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, post operativelypostoperatively, 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 handle barshandlebars 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 focussedfocused 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 fracturesfracture 
• 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