Sacrum and coccyx (lateral view)

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

Indications

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.

 Patient position

• the patient is in a lateral recumbent position
  • 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

Technical factors

• lateral view
• centering point
  • 8-10 cm posterior to the ASIS
• 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

Image technical evaluation

• 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

Practical points

• 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
• the sensitivity of plain radiographs for demonstrating acute injury in this region is relatively low  with conservative treatment occurring in a high proportion of cases