Pelvis

The Pelvis series is a critical component of orthopedic and trauma radiography, serving as the skeletal bridge between the spine and the lower extremities. Accurate imaging of the pelvic girdle is essential for evaluating everything from degenerative joint disease to life-threatening traumatic disruptions of the pelvic ring. In the “Richie Standard,” a high-quality pelvis study must demonstrate symmetry and clear visualization of the sacroiliac joints, the acetabulum, and the pelvic inlet and outlet.

The Goal

To demonstrate the structural integrity of the ilium, ischium, pubis, sacrum, and coccyx, along with the hip joints and proximal femora. These views are the primary diagnostic tools for identifying fractures, dislocations, and metabolic bone diseases.

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Routine & Trauma Projections

1. AP Pelvis

• The Standard: Directed midway between the level of the ASIS and the symphysis pubis.
• Rotation: Internally rotate the entire lower limbs 15°–20°.
• Richie’s Reasoning: This rotation is vital to place the femoral necks parallel to the IR. If you see the lesser trochanters in profile, you haven’t rotated enough, which will foreshorten the femoral necks.

2. Pelvic Inlet (Caudal View)

• The Angle: Direct the Central Ray (CR) 40° caudad (toward the feet).
• The Goal: This view “opens” the pelvic ring to evaluate for anterior or posterior displacement of the pelvic ring and to visualize the pelvic inlet in its entirety.

3. Pelvic Outlet (Cephalad View / Taylor Method)

• The Angle: Direct the CR 20°–35° cephalad for males and 30°–45° cephalad for females.
• The Goal: This projection elongates the pubic and ischial bones to clearly demonstrate fractures of the pelvic rami and the displacement of the pubic symphysis.

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Technical Factors

• SID: 40″ standard for all projections.
• Collimation: Must include the entire pelvic girdle from the iliac crests superiorly to the proximal femora inferiorly.
• Breathing: Suspend respiration during the exposure to prevent motion blur.

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Image Evaluation Criteria (The “Richie” Checklist)

• Symmetry: The iliac wings and obturator foramina should appear symmetric.
• Rotation Check: Lesser trochanters should not be visible (or only minimally visible) on a properly positioned AP Pelvis.
• Joint Visualization: The SI joints and the hip joints must be clearly demonstrated without excessive density.
• Physical Marker: A lead R/L marker must be clear and positioned within the light field without obscuring anatomy.

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Why the Pelvis Series Matters

The pelvis is a closed ring; a fracture in one area often implies a second break or dislocation elsewhere in the circle. The Inlet and Outlet views are the “gold standard” for trauma because a standard AP view can easily hide displacement that occurs in the 3D space of the pelvic ring. Identifying a widening of the pubic symphysis or a vertical shear injury is critical for surgical planning.

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Richie’s Pro-Tips for the Pelvis

Angle Accuracy: When performing the Inlet and Outlet views, ensure your CR is centered to the midline of the patient. Even a slight off-center alignment can cause the anatomy to project off the IR due to the steep tube angles.

Trauma Rotation: In cases of severe trauma or suspected hip fractures, do not attempt to internally rotate the feet. Take the “as-is” AP view first to avoid causing further neurovascular damage.

The “Symphysis” Rule: Always ensure the symphysis pubis is included on the bottom of the film. If you clip the bottom, you might miss a critical pubic ramus fracture.

Physical Markers are Mandatory: Digital markers are not legally or professionally sufficient. Always place your lead markers on the IR.