Lumbar spine (AP/PA view)

The lumbar spine AP view images the lumbar spine which consists of five vertebrae. It is utilised in many imaging contexts including trauma, postoperatively, and for chronic conditions. 

Patient position

• the patient is erect or supine, depending on clinical history
  • ideally, spinal imaging should be taken erect in the setting of non-trauma to give a functional overview of the lumbar spine
  • all imaging of patients with suspected spinal injury must occur in the supine position without moving the patient
• in the supine projection hands are placed by the patient's side
• if performing erect, position the patient in the PA position; this has numerous advantages including reduced dose to the gonadal region and utilisation of beam divergence; arms can be placed by the side, or the handlebars of the erect bucky can be held for patient stability

Technical factors

• anteroposterior projection
• suspended expiration (for a uniform density) 
• centring point
  • the level of the iliac crests at the MSP 
  • the central ray is perpendicular to the image receptor 
• collimation
  • superiorly to include the T12/L1 junction
  • inferior to include the sacral region 
  • lateral to include the transverse processes and sacroiliac joints
• orientation  
  • portrait
• detector size
  • 35 cm x 43 cm 
• exposure
  • 70-80 kVp
  • 40-60 mAs 
• SID
  • 110 cm
• grid
  • yes (ensure the correct grid is selected if using focused grids)

Image technical evaluation

• the entire lumbar spine should be visible, with demonstration of T11/T12 superiorly and the sacrum inferiorly. 
• no patient rotation as evident by central spinous processes and the symmetrical appearance of the sacroiliac joints and iliac wings
• intervertebral joints are visualised 
• adequate image penetration and image contrast is evident by clear visualisation of lumbar vertebral bodies, pedicles, and facet joints, with both trabecular and cortical bone demonstrated

Practical points

• the three column concept of thoracolumbar spinal fractures is of particular importance when assessing this image for pathology
• take particular care when imaging patient on a trauma trolley that the image receptor is aligned to the central ray to prevent anatomy exclusion and grid cut-off
• ideally, the transverse processes should be visible, although demonstration is often obscured by overlying bowel gas; radiographers should ensure over exposure is not a factor contributing to the poor visualisation which could mask a transverse process fracture 
• when imaging in a supine position, a triangular cushion can be placed under flexed knees to reduce lumbar lordosis, and thus aiding to open the intervertebral joints