Sacrum and coccyx (lateral view)

The sacrum and coccyx lateral view is utilised to demonstrate the most distal region of the spine in a lateral position. It is commonly used in conjunction with the AP projection or can be used as a sole projection, depending on department protocols. It is used to demonstrate sacrum and coccyx anatomy, and to investigate the cause of sacral and coccyx pain in both acute and chronic conditions. 

 Patient position

• The radiograph is performed with the patient 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 patient is in a true lateral position

Technical factors

• lateral view
• centring point
  • 8-10 cm posterior to the ASIS ¹
• central ray
  • angled perpendicular to the IR ( 90(90 degrees)
• collimation
  • must adhere to the ALARA principle given the region exposed via the primary beam
  • 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
  • 24x30 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- terminal coccyx 
• no patient rotation as demonstrated by superimposition of the greater sciatic notches and femoral heads  
• adequate penetration should clearly demonstrate the sacrum/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 concurrently in a single position 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