate precisely, and immobilize safely to avoid repeats. Routine gonadal shielding is not recommended under current AAPM/ASRT guidance, including for children; comply with applicable policy and explain the practice to the caregiver.
Follow the facility's ACR–SPR-based pregnancy-screening policy before nonurgent pelvic radiography. Pregnancy is not an automatic reason to withhold a medically necessary examination: the radiologist/referrer should determine justification, and the examination should be optimized to the needed views and collimation. Do not substitute shielding for justification or technique optimization, and do not place routine fetal/gonadal shielding in the field. Urgent care should not be delayed solely to obtain a pregnancy test when the result would not change necessary management.
Osteoporotic bone can make nondisplaced fractures difficult to see. Initial trauma radiographs generally include dedicated AP and horizontal-beam lateral imaging of the affected hip plus an AP pelvis as locally indicated; never force a frog-leg position for suspected fracture. Elevating the opposite limb for a cross-table lateral may be impossible or unsafe with pelvic or contralateral injury, so adapt under protocol. If radiographs are negative or indeterminate but fracture remains suspected, ACR considers noncontrast MRI or noncontrast CT appropriate next imaging; persistent concern after a negative/equivocal CT warrants MRI.
A solid understanding of pelvic anatomy is essential for evaluating your images before sending them to PACS. Here are the key anatomical landmarks to check on every pelvis radiograph:
The superior-most margin of the ilium. Should be symmetric bilaterally. Asymmetric crests suggest rotation or a fracture with displacement.
Complex partly synovial articulations between sacrum and ilia. Asymmetry or widening can reflect positioning, normal variation, or injury and must be interpreted in clinical and cross-sectional context.
Secondary cartilaginous joint at the anterior midline. Width varies with age, sex, pregnancy/postpartum state, projection, and binder placement; do not diagnose or grade instability from a single universal millimetre cutoff.
An imaginary curved line from the medial femoral neck to the inferior border of the superior pubic ramus. Disruption indicates hip dislocation or femoral neck fracture.
Even experienced technologists make positioning errors on pelvis radiographs. Common examples and safe responses include:
Sign: The coccyx is displaced laterally from the pubic symphysis and the obturator foramina/iliac wings are asymmetric. Which foramen appears larger depends on the direction and degree of rotation, so use the full pattern rather than a single rule. Fix: For a nontrauma patient, align the midsagittal plane and make the ASIS equidistant from the table; do not reposition an injured patient merely to obtain textbook symmetry without clearance.
Sign: The femoral necks are foreshortened and the lesser trochanters are prominent. Fix: Only in a routine nontraumatic examination, increase internal rotation toward approximately 15–20° as tolerated. Never use a fixed heel separation or force the limbs in suspected fracture/dislocation.
There is no single ideal numerical angle for every pelvis. Critique the inlet for an en-face pelvic brim and the outlet for adequate sacral/ramus elongation without rotation, against the chosen protocol's reference image. Use the tube angle indicator and adjust within the department's validated range for patient anatomy; do not default every patient and every protocol to 40°.
Sign: Excessive scatter radiation reduces contrast and increases patient dose. Fix: Collimate tightly to the pelvic rim on all four sides. The collimation borders should be visible on the image but just outside the anatomical region of interest.
Sign: Required pubic, sacral, or iliac anatomy is clipped. Angled projections shift anatomy on the detector, but the required detector offset depends on table geometry, SID, detector orientation, and entry point. Preview collimation at the selected angle and follow the local positioning protocol rather than applying a universal shift rule.
Before sending a pelvis series to the radiologist, run through this quick checklist to ensure every image is diagnostically acceptable:
ARRT's published radiography content specifications include AP pelvis, axial anterior pelvic bones (inlet/outlet), and posterior-oblique acetabulum (Judet). ARRT does not promise question frequency or disclose exact items. Learn projection direction, anatomy demonstrated, trauma precautions, and the internally consistent positioning convention taught by your accredited program.
Mastering pelvis positioning requires understanding the anatomy and clinical purpose, using a validated local protocol, adapting safely to trauma, and evaluating coverage, rotation, motion, and detector exposure. Diagnostic adequacy and patient safety take priority over forcing textbook positioning.
📚 Recommended study references: hand-picked textbooks used in radiography programs:
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