Radiography With Richie

AP Pelvis

The AP Pelvis is the foundational projection for evaluating the pelvic girdle, hip joints, and proximal femora. It serves as the primary diagnostic tool for identifying fractures, dislocations, and degenerative joint diseases within the central skeletal framework. In the “Richie Standard,” a high-quality AP pelvis radiograph must demonstrate perfect symmetry and clear visualization of the femoral necks, which requires specific attention to lower limb rotation.

The Goal

To provide a comprehensive frontal demonstration of the pelvic girdle, including the ilium, ischium, pubis, sacrum, coccyx, and both hip joints. This view allows for the assessment of the pelvic ring’s integrity and the relationship between the femoral heads and the acetabulum.

Patient Positioning

  • The Setup: Place the patient in a supine position on the radiographic table with the midsagittal plane centered to the midline.
  • Part Alignment: Ensure the pelvis is not rotated; the distance from the ASIS to the tabletop should be equal on both sides.
  • Rotation: Internally rotate the entire lower limbs 15°–20°.
    • Richie’s Reasoning: This internal rotation is vital because it places the femoral necks parallel to the image receptor (IR). Without this rotation, the femoral necks are foreshortened, and the lesser trochanters will be visible in profile, which can obscure critical anatomy.
  • Pro-Tip: In trauma cases where a hip or pelvic fracture is suspected, do not attempt to rotate the limbs. Perform the AP projection “as-is” to avoid further injury.

Technical Factors

  • Central Ray (CR): Perpendicular to the IR.
  • CR Entry Point: Directed midway between the level of the ASIS and the symphysis pubis (approximately 2 inches inferior to the ASIS).
  • SID: 40″ standard.
  • Collimation: Must include the entire pelvic girdle from the iliac crests superiorly to the proximal femora inferiorly.
  • Breathing: Suspend respiration during the exposure to eliminate motion blur.

Image Evaluation Criteria (The “Richie” Checklist)

  • Symmetry: The iliac wings and obturator foramina should appear symmetric in size and shape.
  • Femoral Neck Visualization: The femoral necks should be demonstrated in their full length without foreshortening.
  • Rotation Check: The lesser trochanters should not be visible, or only minimally visible, on the medial border of the femora.
  • No Motion: Cortical margins and trabecular patterns must be sharp and clear.
  • Physical Marker: A lead R/L marker must be present within the light field and positioned so it does not superimpose over any pelvic anatomy.

Why the AP Pelvis Matters

Because the pelvis is a rigid, closed ring, a fracture in one section often means there is a second disruption elsewhere in the circle. The AP view is the first step in assessing “stability.” If you see widening of the pubic symphysis or the SI joints, it’s a major red flag for a significant injury. Getting the positioning right the first time is essential for accurate surgical or clinical management.

Richie’s Pro-Tips for the AP Pelvis

Center with Confidence: Use the ASIS and the symphysis pubis as your landmarks. If the patient is large, centering can be tricky; feel for the crest and go roughly 2 inches down to find your midline sweet spot. joint or leaves a “gap” in the mid-shaft is a failure of technical standards.

The “Lesser” Secret: If you see the lesser trochanters prominently on your image, you haven’t rotated the feet enough. That 15–20° inward turn is what makes the femoral neck “pop” for the radiologist.

Symphysis Safety: Always ensure the bottom of your light field includes the symphysis pubis. Many fractures occur in the inferior rami, and clipping the bottom of the film means a missed diagnosis.

Physical Markers are Mandatory: Digital markers are not a substitute for lead markers placed on the IR at the time of exposure. It’s about professional standards and legal certainty.

Radiography 101

Pelvis