Sacrum and coccyx (lateral view)

Last revised by Andrew Murphy on 23 Mar 2023

The sacrum and coccyx lateral view is utilized to demonstrate the most distal region of the spine in a lateral position.

This projection is commonly used in conjunction with the AP projection or can be used as a sole projection, depending on department protocols. It helps to visualize pathology of the sacrum and coccyx, and investigates the cause of sacral and coccyx pain in both acute and chronic conditions.

  • the patient is in a lateral recumbent position 1
    • the patient can be either on the left or right lateral recumbent position, depending on which is more comfortable
    • flex the knees
    • a cushion under the waist can aid patient comfort
    • ensure the patient is in a true lateral position
  • lateral view
  • centering point
    • 8-10 cm posterior to the ASIS 1
  • central ray
    • angled perpendicular to the IR (90°)
  • collimation
    • superior to include the L5/S1 articulation
    • inferior to include the distal coccyx
    • anterior to include the entire anterior margin of the sacrum
    • posterior to the skin margin
  • orientation  
    • portrait 
  • detector size
    • 24 x 30 cm 
  • exposure
    • 80 kVp
    • 30-40 mAs 
  • SID
    • 110 cm
  • grid
    • yes
  • the entire sacrum and coccyx should be visible from L5/S1 to terminal coccyx
  • no patient rotation as demonstrated by superimposition of the greater sciatic notches and femoral heads  
  • adequate penetration should clearly demonstrate the sacrum and coccyx region
  • placing lead posterior to the sacrum on the imaging table will help to reduce scattered radiation
  • this projection can be performed individually (separate sacrum and coccyx view), although they are most commonly performed in a single image 1
  • the sensitivity of plain radiographs for demonstrating acute injury in this region is relatively low 2,3 with conservative treatment occurring in a high proportion of cases 4
  • 5-25° of coccygeal flexion is normal on sitting, compared to standing
  • draw lines along the anterior cortical margin
  • may be at the sacrococcygeal or intercoccygeal joint (first mobile segment)
  • >25° suggests hypermobility (marked if >35°)
  • posterior subluxation is not normal -> ligamentous laxity

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Cases and figures

  • Case 1: anteriorly angulated coccyx
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  • Case 2 : coccyx fracture
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  • Case 3: coccygeal fracture
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  • Case 3: coccygeal fracture (magnified view)
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