Pelvis X-Ray (AP)

The AP pelvis radiograph is a foundational examination for evaluating the pelvic ring, hip joints, proximal femora and sacroiliac joints. It is the first-line study in suspected hip fracture, pelvic trauma, degenerative and inflammatory hip disease, and paediatric developmental dysplasia. A single well-positioned AP view provides a large amount of information, though CT is required to fully characterise complex pelvic ring or acetabular injuries.

Indications

Suspected proximal femoral (neck of femur) or pelvic fracture after a fall or trauma
Hip or groin pain and suspected osteoarthritis or avascular necrosis
Suspected sacroiliitis and inflammatory spondyloarthropathy
Paediatric developmental dysplasia of the hip and slipped capital femoral epiphysis
Assessment of pelvic bony metastasis or primary lesion
Post-arthroplasty and postoperative assessment of hardware and alignment
Suspected pubic or sacral insufficiency fractures in the elderly

Contraindications & Cautions

No absolute contraindications
Pregnancy: the fetus lies within the primary beam, so avoid where possible and use ultrasound/MRI alternatives; justify carefully if performed
Moderate gonadal dose (~0.3-0.7 mSv); apply ALARA and consider gonadal shielding where it does not obscure pathology
Avoid unnecessary repeat imaging
In young women, justify against alternatives given gonadal radiation

Patient Preparation

Remove clothing with metallic fasteners, coins in pockets and radiopaque objects from the field
Position supine with legs extended and feet internally rotated ~15 degrees to profile the femoral necks (unless fracture precludes movement)
Do not force internal rotation if a fracture is suspected
Explain the breath-hold and need to stay still
Confirm pregnancy status in women of reproductive age
Support the patient comfortably to minimise motion and pelvic tilt/rotation

Technique & Parameters

Standard projection: AP supine of the whole pelvis, centred midway between the ASIS and symphysis pubis
Coverage from the iliac crests to the proximal femora, including both hips symmetrically
Feet internally rotated 15 degrees to compensate for femoral anteversion and profile the necks
75-85 kVp with a grid
Additional views: lateral or cross-table lateral of the hip, Judet (oblique) views for the acetabulum, inlet/outlet views for the pelvic ring, frog-leg lateral in paediatrics
CT is the standard for characterising complex pelvic ring and acetabular fractures
Ensure symmetry: obturator foramina and iliac wings should appear equal if positioning is correct

Systematic Review

Assess adequacy, rotation and symmetry (obturator foramina, iliac wings)
Trace the pelvic ring as three continuous bony rings - the main pelvic ring and both obturator foramina; ring fractures usually occur in two places
Evaluate both hip joints: joint space, femoral head sphericity, Shenton's line continuity
Assess the femoral necks and trochanters for cortical break or impaction
Evaluate the acetabula (anterior/posterior columns, roof, teardrop)
Assess sacroiliac joints and sacral arcades (arcuate lines) for symmetry
Review the pubic symphysis width and alignment
Inspect visible soft tissues, bowel gas, bladder outline and lower lumbar spine

Key Findings & Significance

Disruption of a cortical outline or trabecular impaction band in the femoral neck indicates a fracture
Loss of Shenton's line continuity suggests a femoral neck fracture or hip displacement
Superior joint-space narrowing, osteophytes and subchondral cysts/sclerosis indicate hip osteoarthritis
Because the pelvis is a ring, a single displaced fracture implies a second break or joint diastasis - look at both sacroiliac joints and pubic rami
Widened, sclerotic or eroded sacroiliac joints suggest sacroiliitis
Subchondral lucency (crescent sign) or femoral head collapse suggests avascular necrosis
Lytic or sclerotic bony lesions suggest metastasis or a primary tumour
In children, a break in Klein's line or widened physis suggests slipped capital femoral epiphysis

Differential Considerations

Femoral neck lucency: fracture, avascular necrosis, metastasis, insufficiency fracture
Sacroiliac abnormality: ankylosing spondylitis, psoriatic/reactive arthritis, infection, osteitis condensans ilii, degenerative change
Solitary lytic lesion: metastasis, myeloma, primary bone tumour, fibrous dysplasia, Paget disease (mixed)
Widened symphysis: traumatic diastasis, osteitis pubis, pregnancy-related, prior surgery
Protrusio acetabuli: rheumatoid arthritis, Paget disease, osteomalacia, familial
Hip joint-space narrowing: osteoarthritis, inflammatory arthritis, septic arthritis, chondrolysis
Paediatric hip abnormality: DDH, SCFE, Perthes disease, septic arthritis

Pearls & Pitfalls

Because the pelvis forms a ring, always search for a second injury when one fracture is found
An impacted or non-displaced neck of femur fracture may show only a subtle sclerotic band or cortical angulation - obtain MRI or CT if clinical suspicion is high
Insufficiency fractures of the sacrum and pubic rami are easily missed in the elderly; consider MRI/bone scan
Assess Shenton's line and the femoral head/neck contour on every film
Rotation and pelvic tilt distort joint spaces and symmetry - confirm positioning before diagnosing asymmetry
Overlying bowel gas, phleboliths and vascular calcification can mimic or obscure lesions
In children, use Klein's line, the acetabular index and Perkin's/Hilgenreiner's lines for hip assessment

Structured Report

State projection, adequacy, rotation and comparison with priors
Report pelvic ring integrity, hip joints, femoral necks, acetabula and sacroiliac joints
Describe any fracture with location, displacement and articular involvement; note the ring principle
Describe degenerative, inflammatory or destructive changes and their distribution
Report arthroplasty components, alignment and any loosening if present
Impression: summarise key findings and recommend CT/MRI where a fracture is occult or a complex injury needs characterisation

References

ACR Appropriateness Criteria: Acute Hip Pain - Suspected Fracture
ACR-SPR-SSR Practice Parameter for the Performance of Radiography of the Extremities and Pelvis
Young JWR, Burgess AR. Radiologic Management of Pelvic Ring Fractures
Resnick D. Diagnosis of Bone and Joint Disorders, Elsevier
Royal College of Radiologists iRefer guidelines

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.

Pelvis X-Ray (AP)

📋 Indications

⛔ Contraindications & Cautions

🧑‍⚕️ Patient Preparation

⚙️ Technique & Parameters

🔎 Systematic Review

🩻 Key Findings & Significance

🧠 Differential Considerations

💡 Pearls & Pitfalls

📝 Structured Report

📚 References