Study Notes on Imaging Techniques for Sacrum, Coccyx, and Scoliosis Evaluation

Introduction to Imaging for the Sacrum and Coccyx

  • Importance of understanding anatomy and positioning for x-ray procedures related to the sacrum and coccyx.
  • Key landmarks:
    • Pubis: Initially considered a landmark but currently not a palpable landmark.
    • Anterior Superior Iliac Spine (ASIS): Corresponds to a specific vertebral level (not explicitly mentioned).

Imaging Techniques for Sacrum and Coccyx

General Overview

  • Imaging typically includes AP axial sacrum and lateral views due to the curvature of the sacral region.
  • Importance of obtaining both views for comprehensive anatomical assessment.

AP Axial Sacrum

  1. Clinical Indications:

    • Urinary bladder should be emptied prior to the procedure.
    • It is preferable to have the lower colon clear of gas and fecal material; may require cleansing enema as ordered.
    • Common challenges: Visibility may be compromised due to stool or gas obscuring anatomy.
    • Patient discomfort: Patients with a broken tailbone may have difficulty lying supine on a hard table.

  2. Procedure Considerations:

    • If the patient cannot lay supine, positioning can be modified to prone while maintaining an angle of 15 degrees cephalad (upward), adjusted to 15 degrees caudad (downward) if necessary.
    • Central ray (CR) typically positioned 2 inches above the pubis.
    • Female sacrum generally shorter and wider than male sacrum.
    • Adjustments needed for pronounced pelvic tilt: increase angle from 15 to 20 degrees.

Evaluation Criteria for Sacrum

  • The sacrum should not be foreshortened; alignment of sacroiliac (SI) joints should appear equidistant.

AP Axial Coccyx

  1. Clinical Indications:

    • Similar challenges with gas and fecal material as with the sacrum.
    • Cautious use of Automatic Exposure Control (AEC): Not recommended due to potential overexposure from surrounding denser anatomy.

  2. Procedure Considerations:

    • Adjust CR angle to 10 degrees caudal if necessary, especially for individuals with more significant anterior curvature of the coccyx.
    • Prone positioning may indicate a 10 degrees cephalad angle adjustment.
    • Goal: Clear visualization of the coccyx relative to adjacent anatomy.

  3. Lateral View of Coccyx:

    • Generally performed as one view; important to avoid scatter which affects image quality.
    • CR should be positioned 3-4 inches posterior from the ASIS.
    • Proper collimation is necessary to avoid unnecessary radiation exposure.

Imaging for SI Joints

  1. AP Axial SI Joints:

    • Central ray angled 30 degrees for males, 35 degrees for females.
    • Visualizes both SI joints simultaneously.
    • PA alternative available, direction modification as necessary.

  2. Posterior Oblique Views (LPO/RPO):

    • Bilateral study for comparative analysis; patient rotated 25-30 degrees to elevate the side of interest.
    • Additional angling of 15-20 degrees may open the joint in cases of tight presentation.
    • Elevated side demonstrates the side being assessed, which contrasts with typical oblique imaging techniques.

Scoliosis Imaging Considerations

  1. Prevalence and Diagnosis:

    • Commonly diagnosed in females between ages 10-14.
    • Often discovered during physical exams that assess physical maturity and growth.

  2. Radiation Exposure Considerations:

    • Pediatric patients diagnosed early may require repeated imaging, leading to cumulative exposure.
    • Need for protective measures for sensitive areas (breast, gonadal, thyroid).

  3. PA vs. AP Projections:

    • PA position significantly reduces radiation dose (90% reduction to breast tissue).
    • Encouragement for facilities to adopt PA methods for scoliosis screening.

  4. Radiographic Techniques:

    • Potential for software applications that create composite images from standard imaging techniques.
    • Utilization of appropriate imaging receptor sizes and comprehensive thoracic/lumbar inclusion in assessments.

  5. Flexion/Extension Scoliosis Evaluation:

    • Similar to cervical and lumbar spine evaluations, side-to-side flexibility and curvature are assessed.

Conclusion

  • Importance of understanding the anatomical details to ensure accurate imaging and diagnosis.
  • Need for awareness regarding radiation exposure, particularly in pediatric patients with conditions like scoliosis requiring lifetime monitoring.