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PelvisDemonstration data

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.